Effects of vitamin D on renal handling of calcium, magnesium and phosphate in the hamster.

The effects of 1,25(OH)2D3 on the renal handling of calcium (Ca), magnesium (Mg), and phosphate (Pi) in the thyroparathyroidectomized (TPTX) hamster were studied in the presence of exogenous PTH. Clearance experiments were performed in the following groups: acutely TPTX animals (group 1), acute TPTX plus continuous infusion of PTH in low or high doses sufficient to (1) reduce or (2) abolish the hypocalcemic effect of TPTX (groups 2 and 3, respectively), and acute TPTX plus Ca (group 4) or Pi (group 5) infusion. Each group was subdivided into control and experimental subgroups. In all animals an initial control phase was followed by a second phase in which experimental animals received an infusion of 1,25(OH)2D3 (1 U prime + 0.5 U/hr) while control animals received only the ethanol vehicle. GFR and urine flow rate, were not altered significantly in any of the groups. PCa and PMg increased significantly in group 3 only. Group 2 showed an increase in FECa (5.2 +/- 1.4 to 13.2 +/ 2.2%, P less than 0.001) and FEMg (7.3 +/- 1.3 to 17.3 +/- 2.2%, P less than 0.001) in response to 1,25(OH)2D3. Group 3 showed a significant increase in FEMg only (2.2 +/- 0.4 to 5.5 +/- 1.0%, P less than 0.01). The changes in the control groups were not significant. The administration of 1,25(OH)2D3 reduced phosphate excretion only in the presence of PTH. The FEPi decreased from 11.9 +/- 2.1 to 3.6 +/- 0.9% (P less than 0.001) in group 2 and 29.2 +/- 4.0 to 16.5 +/- 2.5% (P less than 0.02) in group 3.(ABSTRACT TRUNCATED AT 250 WORDS)