The mechanism of acute cadmium toxicity in the testis of the rat: A cellular and molecular inquiry.

Abstract

The aim of this research was to investigate a mechanism that may help explain the unique susceptibility of the rat testis to cadmium. Two testicular cell populations, the Sertoli and interstitial cells, present logical targets for cadmium in vivo. To keep experimental variability to a minimum, an in vitro system was developed for the isolation and culture of these two cell types from the same cohort of immature rats. The sensitivity of these cells to cadmium was assessed using parameters common to both cell types: morphology, lactate production, protein synthesis, cadmium binding capacity, and the reduction of the vital tetrazolium dye, MTT. It was observed that the interstitial cell cultures were generally unaffected by the presence of cadmium, whereas the Sertoli cell cultures were affected in a dose- and time-dependent manner. Using the MTT assay as an indicator of cytotoxicity, we observed a median lethal concentration (LC$\sb{50}$) of 19.5 uM CdCl$\sb2$ for interstitial cells over a 72 hr time period, while Sertoli cells exhibited a 72 hr LC$\sb{50}$ of 3.85 uM CdCl$\sb2$. The more sensitive Sertoli cells were chosen as a model to investigate a molecular mechanism of toxicity. Primary rat Sertoli cells were exposed to sublethal concentrations of cadmium and the changes in ($\sp{32}$P) -orthophosphate-labelled phosphoproteins using two-dimensional polyacrylamide gel electrophoresis were examined. Resultant autoradiograms showed a delayed dose- and time-dependent increase in intensity of two acidic proteins having identical molecular weights (26,000 kD). These changes were most probably a result of increased synthesis of the proteins. Lead, zinc, and copper did not induce the proteins, whereas mercury could. Pretreatment of the cells with zinc, a cadmium antagonist, partially reduced the effect of cadmium. This research concludes that Sertoli cells are relatively more sensitive to the effects of cadmium than interstitial cells. A time- and dose dependent increase in ($\sp{32}$P) -associated activity to two small Sertoli cell phosphoproteins was consistently seen after cadmium exposure, whereas no effect could be seen using essential, non-toxic metals. This response may be an early indicator in the disruption of cellular homeostasis by cadmium, and will hopefully contribute positive evidence in the search for a molecular mechanism of cadmium toxicity.