Regulation of growth hormone release: evidence against negative feedback in rat pituitary cells

Endocrinology
R A RichmanJ R Florini

Abstract

To determine if the anterior pituitary gland is the site of negative feedback inhibition of GH release, we studied the effect of GH and multiplication-stimulating activity (MSA), a member of the somatomedin family, on isolated rat anterior pituitary cells in primary culture. The effect of GH was examined in two ways: 1) by adding to the cultures human GH (10 ng/ml to 20 microgram/ml) which was biologically active in the rat but not cross-reactive in the rat GH (rGH) RIA, and 2) by comparing rGH secretion in cultures of different cell densities. No suppression of either basal or prostaglandin E1-stimulated rGH release was found. An enhancement observed in serum-free conditions at high human GH concentrations was interpreted as a nonspecific response to protein, because bovine serum albumin produced the same effect. When added in the presence of serum, MSA (1--500 ng/ml) had no effect on rGH secretion. In the absence of serum, there were 71% and 30% increases in the basal and prostaglandin E1-stimulated rates of hormone release, respectively, possibly attributable to a trophic effect of MSA. Six other hormones having structural or functional similarity to either GH or somatomedin also failed to inhibit rGH secretion. Our results ...Continue Reading

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