Effects of orchidectomy and different modes of high dose estrogen treatment on circulating "free" and total 1,25-dihydroxyvitamin D in patients with prostatic cancer.

Serum levels of total 1,25-dihydroxyvitamin D (1,25(OH)2D), vitamin D binding protein (DBP), sex hormone binding globulin (SHBG), testosterone, estradiol 17 beta (E2) and the "free" 1,25(OH)2D index were measured before and during treatment in prostatic cancer patients treated by orchidectomy (n = 15), with combined i.m. polyestradiol phosphate (PEP) + oral ethinyl estradiol (EE) (n = 10) and with i.m. PEP only for 3 months, followed by addition of oral EE (n = 9). Total concentrations of 1,25(OH)2D and DBP were unaffected by orchidectomy and treatment with i.m. PEP only, but were significantly elevated during treatment including oral EE. SHBG levels were unaffected by orchidectomy, slightly increased by i.m. PEP only and greatly increased by oral EE. The free 1,25(OH)2D index was slightly elevated by treatment including oral EE. Evidence was obtained that the increase in 1,25(OH)2D levels observed during oral estrogen treatment was secondary to the estrogen-augmented increase in DBP and not a result of an estrogen-stimulated synthesis of 1,25(OH)2D. Furthermore, the stimulatory effect of estrogen on DBP concentrations seemed to be dependent on the route of administration of the hormone.