Synchronous development of the reproductive tract in adult female Japanese quail has been achieved by manipulation of photoperiod length. This has made possible determination of changes in vitamin D metabolism associated directly with the onset of reproductive maturity. The distribution of polar metabolites of 25-hydroxy [3H] vitamin D3 ([3H]-25-OH-D3) was altered shortly before the onset of egg laying, such that the specific activity of the 25-OH-D3-1α-hydroxylase increased 390%, while the production of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] and an unidentified metabolite (metabolite IV) decreased 37 and 61% respectively. In addition, kidneys of reproductively mature female quail produced a metabolite, tentatively identified as 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3], which was not found in the kidneys of male quail or in those of female quail with immature oviducts. The concentration of oviduct nuclear estrogen receptor-estrogen complex increased to a level comparable to laying female quail very early in reproductive tract development. A 280% increase in kidney size occurred concurrently. In contrast, the altered renal metabolism of [3H]-25-OH-D3 did not occur until much later in development, suggesting that kidney growth and renal metabolism of vitamin D are independently regulated. It appears that the increased specific activity of the 25-OH-D3-1α-hydroxylase immediately prior to egg laying is important in the provision of calcium for shell formation. The close temporal relationship between the altered metabolism of [3H]25-OH-D3 and the onset of medullary bone formation suggests that a vitamin D metabolite may mediate the formation and utilization of medullary bone.
ASJC Scopus subject areas
- Animal Science and Zoology