Circulatory effects of endotoxin on unanesthetized sheep and the response to dopamine.

The cardiovascular effects of endotoxin in the unanesthetized chronically instrumented sheep were investigated. The observations were extended to include the response to intravenous infusions of dopamine to the same sheep at the height of endotoxin action. When the cardiovascular effects of endotoxin in the unanesthetized and anesthetized sheep were compared, there were distinct differences. Unanesthetized sheep tolerated considerably greater dosages of endotoxin. In anesthetized sheep, the compensatory stimulation of the sympathoadrenal system seems to have been blunted and all of the circulatory parameters deteriorate rapidly, ending in death within three hours. In the absence of anesthesia, there was clear evidence of a compensatory sympathoadrenal stimulation, as reflected by the return of most of the circulatory parameters to normal values, and furthermore, the sheep recovered from the effects of endotoxin. The exact mechanism by which anesthesia altered the response of the sheep to endotoxin was not clear. Depression of the baroreceptor and neurohumoral compensatory mechanisms was suggested. The present data indicated that dopamine was a useful agent in correcting the cardiovascular changes brought about by endotoxin.