Abstract
The relationship between the decrease in urinary sex-dependent low molecular weight proteins (LMWP), which exist only in the male rat, and the serum levels of some hormones were examined in this study. Castration of male rats reduced the urinary excretion of LMWP by about 50%. Replacement therapy with testosterone increased the urinary LMWP excretion. Adrenalectomy did not affect the urinary excretion of LMWP. In the adrenalectomized rat, however, corticosterone increased LMWP excretion. Therefore, it is considered that testosterone and corticosterone play a part in the urinary excretion of LMWP under physiological conditions and that the effect of testosterone is more specific than that of corticosterone. Serum concentration of testosterone and corticosterone tended to increase in comparison with the control on the 7th day after chronic treatment with morphine (0.5 mg/g food), when the urinary excretion of LMWP was significantly decreased. Furthermore, after rats were chronically administered morphine following castration or adrenalectomy, the urinary LMWP excretion was markedly decreased in the same way as found in intact animals. On the other hand, the serum thyroxine level of rats treated with morphine for 7 days was significantly lower than that of the control. Thyroxine increased dose-dependently the decreased urinary excretion of LMWP induced by morphine administration. These findings suggest that the decrease in urinary excretion of LMWP after chronic treatment with morphine may be caused by the change of serum thyroxine level via the action of morphine on the endocrine functions.
