CHANGES IN THE PLASMA ERYTHROPOIETIN LEVEL IN RATS FOLLOWING FASTING,AGING, AND ANEMIA

Changes in the plasma erythropoietin (Epo) level in fasted and aged ra ts, and in male F344 rats following phenylhydrazine- and captopril-ind uced anaemia were investigated using an enzyme immunoassay. In male F3 44 rats, the plasma Epo level was decreased upon fasting, and was high er at night than in the day. In both sexes, the level was decreased fr om 5 to 10 weeks of age and remained almost constant from 10 to 19 wee ks of age. The level in male Sprague-Dawley rats was higher than that in male Wistar and F344 rats at 6 and 10 weeks of age. After phenylhyd razine was administered to male F344 rats, anaemia was observed, and t he plasma Epo level increased rapidly, followed by a delayed increase in the reticulocyte count. The plasma Epo level then decreased gradual ly to the initial level 2 weeks after dosing. Upon repeated administra tion of captopril, a decreased plasma Epo level on day 7 and anaemia o n day 28 were observed in male F344 rats. These results suggest that m onitoring the plasma Epo level would be useful in investigating the me chanism by which a chemical induces anaemia. It is also necessary to c onsider the feeding conditions, sampling time, age, sex, and strain of the rats when interpreting the Epo level.