THE EFFECT OF lα‐HYDROXYVITAMIN D3 IN PATIENTS WITH CHRONIC RENAL FAILURE, WITH PARTICULAR EMPHASIS ON THE RENAL HANDLING OF PHOSPHATE

SUMMARY The present study was undertaken to elucidate the clinical, skeletal, intestinal and especially the renal effect of lα-hydroxyvitamin D3 (lα-OHD3), a synthetic vitamin D analogue. Seventeen patients in the uraemic state were investigated before and after long-term treatment (mean 12.6 months) with lα-OHD3. Serum total calcium, serum ionized calcium (Ca2+), phosphorus, alkaline phosphatases, magnesium, parathyroid hormone (iPTH), 241Am-photonabsorptiometry, 99mtechnetium-polyphosphate scintigraphy, intestinal 47Calciurn-absorption and X-ray survey of the skeleton were measured. In the uraemic patients (dialysed as well as non-dialysed), a total or partial normalization of the bone-related parameters was found, including relief of bone pain. In order to evaluate the effect of lα-OHD3 on the renal handling of phosphate, ten non-parathyroidectomized (non-PTX) and five totally parathyroidectornized (PTX) patients were studied. Both groups were investigated before and after administration of lα-OHD3. The PTX patients were vitamin D depleted and hypocal-caemic before the study. During P-infusion, the maximal tubular reabsorption of phosphate (TmP), [51Cr]-EDTA clearance (GFR), parathyroid hormone (iPTH) and Ca2+ were measured. The TmP/GFR-ratio was used as an index of the renal handling of phosphate. It was demonstrated (1)that lα-OHD3 exhibits no antiphos-phaturic effect in man in the absence of PTH, and (2) that the lα-OHD3 induced changes in the renal handhg of phosphate are mediated by suppression of iPTH.