Unilateral nephrectomy and 1,25-dihydroxyvitamin D3

Diagnosis, Treatment, and Prevention of Hemodialysis Emergencies

Given the high comorbidity in patients on hemodialysis and the complexity of the dialysis treatment, it is remarkable how rarely a life-threatening complication occurs during dialysis. The low rate of dialysis emergencies can be attributed to numerous safety features in modern dialysis machines; meticulous treatment and testing of the dialysate solution to prevent exposure to trace elements, toxins, and pathogens; adherence to detailed treatment protocols; and extensive training of dialysis staff to handle medical emergencies. Most hemodialysis emergencies can be attributed to human error. A smaller number are due to rare idiosyncratic reactions. In this review, we highlight major emergencies that may occur during hemodialysis treatments, describe their pathogenesis, offer measures to minimize them, and provide specific interventions to prevent catastrophic consequences on the rare occasions when such emergencies arise. These emergencies include dialysis disequilibrium syndrome, venous air embolism, hemolysis, venous needle dislodgement, vascular access hemorrhage, major allergic reactions to the dialyzer or treatment medications, and disruption or contamination of the dialysis water system. Finally, we describe root cause analysis after a dialysis emergency has occurred to prevent a future recurrence.

Treatment of severe dialysis reactions with the AN69-ST membrane: biocompatibility does matter

Dialysis reactions with biocompatible membranes are rare, and complement activation has been suggested to be a culprit. We report here a case of an incident haemodialysis patient with asthma disease who experienced severe adverse reactions late into dialysis session, with different synthetic membranes (FX 80, Fresenius; Polyflux 17L, Gambro; FX 10, Fresenius; BLS 512, Bellco-Sorin). After replacing the dialyser by the surface-treated AN69 membrane (Nephral ST 500, Hospal), the dialysis sessions became uneventful. The case reinforces the need for biocompatible dialysers with high permeability and adsorptive capacity in susceptible patients experiencing severe dialysis reactions with synthetic membranes.

Relative effects of PTH and dietary phosphorus on calcitriol production in normal and azotemic rats

In moderate renal failure, the serum calcitriol level is influenced by the stimulatory effect of high PTH and the inhibitory action of phosphorus retention. Our goal was to evaluate the relative effect that high PTH levels and increased dietary phosphorus had on calcitriol production in normal rats (N) and rats with moderate renal failure (Nx). Normal and Nx (3/4 nephrectomy) rats were divided into two groups: (1) rats with intact parathyroid glands (IPTG) and (2) parathyroidectomized rats in which PTH was replaced (PTHR) by the continuous infusion of rat 1-34 PTH, 0.022 microgram/hr/100 g body wt, using a miniosmotic Alzet pump. To test the effect of dietary phosphorus, rats received either a moderate (MPD, 0.6% P) or a high phosphorus (HPD, 1.2%) diet for 14 days. The experimental design included pair-fed N and Nx rats with either IPTG or PTHR. Serum calcitriol and PTH levels in N rats fed a MPD were 69 +/- 3 and 40 +/- 5 pg/ml, respectively. In Nx rats on a MPD, serum calcitriol levels decreased only if hyperparathyroidism was not allowed to occur (76 +/- 4 vs. 62 +/- 4 pg/ml in Nx-IPTG-MPD and Nx-PTHR-MPD groups respectively, P < 0.05). Even in N rats on a HPD, high PTH levels (67 +/- 8 pg/ml in the N-IPTG-HPD group) were required to maintain normal serum calcitriol levels (69 +/- 4 vs. 56 +/- 6 pg/ml in Nx-IPTG-HPD and Nx-PTHR-HPD groups, respectively; P < 0.05). In Nx rats on a HPD, the development of secondary hyperparathyroidism (286 +/- 19 pg/ml in the Nx-IPTG-HPD group) prevented a decrease in serum calcitriol levels (68 +/- 7 pg/ml). In contrast, serum calcitriol levels were low in the Nx-PTHR-HPD group (52 +/- 4 pg/ml, P < 0.05), which were deprived of the adaptative increase in endogenous PTH production. In conclusion, our results in rats indicate that in moderate renal failure, an elevated PTH level maintains calcitriol production and overcomes the inhibitory action of phosphorus retention.

