COMPARISON OF CALCIUM KINETICS IN MAN AND RAT

The disappearance from the blood of intravenously-injected radiocalcium in man and the rat can be formally described by a two-termed exponential equation, which may be thought to have been generated by a two-compartment system in dynamic equilibrium with the environment. This paper reports an evaluation and comparison of the rate constants of such a system. In people over the age of 16, the mean system constant was 0.239 day-1 (SE: 0.009) and the mean skeletal constant was 0.148 (SE: 0.008). The corresponding constants were 0.496 day-1 (SE: 0.023) and 0.428 (SE: 0.019) for 4-month-old female Sprague Dawley rats and 0.744 (SE: 0.038) and 0.351 (SE: 0.021) for 10-month-old rats. All of the constants of the rats were significantly higher than those of man. There were no significant changes in man after the age of 16 years, whereas in the rat these constants changed with age. Differences in the constants can be explained by known differences in calcium metabolism and in the growth rates of the two species. Hence, a formal comparison of calcium kinetics in man and the rat yields information consistent with the interpretation that the two systems are comparable. Rate constants may prove useful for interspecies comparisons, as well as for studies of the regulation of calcium metabolism. © 1969 Springer-Verlag.