Static Magnetic Field and Verapamil Effect on Baroreflex Stimulus-Induced Microcirculatory Responses

Abstract

Arterial baroreceptors importantly evolved in blood pressure regulation with significant clinical consequences. We studied the less explored direct effect of the arterial baroreflex on regional microcirculation. Fifty-one experiments were performed in conscious rabbits to investigate the relationship between microcirculation and arterial baroreflex subjected to stimulation with either 0.35 T static magnetic field (SMF) and/or the calcium channel blocker, verapamil. Mean femoral artery blood pressure (MAP), heart rate (HR), and a microphotoelectric plethysmogram (MPPG) of the ear lobe skin microcirculatory network were simultaneously recorded during 120 and 140 min experiments. Baroreflex sensitivity (BRS) was assessed on the basis of the HR/MAP relationship during vasodilator (sodium nitroprusside) or vasoconstrictor (phenylephrine) drug i.v. bolus injections and by power spectral analysis estimating the transfer function from MAP to HR before and after 40 min of 0.35 T SMF (Nd2-Fe14-B magnets) local exposure to sinocarotid baroreceptors and/or verapamil infusion (20 µg/kg/min). We found significant positive correlation between MPPG and BRS (R = 0.44, p = 0.02, n = 28) indicating participation of the baroreflex regulatory mechanism in microcirculation. Both SMF and verapamil increased baroreflex stimulus-induced microcirculatory responses (p < 0.01) indicating augmentation of baroreceptor capacity to regulate microcirculation. The simultaneous application of SMF and verapamil did not affect microcirculatory response suggesting Ca2+ channels as a possible site of SMF impact. Pharmacological and nonpharmacological modulation of the baroreflex stimulus-induced microcirculatory responses implies new possibilities to improve microcirculation in target organs with potential clinical implementation.