Release of red cells from the slowly-exchanging splenic pool after noradrenaline administration

Isolated, denervated, cat spleens were perfused at constant flow with modified Ringer solution. Perfusion, pressure, outflow rate, and outflow red cell concentration were measured against time. After splenic perfusion by 500 ml solution the cell washout curve became a single exponential function, indicating that only cells from the most slowly exchanging red cell compartment remained (these are immature and abnormal cells which adhere to the fine structures of the red pulp). Splenic contraction was induced by injection of 5 mug noradrenaline into the inflow after perfusion by 600 and 1000 ml of fluid, respectively; outflow cell concentration rose 17-fold before returning to baseline value and 32% of red cells in the spleen were expelled. The time course of changes in cell concentration was similar in shape but delayed with respect to that of outflow rate. The transit time of the cells from the site of release to the splenic vein must have exceeded 40 s, which is consistent only with release from the red pulp. Furthermore, at the peak of the cell concentration curve the mean reticulocyte count was 37.8%. Thus immature and abnormal red cells, which comprise the slowly-exchanging compartment, are indeed released from the spleen during contraction.