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1.
Age-dependent interactions between environmental temperature and porcine growth hormone (pGH) treatment on the function of the somatotrophic axis were evaluated in the neonatal pig. At 3 d of age, 40 Landrace x Yorkshire x Duroc piglets received intraperitoneal implants containing either recombinant pGH (0.5 mg/d; n = 20) or vehicle (control; n = 20). Piglets were maintained at either a low (21 degrees C, 50% relative humidity; n = 20) or high (32 degrees C, 50% relative humidity; n = 20) temperature. At 4 and 6 wk of age, 5 pGH-treated and 5 control piglets from each thermal group were sacrificed for tissue collection. Blood samples were collected at the time of sacrifice and analyzed for serum concentrations of GH, insulin-like growth factor 1 (IGF-1), and IGF-2. Liver RNA was analyzed for mRNAs specific for the GH receptor, IGF-1, IGF-2, and IGF binding protein 3. There was no effect of pGH treatment (P = 0.4) on average daily gain; however, both age (P = 0.002) and temperature (P = 0.001) had an effect on average daily gain such that those animals maintained at a low temperature and those sacrificed at 6 wk had greater average daily gains. Serum concentration of GH was elevated (P = 0.003) by pGH treatment and was lowest in the 6-wk-old group (P = 0.008). Serum concentration of IGF-1 was elevated (P = 0.007) by pGH treatment and increased with age (P = 0.01). Liver GH receptor mRNA was unaffected (P > 0.5) by pGH treatment, but was greater in the 6-wk-old group (P < 0.0001) and in piglets maintained at the high temperature (P = 0.04). IGF-1 mRNA was enhanced by pGH treatment (P = 0.0003) and by exposure to the high temperature (P = 0.04), but did not differ (P > 0.5) between age groups. IGF-2 mRNA was greater (P = 0.0009) in the 4-wk-old group and in piglets maintained at the high temperature (P = 0.007), but was unaffected (P = 0.5) by pGH treatment. IGF binding protein 3 mRNA increased with age (P = 0.0004) and was stimulated by pGH treatment in the 6-wk-old group (P = 0.034). The relatively lower level of GH receptor and IGF mRNAs in conjunction with greater growth in the cold environment suggests that somatotrophic gene expression in the liver is not rate limiting for growth in the neonatal pig.  相似文献   

2.
The influences of thermal environment and individual growth rate on somatotroph and lactotroph function were examined in 6-week-old barrows reared entirely in a hot (H: 27–32°C, n = 8) or cool (C: 21°C, n = 10) environment. Growth hormone (GH) and prolactin (PRL) cell contents and responses to growth hormone-releasing hormone (GHRH) or thyrotropin-releasing hormone (TRH) were evaluated in cultured pituitary cells from each animal. Plasma GH, PRL, and insulin-like growth factor-1 (IGF-1) concentrations also were monitored. Thermal environment did not affect in vitro GH secretion, cellular GH content, or plasma GH concentrations. Stimulated in vitro GH release (GHRH-basal) and plasma GH were inversely related to average daily gain (ADG, r = −.76, p < .005 and r = −.51, p < .05, respectively). Cellular GH content also declined as ADG increased (r = −.57, p < .05). Plasma IGF-1 concentrations were not affected by thermal environment and were not related to ADG. Pituitary cells from H animals secreted and contained more PRL than cells from C animals (p < .05). Plasma PRL values were correlated with ADG (r = .54, p < .05), but did not differ between thermal groups. Stimulated in vitro PRL (TRH-vehicle) secretion was positively related with ADG only in the H group (r = .97, p < .001). In contrast, cellular PRL content decreased with ADG in cells from the H barrows (r = −.8, p < .05). Lactotroph function was not related to growth in cells from C pigs. In summary, 1) heat enhanced PRL secretion and cell content; 2) growth and somatotroph function were inversely related; and 3) serum PRL and the PRL response to TRH in cells from H barrows were positively related to growth.  相似文献   

