Catecholamines and endogenous opioid peptides are released in response to stress. Exogenous infusions of epinephrine and beta-endorphin (both in doses of 15, 50, and 80 ng/kg.min sequentially, each dose lasting 30 min) were used to mimic short term stress in both normal weight (body mass index, less than 25 kg/m2) and obese (body mass index, greater than 30 kg/m2) subjects. Fasting plasma insulin, C-peptide, and beta-endorphin concentrations were significantly higher in the obese than in the normal subjects (P less than 0.01-0.005). In lean subjects epinephrine produced significant increases in plasma glucose levels, but no appreciable changes in plasma insulin, C-peptide, or glucagon. Infusion of beta-endorphin in the same subjects caused plasma glucose and glucagon to rise, but insulin and C-peptide levels did not change. The simultaneous infusion of epinephrine and beta-endorphin produced a glycemic response which, although greater, was not significantly different than the sum of the responses to the individual hormone infusions. However, the two hormones had a synergistic interaction on plasma glucagon levels [total glucagon response, 2275 +/- 370 pg/min.mL (ng/min.L); sum of single effects, 750 +/- 152 (+/- SE) pg/min.mL (ng/min.L); P less than 0.01]. The plasma epinephrine [207 +/- 21, 607 +/- 70, and 1205 +/- 134 pg/mL (1130 +/- 115, 3640 +/- 382, and 6577 +/- 691 pmol/L] and beta-endorphin [875 +/- 88, 1250 +/- 137, and 1562 +/- 165 pg/mL (250 +/- 25, 358 +/- 39, and 447 +/- 47 pmol/L] concentrations attained during the infusions of each single hormone were not different from those recorded during the combined hormonal infusion. In obese subjects epinephrine raised plasma glucose levels and caused dose-related increments of plasma glucagon concentrations. Plasma insulin and C-peptide concentrations remained low and rebounded at the end of the infusions. In the same subjects, beta-endorphin produced elevations of plasma glucose, insulin, C-peptide, and glucagon. When the combined hormonal infusion was given to obese subjects, the plasma epinephrine and beta-endorphin concentrations rose to values not significantly different from those in normal weight subjects. However, there was a dramatic increase in plasma glucose exceeding 200 mg/dL (11.1 mmol/L), which remained elevated 30 min after the infusion. The glucagon response was not greater than the sum of the single effects.(ABSTRACT TRUNCATED AT 400 WORDS)