Increased sensitivity of bone to parathyroid hormone in castrated mice

The inhibitory effect of endogenous testosterone on parathormone induced bone changes in mice was studied with the aid of the analysis of calcium and protein content in femur and of plasma calcium and alkaline phosphatase. It was found that the absence of endogenous testosterone for seven days after castration resulted in a decrease in the bone protein and calcium content and in plasma alkaline phosphatase as compared to controls. In parathormone treated castrated mice the protein content of the femur and plasma alkaline phosphatase were raised to control values, but the decrease in the calcium content of the femur was further potentiated. Finally, the administration of parathormone to intact male mice caused only a depletion in calcium content of the femur. It may be concluded that the response of bone to parathormone is enhanced in the absence of endogenous testosterone. In view of this finding one of the possible explanations may be that endogenous testosterone protects the bone by the inhibition of its sensitivity to parathormone.