Endogenous opioids inhibit oxytocin release during nicotine-stimulated secretion of vasopressin in man.
The effects of the opioid antagonist naloxone on the vasopressin (AVP) and oxytocin (OT) responses to nicotine were studied in male non-smokers (21-30 years old). Either saline (n = 6) or naloxone (4 mg bolus + 6 mg/h, n = 6) was infused i.v. during the study. After 60 min infusion the subjects smoked one high-nicotine content cigarette. Naloxone infusion for 60 min did not alter basal plasma AVP or OT levels. Smoking led to a significant rise in plasma vasopressin in both saline and naloxone-infused subjects (P less than 0.05). There was no significant difference in the plasma AVP response to smoking between the two groups. Saline-infused subjects did not show any change in plasma OT in response to smoking. Naloxone infusion was associated with a significant rise in OT from 1.3 +/- 0.1 pmol/l to 4.3 +/- 2.4 pmol/l 5 min after smoking (P less than 0.05). We conclude that there is endogenous opioid-mediated inhibition of OT which prevents its release when AVP is secreted in response to nicotine in man.
Seckl
J R
JR
Department of Medicine, Charing Cross and Westminster Medical School, Westminster Hospital, London, UK.
Johnson
M
M
Shakespear
C
C
Lightman
S L
SL
D000328:Adult; D001127:Arginine Vasopressin / Q000097:blood*; D004723:Endorphins / Q000037:antagonists & inhibitors* / Q000502:physiology; D006801:Humans; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009538:Nicotine / Q000494:pharmacology*; D010121:Oxytocin / Q000097:blood*; D012907:Smoking / Q000097:blood
D004723:Endorphins; D001127:Arginine Vasopressin; D009270:Naloxone; D010121:Oxytocin; D009538:Nicotine