Mathematical model of steroidogenesis in rat and rabbit testes

The purpose of this study was to develop a mathematical model of testicular steroidogenesis which could not only predict steroid secretion but also could be implemented to test the validity of assumptions used in studies of testicular testosterone biosynthesis in rats and rabbits. Since the two predominant fates of testicular steroids are metabolism and secretion, we hypothesized that the data for construction of the model could be observed testicular steroid secretions and that these data could then be used to elucidate intratesticular steroid conversions. Equations based on steroid secretion by testes perfused in vitro were developed to estimate transition probabilities corresponding to steroid secretion or conversion. The model was tested by comparing the predicted steroid secretion rates with those observed for control testes perfused in vitro. In addition, the transition probabilities determined by the model were used to indicate the predominant series of reactions for converting pregnenolone to testosterone. The results presented herein confirm the capability of the model to predict steroid secretion rates and to predict preferred pathways for testosterone biosynthesis in maximally stimulated testes perfused in vitro. Moreover, the model construction required only algebra and steady-state measurements.