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

Abstract

Effects of chronic exposure (25 days) to continuous (CHE) or discontinuous (DHE) hot environment (34°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°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.