Effect of naloxone on oxytocin-induced cortisol decrease in normal men.
iv administration of oxytocin decreases plasma ACTH-cortisol levels in normal men. In contrast, naloxone, a specific opioid antagonist, stimulates cortisol release, suggesting that opioid peptides exert an inhibitory control on ACTH-cortisol secretion. The present study was carried out in an attempt to determine whether an opioid pathway mediates oxytocin action; therefore, we evaluated the effect of naloxone on the decrease of cortisol induced by oxytocin. Six normal men were treated iv with oxytocin (2 IU as a bolus), naloxone (4 mg as a bolus plus 10 mg infused for 2 h) or a combination of the 2 drugs. Plasma cortisol levels were determined in samples taken before and 2 h after drug treatment. As expected, administration of oxytocin significantly decreased cortisol secretion, while naloxone had a stimulatory effect on plasma cortisol levels. When oxytocin injection was followed by administration of naloxone, cortisol levels remained unchanged; thus, naloxone abolished a cortisol decrement in response to oxytocin. These findings show that in man oxytocin requires an active opioid system in order to produce its inhibitory action on ACTH-cortisol secretion, suggesting that this effect of oxytocin could be mediated by an opioid pathway.
Coiro
V
V
Chiodera
P
P
Rossi
G
G
Volpi
R
R
Salvi
M
M
Camellini
L
L
Roti
E
E
D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000328:Adult; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007263:Infusions, Parenteral; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D010121:Oxytocin / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000187:drug effects
D011957:Receptors, Opioid; D009270:Naloxone; D010121:Oxytocin; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone