Abstract

In vivo administration of estradiol benzoate (E₂B) or parathyroid hormone (PTH) stimulates in vitro renal conversion of 25-hydroxyvitamin D₃ [25-(OH)D₃] to 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃] in birds. In the present investigation, the effect of PTH on 1,25-(OH)₂D₃ production was studied in female Japanese quail pretreated with the antiestrogen, tamoxifen citrate (30 mg/kg) daily for 7 days. PTH was injected at two different doses (92 and 275 U.S.P. units/kg) every 8 hours during the last two days of tamoxifen treatment. E₂B (0.1 and 1.0 mg/kg) was injected 24 hours before sacrifice. Control groups received vehicle only. All injections were given intramuscularly. Kidney homogenates were prepared and incubated with tritiated 25-(OH)D₃. E₂B-induced stimulation of 1,25-(OH)₂D₃ production was completely blocked by prior treatment with tamoxifen, but PTH-induced stimulation of 1,25-(OH)₂D₃ production was unaffected by antiestrogen treatment. When PTH and E₂B were injected together, no additive effects on either 1,25-(OH)₂D₃ production or hypercalcemia were observed. The data indicate that estrogen receptors are not an essential link in the chain of events mediating the PTH-induced stimulation of 1,25-(OH)₂D₃ production.