The function of glucocorticoids in thermogenesis.

Studies both in vivo and in vitro implicate glucocorticoids in various aspects of thermogenesis and prevention of heat loss. Many or most of these effects are probably permissive. Adrenalectomized, cold-exposed rats require glucocorticoids for catecholamine-mediated mobilization of free fatty acids, for shivering responses, and for vasoconstriction and piloerection. Glucocorticoid pretreatment of hypothermic hamsters results in a physiological state more similar bioenergetically to hibernation than to hypothermia. For example, such hamsters can arouse to normothermia from a body temperature of 8 C in a 7--8 C cold room. Lipolytic, gluconeogenic, glycogenolic, and pressor actions resulting from several hormone interactions that require glucocorticoids for optimum responses may account for the enhanced thermogenic ability shown by glucocorticoid-pretreated hamsters. Glucocorticoid treatment also results in enhanced blood and liver carbohydrate levels during hypothermia, a condition similar to that occurring in naturally hibernating animals as opposed to the depleted carbohydrate reserves generally seen in hypothermic animals.