MEASUREMENT OF ERYTHROCYTE VOLUMES IN SPLENECTOMIZED HORSES AND SHAM-OPERATED HORSES AT REST AND DURING MAXIMAL EXERCISE

Erythrocyte volumes of thoroughbred horses were measured. The volumes of splenectomized horses and sham-operated horses 2 hr after injection of Cr-50- tagged erythrocytes (at rest) and during maximal exercise w ere measured using the non-radioactive isotope Cr-50. Because splenic erythrocytes are released into circulation during exercise, it was est imated that the erythrocyte volumes of the sham-operated horses during maximal exercise are larger than those of the horses at rest. However , the erythrocyte volumes of the sham-operated horses at rest were abo ut equal to those during maximal exercise. In the splenectomized horse s, furthermore, erythrocyte volumes at rest and those at exercise were nearly equal. From these results, blood stored in the equine spleen i s gradually mixed with circulating blood, and it was clarified that th e phenomenon was completed within 2 hr. Although it is basically impos sible to measure the circulating erythrocyte volume at rest using the erythrocyte tagged method, we observed that it is possible to measure the total erythrocyte volume using the Cr-50 method. Also, the plasma volumes of the splenectomized horses during maximal exercise were foun d to be slightly smaller than those at rest. On the other hand, in the sham-operated horses, the plasma was decreased by a large quantity af ter maximal exercise. Therefore, it was suggested that the spleen part icipates in the phenomenon involving the disappearance of plasma from circulation due to exercise.