Renal handling of phosphate in relation to serum parathyroid hormone levels

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.

1-Alpha-hydroxycholecalciferol-induced changes in the renal heandling of phosphate and the serum parathyroid hormone level

The effect of 1-alpha-hydroxycholecalciferol (1alpha-OH-D3) on the renal handling of phosphate and the immunoreactive parathyroid hormone in serum (i-PTH) has been studied in 10 patients with a wide range of glomerular filtration rate (GFR), maximal tubular reabsorption of phosphate (TmP) and i-PTH. The patients were treated with 2 mug 1alpha-OH-D3 per day for approximately 80 days. Before and after this period of treatment, the TmP, i-PTH, 51Cr EDTA clearance, extracellular volume, standard bicarbonate, and serum calcium were measured in each patient. The TmP/GFR ratio was used as an index of the renal handling of phosphate. The index increased significantly (mean 26.5%, p less than 0.01) during the treatment, while i-PTH decreased significantly (mean 37.0%. p less than 0.01). An inverse significant correlation was demonstrated between TmP/GFR index and i-PTH both before (r = -0.87, p less than 0.001) and after (r = -0.79, p less than 0.01) the administration o alpha-OH-D3, while none of the other factors investigated were correlated to the index. It is concluded that 1alpha-OH-D3 increases the TmP/GFR index and reduces i-PTH in a parallel manner and it is therefore suggested that the 1alpha-OH-D3-induced changes in the renal handling of phosphate may be explained as being mediated solely via the suppression of i-PTH.

Disordered Mineral Metabolism and Vascular Calcification in Nondialyzed Chronic Kidney Disease Patients

It is well established that abnormalities in mineral metabolism are apparent early in the course of chronic kidney disease (CKD) and result in clinically relevant consequences such as renal osteodystrophy. Furthermore, there is emerging evidence linking some of these abnormalities (hyperphosphatemia) to the high cardiovascular morbidity and mortality experienced by nondialyzed patients with CKD. Most studies have evaluated vascular calcification in patients with stage 5 CKD. Reports published over the last 2 years show that the process begins rather early in CKD and is particularly severe among elderly and type 2 diabetic patients. Furthermore, "calcium begets calcium", such that the calcification burden in early CKD is an important predictor of subsequent progression, including the rapid increase seen in stage 5 CKD. There is an increasing body of evidence that supports the thesis that elevated serum levels of phosphorus and calcium and deficiency of inhibitors of calcification (for example, fetuin-A) are important in the progression of vascular calcification in patients with end-stage renal disease. However, the concentrations of calcium and phosphorus shown to induce mineralization in cell culture studies are not observed in most patients until late in stage 4 or stage 5 CKD. Cross-sectional and longitudinal studies have also been unable to show a correlation between serum levels of markers of disordered mineral metabolism and severity of vascular calcification. Future studies should evaluate the pathogenetic role of phosphorus retention, which occurs early in the course of CKD, in the induction and/or progression of vascular calcification. Finally, there is a need to identify alternative pathogenetic mechanisms that may be important causes of the high calcification burden observed early in CKD.

Blood laboratory parameters of carefully selected healthy elderly people

Hematological and biochemical parameters were measured in carefully selected healthy elderly (50 males and 50 females, aged 60-97 years) and young (10 males and 10 females, aged 18-23 years) populations. Most of the parameters measured did not show any age-related variations. It means that any deviation from the present normal ranges established for healthy young subjects should be considered as pathologic in the case of elderly, too. Some parameters showed age-specific changes and hence there is a possibility that their actual normal ranges might be extended towards the upper limit (globulin, IgG, IgA, CIC, C3, BUN, AP for females), or towards the lower limit (creatinine clearance, albumin). Verification of these modifications may indicate that a lot of unnecessary investigations in the case of elderly could be avoided.

Has vitamin D a direct renal effect on the tubular reabsorption of phosphate? A study in parathyroidectomized (PTX) and non-PTX man

The effect of 1-alpha-hydroxycholecalciferol (1alpha-OH-D3) on the renal handling of phosphate and the immunoreactive parathyroid hormone in serum (i-PTH) has been studied in 10 patients with a wide range of glomerular filtration rate (GFR), maximal tubular reabsorption of phosphate (TmP) and i-PTH. The patients were treated with 2 microgram 1alpha-OH-D3 per day for approximately 80 days. Before and after this period of treatment, the TmP, i-PTH, 51Cr EDTA clearance, extracellular volume, standard bicarbonate, and serum calcium were measured in each patient. The TmP/GFR ratio was used as an index of the renal handling of phosphate. The index increased significantly (mean 26.5%, p less than 0.01) during the treatment, while i-PTH decreased significantly (mean 37.0%, p less than 0.01). A significant inverse correlation was demonstrated between the TmP/GFR index and i-PTH both before (r = -0.87; p less than 0.001) and after (r = -0.79; p less than 0.01) the administration of 1alpha-OH-D3, while none of the other factors investigated were correlated to the index. This may suggest that the stimulating effect of biologically active vitamin D on the tubular reabsorption of phosphate is mediated via the parallel suppression of PTH, but does not exclude that biologically active vitamin D exerts a direct effect on the human renal tubule. Therefore, the effect of 1alpha-OH-D3 was studied in 5 totally parathyroidectomized patients, in whom concomitant suppression of PTH would not occur. 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 1alpha-OH-D3 to obtain stable normocalcemia. In patients with absent parathyroid function, no increasing effect of 1alpha-OH-D3 on TmP/GFR could be demonstrated. It is therefore concluded 1) that 1alpha-OH-D3 exhibits no antiphosphaturic effect in the absence of PTH and 2) that the previously demonstrated antiphosphaturic effect of 1alpha-OH-D3 in man is mediated via a concomitant suppression of PTH.