Antihypertensive drugs and baroreflex sensitivity. Effects of rilmenidine

Rilmenidine 1 and 2 mg administered orally (weekly intervals, double-blind, randomized cross-over, placebo-controlled) to six healthy subjects, dose-dependently reduced (p less than 0.05) resting systolic blood pressure (107.0 +/- 5.6, 99.2 +/- 4.5 mmHg) compared with placebo (117.3 +/- 5.2 mmHg). Diastolic blood pressure was also reduced (p less than 0.05), and no change occurred in heart rate or forearm blood flow. Rilmenidine increased (p = 0.05) baroreflex sensitivity when blood pressure was increased with phenylephrine: no change in baroreflex sensitivity occurred during reduction in blood pressure with glyceryl trinitrate. Rilmenidine given at 1- and 2-mg doses reduced (p less than 0.05) systolic blood pressure during "lying to standing," a test of autonomic function (76.3 +/- 9.8, 56.8 +/- 4.5 mmHg), versus results with placebo (95.2 +/- 10.5 mmHg); the R-R intervals associated with these blood pressure reductions were not different (571 +/- 12, 609 +/- 19 msec), versus results with placebo (541 +/- 28 msec). During "sustained handgrip," rilmenidine given at 1- and 2-mg doses reduced (p less than 0.05) systolic blood pressure (146.8 +/- 6.2, 142.3 +/- 7.0 mmHg), versus results with placebo (157.3 +/- 7.5 mmHg); the corresponding R-R intervals were 705 +/- 45 and 675 +/- 49 msec, not different from those with placebo (695 +/- 49 msec). Similar results occurred with other tests of autonomic function ("deep breathing" and "three-minute standing"). In conclusion, rilmenidine increases baroreflex sensitivity to increases in blood pressure with phenylephrine; during tests of autonomic function, the lower blood pressures that occur with rilmenidine are associated with correspondingly greater R-R intervals; this may also indicate enhanced baroreflex sensitivity.