3.
Studies were conducted to determine the specificity and cause of altered pituitary hormone secretion when ewes ingest endophyte-infected (Acremonium coenophialum) GI-307 tall fescue (toxic fescue). Plasma concentrations of prolactin (PRL) but not growth hormone (GH) or thyroid stimulating hormone (TSH) in ewes grazing toxic fescue were significantly lower (P < .01) than concentrations measured in ewes grazing orchardgrass (OG). Comparing hormone secretory responses of ewes grazing each grasstype, ewes on toxic fescue released less PRL following thyrotropin releasing hormone (TRH) challenge than ewes on OG. TSH responses to TRH were not affected by grasstype. At this dose of TRH, GH secretion was not significantly affected in either group of ewes. In a separate study, dopamine hydrochloride (DA) was infused into control ewes to define the effect of a pure dopamine agonist on basal and TRH-stimulated secretion of PRL, GH and TSH. DA depressed both basal and TRH-stimulated secretion of PRL without affecting the basal concentrations or responses of GH or TSH. Based on the assumption that the active agent in toxic fescue responsible for the observed hypoprolactinemia was a dopaminergic agonist, haloperidol (HAL), a DA receptor blocking drug, was administered to ewes grazing toxic fescue or OG. HAL evoked significant PRL secretion unaccompanied by any GH or TSH effect in both toxic fescue and OG ewes. Administration of HAL resulted in a gradual increase over 4 hr in PRL in toxic fescue ewes and prolonged the duration of the PRL response to TRH. No differences in circulating plasma concentrations of DA, epinephrine or norepinephrine were measured in ewes on troxic fescue or OG.

Alterations in pituitary hormone secretion due to toxic factors in fescue were confined to PRL. Hormone secretory responses to TRH and HAL suggest that the effects on PRL are mediated through dopamine-like activity in toxic fescue.  相似文献   


4.
The current study was undertaken to determine the effects of human growth hormone-releasing factor [hpGRF-(1-44)-NH2] on growth performance in pigs and whether this response was comparable to exogenous porcine growth hormone (pGH) treatment. Preliminary studies were conducted to determine if GRF increased plasma GH concentration after iv and im injection and the nature of the dose response. Growth hormone-releasing factor stimulated the release of pGH in a dose-dependent fashion, although the individual responses varied widely among pigs. The results from the im study were used to determine the dose of GRF to use for a 30-d growth trial. Thirty-six Yorkshire-Duroc barrows (initial wt 50 kg) were randomly allotted to one of three experimental groups (C = control, GRF and pGH). Pigs were treated daily with 30 micrograms of GRF/kg body weight by im injection in the neck. Pigs treated with pGH were also given 30 micrograms/kg body weight by im injection. Growth rate was increased 10% by pGH vs C pigs (P less than .05). Growth rate was not affected by GRF; however, hot and chilled carcass weights were increased 5% vs C pigs (P less than .05). On an absolute basis, adipose tissue mass was unaffected by pGH or GRF. Carcass lipid (percent of soft-tissue mass) was decreased 13% by GRF (P less than .05) and 18% by pGH (P less than .05). Muscle mass was significantly increased by pGH but not by GRF. There was a trend for feed efficiency to be improved by GRF; however, this was not different from control pigs. In contrast, pGH increased feed efficiency 19% vs control pigs (P less than .05). Chronic administration of GRF increased anterior pituitary weight but did not affect pituitary GH content or concentration. When blood was taken 3 h post-injection, both GRF- and pGH-treated pigs had lower blood-urea nitrogen concentrations. Serum glucose was significantly elevated by both GRF and pGH treatment. This was associated with an elevation in serum insulin. These results indicate that increasing the GH concentration in blood by either exogenous GH or GRF enhances growth performance. The effects of pGH were more marked than for GRF. Further studies are needed to determine the optimal dose of GRF to administer in growth trials and the appropriate pattern of GRF administration in order to determine whether GRF will enhance pig growth performance to the extent that exogenous pGH does.  相似文献   

