The effect of 1-alpha-hydroxycholecalciferol on the renal handling of phosphate in parathyroidectomized man.
In a previous investigation by our group it was suggested that the stimulating effect of 1-alpha-hydroxycholecalciferol (1-alpha-OH-D3) on the tubular reabsorption of phosphate is mediated via the parallel suppression of the parathyroid hormone (PTH). A direct effect of 1-alpha-OH-D3 on the renal tubule could however not be completely excluded. Therefore, the effect of 1-alpha-OH-D3 was studied in 5 totally parathyroidectomized patients, in whom concomitant suppression of PTH would not occur. TmP/GFR, i.e. the ratio between the maximal tubular reabsorption of phosphate (TmP) and the glomerular filtration rate (GFR), was used as an indicator of the renal handling of phosphate. Estimation of TmP/GFR was performed 1) when the patients were vitamin D depleted and hypocalcemic, and 2) after 14-27 days of treatment with 1-alpha-OH-D3 to obtain stable normocalcemia. In patients with absent parathyroid function, no effect of 1-alpha-OH-D3 on TmP/GFR could be demonstrated. It is therefore concluded that 1-alpha-OH-D3 exhbits no antiphosphaturic effect in the absence of PTH and that the previously demonstrated antiphosphaturic effect of 1-alpha-OH-D3 in man is mediated via a concomitant suppression of PTH.
D000328:Adult; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D006887:Hydroxycholecalciferols / Q000494:pharmacology*; D007684:Kidney Tubules / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism*
D006887:Hydroxycholecalciferols; D010281:Parathyroid Hormone; D010710:Phosphates