Evidence of healing of secondary hyperparathyroidism in chronically hemodialyzed uremic patients treated with long-term intravenous calcitriol

Intraperitoneal Pulse Calcitriol in the Treatment of Secondary Hyperparathyroidism in Patients on Continuous Ambulatory Peritoneal Dialysis

Objective

To determine whether it is practicable to use intraperitoneal calcitriol to treat continuous ambulatory peritoneal dialysis (CAPD) patients with secondary hyperparathyroidism and whether this form of therapy is effective and safe.

Design

A prospective, nonrandomized study.

Setting

Division of Nephrology, Tertiary Hospital.

Method

Eight patients from our CAPD population were recruited (5 F,3 M), aged 24 to 63 years (mean 38.9 ± 7.6 yr). They had been on CAPD for 8 to 84 months (mean 47.6 ± 24.6 months). All the patients had bone biopsy -proven secondary hyperparathyroidism with 2 patients showing mixed lesions. The CAPD system was changed to the twinbag system (Ultrabag, Baxter Healthcare, McGaw Park, IL, U.S.A.) in all 8 patients, who were taught to inject the calcitriol directly through the short transfer set and the Tenckhoff catheter into the peritoneal cavity, twice per week before bedtime. Calcium carbonate or calcium acetate was used as the main phosphate binder. Intact parathyroid hormone level (iPTH), serum ionized calcium (iCa), serum phosphate, and serum total alkaline phosphatase (alk. phos.) levels were measured at baseline and then every 4 weeks. The mean duration of follow-up was 10.5 months ± 1.9 months.

Results

There was a significant drop of iPTH level from the pretreatment level of 100.6 ± 35.8 pmoll L to a level of 63.8 ± 48.7 pmoll L at 24 weeks (p = 0.036). The lowest level of iPTH attained was 43.4 ± 27.0 pmol/L at 48 weeks. Serum total alk. phos. also dropped from 232.4 ± 83.3 lUlL pretreatment to 147.9 ± 52.0 lUlL at 24 weeks (p = 0.017). The decrease in alk. phos. level paralleled the decrease in iPTH level. The mean serum iCa level did not show any significant rise throughout the study period. The maximum dose of calcitriol used was 6.6 ± 1.5 μg/week and the average dose of calcitriol was 5.4 ± 1.2 μg/week. One patient did not respond satisfactorily and she subsequently had a parathyroidectomy. Two episodes of peritonitis occurred during the study period, giving a peritonitis rate of one episode per 42 patient-months. There was no significant change in the urea clearance tests or the peritoneal equilibration tests before and after the study.

Conclusion

Intraperitoneal calcitriol is practicable, effective, and safe in the treatment of secondary hyperparathyroidism in CAPD patients.

Intravenous calcitriol therapy in an early stage prevents parathyroid gland growth

BACKGROUND

Both the phenotypic alterations of parathyroid (PT) cells, e.g. down-regulation of the calcium-sensing receptor, and the increase of the PT cell number in nodular hyperplasia are the main causes of refractory secondary hyperparathyroidism. It is of great importance to prevent PT growth in an early stage.

METHODS

To examine a more effective method of calcitriol therapy for the prevention of PT hyperplasia, we randomized haemodialysis patients with mild hyperparathyroidism to receive either daily orally administered calcitriol (n = 33) or intravenous calcitriol (n = 27) over a 12-month study period. Calcitriol was modulated so as to keep the serum intact PTH level between 100 and 150 pg/ml.

RESULTS

Both groups showed similar reductions of the serum PTH level and similar increases in serum calcium. In both groups, there were no significant changes in the serum phosphate level. Long-term daily oral calcitriol therapy failed to prevent the increase of both maximum PT volume and total volume, as assessed by ultrasonography; however, intravenous calcitriol therapy successfully suppressed this progression. In the daily, oral group, both the bone-specific alkaline phosphatase (BAP) and the N-telopeptide cross-linked of type I collagen (NTX) significantly decreased, which was probably due to the PTH suppression. However, these bone metabolism markers remained stable in the intravenous group. The total dosage of calcitriol during the study was comparable in both groups.

CONCLUSIONS

These data indicate that intravenous calcitriol therapy in an early stage of secondary hyperparathyroidism is necessary to prevent PT growth and to keep a good condition of bone metabolism.

Early hospital readmission was less likely for hemodialysis patients from facilities with longer median length of stay in the DOPPS study

The length of hospital stay is considered to influence hospital readmission in general. The Dialysis Outcomes and Practice Patterns Study (DOPPS), an international prospective observational study undertaken to establish a relationship between facility practices and dialysis outcomes, started in 1996. Results suggest that the duration of hospital stay is significantly correlated with the probability of early readmission in dialysis patients. Thus, early hospital readmission was observed to be less likely for hemodialysis patients from facilities with longer median length of stay. The lengths of hospital stay for hemodialysis patients differed in the three continents studied. Although socioeconomic pressures may drive the lengths of hospital stay, the duration of hospitalization should be determined keeping in mind the safety of clinical course for each disease. In this forum, a 47-year-old female hemodialysis patient with severe secondary hyperparathyroidism, who had been treated with hemodialysis for 21 years, was hospitalized with severe clinical symptoms. Although the clinical symptoms disappeared 10 days after total parathyroidectomy with autotransplantation, severe hypocalcemia persisted despite large amounts of intravenous calcium gluconate. This patient was hospitalized for a long duration owing to the large calcium deficit in her body. Had the length of her hospital stay been shortened, either she could have needed rehospitalization or her condition could have worsened.

Secondary hyperparathyroidism in children with chronic renal failure: pathogenesis and treatment

Despite advances in the management of patients with chronic renal failure, histologic features associated with secondary hyperparathyroidism remain the predominant skeletal findings; however, over the last decade the prevalence of adynamic bone has increased in both adult and pediatric patients with chronic renal failure. The management of children with secondary hyperparathyroidism and mild to moderate chronic renal failure should be started early, and should include correction of hypocalcemia and metabolic acidosis, maintenance of age-appropriate serum phosphorus levels, and institution of vitamin D therapy when serum intact parathyroid hormone (PTH) measurements are elevated to maintain the blood levels within normal limits; however, in children undergoing chronic dialysis therapy, the current recommendation is to maintain the serum intact PTH levels at least 2-4 times the upper limits of normal to prevent the development of low bone turnover disease. Serum calcium, phosphorus, alkaline phosphatase, and PTH levels should be monitored frequently, especially in infants and very young children. Discontinuation or reduction of vitamin D should be considered when there is a rapid decline in PTH levels, persistent elevation in serum calcium and serum phosphorus levels, and a significant diminution in alkaline phosphatase levels. In addition, a reduction in the calcium concentration of the dialysis fluid, and judicious use of calcium-containing salts as phosphate binding agents should also be performed in these patients. Although not yet extensively used in pediatric patients with secondary hyperparathyroidism, several therapeutic alternatives, such as the less calcemic vitamin D analogs, including paricalcitol [19-nor-1,25-(OH)(2)D(2)] and doxercalciferol [1-alpha-(OH)(2)D(2)], calcimimetics, and the availability of a calcium-free, aluminum-free phosphate binder such as sevelamer hydrochloride and lanthanum carbonate, may play significant roles in the future management of children with secondary hyperparathyroidism to promote linear growth, prevent parathyroid gland hyperplasia, avoid calciphylaxis and, in the long run, avert vascular calcifications.

