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  • Title: Production of 1,25-dihydroxyvitamin D3 and formation of medullary bone in the egg-laying hen.
    Author: Castillo L, Tanaka Y, Wineland MJ, Jowsey JO, DeLuca HF.
    Journal: Endocrinology; 1979 Jun; 104(6):1598-601. PubMed ID: 446379.
    Abstract:
    Renal 25-hydroxyvitamin D-1-hydroxylase, the percentage of medullary bone in the femur, plasma calcium, and plasma phosphorus were measured in female chickens reaching maturity. These parameters and plasma 1,25-dihydroxyvitamin D levels were also measured during the daily egg-laying cycle in mature hens. The renal 25-hydroxyvitamin D3-l-hydroxylase becomes elevated in maturing hens before and at the time of ovulation. This elevation in the 1-hydroxylase correlates with the elevation in total plasma calcium concentration but lags and at the time of ovulation and is followed by a further elevation of plasma 1,25-dihydroxyvitamin D levels. The plasma 1,25-dihydroxyvitamin D level remains high until 12 h postovulation. At this time, it falls to the preovulation level. No relationship could be found between the plasma 1,25-dihydroxyvitamin D levels and the changes in medullary bone found during the egg-laying cycle. However, plasma 1,25-dihydroxyvitamin D levels are highest immediately before and during the egg shell calcification phase of the egg-laying cycle.
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