GROWTH HORMONE RELEASE STIMULATED BY EXTRACTS OF STALK MEDIAN EMINENCE IN ADULT MALE RATS ANAESTHETIZED WITH URETHANE

Abstract

The existence in the hypothalamus of a growth hormone releasing factor (GHRF) is universally admitted. Its existence was first demonstrated in vivo when it was shown that intracarotid injections of extracts of stalk median eminence (SME) induce a depletion of pituitary bioassayable growth hormone (GH) (Pecile, M\l=u"\ller,Falconi & Martini, 1965). However, no consistent results have been obtained when preparations containing GHRF have been tested in rats in vivo using radioimmunological methods(Garcia & Geschwind, 1968). No explanation has yet been found why preparations which are known to contain GHRF do not induce any measurable rise of radio-immunoassayable GH in plasma in the rat. Having recently found that adult male rats anaesthetized with urethane are suitable for the study of GH secretion using radioimmunological procedures (Collu, Visconti, Fraschini & Martini, 1971), we used this preparation to study the effect of intracarotid injections of SME extracts. Adult male Sprague\p=m-\Dawley rats, 250\p=n-\300 g body weight, were anaesthetized with urethane (1500 mg/kg, i.p.) at approximately 09.00 h. A polyethylene catheter was inserted into the jugular vein, and another into the left carotid artery. The animals were then allowed to sleep undisturbed and unrestrained for 2 h. Heparin (1-0 mg i