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1.
Changes in net portal and hepatic nutrient flux and oxygen consumption in response to 3-d abomasal casein infusions were studied in seven multicatheterized beef steers. Steers were fed 4.3 kg DM/d of a high-concentrate diet in 12 equal meals. Blood flow (para-aminohippurate dilution) and net flux (venoarterial concentration difference x blood flow) across portal-drained viscera (PDV) and hepatic tissues were measured on d 3 of the abomasal infusions. In two experiments, the response to 300 (300C) and 150 (150C) g casein/d were compared, respectively, to a control water infusion. The 300C increased (P less than .05) arterial blood concentrations of alpha-amino N (AAN), urea N and ammonia; 150C increased (P less than .05) arterial urea N. Urinary urea N excretion was increased (P less than .01) by 300C and 150C. Although 300C increased net PDV release of AAN (P less than .07) and alanine (P less than .10), there was no net change in total splanchnic (TSP) flux due to an increased net hepatic uptake of AAN (P less than .01) and alanine (P less than .05). Net PDV glucose flux was decreased (P less than .05) by 300C, but net hepatic glucose flux was not affected by either level of casein. The 150C increased TSP oxygen consumption (P less than .05) and hepatic oxygen extraction (P less than .10). Approximately 26 and 30% of the casein N infused abomasally appeared in the portal blood as AAN for 150C and 300C, respectively. The sum of net PDV ammonia and AAN fluxes accounted for 47 and 88% of the N infused for 150C and 300C, respectively. These data emphasize the importance of intestinal and liver tissues in regulating the flux of nitrogenous compounds absorbed from the diet.  相似文献   

2.
The net release of insulin, glucagon and somatostatin by the portal-drained viscera (PDV) and their net uptake by the liver in response to 3-d abomasal infusions of casein were measured in seven multicatheterized beef steers. The steers were fed 4.3 kg DM/d of a high-concentrate diet in 12 equal meals (13.1 Mcal ME/d and 95 g N/d). In two separate experiments, the abomasal infusion of 300 g casein/d (300C) or 150 g casein/d (150C) was compared to a water infusion. Plasma flow was measured by indicator dilution and net flux by venoarterial concentration difference x plasma flow. Arterial plasma concentrations of insulin were increased (P less than .02) by either 300C or 150C. The 300C increased (P less than .03) PDV insulin release but did not affect hepatic uptake, resulting in an increased (P less than .03) total splanchnic (TSP) insulin flux. The 300C increased (P less than .05) plasma concentrations of glucagon as the result of decreased (P less than .06) hepatic extraction ratio and not as the result of increased portal release. The portal and hepatic flux of somatostatin measured as somatostatin-like immunoreactivity (SLI) were highly variable and not affected by casein infusions. Arterial plasma concentrations of somatomedin-C were not responsive to abomasal casein infusions. The abomasal infusion of 300C resulted in increased plasma concentrations of insulin via increased PDV release and increased plasma glucagon via decreased hepatic extraction ratio.  相似文献   

3.
The objective of this experiment was to compare net nutrient absorption and oxygen consumption by portal-drained viscera (PDV) of catheterized Holstein steers (333 kg) when fed alfalfa or orchardgrass silage at two equalized intakes. The design was a 4 X 4 Latin square with a 2 X 2 factorial arrangement of alfalfa or orchardgrass fed at 65 or 90 g dry matter/kg.75 live weight daily. Blood flow through PDV (dilution of p-aminohippurate), net nutrient absorption and oxygen consumption (venoarterial concentration differences times blood flow) were measured hourly for 12 h, followed by measurement of N and energy balance over 7 d. Compared with orchardgrass, steers when fed alfalfa absorbed more NH3-N (P less than .05), branched-chain volatile fatty acids (P less than .10) and n-valerate (P less than .05). Silage type did not affect (P greater than .10) blood flow to or O2 consumption by PDV or net absorption of glucose, L-lactate, acetate, propionate, urea-N, alpha-amino N or most amino acids. Oxygen consumption by PDV as a percentage of whole-animal O2 consumption was not different (P greater than .10) for steers when fed orchardgrass (27.2) or when fed alfalfa (23.6). Interrelationships between N and energy metabolism were responsible for the increased (P less than .05) metabolizable energy/kilogram silage dry matter and increased (P = .10) N retention by steers when fed alfalfa compared with orchardgrass. The PDV accounted for a substantial portion of whole-animal O2 consumption.  相似文献   