5.
The present study evaluated somatotrophic gene expression in liver, muscle and adipose tissue 4 d after weaning, a time point corresponding to greatly reduced serum concentrations of insulin-like growth factor (IGF)-1 and IGF-2 in pigs. Two-week-old barrows were either cross-fostered to a sow (SOW, N = 8) or weaned and fed a phase 1 diet containing either 0 or 7% spray-dried plasma (NP, N = 8 and SDP, N = 8; respectively). Piglets were allocated such that two size groups were equivalently represented in each experimental group (small, 3.5–4.3 kg and large, 4.6–5.7 kg). Animals were weighed daily and sacrificed 4 d after weaning for blood and tissue collection. Daily gains of the SOW piglets were significantly greater than those of the weaned pigs for the first 3 d of the experiment (P < 0.0001). Weight gains in the SOW and SDP pigs between d 3 and 4 were equivalently elevated relative to the NP pigs (P < 0.0001). Serum IGF-1 and IGF-2 concentrations were decreased in both NP and SDP compared to SOW (P < 0.0001). Serum IGF-2 levels were significantly lower in small piglets (P = 0.006). A Weaning Group X Size interaction was noted for liver IGF-2 mRNA (P < 0.03), reflecting a higher level of expression in large SOW piglets relative to small SOW piglets. Weaning did not affect IGF-1, IGF-2, or growth hormone (GH) receptor mRNA levels in liver, muscle, or fat (P > 0.05). Liver IGF-binding protein (IGFBP)-3 and acid-labile subunit (ALS) mRNA levels also were unaffected by weaning. Small pigs had lower levels of liver ALS (P = 0.0003), muscle IGF-2 (P = 0.02), and muscle GH receptor (P = 0.006) mRNAs. In contrast, adipose tissue IGF-1 and IGF-2 mRNA levels were greatest in the small piglets (P = 0.001 and 0.029, respectively).  相似文献   

6.
We found previously that porcine growth hormone (pGH) causes an increase in growth rate with a concurrent improvement in carcass composition in pigs. The somatomedin, insulin-like growth factor 1 (IGF-1), is though to play a major role in mediating some of the anabolic actions of GH, while the glucocorticoid hormones are potential counter-regulators of these effects. The present study was conducted to determine the temporal and dose-response relationship between GH administration and serum IGF-1 and cortisol concentrations in pigs. Twelve Yorkshire barrows, fitted with femoral artery catheters, were injected (im) with either 0, 10, 100 or 1,000 micrograms/kg pGH. Blood sampling began 40 min prior to pGH injection and was continued for 37 h. Serum GH, IGF-1 and cortisol concentrations were determined by radioimmunoassay. In control animals, serum GH concentrations ranged from 1.6 to 5.7 ng/ml over 37 h. In the animals treated with increasing doses of pGH, peak serum GH concentrations reached 28, 112 and 286 ng/ml and levels remained elevated for 4, 12 and 24 h, respectively. Serum IGF-1 concentrations were elevated by pGH after a lag time of 4 to 6 h. When the IGF-1 concentrations were integrated over time, the response appeared to be dose-dependent, with an ED50 of 710 micrograms/kg body weight (BW). Data for serum cortisol concentrations showed a great deal of individual variation. A transient increase in cortisol was observed, but only in the group treated with 1,000 micrograms pGH/kg BW. Cortisol levels returned to baseline 2 h after pGH injection.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

