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1.
The concentration and functionality of the -adrenoceptor (-AR) subtypes in the genital tract of cyclic heifers were investigated. In each tissue sample, a single class of 1-ARs was observed, whereas two distinct classes of 2-ARs were discriminated: low-affinity (LA) and high-affinity (HA) 2-ARs. Statistical analysis showed the presence of significantly (p < 0.05) higher concentrations of all -AR subtypes in the follicle than in the corpus luteum. No significant differences were found in the ovary or myometrium between the luteal and follicular phases. In the ovary, the density of 1-ARs was significantly (p < 0.05) higher than that of 2-ARs. By contrast, there were significantly (p < 0.05) more 2-ARs than 1-ARs in the myometrium. As far as 2-ARs are concerned, LA 2-ARs were significantly (p < 0.05) higher than HA 2-ARs in all tested tissues. Competition studies suggested that the rank order of potency of antagonists for 1-ARs was prazosin > phentolamine > yohimbine, whereas for 2-ARs the order of potency was yohimbine phentolamine > prazosin. Functional assays performed on myometrium showed that noradrenaline, phenylephrine and clonidine elicited concentration-dependent contractions only in dioestrus and pro-oestrus preparations and that clonidine was more effective than phenylephrine as a contractile agent. It appeared that there were no significant modifications in -AR affinity or concentration during the different stages of bovine oestrous cycle, whereas the uterine spontaneous activity and the responsiveness to -adrenergic stimulation was strongly influenced by hormonal levels. The modifications of uterine contractility observed during the oestrous cycle may be related to modifications induced in the transductional mechanisms of -ARs.  相似文献   

2.
Stress, stressors and the stress response are terms which represent concepts rather than oeing precisely definable. No single theory of stress has been universally accepted. Selye's General Adaptation Syndrome of stress remains the primary theory for the basis of stress research in food-producing animals; however, other concepts and theories have been developed. This paper reviews current theories and suggests that the complexity of research on stress in food-producing animals can be attributed to the lack of concrete theories and concepts regarding identifiable stressors, the endocrine responses stimulated by potential stressors and the complex and integrated biological changes in the neuro-endocrine system resulting from exposure to hypothesized stressors.  相似文献   

3.
Factor XI (F XI) deficiency is an autosomal recessive coagulopathy found in Holstein cattle. Affected animals have a 50% greater prevalence of repeat breeding. Therefore, several parameters describing ovarian function were studied. Daily blood sampling revealed that progesterone concentrations were slower to decline from a peak at day 16 (p<0.01) to values less than 3 nmol/L in F XI-deficient cows (5.14±0.69 days (mean ± SD) versus 4.05±0.63 days in control animals), resulting in an oestrous cycle length of 24.7±2.1 days compared to 22.9±3.0 days, respectively. This was not due to an alteration in the availability of prostaglandin F2 (PGF2) or oxytocin (OT) involved in luteolysis. No significant differences (p>0.05) were seen between normal (n=7) and F XI-deficient (n=7) cows in the peak values or the area under the curve for the pulse in 13,14-dihydro-15-keto PGF2 in response to OT challenge or in the parameters describing the pulse of ovarian OT secretion after PGF2 injection (n=7 for each) between days 12 and 14. Ovulatory follicular development was assessed by ultrasound monitoring and plasma 17-oestradiol values at 8-h intervals after a luteolytic injection of cloprostenol (n=6 for each). Follicular diameter was smaller (p<0.05) and accompanied by lower peak oestradiol values near the time of ovulation in F XI-deficient cows. The results suggest that the oestrous cycle in F XI-deficient cows is characterized by a slower process of luteolysis that may be associated with smaller follicular development.Abbreviations F XI factor XI - OT oxytocin - PGF2 prostaglandin F2 - PGFM 13,14-dihydro-15-keto-prostaglandin F2 - i.m. intramuscularly  相似文献   

