In the present study we investigated the effect of a selective alpha 1-adrenergic blocker (doxazosin), an angiotensin-converting enzyme (ACE) inhibitor (captopril), and a calcium channel antagonist (nifedipine) on renal function in hypertensive non-insulin-dependent diabetic patients. 30 NIDD hypertensive patients (age = 50 +/- 3 years; BMI = 30 +/- 1 kg/m2) (mean +/- SEM) were studied before and after a 12-week period of antihypertensive treatment. Ten patients were treated with doxazosin (Cardura) (2-8 mg once daily or 8 mg b.i.d.), 9 with captopril (Capoten) (25-50 mg b.i.d.), and 11 with nifedipine (Procardia-XL) (30-60 mg once daily). Blood pressure, creatinine clearance, 24-hour urinary protein excretion, fasting plasma glucose concentration and glycosylated hemoglobin were measured before and after drug treatment. Fasting plasma glucose and glycosylated hemoglobin (HbA1c) were similar in all three groups prior to the start of antihypertensive therapy and did not change significantly from baseline in any treatment groups. In the doxazosin group creatinine clearance rose from 99 +/- 8 to 122 +/- 8 ml/1.73 m2.min (p < 0.01), while 24-hour urinary protein excretion declined from 2.66 +/- 0.05 to 1.76 +/- 0.02 mg/day/ml/1.73 m2.min (p < 0.01). In diabetics treated with captopril creatinine clearance rose from 93 +/- 6 to 109 +/- 9 ml/1.73 m2.min (p < 0.05), while the 24-hour urinary protein excretion fell from 2.70 +/- 0.05 to 2.03 +/- 0.04 mg/day/ml/1.73 m2.min (p < 0.05). In patients treated with nifedipine creatinine clearance did not change (97 +/- 6 vs. 94 +/- 7 ml/1.73 m2.min), while 24-hour urinary protein excretion decreased from 2.84 +/- 0.04 to 1.95 +/- 0.03 mg/day/ml/1.73 m2.min. Systolic and diastolic blood pressure were similar in doxazosin (150 +/- 3/95 +/- 2 mm Hg), captopril (153 +/- 3/93 +/- 1), and nifedipine (155 +/- 4/93 +/- 1) groups prior to the start of antihypertensive therapy and declined to 143 +/- 3/84 +/- 3 (doxazosin), 139 +/- 3/82 +/- 3 (captopril), and 141 +/- 3/84 +/- 1 (nifedipine) mm Hg (all p < 0.01 vs. pretreatment). In summary, both doxazosin and captopril treatment were associated with significant rises in GFR, while all three antihypertensive agents caused a significant decline in proteinuria. These results indicate that alpha-adrenergic blockers, ACE inhibitors, and calcium channel antagonists can safely and effectively be used in the clinical management of non-insulin-dependent diabetic patients with hypertension.