Effectiveness of Pressor Drugs in Beagles Exposed to Mixed Gamma-Neutron Radiations

Summary

Aortic pressure, right atrial pressure, heart rate, and cardiac output were measured; and mean pressure, stroke volume, and peripheral resistance were calculated in 27 male beagles before and after 5000- or 10,000-rad whole body doses of mixed gamma-neutron radiations. The response of these beagles to levarterenol, phenylephrine, or metaraminol was also determined before and after irradiation. Irradiation caused a decrease in aortic pressure, cardiac output, and stroke volume; and an increase in heart rate. Peripheral resistance increased, but not significantly, in irradiated beagles. Phenylephrine and metaraminol were equally effective before and after the dogs were irradiated, while levarterenol was more effective in irradiated dogs. The results are interpreted as follows: (i) radiation induced hypotension cannot be fully explained by radiation effects on peripheral blood vessels; (ii) pressor drugs are effective in irradiated beagles with hypotension, and drug effectiveness is probably decreased only as a terminal event shortly before death; (iii) any direct effect of radiation on the heart is of limited significance in whole body exposure.