Baroreflex control of heart rate and renin release in SHR following administration of felodipine, an antihypertensive Ca2+ antagonist.

Baroreflex control of renin release following acute and prolonged blood pressure reduction by felodipine administration was investigated in conscious spontaneously hypertensive rats (SHR) fitted with arterial and venous catheters. Basal values of mean arterial pressure (MAP), heart rate (HR), and plasma renin activity (PRA) were obtained in SHR and in SHR given felodipine for 2 weeks (SHRF). In SHRFMAP was reduced by 12% (p less than 0.01) versus SHR, but PRA and HR were similar. Acute i.v. infusion of felodipine, during 5 h, maintained MAP reduction by 40%. Initially, HR increased 29 +/- 3% but returned to predrug levels after 3 h. PRA increased from 1.4 +/- 0.5 to 6.5 +/- 1.0 ng/ml/h. After 5 h PRA had reached low levels equal to those in SHR given placebo instead of felodipine. In SHR pretreated with metoprolol neither HR nor PRA increased following felodipine, an indication that the observed changes were neurogenically determined. This suggests that baroreflex control of cardiac and renal function resets within 3-5 h following blood pressure reduction by felodipine.