Somatostatin and its physiological significance in regulating the episodic secretion of growth hormone in the rat.
Somatostatin (SS) is a powerful inhibitor of growth hormone (GH) secretion both in vitro and in vivo, and is generally regarded as having a negative influence on GH secretion and growth. In the conscious rat, the GH secretory pattern, the response to repeated injections of GH-releasing hormone (GHRH), and the feedback mechanism by which GH regulates its own release are all sexually dimorphic and probably reflect a sexually dimorphic pattern of SS release. Prolonged infusions of SS initially block GHRH-induced GH release but responses begin to break through with time. Withdrawal of SS induces a rebound release of GH in vivo, largely dependent on the release of endogenous GHRH. Prolonged exposure to intermittent infusions of SS in normal female rats produces a paradoxical growth response by inducing regular peaks of GH secretion whereas continuous infusions of SS do not. This response is GH-dependent, and is not due to other effects of SS since intermittent infusions of SS do not increase growth in dwarf rats which are deficient in pituitary GH. The sex differences in GH secretion are also reflected in the expression of several GH-dependent liver enzymes, one of which, carbonic anhydrase III, responds to manipulations of the endogenous secretory pattern by SS in both normal and dwarf rats, and appears to be sensitive to differences in basal, rather than peak, GH levels.
Robinson
I C
IC
National Institute for Medical Research, Mill Hill, London.
Jeffery
S
S
Clark
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RG
D000818:Animals; D002256:Carbonic Anhydrases / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D007275:Injections, Intravenous; D008099:Liver / Q000201:enzymology; D008297:Male; D011863:Radioimmunoassay; D051381:Rats; D012727:Sex Characteristics; D013004:Somatostatin / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*
D013004:Somatostatin; D013006:Growth Hormone; D002256:Carbonic Anhydrases