Circulating red cell volume in little brown bats in summer

¹ Department of Zoology, Cornell University, Ithaca, New York

Circulating erythrocyte (RBC) volumes were determined in the little brown bat, Myotis lucifugus, by using a Cr⁵¹-labeling procedure. In 5 min, mixing of labeled cells was 97% complete in active bats and remained so for up to 1 hr after injection, owing to RBC retention by the spleen. Mixing for 5 min appeared less complete when lactating bats were placed in a hibernating environment; the torpor induced in such bats differed from winter hibernation. From late pregnancy to postlactation, active bats averaged 4.4 ml RBC/ 100 g body wt. Blood volume calculated from RBC volume and plasma volume was 11.1 ml/100 g body wt. The per cent RBC in blood samples fell during lactation. High cell volume was associated with high body weight in postlactation bats, but not during late pregnancy or lactation. Some bats had a lower RBC volume after delivery, but a significant cell volume decrease in all bats was not evident until lactation had ceased. Cell volume in late pregnancy was only 17% above that of postlactation bats. No lactation polycythemia was noted.