4.
Gastric distention-volvulus (GDV; at 50 mm of Hg gastric inflation pressure) was experimentally induced in 8 dogs anesthetized using pentobarbital. Hemodynamic indices including heart rate, mean arterial pressure, cardiac output, and coronary blood flow (4 dogs) were measured during a 20-minute period of GDV and for 10 minutes after decompression. Arterial and coronary venous oxygen tensions were also measured for calculation of myocardial oxygen extraction (7 dogs) and myocardial oxygen consumption (4 dogs). Dogs were monitored for 72 hours postoperatively for the occurrence of arrhythmias, then were euthanatized for gross and histologic examination of the heart. Experimental GDV resulted in significant (P less than 0.05) decreases in cardiac output (89%), mean arterial pressure (45%), and coronary blood flow (50%) compared with control values. Myocardial oxygen extraction increased (30%) and overall myocardial oxygen consumption decreased (50%), compared with control values. Evidence of subendocardial necrosis was seen in 6 dogs, 4 of which had developed ventricular arrhythmias 8 to 24 hours postoperatively.  相似文献   

5.
Four calves (avg wt 161 kg) were surgically fitted with indwelling catheters in the femoral artery and femoral, portal, hepatic and mesenteric veins to study the effects of subclinical ammonia toxicity on portal-drained viscera (PDV) and hepatic (HEP) net flux of key metabolites and pancreatic hormones. Hyperammonemia was induced via administration of ammonium chloride (NH4Cl; 12 mumol.kg BW-1.min-1) via the femoral vein catheter for 240 min; infusions were preceded (PRE) and followed (POST) by 60- and 180-min control periods, respectively. Blood samples were obtained from the arterial catheters, and portal and hepatic vein catheters. Net flux rates were calculated by multiplying venoarterial differences by blood flow. Arterial plasma ammonia N peaked (P less than .01) at 327 micrograms/dl; hepatic ammonia extraction increased (P less than .01) from 10 to 23% during NH4Cl infusion. Arterial plasma glucose concentrations increased (P less than .05) during NH4Cl infusion (90.5 vs 82.6 mg/dl) concomitant with trends toward a reduction in net HEP glucose output. Portal-drained visceral release of insulin did not increase (P greater than .10) during NH4Cl infusion despite the steady rise in circulating glucose concentration; however, cessation of NH4Cl infusion resulted in a 109% increase (P less than .05) in PDV insulin release at +60 min POST. Plasma L-lactate, nonesterified fatty acids, urea N and glucagon concentrations and net fluxes were variable throughout the experiment. Results tend to indicate that hyperammonemia reduced hepatic glucose output and glucose-mediated pancreatic insulin release.  相似文献   

6.
Effects of increased ammonia and/or arginine absorption across the portal-drained viscera (PDV) on net splanchnic (PDV and liver) metabolism of nitrogenous compounds and urinary N excretion were investigated in six catheterized Hereford x Angus steers (501 +/- 1 kg BW) fed a 75% alfalfa:25% (as-fed basis) corn-soybean meal diet (0.523 MJ of ME/[kg BW(0.75).d]) every 2 h without (27.0 g of N/kg of dietary DM) and with 20 g of urea/kg of dietary DM (35.7 g of N/kg of dietary DM) in a split-plot design. Net splanchnic flux measurements were obtained immediately before beginning and ending a 72-h mesenteric vein infusion of L-arginine (15 mmol/h). For 3 d before and during arginine infusion, daily urine voided was measured and analyzed for N composition. Feeding urea increased PDV absorption (P < 0.01) and hepatic removal (P < 0.01) of ammonia N, accounting for 80% of increased hepatic urea N output (P < 0.01). Numerical increases in net hepatic removal of AA N could account for the remaining portion of increased hepatic urea N output. Arginine infusion increased hepatic arginine removal (P < 0.01) and hepatic urea N output (P < 0.03) and switched hepatic ornithine flux from net uptake to net output (P < 0.01), but numerical changes in net hepatic removal of ammonia and AA N could not account fully for the increase in hepatic urea N output. Increases in urine N excretion equaled quantities of N fed as urea or infused as arginine. Estimated salivary urea N excretion was not changed by either treatment. Urea cycle regulation occurs via a complex interaction of mechanisms and requires N sources other than ammonia, but the effect of increased ammonia absorption on hepatic catabolism of individual AA in the present study was not significant.  相似文献   

