Comparative effects of food restriction, fasting, diabetes and thyroidectomy on growth hormone and thyrotropin gene expression in the rat pituitary.

Abstract

To examine the molecular basis for the decreased pituitary growth hormone (GH) and thyrotropin (TSH) content during restricted feeding, fasting and diabetes, we measured steady-state levels of mRNA for TSH-alpha, TSH-beta and GH in the pituitary from normal rats either fed ad libitum (C), limited to 75%, 50% and 25% (FR75, FR50, FR25, respectively) of ad libitum intake, or deprived of food for 2 and 4 days (F2 and F4, respectively), and also in streptozotocin-diabetic (D) and D insulin-treated animals. The results from these experimental groups were compared with those in thyroidectomized (Tx) rats. Pituitary mRNA was quantified by Northern blot hybridization with cDNA probes specific for rat TSH-alpha, TSH-beta and GH. Although changes in the pituitary GH mRNA during restricted feeding, fasting and diabetes were similar qualitatively to those induced by hypothyroidism, GH mRNA levels in Tx rats (> 10% of C values) were less than in the other experimental groups (p < 0.001). Pituitaries from FR50, FR25 and D rats also contained less GH mRNA than F2 and F4 animals (p < 0.05). Thyroidectomy resulted in a marked increase in both TSH-beta and TSH-alpha mRNAs, the changes in TSH-beta mRNA being greater than those in TSH-alpha mRNA. In contrast, FR50, FR25, F2, F4 and D rats exhibited a decrease in pituitary TSH-beta mRNA (60%, 50%, 35%, 36% and 33%, respectively, of C values; p < 0.01-0.05) and in TSH-alpha mRNA levels (81%, 64%, 46%, 43% and 36%, respectively, of normal values; p < 0.02-0.05), TSH-beta mRNA showing the greater changes.(ABSTRACT TRUNCATED AT 250 WORDS)