Comparative Efficacy of Oral and Intravenous Calcitriol Treatment in Haemodialysis Patients: Effects on Serum Biochemistry and Cytokine Levels

This study compared the effects of oral and intravenous calcitriol on serum biochemistry parameters and levels of bone-resorptive cytokines in haemodialysis patients. Patients were randomized to receive oral ( n = 18) or intravenous ( n = 16) calcitriol treatment for 6 months. Serum levels of total calcium, ionized calcium, intact parathyroid hormone (iPTH), magnesium, alkaline phosphatase, tumour necrosis factor-α (TNF-α), interleukin (IL)-1 and IL-6 were measured at baseline and after 3 and 6 months of treatment. After treatment, serum levels of iPTH, total calcium, ionized calcium, TNF-α, IL-1 and IL-6 were not significantly different from baseline. The intravenous calcitriol treatment group showed significant decreases in levels of iPTH, TNF-α, IL-1 and IL-6 and a significant increase in total calcium level after 3 and 6 months. There was no significant change in serum ionized calcium levels. Significantly decreased serum alkaline phosphatase and magnesium levels were found in both treatment groups after 3 and 6 months. In conclusion, intravenous calcitriol treatment has a significant depressive effect on iPTH and bone-resorptive cytokines in patients undergoing haemodialysis.

Effects of calcitriol on parathyroid function and on bone remodelling in secondary hyperparathyroidism

BACKGROUND

Secondary hyperparathyroidism (2HPT) develops in chronic renal failure due to disturbances of calcium, phosphorus and vitamin D metabolism. It is characterized by high turnover bone disease and an altered calcium-parathyroid hormone (PTH) relationship. Calcitriol has been widely used for the treatment of 2HPT. However, it remains controversial whether calcitriol is capable of inducing changes of the calcium-PTH curve. The aim of the present study was to examine this issue and to determine the effect of calcitriol on bone remodelling in patients with severe 2HPT.

METHODS

We evaluated 16 chronic haemodialysis patients with severe 2HPT (PTH 899+/-342 pg/ml). Each patient underwent a dynamic parathyroid function test (by infusion of calcium gluconate and sodium citrate) and a bone biopsy before and after a 6 month period of i.v. calcitriol therapy (CTx).

RESULTS

After treatment, eight patients were identified as calcitriol responders and the other eight as non-responders, based on plasma PTH level (<300 pg/ml for responders and >300 pg/ml for non-responders). The first group had higher plasma 25OHD(3) levels (39+/-8 vs 24+/-7 ng/ml, P<0.005). As to the calcium-PTH curve, we found differences in slope (-12.7+/-5.2 vs -21.7+/-11.4, P=0.05), basal/maximum PTH ratio (48.8+/-14.9 vs 71.05+/-20.1%, P=0.01) and time to achieve hypocalcaemia (79.0+/-13.5 vs 94.3+/-13.7 min, P<0.001). Initial histomorphometric parameters did not allow identification of the different groups. After the 6-month CTx, alterations in the calcium-PTH curve were clearly seen in responders [a drop in maximum PTH (from 1651+/-616 to 938+/-744 pg/ml, P<0.05) and minimum PTH (from 163+/-75.4 to 102.2+/-56.7 pg/ml, P<0.005)], associated with an increase in minimum/basal PTH ratio (from 23.3+/-11.6 to 34.5+/-20.4%, P<0.05) and maximum calcium (from 0.99+/-0.07 to 1.1+/-0.09 mmol/l, P<0.05). Set point and slope were not altered after calcitriol treatment, in responders (set point=1.17+/-0.08 vs 1.15+/-0.1 mmol/l, ns; slope=-12.7+/-5.2 vs -12.9+/-9.3, ns) or non-responders (set point=1.21+/-0.05 vs 1.21+/-0.2 mmol/l, ns; slope=-21.7+/-11.4 vs -17.3+/-8.4, ns). Bone formation parameters were reduced in all patients [osteoid surface (OS/BS)=from 57.1+/-21.6 to 41.6+/-26%, P<0.05 for responders, and from 76.7+/-12 to 47.1+/-15%, P<0.001 in non-responders], but non-responders had increased bone resorption [eroded surface (ES/BS)=7.1+/-3.4 vs 16.6+/-4.9, P<0.05].

CONCLUSION

Calcitriol had non-uniform effects on parathyroid function and bone remodelling in uraemic patients. Non-responders exhibited a decoupled remodelling process that could further influence mineral balance or possibly also bone structure. To avoid such undesirable effects, early identification of non-responder patients is crucial when using calcitriol for the treatment of 2HPT.

Differential effects of 19-nor-1,25-(OH)(2)D(2) and 1alpha-hydroxyvitamin D(2) on calcium and phosphorus in normal and uremic rats

BACKGROUND

Calcitriol, 1,25-(OH)(2)D(3) (1,25D), the most active metabolite of vitamin D, has been used in the treatment of secondary hyperparathyroidism (SH) because it controls parathyroid gland growth and suppresses parathyroid hormone (PTH) synthesis and secretion. Due to the calcemic and phosphatemic actions of 1,25D, two analogs with potentially less side effects, 19-nor-1,25-(OH)(2)D(2) (19-nor) and 1alpha(OH)D(2) (1alphaD(2)) are currently being used in the treatment of SH.

METHODS

This study compares the effects of these two analogs on calcium (Ca) and phosphorus (P) metabolism in normal, uremic, and parathyroidectomized (PTX) rats. Using doses of 50 to 250 ng of 19-nor or 1alphaD(2), experiments were conducted in normal and uremic rats.

