STIMULATION IN VIVO OF THE SECRETION OF PROLACTIN AND GROWTH HORMONE BY β-ENDORPHIN

Abstract
Morphine sulfate (MS) and the opioid peptide β-endorphin β-LPH-(61–91) stimulate prolactin and growth hormone release in steroid-primed and non-treated male rats when injected intravenously or intracistemally. On a molar basis β-endorphin is at least 20 times more potent than MS, whereas Met5-enkephalin (β-LPH-(61–65)) and α-endorphin (β-LPH-(61–76)) are devoid of activity at the dose injected (300 μg). The in vivo stimulatory effects of β-endorphin on prolactin secretion are reversed by the opiate antagonist naloxone. The absence of in vitro effect of MS and e-endorphin on prolactin and growth hormone secretion by cultured rat pituitary cells suggest that they have a central nervous system site of action.

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