A functional role for opioid peptides in the differential secretion of vasopressin and oxytocin.
The presence of opioid peptides and opiate receptors in the hypothalamo-neurohypophysial system, as well as the inhibitory effects of enkephalins and beta-endorphin on release of oxytocin and vasopressin have been well documented. The physiological importance of opioid peptides in this classical neurosecretory system, however, has remained illusive. In the present study we tested the effects of naltrexone on the plasma concentrations of oxytocin and vasopressin during dehydration, hemorrhage and suckling in the conscious rat. We obtained evidence supporting the hypothesis that opioid peptides inhibit oxytocin release and thereby promote the preferential secretion of vasopressin when it is of functional importance to maintain homeostasis during dehydration and hemorrhage. Our data support the concept that the coexistence of a neuromodulator and a neurohormone in the same neuron, as demonstrated for vasopressin with dynorphin or leucine-enkephalin, serves to regulate the differential release of two biologically different, yet evolutionarily-related, neurohormones, e.g. oxytocin and vasopressin, from the same neuroendocrine system.
D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D003681:Dehydration / Q000503:physiopathology; D004723:Endorphins / Q000502:physiology*; D005260:Female; D006470:Hemorrhage / Q000503:physiopathology; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D007774:Lactation; D008297:Male; D009271:Naltrexone / Q000494:pharmacology; D010121:Oxytocin / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains
D004723:Endorphins; D001127:Arginine Vasopressin; D010121:Oxytocin; D009271:Naltrexone