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The role of 1,25 dihydroxycholecalciferol in calcium homeostasis of birds
1551
H51 THE ROLE OF 1.25 DIHYDROKYCHOLECALCIFEROL IN CALCIUM HOMEOSTASIS OF BIRDS. Shmuel Hurwitz*, Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. The fractional absorption of calcium (Ca) is a linear function of the mucosal concentration of the D-metabolite 1.25- dihydroxycholecalciferol [1,25-DHCC]. The production of this hormone by the renal tuble is under the control of parathyroid hormone (PTH), the secretion of which is regulated by plasma Ca. The adaptation of Ca absorption mechanism to low-Ca intakes, which improves the economy of calcium is of utmost nutritional importance. When the regulation due to 1.25-DHCC production is bypassed by supplying the bird with exogenous hormone, bone and kidney are unable to prevent hypercalcemia at high intakes of the mineral, demonstrating the importance of the 1,25-DHCC-intestine axis in the regulation of plasma Ca.
1152 ESTIMATION OF THE AMOUNT OF FREE SOMATOMEDIN C (Sm C) IN DIFFERENT STRAINS OF THE DOMESTIC FOWL. Leo M. Huybrechts*, University of Leuven, Belgium and Colin G. Scanes, Dept. of Animal Sciences, Rutgers University, USA. Sex linked dwarf (SLD), control (K) and autosomal dwarf (ADW) chickens at 6 weeks of age have respectively 58.6 ? 5.0% (5). 78.8 + 9.3% (5) and 81.0 ? 11.2% (4) free Sm C in their plasma, as measured by differences in Sm C activity using a radioimmunoassay, in plasma with or without acid treatment to separate Sm C from i%einding proteins. Using the elution patterns of plasma incubated with I-Sm C the same differences were found: 31.9X, 65.9% and 72.1% respectively for the 3 strains. Both the low amount of free Sm C and the elution pattern of the SLD strain are similar to that of hypophysectomized (Hx) chickens; 65.8 t 5.3% (9) with RIA and 27.4% with elution. In the Hx chicken it is clear that this is due to low growth hormone (GH) concentrations (54.7 2 7.8 ng/ml (9)). However in the SLD strain we found normal levels of CH (182.7 5 78.2 ng/ml (8)) and we therefore suggest that in this strain GH lacks to stimulate Sm C and has no inhibiting effect on the binding of Sm C to its binding protein.
H51 THE ROLE OF 1.25 DIHYDROKYCHOLECALCIFEROL IN CALCIUM HOMEOSTASIS OF BIRDS. Shmuel Hurwitz*, Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. The fractional absorption of calcium (Ca) is a linear function of the mucosal concentration of the D-metabolite 1.25- dihydroxycholecalciferol [1,25-DHCC]. The production of this hormone by the renal tuble is under the control of parathyroid hormone (PTH), the secretion of which is regulated by plasma Ca. The adaptation of Ca absorption mechanism to low-Ca intakes, which improves the economy of calcium is of utmost nutritional importance. When the regulation due to 1.25-DHCC production is bypassed by supplying the bird with exogenous hormone, bone and kidney are unable to prevent hypercalcemia at high intakes of the mineral, demonstrating the importance of the 1,25-DHCC-intestine axis in the regulation of plasma Ca.
1152 ESTIMATION OF THE AMOUNT OF FREE SOMATOMEDIN C (Sm C) IN DIFFERENT STRAINS OF THE DOMESTIC FOWL. Leo M. Huybrechts*, University of Leuven, Belgium and Colin G. Scanes, Dept. of Animal Sciences, Rutgers University, USA. Sex linked dwarf (SLD), control (K) and autosomal dwarf (ADW) chickens at 6 weeks of age have respectively 58.6 ? 5.0% (5). 78.8 + 9.3% (5) and 81.0 ? 11.2% (4) free Sm C in their plasma, as measured by differences in Sm C activity using a radioimmunoassay, in plasma with or without acid treatment to separate Sm C from i%einding proteins. Using the elution patterns of plasma incubated with I-Sm C the same differences were found: 31.9X, 65.9% and 72.1% respectively for the 3 strains. Both the low amount of free Sm C and the elution pattern of the SLD strain are similar to that of hypophysectomized (Hx) chickens; 65.8 t 5.3% (9) with RIA and 27.4% with elution. In the Hx chicken it is clear that this is due to low growth hormone (GH) concentrations (54.7 2 7.8 ng/ml (9)). However in the SLD strain we found normal levels of CH (182.7 5 78.2 ng/ml (8)) and we therefore suggest that in this strain GH lacks to stimulate Sm C and has no inhibiting effect on the binding of Sm C to its binding protein.