4.
Haematological estimations and serum biochemical analyses were made on 100 samples collected from clinically healthy Hijin racing camels (Camelus dromedarius) in Kuwait. The red blood cell counts, packed cell volume, haemoglobin concentration, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration and total white blood cell counts were estimated. In the serum biochemical analyses, sodium, potassium, iron, calcium, phosphorus, magnesium, total bilirubin, blood urea nitrogen, creatinine, glucose, total protein and cholesterol concentrations were measured, as were the alanine aminotransferase, aspartate aminotransferase, -glutamyltransferase, creatine kinase and alkaline phosphatase activities. The results are discussed in relation to other findings reported in camels.  相似文献   

5.
Diseases caused by lymphoid leukosis virus (LLV), a retrovirus, take a long time after infection to develop and have a wide variety of pathological manifestations. This long latent period is characteristic of persistent virus infections. Disease produced by LLV infection and its underlying mechanisms is compared with persistent infections caused by other retroviruses in birds and mammals of veterinary importance. The diseases considered for comparison are those caused by reticuloendotheliosis, feline leukaemia, bovine leukosis and equine infectious anaemia viruses. There are significant changes in the immunological status in all diseases caused by these viruses. LLV infections follow this trend with, in manifestations of neoplastic disease, a perturbation of the normal switch that occurs from IgM to IgG synthesis. There are also indications of other immunological disturbances.Factors other than immunological disturbances may contribute to the length of time after infection required for the many forms of LLV infection to appear. Such additional factors may include the operation of biological clocks, such as the arrival of sexual maturity, and also the very nature of retroviruses. These factors, like the immunological changes, play major roles in the maintenance and progression of persistent retrovirus infections.Abbreviations ACTH adrenocorticotropic hormone - AEV avian erythroblastosis virus - AMV avian myeloblastosis virus - BLV bovine leukaemia virus - CAV chicken anaemia virus - EBL enzootic bovine leukaemia - EIAV equine infectious anaemia virus - env envelope gene - FeLV feline leukaemia virus - FeSV feline sarcoma virus - FOCMA feline oncovirus membrane-associated antigen; gag, group antigen gene - HTLV human T-cell leukaemia virus - LLV lymphoid leukosis virus - L/S leukosis/sarcoma - LTR long terminal repeat - MAV myeloblastosis-associated virus - MDV Marek disease virus - MuLV mouse leukaemia virus - ORF open reading frame; pol, polymerase gene - REV reticuloendotheliosis virus - RIF resistance-inducing factor - RSV Rous sarcoma virus  相似文献   

6.
The effects of some 2-adrenoceptor agonists and of the 2-adrenoceptor antagonist atipamezole on food intake and ruminal contractions were studied in dwarf goats. Detomidine, 0.2 µg/kg per min for 10 min, failed to modify food intake during either the first or second observation period (0–30 min and 180–210 min after drug infusion, respectively). Given at a higher dose rate (0.4 µg/kg per min for 10 min), the drug inhibited food consumption during the first observation period, but stimulated food intake during the second period. A similar pattern was observed after IV infusion with medetomidine (0.2 µg/kg per min for 10 min), romifidine (0.4 µg/kg per min for 10 min) or xylazine (1 µg/kg per min for 10 min). The 2-antagonist atipamezole (2 µg/kg per min for 10 min) failed to modify food intake during either the first or second observation period. After treatment with atipamezole, the effects of 2-agonists on feeding behaviour were completely antagonized.The 2-agonists administered at similar dose rates to those used in the food intake experiments induced bradycardia, decreases in body temperature and inhibition of ruminal contractions. The inhibition of ruminal contractions induced by romifidine was partly antagonized by atipamezole pre-treatment. These findings demonstrate that the 2-agonist-induced changes in ruminal contractions do not simply cause changes in feeding behaviour. The drop in body temperature induced by 2-agonists was prevented by atipamezole pre-treatment, whereas the induced bradycardia was not modified by this 2-antagonist.Abbreviations IV intravenous - SEM standard error of the mean  相似文献   

