Experimental determination of "the law of bone remodeling" and effect of rat parathyroid hormone (1-34) infusion on derived parameters.

The dependence of bone remodeling probability on bone age was investigated by fitting a previously described mathematical model to data describing the decline of radioactivity in the femurs of growing rats prelabeled with [3H]tetracycline. The remodeling probability declined with increasing bone age, but because the data were obtained at the whole bone level, several explanations for this finding are possible, and the results cannot be extrapolated beyond the duration of the experiment. A simpler exponential model that assumes remodeling probability is constant can be used to calculate bone resorption rate within a limited time period. A significantly increased bone resorption rate in PTH-infused rats could readily be demonstrated using the exponential model. A more sophisticated statistical analysis was required to discriminate between control and PTH-infused rats using the more complex model in which resorption rate was not constant.