Abstract
The effect of sex hormones and of parathyroid extract (PTE) of the metabolism of 25-hydroxycholecalciferol (25-HCC) in the kidney of Japanese quail was studied
in vitro. Production of 1,25-dihydroxycholecalciferol (DHCC) was stimulated by oestrogen and by PTE and these effects were additive; the action of androgen was to inhibit the 1-hydroxylase. Production of 24,25-DHCC was inhibited by oestrogen and by PTE but androgen had no significant effect. A marked synergism between oestrogen, androgen, and PTE was shown: when all three hormones were administered together a striking increase occurred in 1,25-DHCC production compared with all other hormone treatments. Drugs that inhibited ovulation and shell calcification inhibited the amount of 1,25- relative to 24,25-DHCC produced by the kidney homogenates. These results are discussed in relation to the control of calcium metabolism in laying birds and it is suggested that (a) reproductive steroids are mainly responsible for the long-term increase in calcium absorption that occurs in birds coming into lay by increasing the amount of renal 25-HCC-1-hydroxylase; (b) parathyroid hormone is responsible for the short-term increase in the activity of the renal 1-hydroxylase during the egg cycle.