7.
The effects of weaning and changing post-weaning diet composition on growth patterns and growth-related hormonal profiles were evaluated in neonatal pigs. Forty-eight crossbred piglets were assigned to two groups (n = 24/group) based on weaning at 2 or 3 wk of age (2W and 3W groups, respectively). At weaning, piglets were removed from the sow and placed on a commercial starter ration for the first 11 d post-weaning (Phase I diet). At Day 12 post-weaning, pigs were placed on a growing ration for the remainder of the study (Phase II diet). Body weights and blood samples were collected twice weekly from birth until 42 d of age. Serum insulin-like growth factor (IGF)-1, IGF-2, and average daily gain (ADG) were reduced (P < 0.05) in both groups as a result of weaning, whereas serum growth hormone (GH) was elevated (P < 0.05). Earlier weaning resulted in a greater reduction in growth rate and serum IGF-2 values (P < 0.05). Mild reductions in ADG occurred after the Phase I to II dietary change in both weaning groups (P < 0.05), but serum IGF-1 decreased only in the 2W group (P < 0.05). Growth hormone concentrations tended to increase after the change in post-weaning diets (P = 0.07 and 0.16 in 2W and 3W, respectively). Serum thyroxine (T4) and triiodothyronine (T3) levels were unaltered by weaning but declined in both groups after the change in starter diets (P < 0.05). Changes in cortisol concentrations were not associated with weaning or the change in post-weaning diets. With the exception of serum IGF-1 concentrations, which were elevated in the 2W group, growth and endocrine endpoints were equivalent between experimental groups at the end of the study (42 d of age). These results indicate that earlier weaning and changing solid diets can more severely affect patterns of early growth and related hormone secretion, but effective compensatory mechanisms restore normal physiological and physical development.  相似文献   

8.
Long-term administration of porcine growth hormone-releasing factor (pGRF(1-29)NH2) and(or) thyrotropin-releasing factor (TRF) was evaluated on serum concentrations of growth hormone (GH) thyroxine (T4) and prolactin (PRL). Twenty-four 12-wk-old female Yorkshire-Landrace pigs were injected at 1000 and 1600 for 12 wk with either saline, pGRF (15 micrograms/kg), TRF (6 micrograms/kg) or pGRF + TRF using a 2 x 2 factorial design. Blood samples were collected on d 1, 29, 57 and 85 of treatment from 0400 to 2200. Areas under the GH, T4 and PRL curves (AUC) for the 6 h (0400 to 1000) prior to injection were subtracted from the postinjection periods (1000 to 1600, 1600 to 2200) to calculate the net hormonal response. The AUC of GH for the first 6 h decreased similarly (P less than .05) with age for all treatments. The GH response to GRF remained unchanged (P greater than .10) across age. TRF alone did not stimulate (P less than .05) GH release but acted in synergy with GRF to increase (P less than .05) GH release. TRF stimulated (P less than .001) the net response of T4 on all sampling days. Animals treated with the combination of GRF + TRF showed a decreased T4 AUC during the first 6 h on the last three sampling days. Basal PRL decreased (P less than .05) with age. Over the four sampling days, animals injected with TRF alone showed (P less than .01) a reduction (linear effect; P less than .01) followed by an increase (quadratic effect; P less than .05) in total PRL concentration after injection; however, when GRF was combined with TRF, such effects were not observed (P greater than .10). Results showed that 1) chronic injections of GRF for 12 wk sustained GH concentration, 2) TRF and GRF acted synergistically to elevate GH AUC, 3) TRF increased T4 concentrations throughout the 12-wk treatment period, 4) chronic TRF treatment decreased the basal PRL concentration and 5) chronic GRF + TRF treatment decreased the basal concentration of T4.  相似文献   

9.
Stimulation of swine growth by porcine growth hormone   总被引：7，自引：0，他引：7  
Highly purified porcine growth hormone (pGH; USDA-B1) was administered by im injection (22 micrograms X kg body weight-1 X d-1) to rapidly growing Yorkshire barrows for 30 d. Growth hormone significantly increased growth rate (10%), feed efficiency (4%), cartilage growth and muscle mass. However, pGH did not affect carcass adipose tissue mass. Intramuscular lipid content of the longissimus was increased 50% by pGH administration. Plasma pGH concentration was elevated (7- to 11-fold) for 3 to 5 h post-injection. Chronic administration of pGH depressed pituitary GH content and concentration approximately 45%. No GH antibodies were detected in the plasma of GH-treated swine. Plasma somatomedin-C concentration was increased 55% by GH treatment 3 h post-injection. Plasma glucose and insulin concentrations were both significantly increased in GH-treated swine, suggesting that the animals had developed a state of insulin resistance. Plasma-free fatty acid concentration tended to be higher in GH-treated animals. Treatment of swine with pGH significantly decreased plasma blood urea nitrogen. Assessment of animal health during the trial and postmortem indicated that pGH administration did not have any adverse effects. In summary, treatment of young, rapidly growing swine with pGH stimulated growth performance without affecting animal health or inducing the production of GH antibodies.  相似文献   

