The effects of immediate (1 h) and prolonged (3 weeks) treatment with nitrendipine on systemic and regional hemodynamics were investigated in Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Mean arterial pressure (MAP) was significantly (p less than 0.05) decreased in both WKY (125 +/- 2 versus 108 +/- 3 mm Hg) and SHR (189 +/- 5 versus 141 +/- 10 mm Hg) 1 h following oral nitrendipine administration (10 mg/kg). This was associated with a significant (p less than 0.05) decrease in total peripheral resistance index (TPRI) (0.48 +/- 0.03 versus 0.38 +/- 0.02 units/kg, WKY; 0.69 +/- 0.04 versus 0.56 +/- 0.05 units/kg SHR) but no change in cardiac index (CI). A significant (p less than 0.05) increase in heart rate (HR) (374 +/- 14 versus 407 +/- 11 beats/min) was observed only in WKY. Vascular resistances were reduced significantly (p less than 0.05) in heart and kidney in both SHR and WKY as well as the brain and splanchnic organs of the WKY. Resistance increased significantly in SHR skin. The MAP reduction with prolonged treatment (196 +/- 3 versus 181 +/- 4 and 150 +/- 5 mm Hg) was also associated with a reduced TPRI (0.73 +/- 0.03 versus 0.64 +/- 0.07 and 0.50 +/- 0.03 units/kg) in SHR treated for 3 weeks with nitrendipine (10 and 20 mg/kg/day, respectively). No changes in systemic hemodynamics were observed in similarly treated WKY. Skeletal muscle and splanchnic vascular resistances were reduced (p less than 0.05) in nitrendipine-treated WKY (20 mg/kg/day).(ABSTRACT TRUNCATED AT 250 WORDS)