7.
A double-blind, placebo-controlled study was conducted to compare two vaccines using different adjuvants with regard to their ability to stimulate antibody production against the - and -toxins and the exopolysaccharide of Staphylococcus aureus. The vaccines contained identical antigens, consisting of inactivated whole bacteria of two strains of S. aureus in addition to - and -toxoid. One vaccine contained mineral oil, while the other used a water-soluble acrylic acid polymer resin (Carbopol) as adjuvant. Saline served as the placebo. One hundred and forty ewes were vaccinated twice before lambing, by subcutaneous injection with vaccine or placebo in the region of the supramammary lymph node, and were observed and sampled over a period of 6 months. The vaccine containing mineral oil as adjuvant induced significantly greater immune responses to the - and -toxins than did the vaccine containing Carbopol. The latter vaccine induced higher levels of antibodies to exopolysaccharide. The degree of local adverse reactions did not differ between the two groups. The results indicate differences between the oil-adjuvanted and Carbopol-adjuvanted vaccines with regard to their ability to stimulate antibody production against S. aureus protein antigens in sheep.  相似文献   

8.
This paper reports the milk protein polymorphism, the allele frequencies of variants and the possible linkages among various combinations of milk protein phenotypes in the Kangayam cattle of south India. Milk samples from 156 Kangayam cows were typed by starch gel and polyacrylamide gel electrophoresis for caseins and whey proteins, respectively. All the four milk protein components studied, s1-casein, -casein, -lactoglobulin and -lactalbumin, exhibited polymorphism with high allele frequencies of 0.9231±0.0151 for s1-casein C, 0.9263±0.0148 for -casein A, 0.9135±0.0159 for -lactoglobulin B and a relatively high frequency of 0.6218±0.0275 for -lactalbumin A. The mean heterozygosity estimated over all the four milk protein loci was 0.2420. Genetic equilibrium was observed among all the loci studied, except -lactalbumin. Linkage analysis confirmed the non-independence between s1- and -caseins and between caseins and -lactalbumin phenotypes.  相似文献   

9.
In recent years human and animal cancers have increasingly been shown to have a viral component in their aetiology. Oncogenic viruses will continue to be discovered although with certain cancers there is also an important environmental component, and with others — congenital cancers and cancers of early childhood — an important genetic component. There is thus the probability that cancer may not be an entity. Rather it may be a syndrome, the phenotypic expression of alteration of cellular metabolism, differentiation and cell death. More information is needed on the mathematics of cell division and destruction,in vivo andin vitro, and the involvement of biological clocks, i.e. ageing processes. These data, when available, should help us to understand better the nature of cancer and lead us to more effective methods of prevention and cure.Abbreviations AIDS acquired immunodeficiency syndrome - ALV avian leukosis virus - COFAL complement-fixation test for avian leukosis viruses - FeLV feline leukaemia virus - kb kilobases - L/S viruses leukosis/sarcoma viruses - MMTV mouse mammary tumour virus - MuLV mouse leukaemia virus - wt wild type  相似文献   

10.
Persson Waller, K., Colditz, I.G., Flapper, P. and Seow, H.-F., 1997. Leukocyte and cytokine accumulation in the ovine teat and udder during endotoxin-induced inflammation. Veterinary Research Communications, 21 (2), 101-115The accumulation of leukocytes, ovine serum albumin and the cytokines interleukin-1 (IL-1), tumour necrosis factor- (TNF-), interleukin-8 (IL-8), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interferon- (IFN-) was studied during endotoxin-induced inflammation in lactating and dry ovine udders, and in the teat cisterns of dry ewes after surgical closure of the passage between the teat and udder cisterns. Samples were taken before infusion and hourly up to 10 h after infusion of 0.1, 1 or 10 µg of endotoxin, or infusion of pyrogen-free saline (PFS) as a control. Rectal temperatures were measured.A significant dose- and time-dependent accumulation of leukocytes, mainly neutrophils, was observed in the lactating udders and in the teat cisterns. In the dry udders, the leukocyte accumulation was significant for time but not for dose. Peak numbers of cells were reached at 3-4 h in the dry udders and in the teat cisterns, but not until 10 h after infusion in the lactating udders. The changes in the ovine serum albumin concentrations mostly paralleled changes in leukocyte numbers.A role was indicated for TNF-, IL-8 and GM-CSF, but not for IL-1 and IFN-, during endotoxin-induced inflammation in the ovine udder. Release of TNF-, IL-8 and GM-CSF was most prominent in lactating udders, peaking at 2 or 3 h after infusion, but was also detected in dry udders and teat cisterns. Detectable levels of IL-1 and IFN- were occasionally found in all three groups.  相似文献   

