Synergistic effects of 1,25(OH)2D3 and 24,25(OH)2D3 on duodenal CaBP in rachitic chicks and on eggshell weight in Japanese quails.

The role of 24,25(OH)2D3 in calcium homeostasis is still controversial. In the present study the administration of low doses of 1,25(OH)2D3 and of higher doses of 24,25(OH)2D3 either alone or in conjunction with each other, were studied in rachitic chicks and in Japanese quails. Whereas 24,25(OH)2D3 alone had no significant effect on duodenal CaBP and on alkaline phosphatase in chick serum, it increased the influence of 1,25(OH)2D3 on these two parameters strongly. Also, when 1,25(OH)2D3 and 24,25(OH)2D3 were given simultaneously to Japanese quails, calcium excretion via the egg shell was clearly higher than when either metabolite had been administered alone. These results indicate that 1,25(OH)2D3 and 24,25(OH)2D3 exert a strong synergistic effect in rachitic animals.