Phosphate homeostasis, 1,25-dihydroxyvitamm D(3), and hyperparathyroidism in early chronic renal failure

In early chronic renal failure, low plasma levels of calcitriol (1,25[OH](2)D(3)) do not seem to be merely the consequence of a reduced mass of functional nephrons. Indeed, this alteration can be considered as a compensatory mechanism, as analyzed according to a new concept of inorganic phosphate (P(i)) homeostasis that integrates both 1,25(OH)(2)D(3) production and renal P(i) reabsorption as essential regulating elements. Accordingly, the observed reduction in the renal production of 1,25(OH)(2)D(3) that occurs concomitantly with a decrease in tubular P(i) reabsorptive capacity (TmP(i)/GFR) may well represent a secondary adaptive response to a primary alteration in P(i) homeostasis. This crucial alteration in P(i) homeostasis would consist of an overload of a putative regulated intracellular P(i) pool, the localization of which remains to be determined. The observed hypophosphatemia, hypocalcemia, and PTH hypersecretion would represent alterations secondary to a low TmP(i)/GFR and to reduced 1,25(OH)(2)D(3) production. According to this pathophysiologic sequence, 1,25(OH)(2)D(3), rather than PTH as proposed in a former theory, would be "traded off" to preserve P(i) homeostasis in early chronic renal failure. Both theories predict that dietary P(i) restriction represents a logical preventive therapy at least until the nature of the primary defect in P(i) homeostasis is understood. However, assuming that low 1,25(OH)(2)D(3) levels in early chronic renal failure represent a compensatory phenomenon, this new theory suggests that calcitriol should be only administered at a later stage of the disease, when the production of 1,25(OH)(2)D(3) becomes inappropriately low to maintain mineral homeostasis.

Effects of cyclosporins and transforming growth factor beta 1 on thyroid hormone action in cultured fetal rat limb bones

To study the mechanism of action of thyroid hormones on bone, we examined the effects of immunosuppressive and nonimmunosuppressive cyclosporins, as well as of transforming growth factor beta 1 (TGF beta 1), 17 beta-estradiol (E2), and dihydroxytestosterone (DHT) on thyroxine (T4)- and triiodothyronine (T3)-stimulated bone resorption in fetal rat limb bones. The immunosuppressive cyclosporins A (CsA) and G (CsG) inhibited thyroid hormone (T4 + T3)-stimulated resorption and beta-glucuronidase release into the culture medium, whereas the weak or nonimmunosuppressive cyclosporins D (CsD) and H (CsH) did not show this effect. Increasing the medium calcium concentration reduced the ability of T4 to stimulate 45Ca release, while not significantly affecting the response to CsA. TGF beta 1 elicited a biphasic effect when administered together with T4. During the first 3 days of culture, TGF beta 1 elicited a small, nonsignificant decrease in released 45Ca; during a subsequent 3 days of culture, it enhanced T4-stimulated bone resorption significantly. These effects differed from those of TGF beta 1 on parathormone-stimulated resorption. E2 and DHT did not influence the action of T4 on bone tissue. These results suggest that the mechanism of action of thyroid hormones on bone may involve immune factors, as well.

Calcitriol metabolism in patients with chronic renal failure

We studied calcitriol metabolism in white patients with chronic renal failure and in age- and sex-matched normal subjects. The plasma levels of calcitriol (21.9 +/- 1.6 pg/mL, n = 7, v control, 37.4 +/- 2.9 pg/mL, P less than 0.001), metabolic clearance rate (MCR) of calcitriol (0.45 +/- .01 mL/min/kg v control, 0.58 +/- .02 mL/min/kg, P less than 0.001), and production rate (PR) of calcitriol (14.2 +/- 1.0 ng/kg/d v control, 31.8 +/- 3.2 ng/kg/d, P less than 0.001) were significantly lower in patients with moderate renal failure (average creatinine clearance, 0.59 +/- 0.01 mL/s [35.1 +/- 6.1 mL/min]) when compared with the respective values of normal control subjects. The MCR of calcitriol was determined again in patients with renal failure after they received calcitriol, 1 microgram/d, for 1 week. The MCR remained unchanged (0.46 +/- .04 mL/min/kg, n = 7) and plasma levels of calcitriol were increased to 34.6 +/- 2.77 pg/mL. The mechanism by which the MCR of calcitriol decreases in renal failure is partly due to the presence of inhibitory factors of degradation enzymes in uremic plasma. When the ultrafiltrates of uremic plasma obtained from hemodialysis patients were infused to normal Sprague-Dawley rats, the MCRs of calcitriol (0.20 +/- .01 mL/min/kg, n = 6) were markedly suppressed in comparison to those of rats infused with the ultrafiltrates of normal plasma (0.37 +/- .01 mL/min/kg, n = 6, P less than 0.001). The uremic plasma also contained factors that inhibit the synthesis of calcitriol. We conclude that metabolic degradation of calcitriol is decreased in patients with renal failure, and uremic plasma contains inhibitory factors that suppress the synthesis and degradation of calcitriol.