11.
The synthetic androgen 19-nortestosterone (-NT) has been used illegally as a growth promoter in cattle production in the European Union. Elimination of -NT and its metabolites in plasma, urine and bile was studied in three cattle with cannulated gallbladders following intramuscular injection at a single site of 500 mg of the laurate ester (NTL) containing 300.5 mg -NT. Using enzyme immunoassay quantification, plasma Cmax of free -NT was 0.5±0.15 g/L (mean±SEM). Concentrations of free -NT in plasma were consistently greater than the assay limit of quantification (0.12 g/L) for 32.7±13.42 days. Mean residence time for free -NT in plasma was 68.5±20.75 days. Following sample preparation by immunoaffinity chromatography, high-resolution GC-MS was used to quantify -NT and -NT in urine and bile. -NT was detected irregularly in urine from two of the three animals post injection. The principal metabolite present in the urine, -NT, was detected for 160.3±22.67 days post injection. Cmax for -NT in urine was 13.7±5.14 g/L. Mean urinary AUC0–183 days for -NT was 845.7±400.90 (g h)/L.In bile, -NT was the only metabolite detected for 174.3±8.67 days post treatment. Cmax for -NT in bile was 40.8±12.70 g/L and mean biliary AUC0–183 days for -NT was 1982.6±373.81 (g h)/L. Concentrations of -NT in bile samples were greater than those in urine samples taken at the same time. The mean ratio of biliary:urinary AUC0–183 days was 3.0±0.72. It is concluded that bile is a superior fluid for detection of -NT following injection of NTL, owing to the longer period during which residues may be detected after administration.  相似文献   

12.
This paper describes a study on the oestrous and ovarian activity and responses to prostaglandin F2 (PGF2) administration and artificial insemination in zebu heifers.Four cycling heifers were artificially infected with 5×106 Trypanosoma vivax organisms. Two heifers served as controls. Two injections of PGF2 were given 11 days apart, commencing at the peak of parasitaemia in the infected animals, followed by artificial insemination 72 and 96 h after the second administration of PGF2. Sera were analysed for progesterone by radioimmunoassay, while ovarian activity and oestrus were determined by rectal palpation and visual observation, respectively. All the infected heifers developed the clinical disease. All control and infected heifers had progesterone profiles consistent with luteolysis and the occurrence of oestrus following the second administration of PGF2. Progesterone levels did not return to normal luteal values in infected animals, however, whilst they did so in control animals. No control or infected heifers became pregnant.The findings suggest that PGF2 will induce a non- fertile oestrus in zebu heifers acutely infected with T. vivax. Re-ovulation is also inhibited within 22 days in a majority of infected animals.  相似文献   

13.
The effects of novobiocin (range 0.0125–2 mmol/L) on the hydroxylation of testosterone, the N-demethylation of erythromycin, and the glucuronidation of -naphthol and paracetamol were studied using pig hepatic microsomes, pooled from five animals. The final concentrations of these substrates in the incubation mixtures were selected to meet Vmax conditions. Novobiocin caused a concentration-dependent inhibition of the glucuronidation of paracetamol; the formation of -naphthol-glucuronide was reduced to a lesser degree. These results confirm and extend earlier findings in laboratory animal species that novobiocin inhibits UDP-glucuronosyltransferases (UDPGTs). Moreover, novobiocin strongly inhibited 6-hydroxylation of testosterone. The microsomal N-demethylation of erythromycin and hydroxylation of testosterone at the 15 position were less affected by novobiocin. These results suggest that novobiocin inhibits not only UDPGTs, but also cytochrome P450 (CYP) enzyme activities, probably those belonging to the CYP3A subfamily. More research is needed to reveal which CYPs and UDPGTs are affected by novobiocin in vivo, in order to improve the understanding and probably the predictability of potential drug interactions with this antibiotic.  相似文献   