7.
Our objectives were to determine the influences of supplemental nonprotein N or protein on feed intake, digestibility, and postabsorptive N metabolism in sheep fed a high-concentrate diet for ad libitum consumption. Nine Romanov-sired, crossbred wethers (13 mo old; 52 kg) were fitted with catheters in a mesenteric artery, mesenteric vein, portal vein, and hepatic vein. Wethers consumed a 95% concentrate diet ad libitum. Treatments consisted of control (no supplemental N; 6.6% CP) or supplemental urea (11.4% CP), soybean meal (SBM; 11.2% CP) or ruminally undegradable protein (BFM; 11.2% CP; 50:50 blood meal and feather meal). Intake or apparently digested intake of DM, OM, and energy did not differ between control and N-supplemented (P > 0.40), or between urea- and protein-supplemented (P > 0.40), but were greater (P < 0.05) in SBM- than in BFM-supplemented wethers. Intake and apparently digested intake of N were less (P < 0.01) in wethers fed the control diet than in those receiving N supplementation but were less (P = 0.03) in BFM- than in SBM-supplemented wethers. Neither portal nor hepatic venous blood flows differed (P > 0.15) among treatments. Net portal release and hepatic uptake of alpha-amino N and ammonia N and hepatic release of urea N were greater (P < 0.05) in wethers supplemented with N than in controls, but portal-drained viscera (PDV) uptake of urea N did not differ (P > 0.40) among diets. Splanchnic release of a-amino N and ammonia N did not differ from 0 or among diets (P > 0.10), but net release of urea N was less (P = 0.05) for control than for sheep receiving N supplementation. No differences (P > 0.10) in blood concentration within vessel or net flux across PDV, hepatic, or splanchnic tissues of alpha-amino N, ammonia N, or urea N were observed among wethers receiving supplemental N. Net uptake of oxygen by the PDV did not differ among diets, but hepatic uptake was less (P < 0.05) in control and urea-supplemented sheep than in sheep receiving SBM or BFM. These observations suggest that the source of supplemental N had no large effects on the overall N economy of the animals used in this study.  相似文献   

8.
Four Polwarth castrated male sheep (42 ± 4.4 kg live weight (LW) surgically implanted with chronic indwelling catheters into the mesenteric, portal and hepatic veins, housed in metabolism cages and offered Cynodon sp. hay at rates (g of dry matter (DM)/kg LW) of 7, 14, 21 or ad libitum, were used in a 4 × 4 Latin square experiment to evaluate the effect of the level of forage intake on blood flow and oxygen consumption by the portal‐drained viscera (PDV), liver and total splanchnic tissues (ST). The portal blood flow and the oxygen consumption by PDV linearly increased at increased organic matter (OM) intake. No effect of level of OM intake was obtained for the hepatic artery blood flow and oxygen consumption by liver. As a consequence, the level of OM intake only tended to directly affect hepatic blood flow and oxygen consumption by total ST. Oxygen consumption was linearly and positively related to blood flow across PDV, liver and total ST. The heat production by PDV and total ST, as proportion of metabolizable energy (ME) intake, decreased curvilinearly at increased ME intake. In conclusion, the oxygen consumption by PDV, but not by liver, was directly related to the level of forage intake by sheep. Moreover, when ingested at levels below maintenance, most of ME was spent as heat produced by ST.  相似文献   

9.
Effects of growth hormone-releasing factor (GRF) and intake on net nutrient metabolism by portal-drained viscera (PDV) and liver were measured in six growing Hereford x Angus steers fed a 75% concentrate diet at two intakes in a split-plot design with 4-wk saline or GRF injection periods within 8-wk intake periods. Daily rations were fed as 12 equal meals delivered every 2 h. Steers were injected s.c. for 21 d with either saline or 10 micrograms/kg of (1-29)NH2 human GRF at 12-h intervals. Six hourly measurements of net nutrient flux (venous-arterial concentration different [VA] x blood flow) across PDV and liver were obtained 8 to 10 d after injections began. Energy and N balances were measured using respiration calorimetry during the last week of injections. Greater intake increased blood flow (P less than .01) and net visceral release or removal of most nutrients (P less than .10). Exceptions included a decrease (P less than .10) in net PDV glucose release with greater intake in saline-treated steers and a decrease (P less than .01) in net liver removal of lactate with greater intake. Treatment of steers with GRF decreased net liver removal of alpha-amino N (AAN; P less than .05) and ammonia N (NH3N; P less than .10) and release of urea N (UN; P less than .05), increased liver release of glutamate (P less than .05), and decreased net PDV release of NH3 N (P less than .10). Decreased liver extraction ratio for AAN in GRF-treated steers (P less than .01) implies a direct effect of GRF treatment on liver metabolism separate from changes in liver AAN supply. Proportions of body N retention not accounted for by net total splanchnic AAN release increased with GRF treatment. This suggests a change in peripheral utilization of dietary AAN supply or an increase in total splanchnic N retention.  相似文献   

