Relationship between behavioral and autonomic thermoregulation in the guinea pig

Abstract

This study was conducted to correlate the preferred thermal environment of the unrestrained guinea pig with the activity of its thermoregulatory effectors when maintained under a wide range of ambient temperatures (T a). Eight male guinea pigs were used in a series of experiments on behavioral and autonomic thermoregulatory function. In the behavioral experiment, individual guinea pigs were placed in a temperature gradient for 90 min while their position in the gradient was noted at 5 min intervals during the last 30 min of treatment. Their position in the gradient corresponded to a preferred T a of 30.6±3.8 (S.D.)°C. In the experiments to determine autonomic function, individual guinea pigs were placed in an environmental chamber thermostabilized to T a's of 16 to 34°C. Metabolic rate (MR) and evaporative water loss (EWL) were continuously monitored for 90 min. After the guinea pigs were in the chamber for 90 min their colonic temperature was measured. MR was relatively stable between T a's of 20 to 34°C. The lower critical T a, or the T a below which MR increased above the resting level, was 20°C for the guinea pig. EWL was minimal between T a's of 14 and 28°C. Increasing T a above 28°C led to a gradual increase in EWL. Thermal conductance was minimal and stable between T a's of 14 and 26°C and increased sharply as T a increased above 26°C. Colonic temperature was maintained at 38°C between T a's of 22 to 30°C. Colonic temperature started to decrease at T a's below 22°C and increase above T a's of 30°C. The guinea pig prefers a warm T a which is ∼10°C above the lower critical T a. This relationship between preferred T a and lower critical T a differs considerably to that observed in the mouse and hamster.