Attenuation of metabolic heat production and cold-escape/warm-seeking behaviour during a cold exposure following systemic salt loading in rats.
The reduction of body core temperature (Tcore) after salt loading has been reported. In this study, we tested the hypothesis that, during a cold exposure in rats, (1) salt loading would decrease metabolic rate (MR), reducing Tcore, but (2) Tcore would be maintained when cold-escape/warm-seeking behaviour is available. In the first experiment (n = 7), MR and Tcore were measured by indirect calorimetry and telemetry, respectively, during 26, 20 and 10 degrees C exposure for 1 h each, in that order. In the second experiment (n = 7), each rat was placed in an operant system during the same exposure protocol as in the first experiment, where it could trigger a 40 degrees C air reward for 30 s at 20 and 10 degrees C by moving into specific areas (operant behaviour). In each experiment, rats repeated the same protocol twice with a subcutaneous injection (10 ml kg-1) of either isotonic saline (154 mM) or hypertonic saline (2500 mM). In the first experiment, MR in the isotonic-saline trial increased (P < 0.05) at 20 and 10 degrees C compared with that at 26 degrees C by 21 +/- 5 and 48 +/- 6 %, respectively (means +/- S.E.M.), with Tcore unchanged. However, values for MR and Tcore in the hypertonic-saline trial were lower (P < 0.05) than those in the isotonic-saline trial in any ambient temperature. In the second experiment, Tcore was also lower (P < 0.05) in the hypertonic-saline trial than in the isotonic-saline trial. The counts of the operant behaviour in the hypertonic-saline trial remained unchanged in each exposure period, but those in the isotonic-saline trial increased (P < 0.05) at 10 degrees C. These results may suggest that salt loading attenuates both metabolic and behavioural thermoregulatory responses to the cold.
Konishi
Masahiro
M
Department of Physiology, School of Allied Health Sciences, Osaka University Faculty of Medicine, Yamadaoka 1-7, Suita, Osaka 565-0871, Japan.
Nagashima
Kei
K
Asano
Kento
K
Kanosue
Kazuyuki
K
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001810:Blood Volume / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D003080:Cold Temperature; D003216:Conditioning, Operant / Q000187:drug effects; D006358:Hot Temperature; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D009994:Osmolar Concentration; D010101:Oxygen Consumption / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D022722:Thermogenesis / Q000502:physiology*; D014563:Urodynamics / Q000502:physiology
D007552:Isotonic Solutions; D012462:Saline Solution, Hypertonic