10.
Our objective was to determine the impact of supplemental energy, N, and protein on feed intake and N metabolism in sheep fed low-quality forage. Six Texel x Dorset wethers (16 mo, 63+/-3.1 kg) fitted with mesenteric, portal, and hepatic venous catheters were used in a Latin square design with five sampling periods. Lambs were fed chopped bromegrass hay (4.3% CP) to appetite, and a mineral mixture was given. Treatments were 1) control (no supplement), 2) energy (cornstarch, molasses, and soybean oil), 3) energy plus urea, 4) energy plus soybean meal (SBM), and 5) energy plus ruminally undegraded protein (RUP; 50:50 mixture of blood and feather meals). Supplements were fed once daily (.3% BW). Forage DMI did not differ (P = .13), but intake of total DM, N, and energy differed (P<.01) among treatments. Apparent digestibilities of DM, OM, and energy were less (P<.01) for control than for other treatments. Apparent N digestibility was least for control and energy and greatest for urea treatments (P<.05). As a result, digested DM, OM, and energy ranked from least to greatest were control, energy, urea, SBM, and RUP, respectively. Apparently digested N was 2.44, 2.24, 11.39, 9.80, and 11.25 g/d for control, energy, urea, SBM, and RUP (P<.01; SE = .10). Hour of sampling x treatment was a significant source of variation for blood concentrations of ammonia N and urea N, net ammonia N release from portal-drained viscera (PDV) and liver, and urea N release from splanchnic tissues. These results were primarily because patterns through time for the urea treatment differed from the other treatments. Net PDV release of alpha-amino N did not differ (P>.05) between control and energy treatments. Values for those treatments were about one-half of values for urea, SBM, and RUP treatments, which did not differ (P>.05). Hepatic net uptake (negative release) of alpha-amino N for control was 53% of values for the other treatments, which did not differ (P>.05). Net release of alpha-amino N from splanchnic tissues did not differ among treatments (P = .34) and did not differ from zero. The data indicate that arterial alpha-amino N concentration, hepatic alpha-amino N uptake, PDV release and hepatic uptake of ammonia N, and hepatic release of urea N were greater in energy than in control treatments. We also found that hepatic uptake of alpha-amino N was 187% of PDV release in energy-supplemented lambs. These results suggest that energy supplementation of a protein-limiting diet stimulated mobilization of body protein.  相似文献   

11.
We hypothesized that oscillating dietary CP would improve N retention by increasing the uptake of endogenous urea N by portal drained viscera (PDV), compared with static dietary CP regimens. Chronic indwelling catheters were surgically implanted in the abdominal aorta, a mesenteric vein, a hepatic vein, and the portal vein of 18 growing Dorset x Suffolk wethers (44.6 +/- 3.6 kg of BW). Wethers had ad libitum access to the following diets in a completely randomized block design: 1) Low (9.9% CP), 2) Medium (12.5% CP), or 3) Low and High (14.2% CP) diets oscillated on a 48-h interval (Osc). Dry matter intake was greater (P = 0.04) for the Osc diet (1,313 g/d) than the Low diet (987 g/d) and was intermediate for the Medium diet (1,112 g/d). Nitrogen intake was not different between the wethers fed the Osc (25.4 g/d) and Medium diets (22.2 g/d), but was lower (P < 0.01) in wethers fed the Low diet (16.0 g/d). Wethers fed the Osc diet (6.7 g/d) retained more (P < 0.04) N than did those fed the Medium diet (4.0 g/d). Hepatic arterial blood flow was not different (P = 0.81) between wethers fed the Osc (31 L/h) or Medium diet (39 L/h) but was greater (P = 0.05) in wethers fed the Low diet (66 L/h). Net release of alpha-amino N by the PDV did not differ (P = 0.90) between the Low (37.8 mmol/h) and Medium diets (41.5 mmol/h) or between the Osc (53.0 mmol/h) and Medium diets (P = 0.29). Net PDV release of ammonia N was less (P = 0.05) for the Low diet than for the Medium diet, and this was accompanied by a similar decrease (P = 0.04) in hepatic ammonia N uptake. Urea N concentrations tended to be (P = 0.06) less in arterial, portal, and hepatic blood in wethers fed the Low diet compared with those fed the Medium diet. Wethers fed the Osc diet tended (P = 0.06) to have a greater PDV uptake of urea N than did those fed the Medium diet, but there was no difference between the Osc and Medium diets (P = 0.72) in hepatic urea N release. Net PDV uptake of glutamine tended to be greater (P < 0.07) in wethers fed the Low diet (6.7 mmol/h) than those fed the Medium diet (2.7 mmol/h). These data indicate that oscillating dietary protein may improve N retention by increasing endogenous urea N uptake by the gastrointestinal tract.  相似文献   

