Studies on the Mode of Action of Calciferol. XXXIV. Relationship of the Distribution of 25-Hydroxyvitamin D3Metabolites to Gonadal Activity and Egg Shell Formation in the Quail*

A study was conducted on three groups (mature laying, mature nonlaying, and immature) of female quail (Coturnix coturnix japonica) in order to relate 25-hydroxyvitamin D3 (25OHD3) metabolism to sexual maturation and onset of egg production. Vitamin D-deficient quail were injected a total of four times at 2-day intervals with 3H25OHD3 (2.5 nmol and 1.2 μCi); plasma calcium and metabolites derived from 3H25OHD3 in the various tissues were determined. Plasma calcium and egg shell gland (ESG) weight were higher in laying or mature nonlaying quail than in immature quail. The concentration of 1,25-dihydroxyvitamin D3 1,25-(OH)2D3 was significantly higher in laying than in mature nonlaying and immature quail in plasma (1.36, 0.88, and 0.42 pmol/ml, respectively), intestinal mucosa (1.80, 0.76, and 0.31 pmol/g respectively), and ESG (0.93, 0.38, and 0.30 pmol/g, respectively), but not in muscle (0.12, 0.05, and 0.03 pmol/g). The proportion of vitamin D metabolites present as 1,25-(OH)2D3 and the tissue to plasma ratios in intestine and ESG were higher in the laying than in the mature nonlaying quail. The results suggest that the ESG, like the intestine, is a primary target organ for 1,25-(OH)2D3. Both the intestine and the ESG of the egg-laying bird have the capability of specifically accumulating an additional increment of 1,25-(OH)2D3 above that accumulated by these organs in mature nonlaying birds. This supports the idea that the massive transport of calcium by the ESG, necessary for egg shell formation, may be vitamin D dependent. In addition, it is clear that the changes in gonadal activity during maturation have only minor effects on 25OHD3 metabolism and on 1,25-(OH)2D3 accumulation by the intestinal mucosa and the ESG.