[Determination of the protein requirement for the maintenance of the circulating red-cell mass in the adult rat].

The present study was designed to provide direct information on the protein requirement of 12-month-old-female rats for maintenance of the circulating red cell mass (RCM). Different groups (7) of rats were fed during 30 days one of seven isocaloric diets containing graded levels of casein, from 0% to 10%. RCM was determined by the radio-iron-labelled red cell dilution method at the end of experimental period. Casein requirement level for maintenance of RCM, predicted as the point on the regression line where the value of the dependent variable (delta RCM/100 g body wt) was 0, was 3.6%. This value was identical to that predicted for the maintenance of body weight, which suggests that both are interrelated and that RCM is a function of the body weight. The relation also suggests that the anaemia developing in the adult rat in response to protein depletion could be a type of physiologic adaptation between the body oxygen transport system and the body mass.