14.
Measurement of Cortisol Metabolites in Faeces of Ruminants   总被引：8，自引：0，他引：8  
Twenty-one metabolites were detected in faecal samples collected after infusion of (14C)cortisol into the jugular vein of sheep, using high-performance liquid chromatography/radiometric analysis plus mass spectrometry. One group of metabolites had molecular weights of between 302 and 308, and another group of 350, which indicates that the substances have a C19O3 or a C21O4 structure. Therefore, an enzyme immunoassay against 5-androstane-3-o1-11,17-dione-17-CMO:BSA was established. Faecal samples were collected from 10 cows immediately after transport and then during a course in which non-invasive diagnostic procedures were being taught (course 1). For comparison, faeces were sampled from another 5 cows that were being used for teaching invasive procedures (course 2). Six cows from a university farm served as controls. In the animals used in course 1, the highest concentrations of cortisol metabolites were measured immediately after transport to the university (median value: 2.2 mol/kg faeces). During the first 5 days at the university, the concentrations decreased to 0.52 mol/kg (median) and remained at this level during the rest of the course. The median concentration in the samples that were taken during course 2 (collected about 2 months after transport) was 0.48 mol/kg. There was no significant difference in the excretion of cortisol metabolites between these cows and the controls. We conclude from these data that, using the enzyme immunoassay against 5-androstane-3-o1-11,17-dione-17-CMO, we were able to detect transport/novel environment stress but not the potential disturbance that cows experience during diagnostic procedures.  相似文献   

15.
Small intestine was taken from the caudal flexure of the duodenum and the terminal ileum proximal to the ileocaecal fold of 25 horses, 9 with acute grass sickness (AGS), 12 with subacute grass sickness (SAGS) and 12 with chronic grass sickness (CGS). The motility in the samples was measured isometrically either within 1 h of death or after storage for 24 h at 4°C.In control tissue, noradrenaline produced contractions of muscle strips which did not involve a muscarinic cholinergic mechanism and which were unaffected by the 1 antagonist prazosin but were blocked by the 2 antagonist yohimbine. Pretreatment with the antagonist phentolamine prevented the contractile response to noradrenaline and the background contractions either continued at a reduced rate and amplitude or were abolished after a few minutes. Thus, following blockade, noradrenaline reduced the background contraction rate by an effect on inhibitory adrenoceptors. The rate of background contractions in duodenal preparations was significantly greater than that in control ileal preparations.Although cold storage for 24 h caused a reduction in the background contraction rates of the control preparations, there was no effect on the contractile responses to noradrenaline, the associated pharmacology being similar to that of fresh tissue. This suggests that noradrenaline-evoked contraction was not dependent on enteric neural elements.The response to noradrenaline by grass sickness-affected tissue was generally similar to that of tissue from control horses, with an immediate contraction which was 2 sensitive. The contractile response to noradrenaline after propranolol was significantly reduced in the CGS group and there were significant differences between the AGS, CGS and control groups. There was a significant difference between the ileal preparations from the control and SAGS groups in their response to noradrenaline following pretreatment with propranolol.  相似文献   

16.
The oxidative metabolism of aldicarb (ALD), a carbamate pesticide, and fenbendazole (FBZ), an anthelmintic, was studied using cultured hepatocytes obtained from 4 goats and a bullock and incubated with ALD (50 mol/L) and FBZ (10 mol/L). The parent compounds and the metabolites were measured by HPLC. Both compounds are metabolized at the sulphur atom via two sequential oxidations, first to the sulphoxide (aldicarb sulphoxide and oxfendazole, respectively) and then to the sulphone. Oxfendazole and fenbendazole sulphone from FBZ, and aldicarb sulphoxide from ALD were found in both species. Aldicarb sulphone was not produced by the hepatocyte preparations from the bullock. The good correlation obtained comparing the in vitro results of FBZ metabolism with published in vivo dat obtained on FBZ kinetics in the same species confirmed the usefulness of in vitro models for predictive analysis of in vivo xenobiotic biotransformations.Abbreviations ALD aldicarb - ALDSON aldicarb sulphone - ALDSOX aldicarb sulphoxide - BSA bovine serum albumin - ID internal diameter - EGTA ethylene glycol bis(-aminoethyl ether) N,N,N,N-tetraacetic acid - FBZ fenbendazole - FBZSON fenbendazole sulphone - HBSS Hanks' balanced saline solution - HPLC high-pressure liquid chromatography - LDH lactate dehydrogenase - MFO mixed function oxidase - NCS newborn calf serum - OXF oxfendazole - WME Williams' Medium E  相似文献   