10.
This study focused on the expression of somatotropic axis genes in the skeletal muscle of dairy cattle. A slow-release recombinant bovine growth hormone (GH) (rbGH) formulation was administered to 5 cows, and saline solution (control) was administered to another 5 cows every 2 wk for a total of 10 wk, starting from the peak of lactation. Tissue and blood samples were collected on days 2 and 14 after each rbGH injection. As target genes insulin-like growth factor (IGF)-1, IGF-2, IGFBPs (1, 2, 3, 4, 5, 6), acute labile subunit (ALS), IGF-1 receptor (IGF-1R), GH receptor (GHR), and the known GHR 5′-UTR variants were selected as target genes, and their relative expression was measured using real-time polymerase chain reaction. In GH-treated cows, an increase in expression was observed for GHR 5′-UTR variant 1I on day 14 (P < 0.05), whereas a significant down-regulation of GHR (P < 0.05) was found after comparing values of treated cows between day 2 and day 14. However, only IGF binding proteins (BP)-5 was found to be appreciably up-regulated in GH-treated cows (P < 0.001), which may indicate the importance of this gene in the overall molecular response to GH administration. Our study indicated that GH treatment did not affect the expression of most somatotropic axis genes, despite the marked increase in GH and IGF-1 in blood (P < 0.001). Nor did it have a large impact on the proportion of GHR 5′-UTR variants in the skeletal muscle of lactating cows. Finally, although we observed a significant variation in the expression of some genes, it would appear that the differences between GH-treated cows and controls were not great enough to be considered as reliable indirect indicators of GH treatment in dairy cattle.  相似文献   

11.
In the present study, pigs were treated daily for 7 days with exogenous porcine growth hormone (pGH; 70 micrograms/kg BW) in order to determine whether pGH induced insulin and insulin-like growth factor 1 (1GF-1) resistance in pig adipose tissue. In the first experiment, pituitary-derived pGH (ppGH) decreased basal and insulin-stimulated lipogenesis by 50%. Insulin sensitivity decreased more than 90% as the result of pGH treatment. Sensitivity and responsiveness to IGF-1 were decreased 50% by ppGH. In a second experiment, pigs were treated daily (70 micrograms/kg BW) with exogenous pituitary pGH (ppGH) or recombinant pGH (rpGH) for 7 days in order to determine if the effects of pGH were intrinsic properties of the hormone. Both rpGH and ppGH caused similar decreases in basal rates of lipogenesis, insulin- and IGF-1-stimulated lipogenesis, and insulin and IGF-1 responsiveness in pig adipose tissue. In summary, the decrease in adipose tissue growth of pigs treated chronically with pGH is due in large part to the suppression of fatty acid synthesis and a decrease in the ability of insulin to stimulate lipid synthesis in pig adipocytes. These responses are intrinsic properties of pGH since the effects of rpGH mimicked those of ppGH. The role and importance of a decrease in IGF-1 responsiveness remains to be resolved.  相似文献   