12.
Effects of growth hormone-releasing factor (GRF) and intake on arterial concentrations and net visceral metabolism of hormones were measured in six growing Hereford x Angus steers using a split-plot design with 4-wk injection periods within 8-wk intake periods. Steers were fed a 75% concentrate diet at two intakes and were injected s.c. twice daily with saline or GRF (10 micrograms/kg of BW). Arterial concentrations of growth hormone (GH) were measured on d 1 and d 8 to 10 of injections. Eleven measurements, obtained at 30-min intervals, of arterial concentration and net flux of hormones across portal-drained viscera (PDV) and liver were obtained on d 8 to 10 of injections (six hourly measurements were used for insulin-like growth factor-I [IGF-I] and somatostatin). The area under the GH curve and average and peak GH concentrations were increased (P less than .01) by GRF and were greater (P less than .10) at low than at high intake. Liver removal of GH was not affected by GRF or intake. Arterial IGF-I concentration was increased (P less than .05) by GRF and not affected by intake. Treatments did not affect IGF-I flux across the liver. Arterial insulin concentration was greater (P less than .05) at high than at low intake, in part because of greater (P less than .01) PDV release. Increased (P less than .10) arterial insulin concentration in GRF-treated steers was not attributable to significant changes in PDV or liver net flux. Arterial glucagon concentration was greater (P less than .01) at high than at low intake, in part because of greater (P less than .05) PDV glucagon release and decreased (P less than .10) liver extraction ratio. Effects of intake on arterial concentration of insulin and glucagon were in part due to changes in visceral metabolism, but GRF did not affect PDV or liver hormone metabolism.  相似文献   

13.
We determined the effect of processing method (dry-rolled [DR] vs steam-flaked [SF]) and degree of processing (flake density; FD) of SF sorghum grain on splanchnic (gut and liver) metabolism of energy-yielding nutrients by growing steers. Diets contained 77% sorghum grain, either DR or SF, with SF at densities of 437, 360, or 283 g/L (SF34, SF28, or SF22). Eight multicatheterized steers (340 kg initial BW) were used in a randomized complete block design. Net output or uptake of glucose, L-lactate, VFA, and beta-hydroxybutyrate (BHBA) were measured across portal-drained viscera (PDV), liver, and splanchnic (PDV plus liver) tissues. Net absorption of glucose across PDV was negative and similar for all treatments (average of -104 g/d). Decreasing FD of SF sorghum grain linearly increased (P < or = .04) net absorption and splanchnic output of L-lactate by 20 and 130%, respectively, and hepatic synthesis (P = .06) and splanchnic output (P = .01) of glucose by 50%. Reducing FD did not alter output or uptake of acetate or n-butyrate by gut and liver tissues, but linearly decreased (P = .06) splanchnic output of BHBA by 40%. Net absorption (P = .18) and splanchnic output (P = .15) of propionate tended to be increased linearly by 50% with decreasing FD. Neither processing method (SF vs DR) nor degree of processing (varying FD) altered hepatic nutrient extraction ratios or estimated net absorption and splanchnic output of energy. Maximal contribution of propionate, L-lactate, and amino acids (alpha-amino N) to gluconeogenesis averaged 49, 11, and 20%, respectively. Feeding steers SF compared to DR diets did not alter net output or uptake of energy-yielding nutrients across splanchnic tissues, except net absorption of acetate tended to be greater (P = .13) for steers fed DR. Increasing degree of grain processing in the present study, by incrementally decreasing FD, tended to linearly increase the net absorption of glucose precursors (propionate and lactate), resulting in linear increases in synthesis and output of glucose by the liver to extrasplanchnic tissues (e.g., muscle).  相似文献   