RESULTS

In uremic rats, 19-nor did not increase plasma Ca or P while 1alphaD2 caused a dose-dependent increase in both. In addition, while the Ca x P product remained unchanged in 19-nor-treated rats, it increased progressively with 1alphaD(2)administration. In metabolic studies in normal rats treated with vehicle, 10 ng of 1,25D, 100 ng of 19-nor or 100 ng 1alphaD(2), intestinal calcium absorption and urinary calcium excretion were significantly higher in 1alphaD(2)-treated rats compared to those receiving 19-nor. Similar results were seen for intestinal phosphorus absorption and urinary phosphorus excretion. Finally, the skeletal response to these two analogs was tested in PTX rats fed a calcium-deficient diet and treated daily with 100 ng of 19-nor or 1alphaD(2). The increase in plasma calcium in 1alphaD2-treated rats was markedly higher than in those receiving 19-nor. Similar results were seen in plasma phosphorus when these studies were repeated using a phosphorus-deficient diet.

CONCLUSIONS

These studies demonstrate that when given in large doses to rats 19-nor is less calcemic and phosphatemic than 1alphaD(2). The lower Ca x P product in 19-nor treated rats may be an important consideration in patient therapy. Further studies in patients are necessary to define the clinical applicability of these differences.

Reduced p21, p27 and vitamin D receptor in the nodular hyperplasia in patients with advanced secondary hyperparathyroidism

BACKGROUND

In uremic patients with secondary hyperparathyroidism (2HPT), nodular hyperplasia of parathyroid gland shows a monoclonal pattern of cell proliferation, in which a decreased density of vitamin D receptor (VDR) also is demonstrated. The present study aimed at elucidating the mechanism of parathyroid cell proliferation in relation to cell cycle determinants in patients with advanced 2HPT.

METHODS

The expression of cyclin-dependent kinase inhibitors, p21 and p27, and VDR were examined and compared among four groups of nodular (Nd; N = 23) or diffuse (Df; N = 6) hyperplastic parathyroid glands resected due to 2HPT, primary adenomas (Ad; N = 15), and histologically-normal parathyroid glands (C; N = 20) removed during thyroidectomy. Immunohistochemical analyses for VDR, p21, p27 and Ki67 antigen were performed in formalin-fixed paraffin-embedded tissues by using specific polyclonal antibody. The distribution and the intensity of immunoreactivity was quantified by using NIH imaging, and was expressed as the labeling index (LI) of positive nuclear staining in a random set of 1000 cells.

RESULTS

p21 LI was significantly diminished in both Nd (85 +/- 110; mean +/- SD) and Ad (136 +/- 122) as compared to that in Df (360 +/- 191) or C (359 +/- 228; P < 0.01). p27 LI was also significantly diminished in both Nd (97 +/- 156) and Ad (187 +/- 196) as compared to that in Df (532 +/- 146) or C (631 +/- 170; P < 0.01). VDR LI in Nd (162 +/- 194) was also significantly lower than that in Df (495 +/- 337), Ad (383 +/- 262), or C (659 +/- 234), respectively (P < 0.01). Parathyroid sections with high nuclear VDR expression elicited high p21 and p27 expression. Both p21 and p27 LI in Nd correlated significantly with nuclear VDR LI (r = 0.92; P < 0.01, r = 0.76; P < 0.01), but not with p53 LI, and inversely correlated with the glandular weight (r = 0.44; P < 0.05, r = 0.41; P < 0.05).

CONCLUSIONS

The reduced expression of p21 and p27, in a VDR-dependent manner, is a major pathogenic factor for a nodular parathyroid gland growth.

Use of vitamin D analogs in chronic renal failure

Renal osteodystrophy is the term used to describe the spectrum of bone diseases associated with chronic renal failure. Deficiency of 1,25-dihydroxycholecalciferol (calcitriol) plays a major role in the development of renal osteodystrophy, in particular the evolution of secondary hyperparathyroidism. In recent decades, our understanding of the complex interactions between calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) has increased, resulting in a rational approach to therapy in which vitamin D analogs have become an essential component. The initial vitamin D analogs that have been in widespread clinical use include calcitriol (1,25-[OH](2)D(3)) and alfacalcidol (1alpha-[OH]D(3)). These agents have been extensively studied to optimize their effects on secondary hyperparathyroidism. The occurrence of significant hypercalcemia and hyperphosphatemia limiting their use has led to the development of alternative vitamin D analogs that effectively reduce PTH secretion without causing these complications. Recently, 3 such analogs, 22-oxa-1,25-(OH)(2)D(3) (OCT), 1alpha-(OH)D(2) (doxercalciferol), and 19-nor-1,25-(OH)(2)D(2) (paricalcitol), have been released for clinical use. Only paricalcitol has been studied in comparative human clinical trials with calcitriol in dialysis patients. Preliminary findings suggest a clinical advantage over calcitriol, however, analysis of the larger comparative studies are forthcoming.

Strategies to minimize bone disease in renal failure

The skeletal disorders associated with renal insufficiency result from alterations in calcium, phosphorus, and vitamin D metabolism. Each requires intervention to prevent and control the problem. Hyperparathyroidism and its treatment can also result in extraskeletal complications. To prevent the development of parathyroid hyperplasia and the skeletal complications of chronic kidney disease, it is desirable to initiate interventions early in the course of kidney disease; however, many patients present with established hyperparathyroidism and additional strategies are necessary to suppress hyperparathyroidism. Mainstays of this approach are the control of phosphorus and the use of vitamin D analogs. Phosphorus control requires the use of phosphate binders, preferably non-calcium-containing binders, to prevent intestinal phosphorus absorption. Vitamin D analogs are used to suppress hyperparathyroidism and have the potential to have lesser toxicity than calcitriol. Paricalcitol is the most widely used vitamin D analog in this country and it effectively suppresses hyperparathyroidism with only minimal effects on calcium and phosphorus. A substantial body of data in experimental animals supports the use of paricalcitol as a preferential therapeutic agent. Recently, an additional vitamin D sterol, doxercalciferol, has been introduced, which is metabolized to 1,25-dihydroxyvitamin D(2). Although initially thought to have lesser toxicity than its vitamin D(3) counterpart, recent studies have not provided support for a major difference in this regard. Doxercalciferol is also effective in lowering parathyroid hormone (PTH), though hypercalcemia in hyperphosphatemic episodes occurred relatively frequently during the clinical studies. As these therapeutic strategies are undertaken, it is important not to oversuppress PTH and decrease bone turnover to abnormally low levels because of the risk for adynamic renal bone disease. It is possible that when bone turnover is abnormally low, the extraskeletal deposition of calcium in blood vessels and other tissues is enhanced. Accordingly, constant monitoring is required during treatment, with emphasis on minimizing the calcium load, and, if monitored correctly, a satisfactory control of hyperparathyroidism may be achieved with the agents currently available.

