Mechanisms of temperature regulation in heat-acclimated hamsters

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Abstract
Mechanisms of temperature regulation were assessed by measurements of O2 consumption (.ovrhdot.VO2), body temperature (Tre = rectal, Tsk = skin), evaporative water loss (EWL), regional distribution of blood flow, and blood volume. Hamsters (Mesocricetus auratus) were acclimated to ambient temperatures of 34 or 22.degree. C. .ovrhdot.VO2 of 34.degree. C-exposed animals was reduced to 50% of that of controls at 22.degree. C; EWL with heat exposure was almost double that of controls. Heat-acclimated animals had a slightly elevated Tre in comparison to 22.degree. C-acclimated animals, whereas there was a marked elevation in Tsk with heat exposure, in contrast to control animals at 22.degree. C. Blood flow distribution measurements indicated that with 34.degree. C exposure there was a decreased flow in liver, kidney and intestine; there was an increase to the carcass. Red cell and plasma volumes in heat-acclimated hamsters were decreased below the values of the 22.degree. C controls. Heat acclimation of the hamster appears to involve reduced .ovrhdot.VO2 and increased EWL. Convective and radiative heat loss appear to be maintained by increased Tsk with heat exposure. Nonevaporative heat dissipation mechanisms are of primary importance in thermoregulation of the heat-acclimated hamster, and it is suggested that this is mediated by increased peripheral blood flow with reduced flow to the viscera.