14.
The objective of this study was to determine the pattern of nutrient flux across portal-drained viscera (PDV) and liver in ewes with varying numbers of fetuses. Catheters were placed in the hepatic portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta of each ewe. Plasma flow and net cholesterol, nonesterified fatty acids (NEFA), and glycerol release across the PDV and liver were determined prior to exposure to rams. Ewes were subsequently mated. Two ewes were not pregnant, six ewes gave birth to singles, and 11 ewes gave birth to twins. Additional measurements were taken 103, 82, 61, 39, 19, and 6 d before parturition. There was a net PDV uptake of nonesterified cholesterol in the nonpregnant ewes and a net release in the ewes with singles and twins. Net nonesterified cholesterol hepatic release did not differ with days from parturition (P = .77). There was a net hepatic release of nonesterified cholesterol in the ewes with twins and a net hepatic uptake in the ewes with singles and in nonpregnant ewes (P = .03). There was a net PDV release of NEFA; however, it did not differ with litter size (P = .59) or days from parturition (P = .63). Hepatic NEFA uptake increased with litter size (P = .03) and increased as gestation progressed (P = .006). There was an interaction (P = .04) between litter size and days from parturition for net PDV glycerol release. Net PDV glycerol release in the nonpregnant ewes decreased over time, but release in pregnant ewes tended to increase over time. Hepatic glycerol uptake increased with litter size and increased as gestation progressed. There was a net PDV uptake of triacylglycerol, but it did not differ with litter size (P = .11) or with days from parturition (P = .06). There was a net hepatic release of triacylglycerol, but it did not differ with litter size (P = .59) or with days from parturition (P = .67). Liver utilization of glycerol and NEFA as substrates for metabolism increases as pregnancy progresses. In the nonpregnant ewe, the combined contribution of glycerol and NEFA carbon accounted for 10% of the carbon taken up by the liver, and in ewes pregnant with twins, the combined contribution accounted for 42% of the carbon uptake 19 d before parturition. In conclusion, these data demonstrate NEFA are an important metabolite when determining carbon balance across the liver and their relative contribution to carbon balance increases as pregnancy progresses.  相似文献   

15.
Level of nutrition and splanchnic metabolite flux in young lambs   总被引：1，自引：0，他引：1  
Splanchnic metabolite flux was measured in young lambs given access to a high-concentrate diet either ad libitum (ADLIB) or at a maintenance level (MAINT) for 21 d. Net fluxes of urea N (UN), ammonia N (NH3 N), alpha-amino N (AAN), amino acids, glucose (G), and lactate (L) across the liver and portal-drained viscera (PDV) were measured in 11 crossbred ram lambs (35 kg) surgically fitted with indwelling catheters in the portal, hepatic, and mesenteric veins and mesenteric artery. During the 21-d period, daily N and ME intakes were 24.6 and 10.7 g N/d and 3.02 and 1.28 Mcal/d, respectively, for ADLIB and MAINT lambs. Intakes, thus, were 42% lower for MAINT than for ADLIB lambs. Net portal fluxes of UN, NH3 N, AAN, and L in MAINT lambs were 46%, 84%, 50%, and 74%, respectively, of that in ADLIB lambs. Expressed as a percentage of N intake, the proportion of AAN absorbed by the PDV was higher in MAINT lambs (P less than .05) than in ADLIB lambs. There was no net portal glucose absorption in either group of lambs; however, net hepatic glucose production in MAINT lambs was 48% of that in ADLIB lambs. There was net utilization of glutamine by the PDV; net glutamine flux in MAINT lambs was 49% of that in ADLIB lambs. The liver utilized AAN and NH3 N and produced UN. Splanchnic tissues modulate metabolite flux following changes in feed intake in young ruminants.  相似文献   