Failure of high doses of calcitriol and hypercalcaemia to induce apoptosis in hyperplastic parathyroid glands of azotaemic rats

BACKGROUND

Whether calcitriol administration, which is used to treat secondary hyperparathyroidism in dialysis patients, induces regression of parathyroid-gland hyperplasia remains a subject of interest and debate. If regression of the parathyroid gland were to occur, the presumed mechanism would be apoptosis. However, information on whether high doses of calcitriol can induce apoptosis of parathyroid cells in hyperplastic parathyroid glands is lacking. Consequently, high doses of calcitriol were given to azotaemic rats and the parathyroid glands were evaluated for apoptosis.

METHODS

Rats were either sham-operated (two groups) or underwent a two-stage 5/6 nephrectomy (three groups). For the first 4 weeks, all rats were given a high (1.2%) phosphorus (P) diet to stimulate parathyroid gland growth and then were changed to a normal (0.6%) P diet for 2 weeks. At week 7, three of the five groups were given high doses of calcitriol (500 pmol/100 g body weight) intraperitoneally every 24 h during 72 h before sacrifice. The five groups during week 7 were: (i) normal renal function (NRF)+0.6% P diet; (ii) NRF+0.6% P+calcitriol; (iii) renal failure (RF)+0.6% P; (iv) RF+1.2% P+calcitriol; and (v) RF+0.6% P+calcitriol. Parathyroid glands were removed at sacrifice and the TUNEL stain was performed to detect apoptosis.

RESULTS

At sacrifice, the respective serum calcium values in calcitriol-treated groups (groups 2, 4, and 5) were 15.52+/-0.26, 13.41+/-0.39 and 15.12+/-0.32 mg/dl. In group 3, PTH was 178+/-42 pg/ml, but in calcitriol-treated groups, PTH values were suppressed, 8+/-1 (group 2), 12+/-2 (group 4), and 7+/-1 pg/ml (group 5). Despite, the severe hypercalcaemia and marked PTH suppression in calcitriol-treated groups, the percentage of apoptotic cells in the parathyroid glands was very low (range 0.08+/-0.04 to 0.25+/-0.20%) and not different among the five groups.

CONCLUSIONS

We found no evidence in hyperplastic parathyroid glands that apoptosis could be induced in azotaemic rats by the combination of high doses of calcitriol and severe hypercalcaemia despite the marked reduction in PTH levels that was observed.

Control of secondary hyperparathyroidism by vitamin D derivatives

The treatment of the secondary hyperparathyroidism of chronic renal failure patients has greatly improved during the last 2 decades. Significant progress has been made, in particular in the indication of 1alpha-hydroxylated vitamin D derivatives and patient management using these compounds. Treatment and prevention should start early during the development of chronic renal insufficiency. One of the major remaining problems in more advanced stages of renal failure is that control of plasma phosphate often remains extremely difficult. New inert oral phosphate binders are needed. The nephrology community is still waiting for the advent of nonhypercalcemic and nonhyperphosphatemic vitamin D analogs with PTH suppressive activity equal to the parent compound calcitriol or its immediate precursor, alfacalcidol.

Intermittent doxercalciferol (1alpha-hydroxyvitamin D(2)) therapy for secondary hyperparathyroidism

Hypercalcemia and hyperphosphatemia frequently necessitate vitamin D withdrawal in hemodialysis patients with secondary hyperparathyroidism. In short-term trials, doxercalciferol (1alpha-hydroxyvitamin D(2) [1alphaD(2)]) suppressed intact parathyroid hormone (iPTH) effectively with minimal increases in serum calcium and phosphorus (P) levels. This modified, double-blinded, controlled trial examined the efficacy and safety of 1alphaD(2) use in 138 hemodialysis patients with moderate to severe secondary hyperparathyroidism by using novel dose titration; 99 patients completed the study. Hemodialysis patients with secondary hyperparathyroidism were enrolled onto this study, consisting of washout (8 weeks), open-label 1alphaD(2) treatment (16 weeks), and randomized, double-blinded treatment with 1alphaD(2) or placebo (8 weeks). Oral 1alphaD(2) was administered at each hemodialysis session, with doses titrated to achieve target iPTH levels of 150 to 300 pg/mL. Baseline iPTH levels (897 +/- 52 [SE] pg/mL) decreased by 20% +/- 3.4% by week 1 (P: < 0.001) and by 55% +/- 2.9% at week 16; iPTH levels returned to baseline during placebo treatment but remained suppressed with 1alphaD(2) treatment. In 80% of the patients, iPTH level decreased by 70%, reaching the target level in 83% of the patients. Grouping patients by entry iPTH level (<600, 600 to 1,200, and >1,200 pg/mL) showed rapid iPTH suppression in the group with the lowest level; greater doses and longer treatment were required in the group with the highest level. During open-label treatment, serum calcium and P levels were 9.2 +/- 0.84 (SD) to 9.7 +/- 1.05 mg/dL and 5.4 +/- 1.10 to 5.9 +/- 1.55 mg/dL, respectively. During double-blinded treatment, serum calcium levels were slightly greater with 1alphaD(2) than placebo, but P levels did not differ. During double-blinded treatment, 3.26% and 0.46% of serum calcium measurements exceeded 11.2 mg/dL with 1alphaD(2) and placebo, respectively (P: < 0.01); median level was 11.6 mg/dL during hypercalcemia. Intermittent oral 1alphaD(2) therapy effectively suppresses iPTH in hemodialysis patients with secondary hyperparathyroidism, with acceptable mild hypercalcemia and hyperphosphatemia.

[(99m)Tc]-sestamibi parathyroid scintigraphy in chronic haemodialysis patients: static and dynamic explorations

BACKGROUND

The place of parathyroid gland imaging by [(99m)Tc](technetium)-sestamibi scintigraphy in uraemic patients with secondary hyperparathyroidism remains a matter of debate. The purpose of the present study was (i) to assess its value with respect to plasma intact parathyroid hormone (iPTH) levels and to surgical parathyroidectomy (PTx), and (ii) to explore the possibility of suppressing parathyroid [(99m)Tc]-sestamibi uptake by calcitriol.

