Abstract
We have investigated whether there is circadian variation in the effects of nitric oxide synthase inhibitors on body temperature, physical activity and feeding. We used nocturnally active Sprague-Dawley rats, housed at ≅24°C with a 12:12 h light:dark cycle (lights on 07:00 hours) and provided with food and water ad libitum. Nitric oxide synthesis was inhibited by intraperitoneal injection of the unspecific nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME, 100, 50, 25, 10 mg/kg), or the relatively selective inducible nitric oxide synthase inhibitor aminoguanidine (100, 50 mg/kg), during the day (≅09:00 hours) or night (≅21:00 hours). Body temperature and physical activity were measured using radiotelemetry, while food intake was calculated by weighing each animal's food before as well as 12 and 24 h after each injection. We found that daytime injection of L-NAME and aminoguanidine had no effect on daytime body temperature. However, daytime injection of both drugs did decrease nocturnal food intake (P<0.05) and activity (P<0.05). When injected at night, L-NAME reduced night-time body temperature (P<0.01), activity (P<0.05) and food intake (P<0.05) in a dose-dependent manner, but night-time injection of aminoguanidine inhibited only night-time activity (P<0.05). The effects of nitric oxide synthase inhibition on body temperature, feeding and activity therefore are primarily a consequence of inhibiting constitutively expressed nitric oxide synthase, and are subject to circadian variation.
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Kamerman, P., Mitchell, D. & Laburn, H. Circadian variation in the effects of nitric oxide synthase inhibitors on body temperature, feeding and activity in rats. Pflügers Arch - Eur J Physiol 443, 609–616 (2002). https://doi.org/10.1007/s00424-001-0738-0
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DOI: https://doi.org/10.1007/s00424-001-0738-0