Effects of 12 mT static magnetic field on sympathetic agonist‐induced hypertension in wistar rats

Abstract

We investigated the combined effects of a moderate-intensity static magnetic field (SMF) and two different sympathetic agonists, an alpha(1)-adrenoceptor agonist, phenylephrine and a beta(1)-adrenoceptor agonist, dobutamine, which induced hypertension and different hemodynamics in Wistar rats. Five-week-old male rats were continuously exposed to the SMF intensity of 12 mT (B(max)) with the peak spatial gradient of 3 mT/mm for 10 weeks. A loop-shaped flexible rubber magnet was adjusted to fit snugly around the neck region of a rat (diameter-adjustable to an animal size). Sham exposure was performed using a dummy magnet. Six experimental groups of six animals each were examined: (1) sham exposure with intraperitoneal (ip) saline injection (control); (2) SMF exposure with ip saline injection (SMF); (3) sham exposure with ip phenylephrine (1.0 microg/g) injection (PE); (4) SMF exposure with ip phenylephrine injection (SMF + PE); (5) sham exposure with ip dobutamine (4.0 microg/g) injection (DOB); (6) SMF exposure with ip dobutamine injection (SMF + DOB). Fifteen minutes after the injection of each agent, the first set of parameters, arterial blood pressure (BP) and heart rate (HR), the second set of parameters, skin blood flow (SBF) and skin blood velocity (SBV), or the third set of parameters, the number of rearing (exploratory behavior) responses and body weight was monitored. Each agent was administered three times a week for 10 weeks, and each set of parameters was monitored on different days, once a week. The dose of phenylephrine significantly increased BP and decreased HR, SBF, SBV, and the number of rearing responses in the PE group compared with those in the respective age-matched control group. The dose of dobutamine significantly increased BP and HR, increased SBF, SBV, and the number of rearing responses in the DOB group compared with those in the control group. Continuous neck exposure to the SMF alone for up to 10 weeks induced no significant changes in any of the measured cardiovascular and behavioral parameters. The SMF exposure for at least 2 weeks (1) significantly depressed phenylephrine effects on BP, SBF, SBV, and rearing activity (SMF + PE group vs. PE group); (2) significantly depressed dobutamine effects on BP, SBF, and SBV, and suppressed dobutamine-induced increase in the rearing activity (SMF + DOB group vs. DOB group). These results suggest that continuous neck exposure to 12 mT SMF for at least 2 weeks may depress or suppress sympathetic agonists-induced hypertension, hemodynamics, and behavioral changes by modulating sympathetic nerve activity.

Effects of Static Magnetic Fields on Blood Pressure in Animals and Humans

“…For a summary, please refer to Table 1. Okano and Ohkubo (2007) In particular, our series of studies [60][61][62][63][64][65][66][67], as shown in Table 1, have demonstrated that BP were modulated by moderate intensity SMF in mT level fields in pharmacologically treated animals and genetically hypertensive animals, while there was no change in normal, conscious animals when the values of the BP were within normal range (reference values). Therefore, we concluded that significant bioresponses to therapeutic signals occur when the deviations of the endpoints are far from homeostasis [77].…”

“…In a series of our later experiments [60][61][62][63][64][65][66][67], the previous works on the SMF effects on cutaneous microvasculature and microcirculation in conscious animals were extended. These studies focused on BP changes associated with SMF exposure.…”

“…The combined effects of a SMF (12 mT for 10 weeks) and two different sympathetic agonists were investigated in conscious rats [67]. The two different sympathetic agonists, an 1 -adrenoceptor agonist, phenylephrine and a 1 -adrenoceptor agonist, dobutamine, induced hypertension and different hemodynamics: phenylephrine increased BP and decreased heart rate, skin blood flow, skin blood velocity, and the number of rearing responses; dobutamine increased BP, heart rate, skin blood flow and velocity, as well as the number of rearing responses.…”

“…In summary, significant or nonsignificant arterial BP responses to moderate intensity SMF in mT level fields have been recently reviewed in experimental animals and/or humans: SMF exposures between 1 mT and 400 mT for anywhere between 10 min and 8 weeks (e.g., antihypertensive period for young SHR) could affect arterial BP, cutaneous microcirculation and/or hemodynamics [50,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][77][78][79][80]. The present review is a more up-to-date summary of the research in the relevant areas.…”

“…It has been shown that it is more appropriate to consider biological responses to SMF through the hypothesis of intensity windows, instead of intensity-response dependence [86]. Otherwise, most of the experimental studies showing positive results have been carried out using gradient magnetic fields: the gradient component of SMF at the target site might be responsible for the physiological responses in vivo [65][66][67] and in vitro [87][88][89][90][91][92]. For example, the in vitro effects of gradient fields on action potential generation [87][88], myosin phosphorylation [89] and endothelia tubular formation [90][91][92] have been found mostly in the absolute field gradient range of more than 1 mT/mm (1 T/m) in the target tissues or cells.…”