EFFECTS OF KETANSERIN ON HEART-RATE AND BLOOD-PRESSURE VARIABILITY - IMPLICATIONS FOR THE EFFECT ON THE BAROREFLEX MECHANISMS

Ketanserin is an antihypertensive drug with affinity to both serotonin S-2- and alpha(1)-adrenoceptors. The specific effects of ketanserin o n the baroreflex are not fully understood. We, therefore, studied baro reflex regulation based on blood pressure (BP) and heart rate (HR) res ponses to several maneuvers before and after the administration of 2 x 5 mg of ketanserin i.v. both in supine and in standing posture. Seven young healthy volunteers were investigated. We measured spontaneous v ariability in HR and BP (Finapres), and performed deep inspiration, Va lsalva, and lying-to-standing tests. We also used a modified Valsalva maneuver that consist of Deep Inspiration Breath-holding with closed g lottis and EXpiration: DIBEX maneuver. From the BP recordings, periphe ral resistance (TPR) and stroke volume (SV) were estimated by the Mode lflow method. Thirty minutes after the administration of ketanserin, t here was no significant change in mean HR, BP, spectral power of HR an d BP variability, baroreflex sensitivity, or Valsalva ratio. Thus keta nserin did not affect the cardiac baroreflex mechanism. However, in st anding position, SV increased and TPR decreased under the influence of ketanserin, and BP overshoot after the Valsalva and DIBEX maneuver wa s significantly decreased as well. There was also no reflex recovery o f BP during the DIBEX maneuver in three volunteers, who felt faint. Th ese observations indicate that there is a lack of vasoconstriction. We conclude that ketanserin is not a vasodilator but seems to inhibit va soconstriction.