METHODS

In a first cross-sectional, static study 52 chronic haemodialysis (HD) patients with plasma iPTH levels between 14 and 2791 pg/ml (normal, 10-65 pg/ml) had a [(99m)Tc]-sestamibi scan, and 21 of them underwent surgical PTx. In a second longitudinal, dynamic study 14 chronic HD patients with advanced secondary hyperparathyroidism received short-term calcitriol treatment in an attempt to suppress [(99m)Tc]-sestamibi imaging of parathyroid glands. Calcitriol was given intravenously for 2 weeks, 2 microg after each haemodialysis session. Scintigraphy was carried out before and at the end of this inhibition test.

RESULTS

[(99m)Tc]-Sestamibi scan led to imaging of one or more (maximum three) parathyroid glands in most, but not all, HD patients with plasma iPTH values >600 pg/ml. Based on surgical findings, overall sensitivity of [(99m)Tc]-sestamibi scan in correctly locating parathyroid glands was only 50%, whereas specificity was 100%. In contrast, its sensitivity was 100% in locating single glands in the subgroup of five patients with recurrent hyperparathyroidism. The calcitriol inhibition test showed suppression of [(99m)Tc]-sestamibi uptake by at least one parathyroid gland in eight patients (57%), with complete suppression in five of them (36%). Basal plasma iPTH or decrease of plasma iPTH in response to calcitriol was not predictive of suppressible [(99m)Tc]-sestamibi uptake in the individual case, although mean iPTH was markedly higher in patients with non-suppressible parathyroid glands.

CONCLUSION

Because of its relatively low sensitivity the [(99m)Tc]-sestamibi scan is of limited help in the exploration of uraemic patients with severe secondary hyperparathyroidism before a first surgical PTx. However, it is very useful in locating the remaining parathyroid gland(s) in case of reoperation. The novel calcitriol inhibition test of [(99m)Tc]-sestamibi uptake could help to better distinguish parathyroid glands with non-suppressible, autonomous activity from glands whose activity might be amenable to long-term suppression.

Effect of calcitriol and age on recovery from hypocalcemia in hemodialysis patients

Calcitriol is used to treat hyperparathyroidism in hemodialysis patients. Calcitriol treatment, either through a reduction in parathyroid hormone (PTH) levels or direct effect on bone, decreases the osteoblast and osteoclast surface and bone formation rate. Our study of 13 hemodialysis patients was designed to evaluate whether calcitriol treatment changed the rate of spontaneous recovery from hypocalcemia induced by a low-calcium dialysis. Calcitriol treatment decreased basal PTH levels from 614 +/- 84 to 327 +/- 102 pg/mL (P < 0.001) and maximal PTH levels from 1,282 +/- 157 to 789 +/- 161 pg/mL (P < 0.001), but the rate of serum ionized calcium recovery from hypocalcemia did not change. When the 13 patients were separated based on the median age of 64 years, the predialysis serum ionized calcium level was less in the younger (group I, 44 +/- 6 years; n = 6) than older (group II, 68 +/- 1 years; n = 7) patients (1.05 +/- 0.03 v 1.22 +/- 0.03 mmol/L, respectively; P < 0.01) despite similar basal (group I, 595 +/- 122 pg/mL v group II, 629 +/- 96 pg/mL) and maximal (group I, 1,114 +/- 299 pg/mL v group II, 1,425 +/- 141 pg/mL) PTH levels. Before calcitriol treatment, the rate of serum ionized calcium recovery from induced hypocalcemia was greater (P < 0.05) for similar PTH levels in the older than younger patients. After calcitriol treatment, despite a similar reduction in PTH levels, the rate of calcium recovery increased (P < 0.05) in the younger patients but did not change in the older patients. We also observed that toward the end of the low-calcium hemodialysis, PTH values decreased even though serum ionized calcium level continued to decline when the rate of calcium reduction slowed. In addition, hysteresis, defined as a lower PTH value during the recovery from hypocalcemia than during the induction of hypocalcemia for the same serum calcium concentration, was present during the spontaneous recovery from hypocalcemia. In conclusion, in the hemodialysis patient: (1) age appeared to affect the bone response to PTH and calcitriol treatment, (2) the PTH response to hypocalcemia was affected by a deceleration in the rate of calcium decrease, and (3) hysteresis of the PTH response to hypocalcemia occurred during the spontaneous recovery from hypocalcemia.

Cell biology of parathyroid hyperplasia in uremia

Marked parathyroid hyperplasia of heterogeneous degrees is often seen in chronic dialysis patients with severe secondary hyperparathyroidism. In uremia, parathyroid cell proliferation is initially stimulated by decreased concentration of calcium ions and calcitriol and also by direct effect of phosphate accumulation, leading to diffuse hyperplasia of the parathyroid. Then, small nodules caused by monoclonal cell proliferation form within diffuse hyperplasia, which progress to form nodular hyperplasia. Cells in nodular hyperplasia have a lower density of calcitriol receptor and calcium-sensing receptor than diffuse hyperplasia and are thus more resistant to medical therapy, including calcitriol pulse therapy. One of these nodules may grow more vigorously than the others and may finally occupy a large part of the enlarged gland. Genetic mutations and rearrangements of these cells in nodular hyperplasia remain to be fully elucidated in the near future to establish an effective method for the prevention of parathyroid hyperplasia in uremia.

Long-term effects of small doses of calcitriol in hemodialysis patients with moderate secondary hyperparathyroidism

Prevention of secondary hyperparathyroidism (SHPTH) and treatment of the moderate cases by small p.os doses of Vitamin D has not been thoroughly investigated on the long term, while large doses of Vitamin D have been successful in the short term treatment of this entity. We administered calcitriol p.os 0.5-1.0 microgram, according to iPTH levels, after each dialysis session, in 19 patients (group A) for 36 months. They were ten men and nine women, 63 years old (43-81), with iPTH levels > 4N (419 +/- 185 pg/mL). Seven adenomas were found in five of them (group A1). Serum Ca, phosphate (P) and alkaline phosphatase (AP) were measured every 15-30 days. Serum iPTH and aluminum as well as echogram or scanning of the parathyroid glands were checked every 6 months. Ten additional dialysis patients, seven men and three women, 54.5 years old (36-68), non-significantly different to group A in iPTH levels (290 +/- 225 pg/mL) with three adenomas in two of them (group B1) received no calcitriol and served as controls (group B). Calcitriol treatment significantly lowered serum iPTH levels in group A patients (from 419 +/- 185 to 173 +/- 142 pg/mL, p < 0.0001, delta iPTH: -246 +/- 161 pg/mL); iPTH remained stable in group B patients (delta iPTH: +7.9 +/- 116 pg/mL) with an intergroup significant difference at P < 0.0001. All other parameters measured did not show any significant change. No significant correlation of iPTH to Ca, P or AP was found in A. Initial iPTH levels were higher in A1 and B1 patients and decreased by calcitriol in A1 group. Adenomas in A1 patients did not change in number and size in contrast to B1 where new adenomas appeared (5 patients, 10 glands). Small doses of vitamin D lower high iPTH levels and prevent parathyroid gland hyperplasia. Existing hypertrophy is stabilized under calcitriol treatment both morphologically and biologically.

