The metabolism of vitamin D3 in response to testosterone.

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 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 - alpha - 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.