Normal Egg Hatchability Requires the Simultaneous Administration to the Hen of 1,25-Dihydroxycholecalciferol and 24R,25-Dihydroxycholecalciferol

A previous report [Science 201, 835-837 (1978)] presented evidence that the combined and simultaneous administration of the cholecalciferol (D3) metabolites 1,25-dihydroxycholecalciferol [1,25(OH)2D3] and 24R,25-dihydroxycholecalciferol [24R,25(OH)2D3] to White Leghorn hens was necessary for embryo development and normal egg hatchability; in the absence of 24R,25(OH)2D3 none of the fertile eggs hatched. The present study extends this fundamental observation to a second species, the Japanese quail, Coturnix coturnix japonica and compares the biological actions of the two stereoisomers of the 24,25(OH)2 metabolite, namely the naturally occurring 24R,25(OH)2D3 and its unnatural epimer 24S,25(OH)2D3. Groups of 12-14 vitamin D-depleted adult female Japanese quail were mated with normal male quail and eight consecutive batches of eggs (25-41 eggs from each group) were placed in an egg incubator, and egg hatchability for the fertile eggs monitored on days 21 and 22. The egg hatchability (in percent SD) for each group was: D3 (56.5% 12.8); 1,25(OH)2D3 (1.3% 2.5); 24R,25(OH)2D3 (29.6% 3.1); 24R,25(OH)2D3 + 1,25-(OH)2D3 + 1,25-(OH)2D3 (32.8%); and 24S,25(OH)2D3 + 1,25(OH)2D3 (7.2%). Also for all treatment groups the blood level of the expected vitamin D metabolites were in the normal range, and there were no significant differences in the embryo weights and eggshell thickness (of both hatched and unhatched eggs). These results indicate that the Japanese quail have the inherent capability to discriminate between the stereoisomers of 24,25(OH)2D3 and therefore strongly support the concept that only the naturally occurring 24R,25(OH)2D3 has an identifiable, unique biological role which is different from that of 1,25(OH)2D3.