Relationship between serum phosphorus levels and various outcome measures in adult hemodialysis patients

OBJECTIVE

To compare three different mean serum phosphorus ranges on outcomes related to the control and treatment of hyperparathyroidism (HPTH), to nutritional status, and to quality of life (QOL) in adult hemodialysis (HD) patients.

DESIGN

Patients were grouped based on the mean of five monthly phosphorus levels achieved during the study period. Group 1 included patients whose mean phosphorus levels over the period was <6.0 mg/dL (n = 24); group 2 averaged between 6.0 and 6.9 mg/dL (n = 14); and group 3 averaged >7.0 mg/dL (n = 16). Descriptive comparisons were made between phosphorus groups.

PATIENTS

Fifty-four stable, adult HD patients participated voluntarily.

MAIN OUTCOME MEASURES

Intact-parathyroid hormone (iPTH), calcium x phosphorus product (Ca x P), and change in iPTH, albumin (alb), total protein (tpro), weight (wt) and body mass index (BMI), and scores on a QOL survey. Baseline physical and lab characteristics.

RESULTS

No difference was found between phosphorus levels of <6.0 mg/dL and levels of 6.0 to 6.9 mg/dL in iPTH, Ca x P levels allowing safe calcitriol therapy, nor response to calcitriol treatment. Patients with phosphorus levels >7.0 mg/dL had midstudy iPTH greater than phosphorus levels <6.0 mg/dL. Otherwise the three groups did not differ significantly in iPTH levels. Phosphorus levels 6.0 to 6.9 mg/dL was associated with lowest wt and BMI, but alb and tpro did not differ between the phosphorus groups. Phosphorus levels of >7.0 was associated with highest creatinine levels and youngest age. Subjects in the phosphorus levels of <6.0 mg/dL gp were more likely than the 6.0 to 6.9 mg/dL gp to describe their diet as sufficient and, at baseline, were more likely to relate diet to QOL.

CONCLUSION

Comparison of three levels of serum phosphorus on indicators of outcome in the control and treatment of secondary hyperparathyroidism showed no significant difference in outcome between phosphorus levels of <6.0 mg/dL and phosphorus levels 6.0 to 6.9 mg/dL. However, the data suggests that phosphorus levels of >7.0 mg/dL may relate to significantly higher iPTH and unacceptable Ca x P levels. There were no differences between the groups, suggesting less favorable outcome at any of the three phosphorus levels regarding nutritional status or QOL in this small group of stable, adult HD patients.

A new analog of 1,25-(OH)2D3, 19-NOR-1,25-(OH)2D2, suppresses serum PTH and parathyroid gland growth in uremic rats without elevation of intestinal vitamin D receptor content

We have previously reported that 19-nor-1,25-(OH)2D2, a new analog of 1,25-(OH)2D3, suppresses parathyroid hormone (PTH) secretion in uremic rats in the absence of hypercalcemia or hyperphosphatemia. In the current study, we examined the effect of 19-nor-1,25-(OH)2D2 on parathyroid gland growth and intestinal vitamin D receptor (VDR) content. After induction of uremia by 5/6 nephrectomy, rats were divided into five experimental groups and received intraperitoneal injections of vehicle, 1,25-(OH)2D3 (2 or 6 ng/rat), or 19-nor-1,25-(OH)2D2 (25 or 100 ng/rat) three times a week for 8 weeks. Twelve normal rats received vehicle and served as the normal control group. During the course of the study, rats were maintained on a 1.0% calcium and 0.8% phosphorus diet. The higher dose of 1,25-(OH)2D3, 6 ng, significantly decreased PTH from 52.7 +/- 10.2 pg/mL in the uremic control group to 25.7 +/- 6.7 pg/mL (P < 0.01). This dose of 1,25-(OH)2D3, however, increased serum levels of both ionized calcium (4.71 +/- 0.05 to 4.85 +/- 0.06 mg/dL; P < 0.05) and phosphorus (4.34 +/- 0.30 to 6.67 +/- 0.63 mg/dL; P < 0.01). Both doses of 19-nor-1,25-(OH)2D2 decreased serum PTH as effectively as 1,25-(OH)2D3 without changes in serum calcium or phosphorus. The 100-ng dose of 19-nor-1,25-(OH)2D2 decreased PTH to 20.7 +/- 3.1 pg/mL (P < 0.01) and suppressed parathyroid gland growth by more than 50%. Both doses of 19-nor-1,25-(OH)2D2 also decreased endogenous 1,25-(OH)2D3 levels compared with uremic control rats (25 ng:30.4 +/- 2.0, P < 0.05, and 100 ng:27.9 +/- 3.2, P < 0.01, v 48.4 +/- 6.6 pg/mL). The 6-ng dose of 1,25-(OH)2D3 elevated intestinal VDR content (138.5 +/- 20.0 fmol/mg protein) compared with animals receiving both doses of 19-nor-1,25-(OH)2D2 (25 ng:84.0 +/- 11.9, P < 0.05, and 100 ng:78.4 +/- 10.9, P < 0.01). This was probably attributable to the marked decrease in endogenous 1,25-(OH)2D3 levels caused by both doses of 19-nor-1,25-(OH)2D2 because intestinal VDR correlated directly with serum 1,25-(OH)2D3 (r = 0.963; P = 0.008). Thus, 19-nor-1,25-(OH)2D2 appears to exert a selective action on the parathyroid glands compared with the intestine. Its low calcemic and phosphatemic properties may result from the decreased endogenous 1,25-(OH)2D3 levels that lead to a reduction in intestinal VDR. This selectivity makes this analog ideal for the treatment of secondary hyperparathyroidism.

Are we mismanaging calcium and phosphate metabolism in renal failure?

