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  • Title: Renal clearance of phosphate and calcium in vitamin D-deficient chicks: effect of calcium loading, parathyroidectomy, and parathyroid hormone administration.
    Author: Clark NB.
    Journal: J Exp Zool; 1991 Aug; 259(2):188-95. PubMed ID: 1664453.
    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 to 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.
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