Effect of rat stalk median eminence extracts on rat GH secretion in vivo

Estradiol (0.2 mug), injected subcutaneously for 10 days to adult male rats, increased plasma growth hormone (GH) levels as compared with oil-treated controls. In estradiol-pretreated (10 days), urethane-anesthetized rats, the first as well as the second of two successive intracarotid injections, at 1-hour intervals, of one rat stalk median eminence equivalent evoked a significant rise in plasma radioimmunoassayable GH. Under the same conditions, cerebral cortex extracts (1 equivalent) induced a slight elevation whereas vasopressin (30 mU) or serotonin (200 ng) were ineffective. These results indicate that estrogen-primed, urethane-anesthetized rats can be used to demonstrate GH-releasing activity in rat SME extracts.