Investigation of the salivary 18-hydroxycorticosterone:aldosterone ratio in man using a direct assay

A method for the direct determination of 18-hydroxycorticosterone (18OHB) in human saliva has been developed and validated. Saliva was collected at 30 min and 1 h intervals between 0600 and 2200 h from healthy men and women for the determination of 18OHB (SHB), aldosterone (SA) and glucocorticoids (SGC = cortisol + cortisone). SHB was highly correlated with SA (r = 0.75; P less than 0.001) but even more highly with SGC (r = 0.89; P greater than 0.001). Multiple regression analysis confirmed that SGC was a more important determinant of SHB than was SA. Though the concentrations of 18OHB and aldosterone were highly correlated there was considerable variation in the 18OHB:aldosterone ratio during the period of saliva collection. This ratio tended to be highest in the morning and lowest in the evening and was weakly correlated with SGC level (r = 0.62; P less than 0.01). The 18OHB:aldosterone ratio in saliva approximates to, and is highly correlated with, that in plasma. We suggest that the fluctuations in SHB:SA ratio correspond to the relative rates of secretion of 18OHB and aldosterone and that this ratio is modulated either by ACTH or by cortisol. Whether this indicates that 18OHB is a by-product of glucocorticoid as well as aldosterone metabolism, or whether this implies a separate physiological role for the steroid remains to be clarified.