Role of endogenous ACTH on circadian aldosterone rhythm in patients with primary aldosteronism

We recently reported that stimulation with high-dose ACTH caused different responses in terms of aldosterone secretion in aldosterone-producing adenomas (APAs) and idiopathic hyperaldosteronism (IHA) in patients with primary aldosteronism (PA). However, the role of endogenous ACTH in aldosterone secretion in PA has not been systematically evaluated. In this study, we examined diurnal changes in plasma aldosterone concentration (PAC), and changes in PAC after dexamethasone administration in patients with suspected PA, in order to evaluate the effect of endogenous ACTH on aldosterone secretion. Seventy-three patients admitted to Kyoto University Hospital with suspected PA were included. The patients were classified into non-PA, IHA, and APA groups according to the results of captopril challenge test and adrenal venous sampling. PAC at 0900 h (PAC(0900)), 2300 h (PAC(2300)), and after 1-mg dexamethasone suppression test (PAC(dex)) was measured and compared among the three groups. The PAC(2300)/PAC(0900) and PAC(dex)/PAC(0900) ratios were also analyzed. PAC(2300) and PAC(dex) were lower than PAC(0900) in all three groups. There were no significant differences in PAC(2300)/PAC(0900) among the three groups. However, PAC(dex)/PAC(0900) was significantly lower in the APA group compared with the non-PA and IHA groups. The results of this study indicate that aldosterone secretion in APA patients is more strongly dependent on endogenous ACTH than in IHA and non-PA patients. The results also suggest that factors other than ACTH, such as clock genes, may cause diurnal changes in aldosterone secretion in IHA and non-PA patients.