DEFECTIVE ENDOGENOUS OPIOID RESPONSE TO EXERCISE IN TYPE-I DIABETIC-PATIENTS

Plasma beta-endorphin (beta-E) concentration was determined before, du ring, and after a standardized incremental exercise test to maximal ca pacity in eight type I diabetic patients and eight normal control subj ects. Diabetic patients were studied under normoglycemic and hyperglyc emic conditions in a single-blind random fashion to differentiate betw een the effects of acute hyperglycemia and of diabetes per se on the b eta-E response to exercise. The perceived magnitude of leg effort elic ited by exercise was evaluated using a category scale. Whereas plasma beta-E concentrations increased in control subjects with increasing wo rkload, causing significantly higher beta-E levels at the end of exerc ise than at the beginning (P < .001), no such increase could be observ ed in the diabetic patients under normoglycemic and hyperglycemic cond itions. In addition, baseline plasma beta-E concentrations were signif icantly lower in normoglycemic (P < .01) and hyperglycemic (P < .001) diabetic patients than in control subjects. Even during the recovery p eriod, patients' beta-E levels remained significantly lower than those of control subjects. At submaximal levels of power output, the percei ved intensity of leg effort was significantly higher in normoglycemic and hyperglycemic diabetic patients than in control subjects. We concl ude that in type I diabetic patients, the ability of the endogenous op ioid system to respond to exercise-induced stress is impaired under hy perglycemic and even under normoglycemic conditions. Considering the e ffect of endogenous opioids on stress tolerance, such changes may comp romise exercise performance in diabetic patients. (C) 1996 by W.B. Sau nders Company