Growth Hormone-Releasing Activity of Crude Ovine Hypothalamic Extracts

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Abstract
Summary Crude extracts of ovine SME tissue were effective in depleting pituitary GH of rats at 30 and 60 minutes after injection. Depletion of pituitary GH was estimated by the tibial epiphyseal cartilage test performed in hypophysectomized rats. Injection of extracts into the carotid artery effectively depleted pituitary GH in one of 2 trials, whereas ip or iv injection uniformly evoked GH depletion. There was no apparent difference in the degree of response produced by the 2 latter routes of injection. Extracts were dissolved in several solvents such as physiological saline, 0.1 N acetic acid, or 0.1 M (pH 5.5) ammonium acetate buffer. Extracts dissolved in any of these 3 solvents possessed GH-releasing activity. The ip administration of the acetic acid diluent produced a significant elevation in pituitary GH activity, which is attributed to the irritant effects of the acid. Hypothalamic extract was administered to rats of different sizes in one experiment. GH depletion occurred in rats which weighed either 100 or 200 g, but failed to occur in animals which weighed 500 g. Since the same dose on a weight basis (4 mg/100 g) was given to each group, these results suggest that responsiveness to the GH-releasing factor may decline in older animals. In contrast to the effectiveness of hypothalamic extracts in depleting pituitary GH was the lack of activity of cerebral cortical extracts, synthetic arginine vasopressin, and α melanocyte stimulating hormone. It is concluded that ovine hypothalamus contains a GH-releasing factor.

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