Decreased plasma levels of nitric oxide metabolites, angiotensin II, and aldosterone in spontaneously hypertensive rats exposed to 5 mT static magnetic field

Abstract

Previously, we found that whole body exposure to static magnetic fields (SMF) at 10 mT (B(max)) and 25 mT (B(max)) for 2-9 weeks suppressed and delayed blood pressure (BP) elevation in young, stroke resistant, spontaneously hypertensive rats (SHR). In this study, we investigated the interrelated antipressor effects of lower field strengths and nitric oxide (NO) metabolites (NO(x) = NO(2)(-) + NO(3)(-)) in SHR. Seven-week-old male rats were exposed to two different ranges of SMF intensity, 0.3-1.0 mT or 1.5-5.0 mT, for 12 weeks. Three experimental groups of 20 animals each were examined: (1) no exposure with intraperitoneal (ip) saline injection (sham-exposed control); (2) 1 mT SMF exposure with ip saline injection (1 mT); (3) 5 mT SMF exposure with ip saline injection (5 mT). Arterial BP, heart rate (HR), skin blood flow (SBF), plasma NO metabolites (NO(x)), and plasma catecholamine levels were monitored. SMF at 5 mT, but not 1 mT, significantly suppressed and retarded the early stage development of hypertension for several weeks, compared with the age matched, unexposed (sham exposed) control. Exposure to 5 mT resulted in reduced plasma NO(x) concentrations together with lower levels of angiotensin II and aldosterone in SHR. These results suggest that SMF may suppress and delay BP elevation via the NO pathways and hormonal regulatory systems.

Exposure to a moderate intensity static magnetic field enhances the hypotensive effect of a calcium channel blocker in spontaneously hypertensive rats

“…In the case of neck application of the SMF alone, we found that the exposure to SMF for 5-8 weeks significantly suppressed or delayed the development of hypertension together with increased BRS in SHR. We have previously reported on rats that were allowed to roam freely in their cages with magnetic plates attached, where the whole body exposure to SMF for several weeks significantly prevented the development of hypertension [Okano and Ohkubo, 2003b;Okano et al, 2005b]. However, in the cages with magnetic plates attached, the magnetic field exposure of the rats (whole body) can be changed temporally by their daily movements and activities, especially during night-time.…”

“…Previously we found that whole-body exposure to SMF (5 mT or 10 mT [B max ] for a few weeks) suppressed or retarded BP elevation in stroke-resistant spontaneously hypertensive rats (SHR) by eliciting antipressor effects [Okano and Ohkubo, 2003b;Okano et al, 2005b]. We also showed that whole-body exposure to a SMF (10 mT [B max ] for a few weeks) suppressed a norepinephrine depletor, reserpine-induced hypotensin in KyotoWistar rats by eliciting antidepressor effects [Okano et al, 2005a].…”

Alteration of Nitric Oxide Production in Rats Exposed to a Prolonged, Extremely Low-Frequency Magnetic Field

“…In the present study, prolonged ELF-MF exposure decreased NO production of rats. Okano et al (2005) also demonstrated that EMF decreased plasma levels of nitric oxide metabolites in spontaneously hypertensive rats (SHR). Irmak et al (2002) suggested that ELF-MF may destroy NO by generation of superoxide anion and/or causes a reduction in production of NO.…”

“…In the circulation, NO is metabolized to NOx (nitrite and nitrate) (VanAmsterdam et al, 1996), NOx levels reflect the accumulation of stable NO degradation products (Verdon et al, 1995) and local NO biosynthesis (Xu et al, 2002). Okano et al (2005) stated another mechanism for MF influence on NO reduction could be explained by the antioxidant effect associated with reduced Ang II induced superoxide production. This occurs because Ang II stimulates superoxide formation by activating NADPH and NADH oxidase in vitro (Griendling et al, 1994) and in vivo (Rajagopalan et al, 1996), increased oxidative stress induces elevated NOx levels in unexposed SHR (Chou et al, 1998).…”

“…Kavaliers et al (1998) reported inhibitory effects of magnetic fields on opioid analgesia in the snail which involve attenuation of NO and NO synthase activity. Okano et al (2005) reported that 5 mT SMF decreased the plasma levels of NO metabolites in spontaneously hypertensive rats. Furthermore, Noda et al (2000) suggested that pulsed magnetic fields result in a different effect on NOS activity in the cerebellum of the rats.…”