Acute effects of manidipine on renal blood flow and sympathetic nerve activity in conscious, spontaneously hypertensive rats.

To examine acute effects of manidipine hydrochloride, a new calcium antagonist, on renal blood flow (RBF) in spontaneously hypertensive rats, we recorded changes in RBF as the Doppler shift and a neurogram of renal sympathetic nerve activity (RSNA) simultaneously in a conscious and unrestrained state. An intravenous infusion of manidipine did not decrease RBF until mean arterial pressure (MAP) fell by 20 +/- 1 mmHg and RSNA increased by 98 +/- 18%. At the nadir of RBF (-25 +/- 2%, MAP: -31 +/- 2 mmHg, RSNA: +154 +/- 25%), percent increase in RSNA significantly correlated with percent decrease in RBF (r = -0.802, p < 0.02). On the other hand, the infusion of sodium nitroprusside did not decrease RBF significantly even at a nadir of MAP (-35 +/- 2 mmHg). Air jet stress increased both MAP and RSNA associated with a decrease in RBF. Responses of MAP and RBF were blunted after manidipine infusion while the stress evoked a similar degree of enhancement of RSNA to that of the control trial. Although manidipine may be less effective than nitroprusside in maintaining RBF during abrupt reductions of MAP, the results of this study suggest that antihypertensive treatment with manidipine may be clinically beneficial in maintaining RBF both at rest and during psychologically stressful conditions.