Effect of nitric oxide synthase inhibition on hypercapnia-induced hypothermia and hyperventilation.
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 Nomega-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% CO2). Control animals received saline injections. L-NNA altered the breathing pattern during the control situation but not during hypercapnia. A significant (P < 0.05) drop in body temperature was measured after both L-NNA (40 mg/kg) and 5% inspired CO2, with a drop in oxygen consumption in the first situation but not in the second. Hypercapnia had no effect on L-NNA-induced hypothermia. The ventilatory response to hypercapnia was not changed by L-NNA, even though L-NNA caused a drop in body temperature. The present data indicate that the two responses elicited by hypercapnia, i.e., hyperventilation and hypothermia, do not share NO as a common mediator. However, the L-arginine-NO pathway participates, although in an unrelated way, in respiratory function and thermoregulation.
Barros
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RC
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.
Branco
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LG
D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006935:Hypercapnia / Q000503:physiopathology*; D006985:Hyperventilation / Q000503:physiopathology*; D007036:Hypothermia, Induced; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D015656:Respiratory Mechanics / Q000187:drug effects / Q000502:physiology; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase