Suppressive Effect of β-Endorphin and Naloxone on the Secretion of Cortisol under Stress Conditions in Sheep

Summary

The effect of an infusion of β-endorphin and naloxone into the 3^rd cerebral ventricle on the blood serum concentration of cortisol in non-stressed and stressed anoestrous sheep was studied. The infusion of naloxone alone did not alter the secretion of cortisol in non-stressed animals but the response to footshock was inhibited in that the cortisol values were significantly lower (P < 0.05) when compared with those during the infusion of saline and footshocking. This opiate antagonist also suppressed the cortisol response to an infusion of β-endorphin (P < 0.001 and P < 0.05). When the sheep infused with β-endorphin were additionally exposed to footshock there was less enhancement of the secretion of cortisol (P < 0.001 and P < 0.05). The depressive action of β-endorphin upon cortisol secretion in stressed sheep is matched by corresponding observations on man and it seems that endogenous opioids may inhibit or attenuate some hormonal responses to stress.

Key words

Suppressive effect - β-Endorphin - Naloxone - Cortisol - Stress - Sheep