12.
Background: A recent study of dogs with induced primary hypothyroidism (PH) demonstrated that thyroid hormone deficiency leads to loss of thyrotropin (TSH) hypersecretion, hypersomatotropism, hypoprolactinemia, and pituitary enlargement with large vacuolated "thyroid deficiency" cells that double-stained for growth hormone (GH) and TSH, indicative of transdifferentiation of somatotropes to thyrosomatropes.
Hypothesis: Similar functional changes in adenohypophyseal function occur in dogs with spontaneous PH as do in dogs with induced PH, but not in dogs with nonthyroidal illness (NTI).
Animals: Fourteen dogs with spontaneous PH and 13 dogs with NTI.
Methods: Adenohypophyseal function was investigated by combined intravenous administration of 4 hypophysiotropic releasing hormones (4RH test), followed by measurement of plasma concentrations of ACTH, GH, luteinizing hormone (LH), prolactin (PRL), and TSH. In the PH dogs this test was repeated after 4 and 12 weeks of thyroxine treatment.
Results: In 6 PH dogs, the basal TSH concentration was within the reference range. In the PH dogs, the TSH concentrations did not increase with the 4RH test. However, TSH concentrations increased significantly in the NTI dogs. Basal and stimulated GH and PRL concentrations indicated reversible hypersomatotropism and hyperprolactinemia in the PH dogs, but not in the NTI dogs. Basal and stimulated LH and ACTH concentrations did not differ between groups.
Conclusions and Clinical Importance: Dogs with spontaneous PH hypersecrete GH but have little or no TSH hypersecretion. Development of hyperprolactinemia (and possible galactorrhea) in dogs with PH seems to occur only in sexually intact bitches. In this group of dogs with NTI, basal and stimulated plasma adenohypophyseal hormone concentrations were not altered.  相似文献   

13.
本研究旨在探讨不同泌乳相关激素和生长因子对奶牛乳腺上皮细胞增殖的影响及其与细胞外基质主要成分层黏连蛋白的关系。将正常的荷斯坦泌乳期奶牛乳腺上皮细胞进行体外培养,在未包被或包被层黏连蛋白的条件下,以MTT法检测催乳素(PRL)、牛生长激素(GH)、类胰岛素生长因子-1(IGF-Ⅰ)、类胰岛素生长因子-2(IGF-Ⅱ)对细胞增殖作用的影响。在层黏连蛋白包被条件下,进行血清恢复的同时添加不同泌乳相关激素和生长因子,GH、IGF-Ⅰ有促进细胞增殖的作用(P<0.05),PRL、IGF-Ⅱ有维持细胞存活的作用(P<0.05);无血清时,几种激素和生长因子单独添加均无明显促增殖效应(P>0.05)。无基质条件下,与血清联合使用时,PRL、GH、IGF-Ⅰ、IGF-Ⅱ均对细胞生长有不同程度促进作用(P<0.05);无血清时,仅IGF-Ⅰ使细胞增殖速率显著加快(P<0.05)。层黏连蛋白作为培养基质对于体外培养的泌乳乳腺上皮细胞生长速度没有显著促进作用,但有利于PRL和IGF-Ⅱ发挥促存活作用。PRL、GH、IGF-Ⅰ、IGF-Ⅱ对细胞增殖和存活有促进作用,但需要与血清中其他成分协同才能充分发挥作用,其中IGF-Ⅰ促增殖能力最强。  相似文献   

14.
The relationship between in vitro somatotroph function and growth was examined in piglets demonstrating a continuous range of growth characteristics. Twenty barrows were sacrificed at 3 weeks of age for the collection of pituitary tissue and blood. Pituitary cells from each animal were cultured and exposed to vehicle (culture medium); .1, 1, and 10 nM growth hormone-releasing hormone (GHRH); 2 mM 8-Br-cAMP (cAMP); 100 nM phorbol myristate acetate (PMA); and 59 mM KCl. All secretagogue treatments stimulated growth hormone (GH) secretion (p < .0001). Basal and stimulated GH secretion in culture, intracellular GH content (icGH), and serum insulin-like growth factor-1 (IGF-1) concentrations were all positively correlated with 3-week weight gain (p < .05). Concentrations of GH in the serum sample taken at sacrifice were not related to growth (p < .3). Intracellular GH content was correlated with in vitro GH secretion (p < .01) and serum IGF-1 concentrations (p < .001). Somatotroph function was contrasted in the 7 largest and 7 smallest piglets (large, 8.3 ± .3 kg, n = 7; small, 4.5 ± .2 kg, n = 7). Treatment with GHRH produced a dose-related increase in GH secretion in both experimental groups (p < .0001). No significant size × GHRH interaction was detected (p = .09). When contrasted with the small group, the large group demonstrated elevated GH secretion in culture (p < .01), icGH content (p < .001), and circulating IGF-1 (p < .001). The results of this study raise the possibility of a functional relationship between porcine somatotroph secretory activity and growth, mediated by IGF-1, which may be regulated by the quantity of GH available for release.  相似文献   