17.
The effect of endotoxin induced fever on the steady state concentration of sulphadimethoxine in pigs has been studied.Sulphadimethoxine 20 mg/kg b.wt. was injected at 9 a.m. in an ear vein each day for eleven days. From day 6 until the end of the experiment, endotoxin fromEscherichia coli 1.5 g/kg b.wt. was injected at 9 a.m. and at 3 p.m. The plasma concentration versus time curves were calculated by means of a computer program, assuming a two-compartment model. During the endotoxin injections the plasma concentrations were simulated and compared with those calculated.It was not possible to show any clinically significant changes in pharmacokinetics of sulphadimethoxine after the start of endotoxin injections.  相似文献   

18.
During the past decade it has been discovered that vitamin D3 (cholecalciferol) is converted into 25-hydroxycholecalciferol in the liver and that this compound in converted in the kidney into 1, 25-dihydroxycholecalciferol. These metabolites and particularly 1, 25-dihydroxycholecalciferol, rather than vitamin D itself, have powerful effects on calcium metabolism, stimulating the absorption of calcium from the gastrointestinal tract and the resorption of calcium from bone. A synthetic analogue of these metabolites, 1-hydroxycholecalciferol, is rapidly converted in the liver into 1, 25-dihycroxycholecalciferol. Thus the two metabolites and the synthetic analogue may be valuable for the prevention on treatment of milk fever.The three compounds, when administered in doses ranging from 0.5 to 32g/kg bodyweight increase the concentrations of calcium and phosphorus in the blood plasma of cattle more quickly than much larger doses of vitamin D3. Their principal effect is to stimulate the absorption of calcium from the gastrointestinal tract. At the same time they decrease the plasma concentration of magnesium slightly. Trials of 25-hydroxycholecalciferol and 1-hydroxycholecalciferol in the prevention of milk fever have shown promising results.
Kurzfassung Im vergangenen Jahrzehnt hat man festgestellt, dass das Vitamin D3 (Cholecalciferol) in der Leber in 25-Hydroxycholecalciferol umgewandelt wird und die Nieren diese Verbindung wiederum in 1, 25-Dihydroxycholecalciferol umbilden. Mehr noch als Vitamin D selbst zeigen diese Metaboliten und hier insbesondere das 1, 25-Dihydroxychlecalciferol umfangreiche Auswirkungen auf den Kalziummetabolismus, indem sie die Kalziumabsorption aus dem Magen-Darmtrakt und die Kalziumresorption der Knochen anregen. Ein synthetischer Analogstoff zu diesen Metaboliten, das 1- Hydroxycholecalciferol, wird in der Leber rasch in 1, 25-Dihydroxycholecalciferol umgewandelt. Die beiden Metaboliten und der synthetische Analogwirkstoff könnten daher für die Milchfieberprophylaxe bzw-therapie von Nutzen sein.Werden die drei Verbindungen in Dosen von 0,5 bis 32g/kg Körpergewicht verabreicht, so erhöht sich die Kalzium-und Phosphorkonzentration im Blutplasma der Kühe schneller als bei bedeutend höheren Dosen von Vitamin D3. Ihre Hauptwirkung liegt in der Anregung der Kalzium-absorption aus dem Magen-Darmtrakt. Gleichzeitig bauen sie jedoch auch in geringfügigem masse die Magnesiumkonzentration im Plasma ab. Versuche mit 25-Hydroxycholecalciferol und 1-Hydroxycholecalciferol haben bei der Milchfieberprophylaxe vielversprechende Ergebnisse gezeigt.
