Estimation of the life span of red blood cells in the growing animal in different nutritional states.

In this study the model of Shemin and Rittenberg for estimating the life span of red blood cells was extended so that non-steady-state conditions, exemplified by growth or changing physiological states, might be considered. The parameters were estimated by use of the modified Gauss-Newton method. The biological data that were used came from growing sheep in different physiological states with regard to copper. The model was extended to include changes in total blood hemin and changes in blood hemin synthesis that may occur with time. In the present study a linear function was taken as a first approximation. The model appeared to be a sufficiently good approximation in the study reported herein. It was found, however, that the parameters associated with changes in hemin should be estimated from ancillary measurements such as blood volume, Hb, body weight, etc., in order to obtain a good fit or definition of the model.