- The current studies were undertaken to investigate the effects of chronic porcine growth hormone (pGH) administration on swine growth performance and binding of pGH and insulin to swine liver microsomal membranes. Highly purified pGH was administered daily by im injection (22 (mu)g/kg body weight) to rapidly growing Yorkshire barrows ((TURN)32 kg) for 30 days. Liver microsomal membranes were prepared from (TURN)60 kg barrows that had been treated with pGH for 30 days., Growth hormone treatment significantly increased growth rate (10%), feed efficiency (4%), cartilage growth and muscle mass. However, pGH did not affect carcass adipose tissue mass. Somatomedin-C (Sm-C) concentration in plasma from animals treated with pGH for 30 d was 55% higher (P < .05) than for control pigs. The temporal pattern of plasma Sm-C in pigs treated with 22 (mu)g or 44 (mu)g of pGH/kg indicatd that Sm-C concentration was elevated 1.5-fold (with 22 (mu)g) and 1.7-fold (with 44 (mu)g) between 4 and 22 h post-injection. Plasma glucose and insulin concentrations were both significantly increased in pGH-treated swine, suggesting that pGH had affected glucose metabolism by modulating tissue sensitivity to insulin. Plasma free fatty acid levels were higher in pGH-treated swine. Chronic administration of pGH depressed pituitary GH content and concentration approximately 45%, indicating that exogenous pGH exerted feedback inhibition on endogenous pGH production. Assessment of animal health during the trial and postmortem indicated no adverse effects of pGH treatment., and Binding of pGH to a specific receptor in swine liver microsomal membranes was time, pH, and membrane protein dependent. Specificity studies indicated that binding of labeled pGH was decreased more than 90% when 100 ng/ml of unlabeled pGH was added and that porcine prolactin poorly bound to pGH receptors (0.1% potency). Long-term (30 d) administration of pGH decreased pGH binding to liver microsomal membranes. This decrease was due to a decline in pGH receptor number. Whether this decrease in pGH binding is associated with a decrease in tissue sensitivity to pGH remains to be determined. However, pGH treatment did not affect insulin binding to swine liver microsomal membranes. This may support the suggestion that insulin resistance, often induced by a state of excess GH, is mediated at the postreceptor level.
- Dissertation Note:
- Ph.D. The Pennsylvania State University 1985.
- Source: Dissertation Abstracts International, Volume: 46-06, Section: B, page: 1755.
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