Growth Hormone Releasing Activity in Rhesus Monkeys of Crude Ovine Stalk Median Eminence Extracts1

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Abstract
Intravenous injections of crude extract of ovine stalk median eminence (SME) produced significant increases in plasma growth hormone (GH) in unanesthetized rhesus monkeys. The effective dose was 15–30 mg/kg. The plasma GH response was specific, i.e., due to substance(s) in SME, because injections of saline, trypsin-treated SME, crude ovine cerebral cortical extract or thioglycollate-treated argin-ine-8-vasopressin (thio-AVP) failed to produce significant responses. Since crude SME had pressor activity, it was possible that all the GH releasing activity of SME was due to the vaso-pressin in the extract. This possibility was rejected when it was shown that thioglycollate abolished pressor activity of SME and reduced, but did not abolish, GH releasing activity. Identical thioglycollate treatment of AVP abolished both pressor activity and its GH releasing activity. All GH releasing activity of SME was abolished by tryptic digestion. This strongly suggests, but does not prove, that all the GH releasing substances in SME are peptides. The relationship between the specific, thioglycollate-stable GH releasing activity of ovine SME described in this paper and the specific ovine GH-RF which depletes rat pituitary GH activity remains to be established. (Endocrinology83: 25, 1968)

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