Elevated Resting and Exercise-Induced Cortisol Levels after Mineralocorticoid Receptor Blockade with Canrenoate in Healthy Humans

Activation of central nervous mineralocorticoid receptors (MRs) has been shown to inhibit the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis in animals. Here, we examined whether MRs in humans likewise regulate HPA activity in response to a physiological stressor. In a balanced, randomized, double-blind, cross-over trial, 12 healthy men were treated with either two injections of 200 mg canrenoate or placebo 24 and 8 h before an intense physical exercise taking place between 1600 and 1700 h. Exercising was preceded by a 60-min rest period and followed by another 90-min rest. Blood was collected in regular intervals to determine ACTH, cortisol, and human GH (hGH). Exercise induced a significant rise in cortisol, ACTH, and hGH. Cortisol levels, however, were significantly higher after canrenoate, compared with placebo, whereas ACTH and hGH concentrations did not differ. The increase in cortisol was already significant during rest before exercise and continued to be elevated throughout the whole experiment. We conclude that MR blockade leads to a tonically increased cortisol secretion both during rest and under stimulation. The undiminished concentration of ACTH in the presence of elevated cortisol levels suggests that blockade of MR shifts the set point for cortisol feedback inhibition of the HPA axis toward higher cortisol levels.