Adrenal responses in high and low ACTH response lines of chickens during acute heat stress

Abstract

Lines of chickens, selected for seven generations according to their high and low responsiveness to ACTH, were acclimatized to 24°C and 45% relative humidity (RH) and then subjected to acute heat stress (45°C and 45% RH). No differences in plasma corticosterone were found between high- and low-response lines when the chickens were in a nonheated environment. During the heat stress episode there were significant elevations of plasma corticosterone in both lines, but the response of high lines was significantly greater. This response was shorter lived in the high line than in the low line. Plasma norepinephrine concentrations were greater in the low-response line maintained at moderate temperature; but during acute heat stress, the elevation of this amine was greater and more rapid in the high-response line. Plasma epinephrine levels were not significantly different in the two lines when maintained at moderate temperature; however, levels were elevated more rapidly in the high-response line than in the low-response line during heat stress. No differences between lines for adrenal norepinephrine and epinephrine were observed in chickens maintained at moderate temperature, and heat stress had no significant effect on adrenal norepinephrine level. There were, however, significant reductions in adrenal epinephrine levels during acute heat stress, but rates of decline were essentially the same for both the high- and the low-response lines. The data indicated that in the domestic fowl, the adrenal cortical response may precede the adrenal medullary response in chickens that are subjected to acute heat stress. The inherent differences between response lines may have been due to differences in their abilities to maintain an extended responsiveness to the imposed stress.