Comparison using central core model of renal medulla of the rabbit and rat.

The studies presented here use a central core model of the renal medulla, the details of which have been given elsewhere (Foster et al., Mathematical Biosci. 32: 307-335, 337-360, 1976). The central core model of the rabbit medulla predicts concentration gradients and volume flow rates in line with what is known for the rabbit. The handling of urea, however, is not consistent with the scheme proposed by Kokko and Rector (Kidney Intern. 2: 214-233, 1972). Moreover, the low concentration of urea predicted for the urine suggests an absence in the model of some form of mediated transport for urea in the inner medulla. The central core model of the rat medulla failed to predict results consistent with what is known about the rat. Substitution of the rabbit thermodynamic parameters into the model for the rat resulted in predictions that more closely resembled what one might expect, but were not entirely satisfactory. The implication is that there may be an interspecies difference in the concentration machinery between the rabbit and rat.