Experimental and clinical data suggest that primary aldosteronism (PA) may be associated with cardiovascular hypertrophy and fibrosis, in part independent of the BP level. Whether PA may also result in specific deleterious effects on the kidneys was less studied. In 25 patients with tumoral PA, renal studies (urinary excretion of proteins, GFR, and effective renal plasma flow [ERPF], as clearances of technetium-labeled diethylene triaminopentaacetic acid and 131I-ortho iodohippurate, respectively) were performed both before and 6 mo after surgical cure. A control group consisting of patients with essential hypertension (EH) was studied before and after 6 mo of antihypertensive therapy. At baseline, PA and EH patients were similar with respect to demographic data, duration and level of hypertension, and GFR and ERPF. Urinary excretion of albumin and beta2 microglobulin were higher in PA than EH (88 +/- 26 versus 39 +/- 12 and 0.91 +/- 0.23 versus 0.26 +/- 0.19 mg/24 h, respectively; both P < 0.05). Adrenalectomy was followed by a decrease in arterial BP (by 28 +/- 3/13 +/- 2 mmHg), urinary excretion of albumin and beta2 microglobulin (by 48 +/- 19 and 0.53 +/- 0.21 mg/24 h, respectively), and GFR and ERPF (by 15 +/- 3 and 54 +/- 15 ml/min per 1.73 m(2), respectively). In EH, a similar decrease in pressure was associated with a decrease in albuminuria but no change in GFR or ERPF. In 17 of the 25 PA patients who received a 6-mo treatment of spironolactone, both GFR and ERPF decreased in parallel with BP, similar to what was observed after surgery. These data suggest that PA was associated with relative hyperfiltration, unmasked after suppression of aldosterone excess.