The technique described by Porter, Kamberi et al. (1) for perfusion of the anterior pituitary via a microcannula inserted into a hypophyseal portal vessel was used for testing growth hormone-releasing hormone (GH-RH) activity in extracts of rat stalk-median eminence in urethaneanesthetized male rats. Plasma GH levels were measured by radioimmunoassay. Various amounts of stalk median eminence (SME) or cerebral cortex (CC) extract from intact male rats were infused into a hypophyseal stalk vessel. Arginine vasopressin, 8 mU, as contained in 6/10 of rat SME served as a control for vasopressin contamination in the crude material. All infusions were made in 60 μl of isotonic saline over 30 min. After 0.3 and 0.6 SME, radioimmunoassayable GH in plasma increased by 85.3 ± 33.5 ng/ml and 254.9 ± 25.8 ng/ml, respectively. Infusion of 0.3 CC was ineffective, but after 0.6 CC equivalent to 0.6 SME, a moderate increase of 46.3 ±11.3 ng/ml occurred within 30 min. Sham operation, saline infusion, and infusion of 8 mU of arginine vasopressin did not change plasma GH levels appreciably. GH-RH activity in rat SME, as tested by this method, appeared to be unstable on prolonged storage, even at –20 C.
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