EFFECT OF INTRACEREBROVENTRICULAR INJECTION OF ATROPINE ON METABOLIC RESPONSES DURING EXERCISE IN UNTRAINED RATS

To investigate the role of the central cholinergic system in the regul ation of metabolism during exercise, wt. injected atropine (5 x 10(-7) mol) into the lateral cerebral ventricle of normal and adrenodemedull ated (ADM) untrained rats submitted to exercise on a treadmill (15 m m in(-1), 5% grade) until exhaustion. Concentrations of blood glucose, p lasma free fatty acids (FFA), and lactate were measured before and eve ry 10 min after the start of exercise for a period of 60 min. Adrenome dullectomy had no effect on the maximal capacity of exercise (MCE), bu r atropine administered intracerebroventricularly (i.c.v.) reduced the maximal capacity of exercise of both normal and ADM rats. In normal r ats, blood concentrations of glucose and plasma free fatty acids remai ned essentially unchanged compared to the levels at rest, whereas in A DM rats a rapid increase in plasma glucose and plasma free fatty acids levels occurred during exercise. These data indicate that adrenomedul lectomy disrupted the accuracy of the feedback mechanism that regulate s the mobilization of extramuscular fuels during exercise in normal ra ts. In addition, ADM rats showed an increased lipid mobilization as a source of energy during exercise, which might explain the increased pl asma glucose by an inhibition of muscle glucose uptake. These results suggest that central cholinergic neurons might be involved in the cont rol of energy substrate adjustment during exercise, thereby reducing t he maximal capacity of exercise. In addition, the results of this stud y suggest that the adrenal elands are important for an accurate feedba ck mechanism during exercise. (C) 1998 Elsevier Science Inc.