Effects of beta-endorphin fragments on plasma levels of vasopressin

Plasma vasopressin levels are significantly decreased after intracerebroventricular (icv) administration of β-endorphin (βE), but not of des-tyrosine βE (DTβE). The βE induced decrease of vasopressin levels, which occurs in normal as well as in water deprivated rats, can partially be blocked by naltrexone. γ-Endorphin (γE), α-endorphin (αE), DTγE and DTαE did not affect basal levels of vasopressin, but γE and DTγE further increased the elevated vasopressin levels in water deprivated rats. Naltrexone antagonized this increase following γE administration, but not that induced by DTγE. The results suggest that the effects of βE and its fragments on plasma vasopressin levels are mediated by multiple opiate and non-opiate receptor systems.