Secondary hyperparathyroidism and renal osteodystrophy are the consequences of abnormal calcium, phosphate, and calcitriol metabolism ensuing from renal failure. Evidence suggests that calcium balance tends to become negative as we grow older than 35 years of age; however, the current dialysis modalities provide patients regardless of age with excessive calcium during dialysis. Administration of calcitriol in the management of hyperparathyroidism further increases the calcium and phosphate absorption. Furthermore, the current thrice-weekly renal replacement therapies fail to remove the daily absorbed phosphate, and we have to use calcium carbonate as a primary phosphate-binding agent to reduce intestinal phosphate absorption. The large calcium mass transfer and phosphate retention could lead to soft tissue calcification, especially in older end-stage renal disease (ESRD) patients. Consequently, only by maintaining a negative calcium balance during renal replacement therapy can we safely use calcitriol and calcium carbonate for the management of secondary hyperparathyroidism. Recent studies have indicated that phosphate restriction alone independent of plasma calcitriol or calcium can lower plasma parathyroid hormone (PTH) in renal failure and prevent hyperplasia of parathyroid glands. Therefore, phosphate control perhaps is the most important means to prevent secondary hyperparathyroidism. Previous studies have shown that ferric compounds are potent phosphate-binding agents; hence, these compounds warrant further trial in the management of phosphate metabolism in renal failure.

US imaging and color Doppler in patients undergoing inhibitory therapy with calcitriol for secondary hyperparathyroidism

The aim of this study was to evaluate the changes in volume, structure, and flow pattern of parathyroid glands in uremic patients with secondary hyperparathyroidism treated with long-term intravenous calcitriol (CTL) therapy. Ultrasonography was used to follow-up volume changes occurring in 18 enlarged glands in 11 patients during an 18-month period; in 6 of these cases, 11 glands were followed-up also with color-Doppler to monitor variations in flow pattern. Vascularization was classified using three grades: grade 0 = no color signal; grade I = vessels covering less than 50 % of glandular cross-sectional area; grade II = vascular signals covering more than 50 % of glandular cross-sectional area. No significant changes in volume were demonstrated during the 18 months of follow-up. On the contrary, significant decrease in flow was observed with almost complete disappearance of color-Doppler signals. This finding related well with the observed decrease in parathormone blood levels. Lack of volume changes during medical therapy demonstrates the inability of US alone to monitor the effect of this treatment on the parathyroid glands. Conversely, the observed intraglandular flow reduction indicates the possibility to use color Doppler to monitor the effects of CLT in uremic hemodialyzed patients with secondary hyperparathyroidism. This imaging procedure can be proposed for follow-up of the response of the parathyroid glands to therapy.

Effective suppression of parathyroid hormone by 1 alpha-hydroxy-vitamin D2 in hemodialysis patients with moderate to severe secondary hyperparathyroidism

Calcitriol, as used for treating secondary hyperparathyroidism, has a low therapeutic index. The safety and efficacy of the vitamin D analog, 1 alpha (OH)-vitamin D2, (1 alpha D2), which has less toxicity in animals than 1 alpha (OH)-vitamin D3, was tested in a multicenter study of 24 hemodialysis patients with secondary hyperparathyroidism [serum intact (i) PTH > 400 pg/ml]. Calcium-based phosphate binders alone were used to maintain serum phosphorus < or = 6.9 mg/dl. After eight weeks without calcitriol (washout), oral 1 alpha D2, 4 micrograms/day or 4 micrograms thrice weekly, was started, with the dose adjusted over 12 weeks to maintain serum iPTH between 130 and 250 pg/ml. Pre-treatment serum iPTH fell from 672 +/- 70 pg/ml (SEM) to 289 +/- 36 after treatment (P < 0.05). The maximal decrease in serum iPTH was 48 to 96%, with 87.5% of patients reaching target iPTH levels. The final dose of 1 alpha D2 average 14.2 micrograms/week. Pre-treatment serum calcium rose modestly from 8.8 +/- 0.2 mg/dl to 9.5 +/0 0.2 after treatment (P < 0.001). Only once did modest hypercalcemia (serum Ca > 11.2 mg/dl) necessitate stopping treatment. Neither the average serum P level, the incidence of hyperphosphatemia, nor the dose of phosphate binders changed from washout to treatment. Thus, oral 1 alpha D2 is highly efficacious in suppressing secondary hyperparathyroidism in hemodialysis patients and is safe despite exclusive use of calcium-based phosphate-binders. Future studies should clarify the optimal dosage regimen.

Benefits of calcitriol therapy and serum phosphorus control in dogs and cats with chronic renal failure. Both are essential to prevent of suppress toxic hyperparathyroidism

Daily oral calcitriol at low doses is safe and effective in the control of renal secondary hyperparathyroidism in dogs and cats. Low doses of calcitriol are most effective when started early in uremia before the advanced stages of renal secondary hyperparathyroidism. At early stages calcitriol both diminishes PTH synthesis in the parathyroid cells present and prevents the hyperplasia that, if unchecked, results in the most extensive an difficult-to-control hyperparathyroidism. The salutary effects on the dog's or cat's sense of well being, appetite, activity, strength, and lifespan as reported by the veterinarians of our survey are attributed primarily to keeping PTH levels below a toxic threshold. Additionally, some of the benefits achieved by calcitriol are likely a direct consequence of calcitriol interacting with the vitamin D receptor in a wide variety of tissues throughout the body. Phosphorus restriction through a combination of diet and intestinal phosphate binders is important to allow calcitriol therapy to successfully lower PTH levels, but it likely has no direct effects that are independent of interactions involving calcitriol. Phosphorus restriction is also important to minimize chances for adverse tissue mineralization. Calcitriol therapy can be considered for treatment of chronic renal failure after serum phosphorus has been decreased to less than 6.0 mg/dL in patients in whom it was initially elevated. Calcitriol supplementation to dogs and cats with chronic renal failure makes good endocrinologic sense. Calcitriol deficits cause increased PTH and, as these two hormones are designed to maintain calcium and phosphorus homeostasis, the PTH increase is initially adaptive. One of the important effects of PTH is to stimulate additional calcitriol formation as a powerful means to raise blood calcium through increased calcium absorption from the diet. With too great an increase in PTH, however, its effects become harmful to many tissues due to the widespread distribution of the PTH receptor in many cell types that are likely normally responsive only to the paracrine PTH-related peptide that shares the PTH receptor. Exogenous supplemental calcitriol administration allows concentrations of calcitriol in the bloodstream to remain normal without the toxic consequences of excessive PTH secretion that would otherwise be provoked. Studies involving young dogs with subtotal nephrectomy may not parallel those on older dogs and cats with spontaneous chronic renal failure. In particular, higher doses are needed to effect PTH change in these young dogs than we have found necessary for older dogs and cats. Because survey participants agreed most strongly with the idea that their calcitriol-treated dogs and cats were living longer than comparably uremic animals they had treated previously, further studies to evaluate the ability of calcitriol to retard the progression of renal lesions and loss of excretory renal function seem warranted. Additional studies to document the beneficial effects of calcitriol on the many organs adversely affected by excess PTH during uremia are also needed because findings thoroughly documented and proven in humans and rats may not always extrapolate to dogs and cats.

