Heart Rate in Rats Exposed to Constant Magnetic Fields

Ohkubo

2002

Bioelectromagnetics

Spreading evidence suggests that environmental and artificial magnetic fields have a significant impact on cardiovascular system. The modulation of cardiovascular regulatory mechanisms may play a key role in observed effects. The objective was to study interrelated impacts of artificial static magnetic field (SMF) and natural geomagnetic field (GMF) on arterial baroreceptors. We studied baroreflex sensitivity (BRS) in conscious rabbits before and after 40 min of sham (n = 20) or application of Nd2-Fe14-B alloy magnets (n = 26) to the sinocarotid baroreceptor region in conjunction with GMF disturbance during the actual experiment, determined by K- and A(k)-indexes from a local geomagnetic observatory. SMF at the position of baroreceptors was 0.35 T. BRS was estimated from peak responses of mean arterial pressure (MAP) and heart rate expressed as percentages of the resting values preceding each pair of pressure (phenylephrine) and depressor drug (nitroprusside) injections. We observed a significant increase in BRS for the nitroprusside depressor test (0.78 +/- 0.1 vs. 1.15 +/- 0.14 bpm/mmHg%, initial value vs. SMF exposure, P <.0002) and a tendency for phenylephrine pressor test to increase in BRS. Prior to SMF exposure, a significant positive correlation was found between actual K index values and MAP (t = 2.33, P =.025, n = 46) and a negative correlation of the K index with BRS (t = -3.6, P =.001, n = 46). After SMF exposure we observed attenuation of the geomagnetic disturbance induced a decrease in BRS. Clinical trials should be performed to support these results, but there is a strong expectation that 0.35 T SMF local exposure to sinocarotid baroreceptors will be effective in cardiovascular conditions with arterial hypertension and decreased BRS, due to a favorable SMF effect on the arterial baroreflex. Magnets to the sinocarotid triangle along with modification of the pharmacotherapy for hypertension should be especially effective on days with intense geomagnetic disturbance, in moderating sympathetic activation and baroreceptor dysfunction.

Section: Possible Interpretationssupporting

confidence: 77%

Artificial static and geomagnetic field interrelated impact on cardiovascular regulation

Ohkubo

2002

Bioelectromagnetics

“…This approach allows identification of most sensitive biological structures and determination of mechanisms or sequences of changes in physiological functions that give rise to the observed biological effects. It has already been reported earlier that SMF of different intensity significantly affect hemodynamics including blood pressure, heart rate (Beischer 1969, Jehenson et al 1988, Gmitrov et al 1990, 1995, Lazetic and Pekaric-Nadj 1993, Gmitrov 1996, Okano and Ohkubo 2001, 2005a, 2005b, Veliks et al 2004) and microcirculation (Okano et al 1999, Gmitrov et al 2002, Morris and Skalak 2005, 2008, Gmitrov 2007b. It is widely recognised that arterial baroreceptors play a key role in the operation of cardiovascular functions and in the reflex regulation of blood pressure, under normal and pathological conditions.…”

Section: Introductionmentioning

confidence: 96%

Static magnetic field blood pressure buffering, baroreflex vs. vascular blood pressure control mechanism

International Journal of Radiation Biology

2010

“…Increasing evidence suggests that static magnetic ®elds (SMFs) with high magnetic¯ux densities have a signi®cant effect on the cardiovascular system [Beischer, 1969;Jehenson et al, 1988;Lazetic and Pekaric-Nadj, 1993;Gmitrov et al, 1995;Gmitrov and Ohkubo, 1998]. …”

Section: Introductionmentioning

confidence: 99%

Effect of 0.25 T static magnetic field on microcirculation in rabbits

Ohkubo

Okano

2002

Bioelectromagnetics

We showed previously in rabbits that 0.2 and 0.35 T static magnetic field (SMF) modulated systemic hemodynamics by arterial baroreceptors. We now have measured the effect of 0.25 T SMF on microcirculation within cutaneous tissue of the rabbit ear lobe by the rabbit ear chamber (REC) method. Forty experimental runs (20 controls and 20 SMF) were carried out in eight different rabbits with an equal number of control and SMF experiments on each individual. Rabbits were sedated by pentobarbital sodium (5 mg/kg/h, i.v.) during the entire 80 min experiment. SMF was generated by four neodium-iron-boron alloy (Nd2-Fe14-B) magnets (15 x 25 x 30 mm, Neomax, PIP - Tokyo Co., Ltd., Tokyo, Japan), positioned around the REC on the observing stage of an optical microscope. The direct intravital microscopic observation of the rabbit's ear microvascular net, along with simultaneous blood flow measurement by microphotoelectric plethysmography (MPPG), were performed PRE (20 min, baseline), DURING (40 min), and POST (20 min) magnetic field exposure. The control experiments were performed under the same conditions and according to the same time course, but without magnetic field. Data were analyzed comparing MPPG values and percent change from baseline in the same series, and between corresponding sections of control and SMF runs. In contrast to control series (100+/-0.0%-90.0+/-5.4%-87.7+/-7.1%, PRE-EXPOSURE-POST), after magnetic field exposure we observed increased blood flow (100+/-0.0%-117.8+/-9.6%*-113.8+/-14.0%, *P<0.05) which gradually decreased after exposure cessation. We propose that long exposure of a high level nonuniform SMF probably modifies microcirculatory homeostasis through modulation of the local release of endothelial neurohumoral and paracrine factors that act directly on the smooth muscle of the vascular wall, presumably by affecting ion channels or second messenger systems.