ARMED FORCES RADIOBIOLOGY RESEARCH INST BETHESDA MD
Beagles were subjected to 1500 rads of whole-body pulsed gamma- neutron radiation. Forty-eight and seventy-two hours later the animals were anesthetized and the major cardiovascular parameters were obtained. Thereafter, the hemodynamic regulation was studied after intravenous administration of 5.0 microgramskg epinephrine. It was observed that at 48 hours postirradiation, the major cardiovascular parameters were unchanged. After 72 hours, with the exception of the mean blood pressure, significant hemodynamic deterioration developed. The average stroke volume and stroke work decreased 50 percent as compared with the control nonirradiated average values. The median total peripheral resistance, meanwhile, increased in the same magnitude. The blood pressure response after epinephrine was prolonged and significantly higher at 1 minute postinjection in the 48-hour group. The vagal reflex bradycardia became less expressed. After 72 hours postirradiation the epinephrine-induced cardiovascular regulation was further deteriorated. The epinephrine effect demonstrated that in the gastrointestinal radiation syndrome prior to the cardiovascular collapse, a latent imbalance of alpha and beta adrenergic activity is already present. The data indicate further that the cardiovascular deterioration is peripheral rather than myocardial in origin. This study supports the concept that functional vascular alterations underlie the development of the so-called gastrointestinal radiation syndrome.