Dependence of the calorigenic effect of adrenaline on the secretory activity of the adrenal medulla in posthypothermic rats.

Posthypothermic rats, 13 h after spontaneous rewarming as well as between days 6 and 7, produced the same quantity of heat as euthermic control animals. At the same time both urinary adrenaline excretion and adrenaline content of the adrenals were markedly changed. In the initial phase of the posthypothermic state (13 h after spontaneous rewarming) urinary adrenaline excretion was significantly increased whereas adrenaline content in the adrenals was lower than in normothermic control rats (P less than 0.001). Between days 6 and 7 after rewarming, the rate of urinary adrenaline excretion and adrenaline content in the adrenals returned to the control values. The calorigenic effect of exogenous adrenaline (50 microgram/100 g), found in the euthermic control rats, was not observed in posthypothermic animals 13 h after spontaneous rewarming when the secretory activity of the adrenal medulla was increased. The restitution of the calorigenic action of exogenous adrenaline occurred between days 6 and 7 after hypothermia.