15.
From case studies in humans it is known that primary hypothyroidism (PH) may be associated with morphological and functional changes of the pituitary. There is no insight into the time scale of these changes. In this study, seven beagle dogs were followed up for 3 years after the induction of primary hypothyroidism. Three of these dogs were followed up for another 1.5 years while receiving l-thyroxine. Adenohypophyseal function was investigated at 2-month intervals with the combined intravenous injection of CRH, GHRH, GnRH, and TRH, and measurement of the plasma concentrations of ACTH, GH, LH, PRL, and TSH. In addition, after 2 years of hypothyroidism a single TRH-stimulation test and a somatostatin test were performed, with measurements of the same pituitary hormones. Every 6 months the pituitary gland was visualized by computed tomography (CT). Induction of PH led to high plasma TSH concentrations for a few months, where after concentrations gradually declined to values no longer significantly different from pre-PH values. A blunted response to stimulation of TSH release preceded this decline. Basal plasma GH concentrations increased during PH and there was a paradoxical hyperresponsiveness to TRH stimulation. Basal GH concentrations remained elevated and returned only to low values during l-thyroxine treatment. Basal PRL concentrations decreased significantly during PH and normalized after several months of l-thyroxine treatment. The pituitary gland became enlarged in all dogs. Histomorphology and immunohistochemical studies in 4 dogs, after 3 years of PH, revealed thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and decreased numbers of mammotrophs. Several cells stained for both GH and TSH. In conclusion, with time PH led to a loss of the TSH response to low T4 concentrations, hypersecretion of GH, and hyposecretion of PRL. The enlarged pituitaries were characterized by thyrotroph hyperplasia, large vacuolated thyroid deficiency cells, and double-staining cells, which are indicative of transdifferentiation.  相似文献   

16.
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18.
GH secretion is increased in scrapie-diseased sheep. Although the role of the somatotropic axis as a neurotrophic and neuroprotective factor is well documented, no studies have been carried out on the mechanisms and functional significance of somatotropic perturbation in the pathophysiology of prion-associated neurodegenerative disease. The goal of this study was to test the hypothesis that increased GH secretion observed in a natural animal prion disease, scrapie, might reflect a general lack of action of IGF-1 and, more particularly, a suppressed IGF-1 negative feedback. The effect of human recombinant IGF-1 (rhIGF-1) on spontaneous and GHRH-induced secretions was studied in so-called “scrapie-resistant” and “scrapie sensitive” rams in vivo and in vitro on pituitary dissociated cells from both groups. The effect of rhIGF-1 infusion on spontaneous and GHRH-induced GH secretions was evaluated during the preclinical and clinical stages of the disease in vivo. Our results indicated that rhIGF-1 suppressed spontaneous GH secretion but not GHRH-induced secretion in vivo. RhIGF-1 had no effect on spontaneous and GHRH-induced GH secretion from dissociated pituitary cells. Clinical scrapie was associated with a significantly greater rhIGF-1-induced inhibition of GH spontaneous secretion (mean ± S.E.M. inhibition of GH secretion: 31 ± 8% vs. 45 ± 4% in control and scrapie-affected rams, respectively). It can be concluded that the increase in GH secretion in scrapie-affected animals does not reflect a global lack of action of IGF-1. Further investigations are required to determine if other IGF-1 effects and more particularly neuroprotective mechanisms are altered in prion-associated neurodegenerative diseases.  相似文献   