Effect of vitamin D metabolites on calcitriol metabolism in experimental renal failure

Previous studies from our laboratory have demonstrated that metabolic clearance rate (MCR) of calcitriol is decreased in experimental renal failure. In this experiment, we examined the effects of calcitriol, 25-hydroxyvitamin D3 (25(OH)D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) on the MCR of calcitriol in renal failure produced in rats by partial nephrectomy. The MCR of calcitriol in these rats with renal failure was significantly lower than in control rats with sham operations. Plasma concentrations of calcitriol did not differ between the rats with moderate renal failure and control rats (sham, 74.7 +/- 3.6 pg/ml, N = 7; renal failure, 67.7 +/- 6.0, N = 6; serum creatinine 0.56 +/- 0.02 mg/dl vs. 0.96 +/- 0.02); however, the levels were significantly lower in rats with severe renal failure (sham, 66.5 +/- 5.1 pg/ml, N = 7, severe renal failure, 49.6 +/- 2.1 pg/ml, N = 8; serum creatinine 0.53 +/- 0.01 mg/dl vs. 1.40 +/- 0.03). Subcutaneous infusion of calcitriol (10 ng/kg/day) in rats with severe renal failure for one week significantly increased the MCR of calcitriol (0.22 +/- .01 vs. 0.17 +/- .01 ml/min/kg, P less than 0.001). Infusion of 25(OH)D3 (600 ng/day) or 24,25(OH)2D3 (1 microgram/day) in rats with renal failure for one week also increased the MCR of calcitriol (25(OH)D3, 0.25 +/- 0.01 ml/min/kg; 24,25(OH)2D3, 0.25 +/- 0.01, both P less than 0.001) when compared to rats with renal failure infused with vehicle (0.21 +/- 0.01). Administration of 24,25(OH)2D3 significantly lowered the plasma levels of calcitriol in rats with renal failure (52.3 +/- 3.1 pg/ml, P less than 0.05) in comparison to the rats with renal failure infused with vehicle (67.7 +/- 6.0).(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin D kinetics in vivo: effect of 1,25-dihydroxyvitamin D administration

Administration of 1,25-dihydroxyvitamin D [1,25(OH)2D] can increase the metabolic clearance rate (MCR) of 25-hydroxyvitamin D [25(OH)D]. To determine whether administration of 1,25(OH)2D can also influence the metabolic clearance rates (MCR) of 1,25(OH)2D and 24,25-dihydroxyvitamin D 24,25(OH)2D, we measured metabolic clearance of 1,25(OH)2D, 24,25(OH)2D, and 25(OH)D in rats in which the serum concentration of 1,25(OH)2D was increased by continuous infusion. Infusion of 1,25(OH)2D (12 days at 75 pmol/day) increased serum 1,25(OH)2D from 128 +/- 11 to 244 +/- 14 pg/ml (P less than 0.005) and increased MCR from 169 +/- 13 to 210 +/- 9 microliters.min-1.kg-1 or 24% (P less than 0.025). Increasing serum 1,25(OH)2D to 330-360 pg/ml increased MCR 72%. Infusion of 1,25(OH)2D decreased serum 24,25(OH)2D from 3.5 +/- 0.5 to 2.4 +/- 0.3 ng/ml (P less than 0.05), increased MCR from 25 +/- 2 to 48 +/- 6 microliters.min-1.kg-1 (P less than 0.0025), and increased the production rate (PR) from 70 +/- 11 to 124 +/- 26 pg.min-1.kg-1 (P less than 0.05). Infusion of 1,25(OH)2D decreased serum 25(OH)D from 13.0 +/- 0.5 to 8.0 +/- 0.5 ng/ml (P less than 0.005) and increased MCR from 45 +/- 1 to 75 +/- 7 microliters.min-1.kg-1 (P less than 0.001) but had no effect on PR. The data indicate that increasing serum 1,25(OH)2D by chronic administration can increase the MCR of 1,25(OH)2D and suggest that 1,25(OH)2D can feedback regulate its serum concentration by regulating its MCR. The data also suggest that 1,25(OH)2D administration can increase the MCRs of 24,25(OH)2D and 25(OH)D.

