beta-Endorphin: pituitary and adrenal glands modulate its action.

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Abstract
Hypophysectomized rats are supersensitive to the hypothermic effects of morphine and .beta.-endorphin injected i.v., as early as 1 wk after surgery. At 2 wk after surgery, there is a significant increase in the antinociceptive potency for these opiates. The route of opiate injection must be considered in interpretations of these results. The enhanced opiate potency following s.c. morphine injection in hypophysectomized rats may be partially explained by adrenal dysfunction, as demonstrated by a similar sensitization to s.c. morphine following adrenalectomy. By contrast, no enhancement of opiate potency was observed on direct intraventricular injection of morphine or .beta.-endorphin in adrenalectomized rats. The potency of i.v. .beta.-endorphin is profoundly enhanced in adrenalectomized mice; 5 out of 9 animals died when injected with a dose of the peptide that produced only mild analgesia in sham controls. The complete reversal of this i.v. .beta.-endorphin supersensitivity by dexamethasone implies a possible physiological interplay between the peptide and adrenal function.