Effects of thyroid hormone deficiency and replacement on rat hypothalamic growth hormone (GH)-releasing hormone gene expression in vivo are mediated by GH

Molecular Endocrinology
T R DownsL A Frohman

Abstract

The role of thyroid hormone and GH in the regulation of hypothalamic GH-releasing hormone (GRH) gene expression in the rat was examined after the induction of thyroid hormone deficiency by thyroidectomy. Thyroidectomy resulted in a time-dependent decrease in hypothalamic GRH content, which was significant by 2 weeks postoperatively, and a reduction in pituitary GH content to 1% of the control level by 4 weeks. In contrast, GRH secretion by incubated hypothalami under both basal and K(+)-stimulated conditions was increased after thyroidectomy. Hypothalamic GRH mRNA levels also exhibited a time-dependent increase, which was significant at 1 week and maximal by 2 weeks after thyroidectomy. Administration of antirat GH serum to thyroidectomized rats resulted in a further increase in GRH mRNA levels. T4 treatment of thyroidectomized rats for 5 days, which also partially restored pituitary GH content, lowered the elevated GRH mRNA levels. However, comparable effects on GRH mRNA levels were observed by rat GH treatment alone. These results suggest that the changes in hypothalamic GRH gene expression after thyroidectomy in the rat are due to the GH deficiency caused by thyroidectomy, rather than a direct effect of thyroid hormone on th...Continue Reading

Citations

Jan 1, 1990·Acta Paediatrica Scandinavica. Supplement·L A FrohmanM A Frohman
Jul 30, 2016·Biomedicine & Pharmacotherapy = Biomédecine & Pharmacothérapie·Eatemad A Awadalla, Alaa-Eldin Salah-Eldin
Jul 27, 2006·Journal of Neuroendocrinology·T PrinsH A Delemarre-van de Waal
Apr 1, 1992·Journal of Endocrinological Investigation·R ValcaviI Portioli
Apr 30, 1999·Physiological Reviews·E E MüllerD Cocchi
Mar 1, 1993·Journal of Endocrinological Investigation·J M Rondeel, I M Jackson
Jul 1, 1993·The Journal of Pediatric Endocrinology·M T Bluet-PajotC Kordon

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