Increased urinary free cortisol: A potential intermediate phenotype of essential hypertension
We evaluated urinary cortisol excretion as a potential intermediate phenotype of essential hypertension in 153 white patients with essential hypertension and 18 normotensive white control subjects. Analyses were controlled for dietary sodium and gender to adjust for potential confounding effects of these variables on cortisol excretion. Urinary cortisol excretion measured on both high- and low-salt diets was significantly related to hypertension by repeated measures ANCOVA (P=.02). Additional determinants of urinary free cortisol included dietary sodium intake and gender; cortisol excretion was significantly higher in men (P=.0006) and during a high-sodium diet (P=.0001). Maximum likelihood analysis showed urinary cortisol to have a bimodal distribution on both 200-mmol (P<.01) and 10-mmol (P<.002) sodium diets in hypertensive subjects. On the low-salt diet, the mean urinary cortisol in normotensive subjects (108.7+/-44.7 nmol/d) was similar to the mean of hypertensive subjects in the low mode (127.2+/-43.0 nmol/d). The high mode comprised 31.2% of the hypertensive population and had a mean urinary cortisol of 224.3+/-93.8 nmol/d. Subjects with the highest urinary free cortisol showed the least sensitivity of blood pressure to dietary sodium loading (P<.05). These data suggest that there is an association between salt-resistant hypertension and high urine cortisol levels. This association may have a genetic basis.