The effect of intravenous injection of epinephrine on blood volume, red cell volume, and hematocrit was studied. The effects of such a challenge on anesthetized intact, awake intact, and awake splenectomized rats were compared.The epinephrine challenge caused significant increases in the hematocrits of anesthetized animals and highly significant increases in the awake intact animals. No other statistically significant changes occurred in the parameters studied.The results indicate that the rat sequesters red blood cells in the spleen which are released with an appropriate challenge. This release response is attenuated by sodium pentobarbital anesthesia. It was not possible to detect an increase in blood volume or in red cell volume by using Cr51 tagged cells as tracers.Ball State UniversityMuncie, IN 47306