Resume Au cours de la dernière décennie, on a découvert que la vitamine D3 (cholécalciférol) se transformait en 25-hydroxycholécalciférol dans le foie et que ce composé se transformait en 1, 25-dihydroxy-cholécalciférol dans le rein. Ces métabolites, et en particulier le 1, 25-dihydroxycholécalciférol, ont, plus que la vitamine D elle-même, des effets puissants sur le métabolisme du calcium: ils stimulent l'absorption du calcium de l'appareil gastrointestinal et la résorption du calcium des os. Une substance homologue synthétique de cés metabolites, le 1-hydroxycholécalciférol, se transforme rapidement en 1, 25-dihydroxycholécalciférol dans le foie. Les deux métabolites et la substance homologue synthétique peuvent donc s'avérer précieux dans la prévention ou le traitement de la fièvre laiteuse.Administrés en doses allant de 0,5 à 32g/kg de poids corporel, ces trois composés augmentent les concentrations de calcium et de phosphore dans le plasma sanguin du bétail plus rapidement que des doses beaucoup plus fortes de vitamine D3. Ils ont pour principal effet de stimuler l'absorption du calcium de l'appareil gastro-intestinal. Simultanément, ils réduisent légèrement la concentration de magnésium dans le plasma. Les essais d'utilisation du 25-hydroxycholécalciférol et du 1-hydroxycholécalciférol pour la prévention de la fièvre laiteuse ont donné des résultats prometteurs.
Riassunto Nel corso dell'ultimo decennio si è scoperto che la vitamina D3 (colecalciferolo) viene trasformata nel fegato in 25-idrossicolecalciferolo, il quale, a sua volta, si trasforma nel rene in 1, 25-diidrossicolecalciferolo. Detti metaboliti, ed in specie l'1, 25-diidrossicolecalciferolo., più che la stessa vitamina D, hanno potenti effetti sul metabolismo del calcio, poichè ne stimolano l'assorbimento da parte dell' apparato digerente e l'anabolizzazione da parte delle ossa. Un composto sintetico analogo di questi metobiliti, l'1, idrossicolecalciferolo, viene rapidamente trasformato nel fegato in 1, 25-diidrossicolecalciferolo. Perciò i due metaboliti e il composto sintetico analogo possono essere utili per la profilassi e la cura della febbre da latte.I tre composti, se somministrati in dosi da 0.5 a 32g/kg peso corporeo, aumentano la concentrazione del calcio e del fosforo nel plasma sanguigno del bestiame più rapidamente di dosi molto maggiori di vitamina D3. Il loro effetto principale è quello di stimolare l'assorbimento del calcio da parte dell'apparato digerente. Contemporaneamente, essi riducono leggermente la concentrazione di magnesio nel plasma. Esperimenti con il 25-idrossicolecalciferolo nella profilassi della febbre da latte hanno dato risultati promettenti.
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19.
In order to assess the effect of suckling regime on calf growth and milk yield and offtake of zebu cattle in Mali, 59 zebu cow–calf pairs were allocated to suckling regimes: RI, cows were milked completely and the milk was bottle-fed ad libitum to their calves; RII, calves were suckled ad libitum by their dams prior to milking; RIII, cows were milked partially then allowed to suckle their calves; RIV, ad libitum suckling of calves prior to milking during the first three months of lactation and partial milking prior to suckling thereafter. The highest lactation milk yield (1150.6 kg) and offtake (647.6 kg), but the poorest calf growth (261 g/d to weaning) were observed in RIII. RIV significantly improved calf growth, 310 g/d, while allowing a milk offtake of 294.4 kg.  相似文献   

20.
The motility of the mammalian gastro-intestinal tract is regulated by a number of neuronal systems. The postganglionic, intramural parts of these systems are characterized by their neurotransmitters as cholinergic, adrenergic and purinergic nerves, respectively. The transmitter acetylcholine evokes contractions of the smooth muscle cell, whereas both noradrenalin and the transmitter from the purinergic nerves, presumably ATP, induce relaxations of smooth muscles. Agents and actions which influence the neurohumoral transmission and the mechanisms underlying the effects induced by the transmitters in smooth muscle cells are reviewed.  相似文献   

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