MECHANISM OF THE EFFECT OF EPINEPHRINE ON THE VENOUS HEMATOCRIT VALUE OF THE NORMAL UNANESTHETISED DOG

Abstract

When epinephrine is administered by vein in single large doses to adult intact dogs there is sometimes a decided increase in venous hematocrit. Some dogs uniformly show a marked increase and others minimal changes. In the animals in which there is an increase in hematocrit there is no corresponding change in the circulating red cell mass as directly detd. by the donor-isotope-red cell procedure. Since splenectomy abolishes the hematocrit response to epinephrine and since no reserve cells are found to be poured into the circulation after adrenalin, another mechanism than the outpouring of reserve cells from the contracted spleen must be postulated to account for the increase in venous hematocrit. A suggested explanation may be an increase in the effective number of blood vessels of small inside diam. as well as a reduction in the caliber of many vessels by vasoconstriction, both factors leading to an increased fraction of plasma in sluggish circulation.