P-glycoprotein influences urinary excretion of aldosterone in healthy individuals.

P-glycoprotein (P-gp), the product of the ABCB1 gene, is involved in the transport of aldosterone and cortisol in adrenal cells in vitro but its physiological role in humans remains controversial. Our objective was to test the influence of P-gp polymorphisms on aldosterone. We evaluated plasma aldosterone concentration (PAC), urinary aldosterone, and blood pressure in a cohort of white normotensive men at baseline on diets unrestricted for sodium and potassium and after a 5-day treatment with 500 mg b.i.d. clarithromycin, a P-gp inhibitor. Included were 20 homozygous wild-type (P-gp0), 20 heterozygous (P-gp1), and 20 individuals with combined 2677G>T/A-3435C>T loss-of-function polymorphism of the ABCB1 gene (P-gp2). At baseline, PAC, urinary aldosterone, urinary free cortisol to urine creatinine ratios, and blood pressure did not differ in the three genotypes. After clarithromycin administration, the urinary aldosterone to creatinine ratio increased by an average of 30% in the entire cohort (P < 0.001, n = 60). Increases were pronounced in P-gp1 (+40%; P = 0.014) and P-gp2 individuals (+50%; P = 0.020) but lesser and were NS in P-gp0 individuals (+10%; P = 0.259). PAC also increased from baseline after clarithromycin treatment in all individuals (+19%, P = 0.050); however, the increase in PAC was NS when the three genotypes were analyzed separately. In our experimental conditions, the interaction between P-gp inhibition and the ABCB1 genotype, suggests that aldosterone is indeed a physiological endogenous substrate of P-gp in humans and that P-gp interferes with the net equilibrium between aldosterone secretion and elimination processes in humans.Clinical Trial Registration - URL: http://www.clinicaltrials.gov. Unique identifier: NCT01627665.