The Metabolism of Vitamin D₃ in Response to Testosterone

Summary

: Sex steroids were suggested as regulators of vitamin D metabolism. While considerable data is available regarding interaction between estradiol and vitamin D, very little is known about interactions between testosterone and vitamin D. A similar gap exists with regard to the involvement of the vitamin D endocrine system in the pathogenesis of the female versus the male osteoporosis syndrome. In the present study we studied the effect of long-term treatment with testosterone on the metabolism of vitamin D in vitamin D₃ replete sexually immature male chicks. We were able to show that under this treatment, circulating levels of 1,25-dihydroxy vitamin D₃ (1,25(OH)₂D₃) are significantly reduced, but intestine and bone concentrations are significantly increased. The increased concentration of 1,25(OH)₂D₃ in bone was accompanied by an increase in the ash content of this tissue. The reduction in serum 1,25(OH)₂D₃ was not dependent on reduced activity of the renal 25-hydroxy vitamin D₃ - 1α - hydroxylase. Based on these findings it is proposed that testosterone is involved in the stimulation of the biological response to vitamin D in the classical target-organs, such as intestine and bone, and this observation may provide partial explanation to the pathogenesis of osteoporosis in hypogonadal men.