The influence of exposure to different levels of cadmium on the secretion and biological halflife of corticosterone in the rat.

The adrenal cortex is one of various tissues where elevated concentrations of cadmium have been found. To determine whether this accumulation would lead to an alteration in the function of the adrenal cortex, corticosterone secretion and its turnover in the blood pool were studied in the rat at various levels of cadmium exposure. Weanling male rats received cadmium with drinking water. Within eight weeks of exposure to cadmium concentrations of 30, 150 and 300 mg/l in the drinking water the biological half-life of corticosterone in blood had decreased. It is not known whether this was due to an increase in degradation of the hormone or an increase in excretion. At exposures up to 150 mg cadmium/l this loss of hormone from the blood was sufficiently compensated, or even over-compensated for by an increased rate of corticosterone secretion by the adrenals. At an exposure of 300 mg cadmium/l, however, the secretion rate had decreased below that of the controls, thus leading to a decrease in the corticosterone level in blood. The lack of ability to compensate for the loss of the hormone from blood signals functional insufficiency of the adrenal cortex. This occurred at a concentration of 5.6 micrograms Cd/g fresh adrenal tissue, which is approximately 5 times the cadmium concentration reported for the adrenals of "unexposed" humans. Whether the secretory inhibition originates in the adrenal cortex itself or in its regulating system could not be conclusively demonstrated by this experiment.