Nitrendipine, a new calcium entry blocker, was administered to renovascular hypertensive rats (2K1C Goldblatt) (RHR, n = 8) and sham operated control rats (ShC, n = 8) to evaluate the effects on left ventricular hypertrophy and regional blood flow using radioactive microspheres. Nine untreated RHR and 8 untreated ShC served as control groups. After 6 weeks treatment (20 mg/kg subcutaneously, every other day), blood pressure reduced significantly in both RHR and ShC associated with a reduction in total peripheral resistance. Significant reversal of left ventricular hypertrophy was noted in RHR (1278 +/- 41 to 1024 +/- 19 mg, p less than 0.01), but not in ShC. There was a significant relationship between blood pressure and left ventricular mass in both untreated rats (r = 0.955, p less than 0.001) and treated rats (r = 0.729, p less than 0.005). Nitrendipine increased coronary blood flow in RHR (430 +/- 30 to 566 +/- 47 ml/m/100g, p less than 0.05) as well as in ShC (375 +/- 15 to 508 +/- 29 ml/ml/100g, p less than 0.05), without increasing cardiac oxygen demand. Renal blood flow was unchanged, whereas cerebral blood flow was significantly increased in both RHR (128 +/- 6 to 164 +/- 13 ml/m/100g, p less than 0.01) and ShC (124 +/- 7 to 173 +/- 5 ml/m/100g, p less than 0.01). Thus, long treatment of nitrendipine effectively regressed cardiac hypertrophy toward normal. Nitrendipine reduced total peripheral resistance; however, the effects on regional blood flow were not uniform among various organs.