Estradiol-induced stimulation of 25-hydroxyvitamin D3-1-hydroxylase in vitamin D-deficient Japanese quail.

The dose-response relationship of estradiol benzoate (E2B)-induced increase of in vitro 1,25-dihydroxyvitamin D3 - 1,25-(OH)2D3 - production in Japanese quail raised on a vitamin D-deficient diet was investigated. 4-week-old male and female Japanese quail, initially raised on a normal calcium and vitamin D diet, were placed on a vitamin D-deficient diet for an additional 4 weeks. At 8 weeks of age, E2B was injected intramuscularly at three different doses (0.03, 0.3 and 3.0 mg/kg) daily for 5 days. Two control groups received an equal volume of vehicle only (0.5 ml/kg, 95% ethanol). Kidney homogenates were incubated with tritiated 25-hydroxyvitamin D3 (25-OH-D3). All three doses of E2B stimulated 1,25-(OH)2D3 production beyond the basal level in both sexes but to a much greater extent in the female. Maximal stimulation was observed with the lowest dose (0.03 mg/kg) of E2B. There was no detectable 24,25-dihydroxyvitamin D3 production in any group. A rise in plasma calcium and phosphorus was seen at all three dose levels of E2B in both sexes. The femur dry weight increased significantly only at the two higher doses of E2B in both sexes. It is concluded that E2B injection in vitamin D-deficient Japanese quail can stimulate 25-OH-D3-l-hydroxylase activity beyond the already stimulated basal.