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Search for other papers by I Louveau in
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During pubertal maturation, the increase in blood concentrations of sexual steroids is associated with a spurt in plasma IGF-I in primates, rats and cattle. However, data on the influence of sex steroids on plasma IGF-I during this physiological period are contradictory. Therefore, the present experiment was undertaken to understand better the relationships between pubertal development, energy metabolic regulation and the IGF-I/IGFBP system in crossbred gilts (Large White x Landrace). Circulating concentrations of hormones and metabolites were examined in ovariectomized (n = 6) and sham-operated females (n = 9) during sexual development. Surgery and first blood samplings were performed at 70 days of age. Growth curves were similar in ovariectomized and entire females. First oestrus and ovulation occurred between 178 and 209 days in entire gilts. From 84 days of age, plasma FSH concentration was lower in sham-operated than in ovariectomized gilts (P < 0.01) showing the negative feedback exerted by ovarian secretions on the gonadotrophin axis in entire gilts. Preprandial concentration of plasma glucose was not influenced by age whereas plasma free fatty acids decreased with age (P < 0.01). Concentrations of both metabolites were similar in ovariectomized and entire gilts. Plasma IGF-I and 43-39 kDa IGFBP levels increased whereas plasma 34 kDa IGFBP decreased with age (P < 0.01) and none of the levels differed between ovariectomized and entire gilts (P > 0.1). This experiment shows that gonadal steroids are not involved or play only a minor role in the control of IGF-I and IGFBP plasma levels during pubertal development in the female pig.
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The ability of GH to decrease fatness and insulin-regulated events such as lipogenic enzyme activities is well known in pigs. Nevertheless, the precise mechanism underlying these actions has not been elucidated yet. Expression of the transcription factor sterol regulatory element binding protein (SREBP)-1 has been reported as a key mediator of insulin action in rat hepatocytes and adipose cell lines. The present study aimed to determine whether the regulation of lipogenesis by GH and/or insulin in porcine adipocytes also involved SREBP-1. Isolated adipocytes, obtained from perirenal or s.c. adipose tissue samples of female pigs (51+/-0.4 kg; n=17), were cultured in serum-free medium in the absence or presence of these hormones for up to 4 days. Glucose incorporation and fatty acid synthase activity were increased by insulin in a dose-dependent manner in adipocytes of both sites. The increase was maximal at 1.7 and 17 nM in s.c. and perirenal adipocytes respectively, suggesting inter-depot differences in the regulation of lipogenesis by insulin. These insulin-stimulated events were decreased by GH (1 nM). No change in SREBP-1 mRNA levels was observed in response to GH and/or insulin. Taken together, these data indicate that the regulation of lipogenesis by insulin and GH appears to not involve changes in SREBP-1 mRNA levels in porcine adipocytes.
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The present study was undertaken to determine the effect of GH administration on GH and IGF-I receptors in skeletal muscle compared with liver in growing pigs. Plasma IGF-I and GH-binding protein (GHBP) levels were also determined. Twelve Large White pigs (castrated males) were treated daily with 100 micrograms pituitary porcine GH (pGH) per kg body weight or vehicle for 41 days intramuscularly. Relative to controls, pGH administration increased plasma IGF-I concentrations by 3.3-fold. Administration of pGH had no effect on plasma GHBP levels. In liver, 125I-labelled bovine GH (bGH)-specific binding (P < 0.05) and GH receptor (GHR) mRNA levels (P < 0.05) were higher in pGH-treated than in control pigs. In longissimus dorsi (LD), 125I-labelled bGH specific binding did not differ significantly between the two groups while GHR mRNA levels (P < 0.05) were lower in pGH-treated than in control pigs. Administration of pGH had no effect on 125I-labelled bGH-specific binding and GHR mRNA levels in trapezius (TR). 125I-Labelled IGF-I-specific binding in liver was unaffected by pGH administration. Similarly, in liver, LD and TR, IGF-I receptor mRNA levels were not different between pGH-treated and control animals. It can be concluded that (1) GH binding and IGF-I receptor mRNA are not affected by GH in skeletal muscle, (2) GH influences GHR in a tissue-specific manner and (3) hepatic GHR and GHBP levels are not co-regulated.
Search for other papers by S Schnoebelen-Combes in
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Abstract
The present study was undertaken to examine the developmental pattern of GH receptor (GHR) and GHR gene expression in skeletal muscle (longissimus dorsi and trapezius (TR)) and liver from the last third of gestation until 1 year of age in male Large White (LW) and Meishan (MS) pigs. Plasma GH-binding protein (GHBP) levels were also measured. 125I-Labelled bovine GH (bGH) specific binding (not determined in foetal TR) and GHR mRNA were detected in skeletal muscle from 75 days of gestation until the adult stage with no clear age-related changes. By contrast, 125I-labelled bGH specific binding and GHR mRNA were undetectable or barely detectable in foetal liver. After birth, 125I-labelled bGH specific binding (P<0·001) and GHR mRNA in liver increased with age. The level of bGH binding to liver membranes was higher in MS than in LW pigs at 1, 45, 80 and 120 days of age and did not differ between breeds at the other ages. Specific binding of 125I-labelled human GH (hGH) to plasma GHBP was easily detected as early as 75 days of gestation and increased with age (P<0·001). The level of hGH binding to plasma GHBP was higher in MS than in LW pigs at 1, 80 and 120 days of age. It can be concluded that (1) the developmental expression of the GHR is tissue-specific, (2) the presence of GHBP in foetuses despite the absence of GHR in liver suggests that other tissues such as skeletal muscle could contribute to the generation of GHBP and (3) the presence of GHR in skeletal muscle as early as 75 days of gestation suggests that GH may play a role in foetal muscle growth.
Journal of Endocrinology (1996) 148, 249–255
