Suppression of Triiodothyronine-Induced Growth Hormone Gene Expression by Insulin-Like Growth Factor-I in Thyroidectomized Rat Pituitary Cells
The secretion of GH from the anterior pituitary is under hypothalamic control and also under complex multihormonal regulation. Thyroid hormone plays a major role in stimulating GH gene expression. Somatomedin C has been shown to inhibit GH secretion in vivo and in vitro. We have previously shown that physiologic levels of insulin inhibit basal and T3-stimulated GH secretion and mRNA levels by GH3 pituitary tumor cells (1,2) and by normal rat pituitary cells (3,4). The recent availability of a recombinant human IGF-I analogue (5) has allowed us to examine the effects of the peptide on T3-induced GH in vitro secretion by thyroidectomized rat pituitary cells. The aim of this study was to characterize the effect of IGF-I on GH gene expression induced by physiologic levels of T3.
KeywordsHypothalamic Control Secretion Pituitary Cell
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