Involvement of Opioid Peptides in the Inhibition of Oxytocin Release by Heat Stress in Lactating Mice

Acute heat stress inhibited suckling-induced milk yield in lactating mice but did not decrease milk yield obtained by suckling following oxytocin administration. Injections of naltrexone, 2.5 and 5 mg/kg, prior to heat exposure significantly reduced the inhibition of milk yield during suckling. These results suggest that endogenous opioid peptides may be involved in the mechanism of inhibition of reflex release of oxytocin by stress.