16.
The effects of endophyte-infected fescue (Kentucky 31) hay and cimetidine on respiration rates, rectal temperatures and hepatic antipyrine uptakes of three mature ewes were measured in 15 experiments. Hepatic antipyrine uptake was measured as an indirect indicator of hepatic mixed-function oxidase (MFO) activity. Five experiments on each ewe were conducted during consumption of endophyte-free (one exp/ewe, control), endophyte-infected (two exp/ewe, EIF) and endophyte-infected fescue hay plus cimetidine (800 mg/d i.v., two exp/ewe, EIFC). Respiration rates increased (P less than .05) 2.6-fold after 11 d on EIF from 26 to 68 and decreased (P less than .025) to 27 breaths/min after 4 d of cimetidine treatment. Rectal temperatures increased (P less than .05) 1.1 degrees C after 8 d on EIF. Cimetidine lowered temperatures to control levels by d 4. Endophyte-infected fescue hay increased (P less than .05) hepatic antipyrine uptake 70% after 11 d, but uptake was lowered to control levels by cimetidine by d 4. Increased respiration rates and rectal temperatures in animals consuming EIF seem to be related to increased MFO activity. Cimetidine reversed some of these effects.  相似文献   

17.
The effect of feed intake level (.6, 1.0, and 1.6 x maintenance energy and protein requirements, M) on splanchnic (portal-drained viscera [PDV] plus liver) metabolism was evaluated in six multicatheterized beef steers (398 +/- 27 kg), using a double 3 x 3 Latin square design. On the last day of each 21-d experimental period, six hourly blood samples were collected from arterial, portal, and hepatic vessels. Due to catheter patency, PDV fluxes were measured on five steers, and liver and splanchnic fluxes on four steers. Increasing intake elevated (P < .01) splanchnic release of total (T) amino acids (AA), through increases (P < .01) in PDV release of both essential (E) and nonessential (NE) AA, in spite of a tendency (P < .20) for increased liver removal of NEAA. The PDV release of AA N represented 27 and 51% of digested N for 1.0 and 1.6 x M, respectively. At 1.0 and 1.6 x M, the liver removed 34% of total AA released by the PDV. For individual AA, portal flux of most EAA increased (P < .05) with feed intake, and the increase (P < .10) in splanchnic flux was accompanied by increased arterial concentration for all EAA except histidine, lysine, and methionine. This suggests that these might be limiting AA for this diet. On a net basis, most individual NEAA were released by the PDV except glutamate and glutamine, which were removed by the digestive tract. There was a net removal of NEAA by the liver, except for aspartate and especially glutamate, which were released. Ammonia release by the PDV tended (P < .20) to increase with intake and represented 69, 53, and 45% of digested N at .6, 1.0, and 1.6 x M, respectively. Urea removed by the PDV, unaffected by intake, represented 32, 33, and 21% of the digested N. Arterial glucose concentration increased linearly (P < .01) with greater intake, whereas net liver and splanchnic glucose release increased in a quadratic (P < .05) manner. Net PDV glucose release represented 26% of net glucose hepatic release at 1.6 x M. Intake elevated (P < .10) both insulin and glucagon arterial concentrations, resulting from a larger increment of portal release (P < .01) than hepatic removal (P < .05). Intake-based variations in IGF-I and NEFA arterial concentrations (P < .05) were not related to changes in splanchnic metabolism. These results clearly show the crucial role of the splanchnic tissues in regulating the profile and quantity of AA and concentrations of glucose and pancreatic hormones reaching peripheral tissues.  相似文献   

18.
Effects of a 3-d mesenteric vein n-butyrate infusion (25 mmol/h) on net metabolism of nutrients by portal-drained viscera (PDV) and liver were measured in six Hereford x Angus steers. Steers were fed a pelleted 75% concentrate: 25% alfalfa diet at 135 kcal of ME/kg BW.75. Six measurements of blood flow and net metabolism of nutrients were obtained at hourly intervals immediately before beginning and ending n-butyrate infusion. Measurements were obtained during two trials, with three steers (457 kg BW, 28 mo of age in Trial 1; 478 kg BW, 19 mo of age in Trial 2) in each trial. The infusion of n-butyrate increased (P less than .01) net PDV release of n-butyrate. Infusion increased net liver removal of n-butyrate (P less than .01) and L-lactate (P less than .02) and release of beta-hydroxybutyrate (BOHB; P less than .02) and increased (P less than .03) liver extraction ratio for alanine. Net total splanchnic (PDV plus liver) release of n-butyrate (P less than .03) and BOHB (P less than .01) were increased, and net total splanchnic release of L-lactate (P less than .05) and propionate (P less than .07) were decreased by n-butyrate infusion. The infusion of n-butyrate decreased (P less than .01) net PDV release and liver removal of propionate in five of six steers. Infusion had no effect (P greater than .10) on insulin and glucagon concentration or net flux. In a companion in vitro study, L-lactate metabolism to glucose and CO2 by calf hepatocytes was decreased (P less than .08) by n-butyrate addition (2.5 mM). Effects of n-butyrate on liver L-lactate and alanine metabolism suggest that pyruvate carboxylase activity was increased, but our study failed to show a consistent effect of n-butyrate infusion on liver glucose production.  相似文献   

