NITRIC-OXIDE INCREASES CUTANEOUS AND RESPIRATORY HEAT DISSIPATION IN CONSCIOUS RABBITS

The influence of systemic nitric oxide (NO) donor infusion and NO synt hase inhibition on major thermoregulatory mechanisms was investigated under thermoneutral conditions (24 degrees C) in the conscious rabbit. Both low (25 nmol.min(-1).kg(-1))- and high-dose (75 nmol.min(-1).kg( -1)) infusion of the NO donors 3-morpholinosydnonimine-hydrochloride a nd S-nitroso-N-acetylpenicillamine augmented respiratory heat dissipat ion due to raised respiratory frequency (RF) and evaporative water los s (REWL). At the higher dose of NO donor, RF and REWL increased (from 107 +/- 16 to 156 +/- 19 breaths/min and from 7.12 +/- 0.97 to 11.29 /- 1.29 mg. min(-1).kg(-1); P < 0.05), and, combined with a moderate r ise in cutaneous heat dissipation (ear skin temperature increased from 29.03 +/- 1.76 to 33.29 +/- 2.71 degrees C; P < 0.05), deep body temp erature was slightly reduced (-0.1 degrees C, P > 0.05) without a chan ge in metabolic heat production. In contrast, blockade of endogenous N O synthesis induced a sustained rise in body temperature (0.2 degrees C, P < 0.05), concomitant with a reduction in both RF and REWL (from 1 31 +/- 11 to 94 +/- 12 breaths/min and from 10.86 +/- 1.14 to 8.70 +/- 0.88 mg.min(-1).kg(-1), P < 0.05), whereas metabolic heat production decreased slightly and cutaneous heat dissipation was minimally altere d. The data indicate that, under thermoneutral conditions, systemicall y applied NO primarily influences body temperature in the conscious ra bbit by modulating the rate of respiratory heat dissipation, whereas t he roles of cutaneous heat dissipation and metabolic heat production a re relatively minor.