Vitamin D metabolism: physiological regulation in egg-laying Japanese quail

Homogenates of kidney removed from reproductivity active female Japanese quail were incubated with tritiated 25-hydroxyvitamin D3, and the metabolites were extracted and identified by chromatographic methods. Kidneys removed from birds with and without an egg in the oviduct revealed that ovulation results in enhanced production of 1, 25-dihydroxyvitamin D3, the active hormonal form of vitamin D3. Further examination of this phenomenon in relation to the ovulatory cycle revealed that 1, 25-dihydroxy-vitamin D3 production is enhanced throughout the 24 h following ovulation. Particularly important is the finding that its synthesis is already enhanced during the first 6 h after ovulation, at a time before any calcification of the egg shell begins. If, following oviposition, no ovulation occurs, 1, 25-dihydroxy-vitamin D3 production decreases rapidly and significantly within the first 6 h following oviposition. This study has revealed for the first time a physiological state, namely the reproductive period in the female bird, in which endogenous control over 1, 25-dihydroxyvitamin D3 production is exhibited without any previous manipulation, dietary or otherwise, of the animals.