CAPSAICIN-SENSITIVE NERVES AND ENDURANCE EXERCISE IN THE RAT

The purpose of our study was to clarify the role of capsaicin-sensitiv e nerves in the control of plasma catecholamine and glucose concentrat ions during exercise. In vehicle-treated rats, plasma epinephrine (E) and norepinephrine (NE) levels were significantly higher in animals ex ercised to exhaustion than in the group sacrificed at rest. However, i t was not the case for the neonatally capsaicin-treated animals. The e pinephrine and norepinephrine levels were not significantly higher in the capsaicinized animals exercised to exhaustion than in those studie d at rest. As a result, plasma epinephrine and norepinephrine levels w ere higher in control than in capsaicinized exhausted animals. Impairm ent of capsaicin-sensitive nerves by the neonatal capsaicin treatment prevented the exercise-induced increase of catecholamine output despit e a significant decrease in plasma glucose levels and a lower liver gl ycogen content at rest. We suggest that this impairment of catecholami ne output during exercise was caused by depletion of substance P in C- fibers directed to the adrenal medulla. This is supported by the obser vation of a lower plasma epinephrine level in capsaicin-treated rats. We conclude that C-fibers are therefore involved in the control of cat echolamine secretion by the adrenal medulla during exercise to exhaust ion. However, such an impairment of catecholamine output was not assoc iated with a further decrease in plasma glucose levels or a shorter ti me-to-exhaustion. This also suggests that a partial dysfunction of the adrenal medulla is not sufficient to alter exercise endurance and pla sma glucose levels.