SERUM IMMUNOREACTIVE ERYTHROPOIETIN AND RED-BLOOD-CELL MASS DURING PREGNANCY IN CONSCIOUS RATS

Serum erythropoietin concentration increases during human pregnancy an d presumably accounts for expansion of red blood cell mass. The mechan ism(s) underlying gestational changes of serum erythropoietin are unkn own. Moreover, if erythropoietin synthesis increases, then the organ(s ) responsible need to be identified. To address these and other questi ons about erythropoietin in pregnancy, we first set out to establish a n animal model. Chronically instrumented, conscious unrestrained rats were studied. Cr-51-labeled red blood cells and radioimmunoassay were used to assess red blood cell mass and serum erythropoietin, respectiv ely. Except for a lower hematocrit (P < 0.05 vs. virgin rats) and a sl ightly higher plasma volume (P value not significant) for gravid rats on gestational day 6, all other variables measured in early pregnancy rats were comparable to those measured in virgin control animals. Sign ificant increases in total blood volume, plasma volume, and red blood cell mass were observed by gestational day 13 (midpregnancy) when comp ared with virgin control rats. These changes were even more pronounced on gestational day 20. Serum immunoreactive erythropoietin was also s ignificantly increased at both of these stages of pregnancy. We conclu de that the gravid rat is a reliable animal model of human gestation i n which to further investigate erythropoietin in pregnancy.