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Thyroid and Glucocorticoid Hormone Regulation of Rat Pituitary Growth Hormone Messenger Ribonucleic Acid as Revealed by in Situ Hybridization

MRC Group in Molecular Endocrinology, Laval University Medical Center Quebec, GlV 4G2 Canada

Address all correspondence and requests for reprints to: Dr Georges Pelletier, MRC Group in Molecular Endocrinology, Research Centre, Laval University Medical Centre, 2705 boulevard Laurier, Ste-Foy, Quebec, GlV 4G2 Canada.

Abstract

The effect of thyroid and glucocorticoid hormones on GH mRNA have been largely studied using tumor cell lines. To investigate the role of these hormones in vivo, we have used in situ hybridization techniques to study GH mRNA regulation in the rat pituitary. The amount of mRNA encoding for GH was dramatically reduced after 1 month of treatment with 6-N-propyl-2-tiouracil. However, daily injections of L-T₄ for 10 days restored GH mRNA to control levels. Similarly, adrenalectomy decreased GH mRNA levels, and subsequent daily injections of dexamethasone for 1 and 5 days restored the levels of GH mRNA to those before adrenalectomy. Moreover, 6-N-propyl-2-tiouracil treatment in combination with adrenalectomy dramatically reduced pituitary levels of GH mRNA, which were increased by administration of both thyroid hormones and glucocorticoids. These results show that the effects of thyroid and glucocorticoid hormones on GH synthesis are largely mediated by the hypothalamus. Our results obtained in implanted pituitaries under the kidney capsula demonstrated that these two hormones also exert a smaller effect of GH mRNA directly at the pituitary level.

Received March 24, 1989.

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				T. L. Miller and K. E. Mayo Glucocorticoids Regulate Pituitary Growth Hormone-Releasing Hormone Receptor Messenger Ribonucleic Acid Expression Endocrinology, June 1, 1997; 138(6): 2458 - 2465. [Abstract] [Full Text] [PDF]