CIRCULATORY FAILURE INDUCED BY 35 GHZ MICROWAVE-HEATING - EFFECTS OF CHRONIC NITRIC-OXIDE SYNTHESIS INHIBITION

Sustained exposure to radiofrequency radiation of millimeter wave (MMW ) length produces hyperthermia and subsequent circulatory failure. Thi s study sought to determine whether this phenomenon is altered by chro nic pretreatment with the nitric oxide (NO) synthesis inhibitor N-omeg a-nitro-L-arginine methyl ester (L-NAME). Rats drank either 1) water, 2) water + L-NAME, or 3) water + L-NAME + L-arginine (at 20 and 50 tim es the dose of L-NAME) for 14 days, Ketamine-anesthetized rats were ex posed to MMW until mean arterial blood pressure (MAP) fell to 75 mmHg, at which point MMW exposure was discontinued. MAP initially increased during exposure in all groups; the presser response in L-NAME-treated rats was greater than that in water-drinking rats. Subsequently, MAP fell in all groups. The MMW exposure time required to reach MAP = 75 m mHg was significantly reduced in L-NAME-treated rats, although surviva l times (post-MMW) of L-NAME-treated and control rats were not statist ically different. Coadministration of L-arginine abolished the enhance d presser response produced by L-NAME, but did not completely reverse the shortened MMW exposure time in L-NAME-treated rats. Thus, chronic NO synthesis inhibition with L-NAME reduces the ability of rats to wit hstand 35 GHz microwave heating, suggesting that NO does not mediate t he hypotension produced by this form of hyperthermia.