1,25-dihydroxyvitamin D3 and 22-oxacalcitriol prevent the decrease in vitamin D receptor content in the parathyroid glands of uremic rats

Decreased content of the 1,25-dihydroxyvitamin D3 receptor (VDR) in parathyroid glands from patients and animals with chronic renal failure has been implicated in the pathogenesis of secondary hyperparathyroidism. In these studies, we examined the regulation of VDR by 1,25-dihydroxyvitamin D3 (1,25-D3) and 22-oxacalcitriol (OCT) in parathyroid glands of uremic rats. After eight weeks of renal failure, VDR content in parathyroid glands of uremic rats was decreased (400 +/- 42 vs. 729 +/- 47 fmol/mg protein in normal control rats, P < 0.05) and strongly correlated with serum 1,25-D3 levels (r = 0.829, P = 0.0001). Treatment with either 1,25-D3 or OCT prevented the decrease in VDR. We conclude that low serum 1,25-D3 levels, at least in part, account for the decrease in VDR content in parathyroid glands of uremic rats and that treatment with 1,25-D3 or OCT prevents this decrease ameliorating the development of secondary hyperparathyroidism.

Calcitriol administration in end-stage renal disease: intravenous or oral?

1,25-Dihydroxyvitamin D deficiency plays an important role in the pathogenesis of secondary hyperparathyroidism, and adequate replacement of this hormone is considered essential to normalize parathyroid gland function and restore bone homeostasis in patients with advanced renal failure. Although initial uncontrolled clinical trials suggested the superiority of intravenous calcitriol treatment, more recent controlled investigations show that different routes (oral versus intravenous), frequency (daily versus intermittent), and dosing (physiological versus pharmacological) of calcitriol administration are clinically equivalent. Overall, the response to calcitriol treatment depends more on the severity of secondary hyperparathyroidism and the presence of confounding variables, such as hyperphosphatemia and acquired abnormalities of parathyroid cell function, than the method of calcitriol administration.

The renal bone diseases in children treated with dialysis

Renal osteodystrophy represents a spectrum from high- to low-turnover bone lesions. The specific pattern, however, may change during selected therapeutic interventions. As in the past, osteitis fibrosa remains the most frequent histologic lesion in pediatric patients on dialysis, although recently the prevalence of low-turnover bone lesions without aluminum toxicity has been increasing in the pediatric population. This may be a consequence of aggressive calcitriol and calcium therapy. The different factors involved in the development of secondary hyperparathyroidism include hyperphosphatemia, hypocalcemia, altered vitamin D synthesis, impairments in parathyroid hormone (PTH) secretion and metabolism, and, recently, possible downregulation of renal PTH/PTH-rP messenger RNA receptor. New developments in molecular biology have demonstrated the relationship between vitamin D and PTH. The use of high-dose pulse intravenous, intraperitoneal, and oral calcitriol therapy has significantly decreased serum PTH levels and retarded the progression of osteitis fibrosa. These therapeutic interventions, however, may have led to the development of adynamic bone lesions. The impact of adynamic bone lesions in the young and growing skeleton remains to be determined.

The importance of dosing intravenous calcitriol in dialysis patients with severe hyperparathyroidism

The current study evaluates the use of intravenous (IV) calcitriol in 10 patients with severe hyperparathyroidism (HPTH). Patients with parathyroid hormone (PTH) > 1,200 pg/m and serum P < 6.5 mg/dL were studied. Ten patients with a mean PTH of 1,826 +/- 146 pg/mL were treated for a mean of 48 weeks with a dose of IV calcitriol commensurate to the level of PTH. The initial calcitriol dose had to be increased in seven patients. The mean maximum dose of calcitriol was 3.8 micrograms thrice weekly. There was a dramatic decrease in PTH levels, and by the end of the study it was 211 +/- 48 pg/mL. Alkaline phosphatase decreased from 582 +/- 3 to 120 +/- 12 IU/L. Serum Ca and P remained unchanged in most patients. There were three episodes of hyperphosphatemia in one patient, and another had a hypercalcemic episode. In conclusion, patients with severe HPTH respond very well to IV calcitriol, provided that dosing of calcitriol is commensurate to PTH levels, and hyperphosphatemia is kept under control.

A new analog of calcitriol, 19-nor-1,25-(OH)2D2, suppresses parathyroid hormone secretion in uremic rats in the absence of hypercalcemia

The active metabolite of vitamin D, calcitriol (1 alpha,25-(OH)2D3), suppresses parathyroid hormone (PTH) gene transcription. Although 1 alpha,25-(OH)2D3 is effective in suppressing secondary hyperparathyroidism (SH) in uremic patients, the mandatory use of large amounts of calcium salts to control serum phosphorus may preclude, in some patients, the use of ideal therapeutic doses of 1 alpha,25-(OH)2D3 because of hypercalcemia. We have studied a new analog of calcitriol, 19-nor-1 alpha,25-(OH)2D2, that possesses low calcemic and phosphatemic activity. Uremic rats received vehicle, 1 alpha,25-(OH)2D3 (2.0, 4.0, or 8.0 ng/rat) or 19-nor-1,25-(OH)2D2 (8.0, 25 or 75 ng/rat) intraperitoneally (IP) every other day for a period of 8 days. Pretreatment and posttreatment values of intact PTH were measured. The normal values for rat intact-PTH were 22 +/- 4.2 pg/mL and for ionized calcium (ICa) 4.77 +/- .07 mg/dL. The only dose of 1 alpha,25-(OH)2D3 that achieved a significantly, suppressed PTH (P < 0.01) was the 8.0 ng/rat. PTH decreased from 202 +/- 31 to 90 +/- 20 pg/mL. However, ICa increased from 4.81 +/- 0.08 to 5.08 mg/dL from uremic control (P < 0.02). Conversely, all doses of 19-nor-1,25-(OH)2D2 were effective in suppressing PTH, and none produced an elevation in ICa that was significantly different from that of vehicle-treated uremic rats. The maximum effect was achieved with the 75 ng/rat dose, which decreased PTH from 193 +/- 49 to 53 +/- 16 pg/mL (a decrease in 72.5%).(ABSTRACT TRUNCATED AT 250 WORDS)