Metabolic role of the exercise-induced increment in epinephrine in the dog

The role of the exercise-induced increment in epinephrine was studied in five adrenalectomized (ADX) and in six normal dogs (C). Experiments consisted of an 80-min equilibration period, a 40-min basal period, and a 150-min exercise period. ADX were studied with epinephrine replaced to basal levels during rest and to increased levels during exercise to simulate its normal rise (HE) and on a separate day with epinephrine maintained at basal levels throughout the study (BE). Cortisol was replaced during rest and exercise in ADX so as to simulate the levels seen in C. Glucose was infused as needed in ADX to maintain the glycemia evident during exercise in C. Glucose production (Ra) and utilization (Rd) were assessed isotopically. In C, epinephrine had risen by 95 +/- 25 pg/ml by the end of exercise. In HE, the increment in epinephrine (117 +/- 29 pg/ml) was similar to that seen in C, whereas in BE epinephrine fell by 18 +/- 9 pg/ml. Basal norepinephrine levels were 139 +/- 9, 260 +/- 25, and 313 +/- 33 pg/ml in C, HE, and BE, respectively. In response to exercise, norepinephrine increased by nearly twofold in all protocols. Basal and exercise-induced changes in plasma glucagon and insulin were similar in C and ADX. Ra increased similarly in C (5.3 +/- 0.6 mg.kg-1.min-1) and HE (4.9 +/- 0.6 mg.kg-1.min-1). In BE, Ra rose normally for the initial 90 min but then declined resulting in a rise of only 2.9 +/- 0.5 mg.kg-1.min-1 after 150 min of exercise.(ABSTRACT TRUNCATED AT 250 WORDS)