The effects of streptozotocin diabetes on the level of growth hormone, growth hormone releasing hormone, and somatostatin mRNA was measured in control rats, in diabetic rats maintained on insulin, and in diabetic rats in which insulin had been withheld for 3 days. Total cytoplasmic RNA samples were prepared from the pituitary and hypothalamic tissues of each animal and analyzed by dot blot or Northern blot hybridization. No significant difference was observed between control and insulin-treated groups with regard to body weight or plasma glucose concentration. The insulin withdrawal group had significantly higher plasma glucose concentrations and lower body weights, confirming diabetic status. There was no significant difference in the level of growth hormone, growth hormone releasing hormone, and somatostatin mRNA among any of the three groups however. We conclude that alterations in the regulation of circulating growth hormone in the streptozotocin-induced diabetic rat, removed from insulin treatment for 3 days, did not occur at the transcriptional or RNA processing level. This conclusion extends to hypothalamic growth hormone releasing hormone, and somatostatin gene expression as well. Regulatory changes in growth hormone level previously noted during insulin withdrawal in the streptozotocin-induced diabetic rat could be the result of post-transcriptional processes operating at the level of hormone synthesis or release.Key words: growth hormone, growth hormone releasing hormone, somatostatin, insulin, streptozotocin-induced diabetes, mRNA.
494 EFFECT OF HYPERTHYROIDISM UPON HUMAN PANCREATIC GROWTH HORMONE RELEASING HORMONE (HPGRH)-INDUCED SECRETION OF GROWTH HORMONE (GH) IN THE ADULT MALE RAT