Effect of nitric oxide synthase inhibition on hypercapnia-induced hypothermia and hyperventilation

Departamentos de Fisiologia, Faculdade de Odontologia de Ribeirão Preto and Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, 14040-904 Ribeirão Preto, São Paulo, Brazil Hypercapnia elicits hypothermia in a number of vertebrates, but the mechanisms involved are not well understood. In the present study, we assessed the participation of the nitric oxide (NO) pathway in hypercapnia-induced hypothermia and hyperventilation by means of NO synthase inhibition by using N -nitro- L -arginine ( L -NNA). Measurements of ventilation, body temperature, and oxygen consumption were performed in awake unrestrained rats before and after L -NNA injection (intraperitoneally) and L -NNA injection followed by hypercapnia (5% CO 2 ). Control animals received saline injections. L -NNA altered the breathing pattern during the control situation but not during hypercapnia. A significant ( P