Sleep deprivation in the rat: XIX. Effects of thyroxine administration

Chronic total sleep deprivation (TSD) in the rat produces an initial elevation and then declining body temperatures, increasing metabolic rate and eventual death. Because TSD rats will engage in warming behavior, one hypothesis is that the metabolic increase is an unsuccessful attempt at warming to combat a lethal hypothermia. However, TSD rats also undergo weight loss and progressive deterioration of skin and fur, suggesting TSD-induced pathological catabolic activity, possibly secondary to increased metabolic rate, that could be lethal. To evaluate these alternatives, the metabolic rate of rats was increased by thyroxine (T4) treatment while subjecting them to TSD. Compared to TSD rats not given T4, they had higher metabolic rates, higher body temperatures and reduced warming behavior, but their survival period was 37% shorter. Thus, it is unlikely that hypothermia is the cause of death in TSD rats. Weight and appearance declined more rapidly in T4-treated rats, but at the same proportions of survival time, skin pathology and decline in appearance were less evident in T4-treated rats than in TSD rats not given T4. Thus, there is some doubt whether a general pathological catabolic process is the cause of death. It is also possible that a specific morbid process normally reversed by sleep was accelerated by T4 administration.