Light and darkness effect on adrenocortical secretion of rats exposed to stress.

The investigations were carried out on sexually mature Wistar rats divided into three groups: control group, a group kept always in darkness, and a group exposed continually to light. In each group a subgroup was isolated which was subjected to formalin stress. In all animals aldosterone and corticosterone concentrations in adrenal venous blood were determined spectrophotometrically. Thin layer chromatography was used for separation of steroids. It was found that keeping the rats in darkness caused a fall in the concentrations of corticosterone and aldosterone, while stress caused in the rats kept in darkness a rise of the concentrations of both these hormones. Continuous exposure to light reduced the concentration of aldosterone to undetectable values and of corticosterone by 90% in relation to the control group. Decrease of hormones level was observed in the stressed and non-stressed subgroups.