Effects of reserpine on circulation of the rat after microwave irradiation

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Abstract
Hyperthermia of 40.5 C was induced in anesthetized white rats by microwave exposure (2,450-Mc continuous wave, .08 w/cm2). Thermal response was accompanied by increased cardiac output, stroke volume, cardiac work, and heart rate. Blood pressure and total peripheral resistance decreased. Administration of reserpine as a single dose of 2.5 mg/kg body wt. 1 day before the experiment depleted the myocardial norepinephrine, but did not eliminate the accelerated heart rate and increase of cardiac output during hyperthermia. Hyperthermia after reserpine did not alter significantly the stroke volume and blood pressure, and the peripheral resistance decreased. These data suggest that the circulatory adaptation to microwave hyperthermia is mediated not only through the sympathetic nervous system, but by other mechanisms such as direct cardiac response to the increased tissue temperature.