19.
Objectives of this study were to evaluate effects of seven sire breed groups and three levels of daily ME intake (DMEI = 132 or 189 kcal ME/kg BW(0.75) or ad libitum), beginning 5 mo prepartum, on BCS, length of postpartum anestrus, and circulating concentrations of IGF-1 and GH in F1 cows (six to eight cows per sire breed in each DMEI group) out of Angus or Hereford dams. At the initiation of the study, BW were 522, 530, 548, 572, 575, 577, and 595 kg for cows sired by Longhorn, Galloway, 1960s Hereford or Angus, 1980s Hereford or Angus, or Nellore, Salers, and Shorthorn bulls, respectively (SE = 13; P < 0.001 for sire breed). After 4 mo on DMEI treatment during the pre-partum period, cows fed 132 kcal of ME/kg BW(0.75)gained little to no BW; cows fed 189 kcal ME/kg BW(0.75) gained 50 kg; and cows fed ad libitum gained 70 kg (all groups differ P < 0.05). Concentrations of progesterone in weekly blood samples collected 2 to 14 wk after calving were used to establish when normal luteal function resumed to predict length of postpartum anestrus. Length of anestrus was affected by level of DMEI in cows sired by Galloway, Longhorn, and Nellore bulls, but not other breeds (P < 0.02 for interaction of sire breed and DMEI). Level of DMEI, but not sire breed, affected (P < 0.01) BCS at wk 2 postpartum. Concentrations of IGF-1 at wk 2 postpartum differed (P < 0.001) due to sire breed, and changes in concentrations of IGF-1 from wk 2 to 14 were influenced (P < 0.03) by the interaction of sire breed and level of DMEI; which was primarily the result of differences in rate of decrease over time among different sire breed x level of DMEI groupings. Concentrations of GH did not differ due to sire breed but varied (P < 0.001) due to the interaction of DMEI and week postpartum, for which concentrations of GH did not differ at wk 2 but increased over time at rates that were inversely proportional to level of DMEI. Length of anestrus was negatively associated (P < 0.05) with day of calving, BCS, and BW. When effects of sire breed and level of DMEI were accounted for (residual correlation), length of anestrus was inversely associated (P < 0.01) with IGF-1 concentrations. Breed of sire influenced length of postpartum anestrus and energy balance, as predicted by IGF-1, in crossbred cows fed varying levels of DMEI.  相似文献   

20.
To study the regulation of leptin secretion in sheep, we infused glucose (0.32 g/h/kg for 12 h) into GH-transgenic animals (n = 8) that have chronically high plasma concentrations of ovine GH and insulin, but low body condition and low plasma leptin concentrations, and compared the responses with those in controls (n = 8). In both groups, the infusion increased plasma concentrations of glucose and insulin within 1 h and maintained high levels throughout the infusion period (P < 0.0001). Compared with controls, GH-transgenics had higher concentrations of insulin, IGF-1, GH (all P < 0.0001) and cortisol (P < 0.05), but lower GH pulse frequency (P < 0.0001). Overall, leptin concentrations were lower in GH-transgenics than in controls (P < 0.01). A postprandial increase in leptin concentrations was observed in both groups, independently of glucose treatment, after which the values remained elevated in animals infused with glucose, but returned to basal levels in those infused with saline, independently of transgene status. In both GH-transgenics and controls, glucose infusion did not affect the concentrations of GH, IGF-1, or cortisol. In conclusion, GH-transgenic and control sheep show similar responses to glucose infusion for leptin and other metabolic hormones, despite differences between them in body condition and basal levels of these hormones. Glucose, insulin, GH, IGF-1 and cortisol are probably not major factors in the acute control of leptin secretion in sheep, although sustained high concentrations of GH and IGF-1 might reduce adipose tissue mass or inhibit leptin gene expression.  相似文献   

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