Metabolic responses of unanesthetized rats to manipulation of skin temperature

Body temperatures of albino rats are highly variable compared to those of larger mammals. This paper demonstrates that much of that variability can be attributed to shifts of body temperature thresholds for metabolic response accompanying disturbance or arousal. It also shows that the open-loop gain (OLG) of the metabolic temperature-regulating system is as high as that in larger mammals, ruling out low gain as the source of the variability. Skin temperature (T-sk) of shaved rats was controlled by immersion to the neck in a water bath. Metabolic rate (M), measured during step changes of T-sk and during more gradual changes of colonic (T-c) and hypothalamic (T-hy) temperature, was proportional to deviations of both T-c and T-sk below their respective thresholds. The absolute values of the coupling function (alpha) relating M to T-c were proportional to T-sk; the absolute values of the coupling function (beta) relating M to T-sk were proportional to T-c. Thus, the gain of the system changed systematically with body temperatures. The thresholds of T-sk and T-c below which M increased were inversely proportional to T-c and T-sk, respectively, as well as shifting in response to some unknown variable designated arousal.