Plasma corticosterone response in continuous versus discontinuous chronic heat exposure in rat.

Effects of chronic exposure (25 days) to continuous (CHE) or discontinuous (DHE) hot environment (34 degrees C) on growth rate, food intake and cortico-adrenal function were studied in adult male rats. Growth rate and food intake were 40 and 31% less respectively in CHE and 7 and 9% less respectively in DHE than in control (CE) animals. The adrenal response to heat (40 degrees C) was reduced by 54 and 82% in CHE and DHE rats respectively but the plasma corticosterone (B) response to exogenous ACTH and ether stress was not altered by chronic heat. The plasma B rhythm was altered only in CHE rats which exhibited a 40% decrease in amplitude and a delayed nocturnal recession of plasma B values. These results indicate that 1) CHE induced major alterations of behavior specially during the nocturnal period of the L-D cycle, 2) that the altered circadian B rhythm of CHE rats could be linked to changes in feeding behavior and to reduced metabolic activity, 3) and that CHE induced a poorer adaptation than DHE.