THE METABOLISM OF VITAMIN-D-3 IN RESPONSE TO TESTOSTERONE

Sex steroids were suggested as regulators of vitamin D metabolism. Whi le considerable data is available regarding interaction between estrad iol and vitamin D, very little is known about interactions between tes tosterone and vitamin D. A similar gap exists with regard to the invol vement of the vitamin D endocrine system in the pathogenesis of the fe male versus the male osteoporosis syndrome. In the present study we st udied the effect of long-term treatment with testosterone on the metab olism of vitamin D in vitamin D-3 replete sexually immature male chick s. We were able to show that under this treatment, circulating levels of 1,25-dihydroxy vitamin D-3 (1,25(OH)(2)D-3) are significantly reduc ed, but intestine and bone concentrations are significantly increased. The increased concentration of 1,25(OH)(2)D-3 in bone was accompanied by an increase in the ash content of this tissue. The reduction in se rum 1,25(OH)(2)D-3 was not dependent on reduced activity of the renal 25-hydroxy vitamin D-3 - 1 alpha - hydroxylase. Based on these finding s it is proposed that testosterone is involved in the stimulation of t he biological response to vitamin D in the classical target-organs, su ch as intestine and bone, and this observation may provide partial exp lanation to the pathogenesis of osteoporosis in hypogonadal men.