Relation between plasma beta-endorphin and the ventilatory response to hypercapnia in humans.

1. Endogenous opioids have been implicated in the control of breathing in neonates, but their role in ventilatory control in adults remains unclear. 2. We studied the relationship between circulating immunoreactive beta-endorphin and the ventilatory and mouth occlusion pressure responses to hypercapnia in 12 healthy male subjects. In addition, we examined the effect of repetitive hypercapnia on plasma beta-endorphin and cortisol levels. 3. A weak but significant negative relationship between the ventilatory response to hypercapnia and basal plasma beta-endorphin levels was observed (r = -0.35, P less than 0.01). A similar negative relationship was noted between mouth occlusion pressure response to hypercapnia and basal plasma beta-endorphin levels (r = -0.36, P less than 0.01). 4. Repetitive hypercapnia prevented the fall in plasma cortisol that occurred under control conditions (P less than 0.02) but had no effect on plasma beta-endorphin. 5. We conclude that plasma beta-endorphin may play a role in the central chemical control of breathing in man.