[Release of beta-endorphin and beta-lipotropin during submaximal exertion in sedentary and active subjects. Endogenous opiate peptides during exertion in sedentary and active subjects].

Some recent studies suggest that changes in the endogenous opioid peptides (POE) secretion during stress may be involved in various hemodynamic, respiratory and hormonal responses to exercise. To evaluate the relationship between fitness and POE release, 10 mixed-type exercise trained athletes (A) and 10 sedentary normal controls (C) were examined by bicycle stress testing; maximum oxygen uptake (VO2max) and peak work load (PWL) were greater in A than C (VO2max = 61.8 +/- 5.2 vs 40.2 +/- 6.1 ml/kg; PWL = 1525 +/- 229 vs 915 +/- 305 kgm.both p less than 0.01). After 24 hours A and C underwent rectangular bicycle stress testing (two 20' steps at 60% and 80% VO2max). Total plasmatic beta-endorphin (BEP) and its precursor beta-lipotropin (BLPH) were dosed by radioimmunoassay at rest, at 60% VO2max, at 80% VO2max and after complete recovery. Physical exercise caused a transient rise of BEP + BLPH plasma levels in both A and C. In A the increase was greater and occurred earlier than in C. The POE release under submaximal exercise showed a close correlation with oxygen uptake and therefore with fitness. This relation appeared in A at both low and high effort levels, whereas in C it was more strict at higher effort level. There results suggest that POE system play an important role in the adaptive mechanisms in sport practice.