Vitamin D metabolism in bullfrogs and Japanese quail: Effects of estradiol and prolactin

Estradiol benzoate injection (5 mg/kg im daily) in the bullfrog for 15 days significantly increased both the plasma calcium level and the in vitro renal production of 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2D 3] from 25-hydroxyvitamin D 3 [25-(OH)D 3]. A lower dose (3 mg/kg im daily for 6 days) failed to show significant responses. Ovine prolactin injection (0.5 mg/kg im twice daily for 5 days) in Japanese quail also significantly increased both the plasma calcium level and the in vitro renal production of 1,25-(OH) 2D 3. A higher dose of prolactin (1.0 mg/kg in twice daily for 4.5 days) also stimulated in vitro renal production of 1,25-(OH) 2D 3 and depressed that of 24,25-(OH) 2D 3 but did not increase the plasma calcium significantly. On the other hand, a hypercalcemic dose of ovine prolactin (0.5 mg/kg im daily for 9 days) in the bullfrog failed to elicit any stimulation of in vitro renal production of 1,25-(OH) 2D 3. Bullforg kidney homogenates do not contain an inhibitor of the 25-(OH)D 3-1-hydroxylase enzyme, as has been observed in homogenates prepared from mammalian kidneys.