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


Endocrinology 108(6): 2287-2292
Regulation of growth hormone release: evidence against negative feedback in rat pituitary cells
To determine if the anterior pituitary gland is the site of negative feedback inhibition of GH [growth hormone] release, the effect of GH and multiplication-stimulating activity (MSA), a member of the somatomedin family, on isolated rat anterior pituitary cells in primary culture was studied. The effect of GH was examined in 2 ways: by adding to the cultures human GH (10-20 .mu.g/ml) which was biologically active in the rat, but not cross-reactive in the rat GH (rGH) radioimmunoassay and by comparing rGH secretion in cultures of different cell densities. No suppression of either basal or prostaglandin[PG]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 PGE1-stimulated rates of hormone release, respectively, possibly attributable to a trophic effect of MSA. Five other hormones [epidermal growth factor, nerve growth factor, placental lactogen, prolactin, and proinsulin] having structural or functional similarity to either GH or somatomedin also failed to inhibit rGH secretion. These results do not support the hypothesis that GH or somatomedin exerts a negative feedback effect on GH release directly on the anterior pituitary gland. Most likely, the hypothalamus or a higher brain center is the site for such regulation.


Accession: 006288295

PMID: 6112137

DOI: 10.1210/endo-108-6-2287



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