Abstract
Serum and renal clearance values of phosphate and calcium were measured and compared in 4 week‐old vitamin D‐deficient and vitamin D‐replete chickens (Gallus gallus). D‐deficient chicks had significantly lower body weights and serum calcium values; however, their renal functions were not different from D‐replete controls. Serum calcium values in D‐deficient birds did not change in response to parathyroid hormone (PTH) administration; however, they did drop significantly in response to parathyroidectomy (PTX). Serum phosphate values of D‐deficient birds, but not D‐replete birds, rose significantly after PTX.
Clearance of phosphate is known to increase after administration of PTH. This conspicuous effect was absent in PTH‐injected vitamin D‐deficient chickens. PTX caused the excretion of phosphate to drop in both D‐deficient and D‐replete birds to near zero. Conversely, PTX of both D‐deficient and D‐replete chickens stimulated the excretion of more calcium than in controls.
Calcium loading elevates the fractional excretion of calcium in both D‐deficient and D‐replete birds. It also causes a decrease in phosphate excretion in both groups, presumably by inhibiting the secretion of PTH. PTH administration of D‐replete, calcium‐loaded birds caused increased phosphate excretion (as it did in normal controls), an effect that was not seen in similarly treated D‐deficient birds.
Therefore most renal functions studied after calcium loading, PTH administration, or PTX are not altered by vitamin D deficiency in the chicken. The major significant finding is that vitamin D‐deficient chickens do not excrete increased amounts of phosphate in response to PTH stimulus.