Temporal changes in the activity of endogenous opioid mechanisms regulating oxytocin secretion in saline-loaded rats.
The effect of the opiate antagonist naloxone on neurohypophyseal hormone secretion has been investigated in rats given 2% NaCl to drink for 0-9 days. Naloxone elicited a rise in plasma levels of oxytocin (OT), but not arginine-vasopressin (AVP), on days 1-3 only, the greatest response being on day 2. In a further experiment, the OT response to an acute stimulus (1.5 M NaCl, i.p.) was found to be similar in controls and rats drinking 2% NaCl for 7 days, indicating that depletion of readily releasable hormone was not the cause of the loss of sensitivity to naloxone; rather a down-regulation of opiate receptor mechanisms may be responsible. The temporal changes in opiate antagonist-sensitivity in saline-loaded rats may provide a functional paradigm for the investigation of regulatory opiate mechanisms in neural tissue.
Medical Unit, Charing Cross and Westminster Medical School, Westminster Hospital, London U.K.
D A
DA
Carter
S L
SL
Lightman
D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood; D001696:Biomechanical Phenomena; D004723:Endorphins / Q000502:physiology*; D005260:Female; D009270:Naloxone / Q000494:pharmacology; D010121:Oxytocin / Q000097:blood / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D004723:Endorphins; D001127:Arginine Vasopressin; D009270:Naloxone; D012965:Sodium Chloride; D010121:Oxytocin