Metabolic clearance rate and production rate of calcitriol in uremia

We have previously demonstrated that while both normal humans and dogs tightly control serum calcitriol levels after 25(OH)D administration, anephric humans and 5/6 nephrectomized dogs significantly increase circulating 1,25(OH)2D when supraphysiological concentrations of 25(OH)D are reached in serum. Plasma 1,25(OH)2D level is determined not only by its rate of production but also by its rate of degradation. To further characterize the mechanisms involved in the responses to 25(OH)D therapy in normal circumstances and in chronic uremia, we measured metabolic clearance rate (MCR) and production rate (PR) of 1,25(OH)2D in normal dogs and in dogs with moderate and severe renal failure, at normal and supraphysiological serum concentrations of 25(OH)D. Basal MCR in uremic dogs, either with moderate or with severe renal failure, did not differ significantly from normals (6.7 +/- 0.7, 6.8 +/- 0.4 and 6.8 +/- 0.3 ml/min, respectively). Oral 25(OH)D administration for two weeks did not affect MCR either in normal animals or in both groups of uremic dogs. 25(OH)D treatment did not affect production rates in normal dogs and in animals with moderate renal failure (with normal basal values of 1,25(OH)2D), but significantly increased 1,25(OH)2D production from 0.13 +/- 0.01 to 0.25 +/- 0.04 micrograms/day (P less than 0.05) in dogs with severe renal insufficiency. These data suggest that it is the basal level of 1,25(OH)2D which regulates the synthesis of 1,25(OH)2D in response to 25(OH)D administration in normal and uremic animals.

Production and metabolic clearance of calcitriol in acute renal failure

Metabolic clearance rate (MCR) and production rate (PR) of calcitriol were studied three and seven days after ischemic acute tubular necrosis (ATN). Creatinine clearance was decreased three days after clamping the renal arteries (0.42 +/- 0.03 ml/min/100 g, N = 6 in ATN vs. 0.68 +/- 0.09, N = 7 in sham controls; P less than 0.001). Plasma concentrations (24.1 +/- 1.9 pg/ml) and PR of calcitriol (9.8 +/- 0.91 ng/kg/day) were significantly lower in ATN rats three days after ischemic insult when compared to sham control rats, respectively (76.6 +/- 7.3 pg/ml, and 29.6 +/- 3.3 ng/kg/day; both P less than 0.01). The MCRs of calcitriol were not different between ATN (0.28 +/- 0.02 ml/min/kg) and sham control rats (0.27 +/- 0.01). By the seventh day after ischemic injury, when creatinine clearance of ATN rats returned to normal, both the PR and plasma concentrations of calcitriol also returned to normal values in these animals. In order to assess the effect of uremia on calcitriol metabolism, MCR and PR of calcitriol were measured in rats with reinfusion of their urines for 24 hours. The PR of calcitriol was significantly decreased (9.42 +/- 1.21; vs. controls, 20.5 +/- 2.9 ng/kg/day, P less than 0.001) in uremic animals. Since decreased PR of calcitriol was also accompanied by decreased MCR of calcitriol, plasma concentrations of calcitriol of the uremic rats with intact kidneys remained within normal values. We conclude that the PR of calcitriol is decreased early in ATN rats. Although the MCR was not decreased in mild ATN rats, it may decrease in severe acute renal failure.

Compensatory renal growth: modulation by calcium PTH and 1,25-(OH)2D3

To further elucidate the mechanisms by which compensatory renal growth (CRG) can be influenced by calcium and calcium regulating hormones, the influence of dietary calcium and phosphorus, parathyroid hormone (PTH) or 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was evaluated in unilaterally nephrectomized (UNI-NX) rats. These animals were sacrificed three days after UNI-NX and CRG of the remaining kidney was assessed by kidney wt, RNA and DNA gains, and by 3H-thymidine incorporation. The degree of CRG was enhanced in animals given a low dietary calcium and, conversely, was decreased in those receiving a phosphorus-poor diet. In thyroparathyroidectomized (TPTX) rats, PTH administration resulted in a dose proportional stimulation of CRG. When 1,25-(OH)2D3 was given to vitamin D deficient animals, the degree of CRG was enhanced in a dose proportional manner. In another experiment, TPTX-vitamin D deficient rats were given the same amount of 1,25-(OH)2D3 by miniosmotic pump infusion. In these animals, dietary calcium restriction, instead of stimulating, inhibited CRG. From these observations we conclude that calcium and calcium regulating hormones modulate CRG, and hypothesize that the effects observed are mediated through changes in cell calcium.