19.
Our objectives were to determine effects of grain processing on splanchnic (gut tissues and liver) N metabolism and whole-body N balance by growing steers and to ascertain the relative contributions of ruminal and intestinal tissues to net absorption and utilization of N-containing nutrients. Seven beef steers (348 kg initial BW), surgically implanted with appropriate catheters, were fed diets containing 77% steam-flaked (SF) or dry-rolled (DR) sorghum grain. Blood flows and net output or uptake of ammonia N, urea N, and alpha-amino N (estimate of amino acids) were measured across portal-drained viscera (PDV or gut tissues) and intestinal, ruminal, hepatic, and splanchnic tissues (PDV + hepatic). The experimental design was a crossover between DR and SF diets, with six samplings of blood at 2-h intervals on 2 d for each steer. Nitrogen intake (139 +/- 3 g/d), output in urine (43 +/- 2 g/d), and retention (40 +/- 3 g/d) were similar for both processing treatments. When steers were fed SF sorghum compared to DR sorghum, N retention as a percentage of N intake was numerically greater (P < 0.12), output of fecal N was numerically lower (P < 0.13), and urinary urea N was lower (P < 0.04). For SF vs DR, net uptake of alpha-amino N by liver was higher (P < 0.04; 20 vs 9 g/d) and was numerically lower (P < 0.16) for ruminal tissues (15 vs 33 g/d). Feeding steers SF compared to DR tended to increase net transfer (cycling) of blood urea N to PDV (57 vs 41 g/d; P < 0.07), increased cycling to intestinal tissues (15 vs 6 g/d; P < 0.05), and numerically increased transfer to ruminal tissues (42 vs 32 g/d; P < 0.12) but did not alter other net output or uptake of N across splanchnic tissues. Total urea N transfer (blood + saliva) was similar for both treatments. Net uptake of alpha-amino N by ruminal tissues was about 30% of the net amount of alpha-amino N absorbed across the intestinal tissues. In summary, most of the blood urea N cycled from the liver to gut tissues was transferred to ruminal tissues for potential microbial protein synthesis, and the net ruminal utilization of alpha-amino N was about 30% of that absorbed from intestinal tissues. Feeding growing steers SF compared to DR sorghum diets numerically increased whole-body N retention (percentage of N intake) by about 15% and tended to increase transfer of blood urea N to the gut by about 40%, which could increase the supply of high-quality microbial protein for absorption.  相似文献   

20.
Six Holstein steers (mean +/- SE BW = 344 +/- 10 kg) fitted with hepatic, portal, and mesenteric vein and mesenteric artery catheters and a ruminal cannula were used in a 6 x 6 Latin square design to evaluate the effects of increasing ruminal butyrate on net portal-drained visceral and hepatic nutrient flux. Steers were fed a 40% brome hay, 60% concentrate diet in 12 portions daily at 1.25 x NEm. Water (control) or butyrate at 50, 100, 150, 200, or 250 mmol/h was supplied continuously via the ruminal cannula. Simultaneous arterial, portal, and hepatic blood samples were taken at hourly intervals from 15 to 20 h of ruminal infusion. Portal and hepatic blood flow was determined by continuous infusion of P-aminohippurate, and net nutrient flux was calculated as the difference between venous and arterial concentrations times blood flow. Ruminal and arterial concentrations and total splanchnic flux of butyrate increased (P less than .01) with increased butyrate infusion. Arterial concentrations of acetate (P less than .10), alpha-amino-N (P less than .05), and glucose (P less than .01) decreased with increased butyrate, whereas arterial beta-hydroxybutyrate (P less than .01) and acetoacetate (P less than .05) increased. Increased butyrate produced an increased portal-drained visceral flux of acetoacetate and an increased net hepatic flux of beta-hydroxybutyrate. Urea N and glucose net portal and hepatic fluxes were not affected by ruminal butyrate. Alpha-amino-N uptake by the liver decreased with increased butyrate (P less than .10). Simple linear regression (r2 = .985) indicated that 25.8% of ruminally infused butyrate appeared in portal blood as butyrate. Only 14% could be accounted for as net portal-drained visceral flux of acetoacetate plus beta-hydroxybutyrate.  相似文献   

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