ENDOGENOUS OPIOID SYSTEM DURING INSPIRATORY LOADING IN PATIENTS WITH TYPE-I DIABETES

To investigate the activity of,the endogenous opioid system in patient s with insulin-dependent diabetes mellitus during ventilatory stress s ituations, we measured plasma beta-endorphin levels in six male and fi ve female diabetic patients breathing against fatiguing inspiratory re sistive loads. The patients had to generate with each inspiration an e sophageal pressure (Pes) 80% of maximum until they were exhausted and could no longer develop target Pes. The loaded breathing run was repea ted three times with a 1-min interval between each run. Duty cycle, ti dal volume, and breathing frequency were constant in all tasks. For ea ch run plasma beta-endorphin levels were measured, inspiratory effort sensation assessed using a modified Borg scale, and inspiratory muscle endurance evaluated by the length of time the task could be maintaine d (Tlim). A group of 11 sex-, age-, height-, and weight-matched health y individuals served as control subjects. Tlim was significantly lower in the diabetic patients. Evaluating respiratory effort during the th ree test runs in control subjects at a time corresponding to the break point of loaded breathing in patients showed significantly lower Borg ratings in the control group than in the patient group. Baseline plas ma beta-endorphin was significantly lower in the diabetic patients (10 .6 +/- 2.1 versus 27.0 +/- 4.2 pg/ml, p < 0.01). Additionally, whereas resistive loaded breathing caused a further increase in plasma beta-e ndorphin concentration in the control group (p < 0.005), absolutely no increase was found in the diabetic patients. We conclude that the end ogenous opioid system in insulin-dependent diabetic patients does not respond to stress caused by breathing against fatiguing inspiratory re sistive loads.