Beneficial effects of calcimimetics on progression of renal failure and cardiovascular risk factors

In renal failure, parathyroid hormone (PTH) is not only involved in the genesis of disturbed calcium/phosphate metabolism and ostitis fibrosa; it is also a permissive factor in the genesis of hypertension, cardiovascular damage, and dyslipidemia. The allosteric activator of the calcium sensing receptor NPSR-568 (R-568) has been shown to reduce the serum intact PTH (iPTH) concentration in uremic rats. It was the purpose of this study in subtotally nephrectomized (SNX) rats to compare pharmacologic abrogation of secondary hyperparathyroidism by R-568 with parathyroidectomy (PTX). The effects on progression of renal failure, BP, and lipid and structural parameters of kidney and heart were studied. Four groups of male SD-rats were studied: (1) sham-operated + vehicle-treated rats (controls); (2) SNX + vehicle-treated rats (SNX); (3) parathyroidectomized SNX + vehicle-treated rats (SNX+PTX); and (4) SNX + calcimimetic R-568-treated rats (SNX+R-568). R-568 (50 micro mol/kg per d) was administered by gavage. Eight weeks after SNX, serum creatinine concentration, urinary albumin excretion, BP, and serum LDL-cholesterol concentration were significantly lower in both R-568-treated and parathyroidectomized SNX compared with vehicle-treated SNX. In addition, structural abnormalities of the kidney (glomerulosclerosis, tubulointerstitial changes) and the heart (interstitial fibrosis, capillary length density, arteriolar wall thickness) were significantly less pronounced than in vehicle-treated SNX. It is concluded that in experimental renal failure abrogation of hyperparathyroidism by administration of a calcimimetic or PTX similarly attenuates progression of renal failure. Furthermore, it interferes with the development of cardiovascular risk factors and cardiac remodeling.     

Effect of antioxidant therapy with dl-alpha-tocopherol on cardiovascular structure in experimental renal failure

BACKGROUND: Chronic renal failure is characterized by remodeling of the structure of the heart and the vasculature, for example, left ventricular hypertrophy, myocardial fibrosis, capillary/myocyte mismatch, as well as thickening of intramyocardial arteries and of peripheral arteries and veins. Furthermore, uremia is a state of increased oxygen stress. It was the purpose of this study to examine whether these findings are interrelated. METHODS: To investigate whether antioxidative therapy with dl-alpha-tocopherol (Toco; vitamin E) interferes with the development of abnormal cardiovascular structure in experimental renal failure, 28 male Sprague-Dawley rats were subjected to partial renal ablation (subtotal nephrectomy, SNX) or to sham operation (sham). SNX were either left untreated or received the antioxidant Toco (2 x 1500 IE/kg BW/week in the pellets). Blood pressure was measured using tail plethysmography. The experiment was terminated after 12 weeks. Heart and left ventricular weight were determined and the following parameters were measured using morphometry and stereology: volume densities of cardiomyocytes, capillaries and non-vascular interstitium; length density and total length of cardiac capillaries, wall thickness of intramyocardial arterioles and of the aorta. RESULTS: Systolic blood pressure and body weight were comparable in all groups. Treatment with Toco led to significantly increased plasma concentrations of Toco. Left ventricular weight and wall thickness of intramyocardial arteries were significantly higher in both SNX groups compared to sham controls. Volume density of the cardiac interstitial tissue was significantly higher in untreated SNX than in Toco treated SNX and sham control rats. Length density of capillaries was significantly lower in untreated SNX than in control rats; however, the values were significantly higher, and even higher than in sham controls, when SNX were treated with Toco. CONCLUSIONS: Treatment with the antioxidant dl-alpha-tocopherol prevented cardiomyocyte/capillary mismatch, and to some extent also myocardial fibrosis in rats with renal failure. The results point to a role of oxidative stress in the genesis of myocardial interstitial fibrosis and capillary deficit of the heart.     

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilage growth plate of uraemic rats

PTH/PTHrP receptor mRNA is down-regulated in epiphyseal cartilagegrowth plate of uraemic rats. Growth retardation, hypocalcaemia,hyperphosphataemia, and skeletal resistance to the action ofPTH are well known features of advanced chronic renal failure(CRF). It has been suggested that the downregulation of renaland skeletal PTH receptors (PTH/PTHrP-R) could play an importantrole in the occurrence of these abnormalities. In the presentstudy, four uraemic (4 weeks after 5/6 nephrectomy) and fourcontrol (sham-operated) rats were analysed for PTH/PTHrP-R mRNAexpression at the proximal femoral and tibial growth platesby in situ hybridization. Uraemic rats had plasma biochemicalabnormalities of advanced CRF including high creatinine, phosphate,and PTH, and low calcium and calcitriol levels. The femoraland tibial bones of uraemic animals were shorter in length thanthose of control rats, and had reduced width and cellularityof the epiphyseal cartilage growth plate. Mean (±SD)tibia growth plate width was 152±30 µm in uraemicrats, compared with 170±35 µm in control rats.The difference was mostly due to a marked reduction of the zoneexpressing PTH/PTHrP-R (mature chondrocytes) which was 30±5µm in tibias from uraemic versus 44±10 µmin tibias from control rats. The hybridization signals of PTH/PTHrP-Rper individual cell were quantified on dark field images usinga computer-assisted image analysis system. The number of grainsin PTH/PTHrP-R positive cells was also decreased in uraemicrats, 103±13 compared with 123±14 arbitrary units(dark pixel density)/cell in control rats (P 0.005). In conclusion,these data indicate that rats with severe CRF and secondaryhyperparathyroidism have reduced epiphyseal cartil age PTH/PTHrP-RmRNA expression. This alteration may be relevant in the pathogenesisof growth retardation in uraemia.     

Influence of specific and non-specific endothelin receptor antagonists on renal morphology in rats with surgical renal ablation

BACKGROUND.: Studies in experimental models of chronic renal failure suggestan important role for the endothelin system in the developmentof renal scarring. Endothelin receptor (ETR) anatagonists interferewith progression, but it has not been resolved (i) whether thisis true for all models of renal damage, (ii) to what extentthe effect is modulated by systemic blood pressure and (iii)whether the effect is similar for ET_AR and ET_A/ET_BR antagonists. STUDY DESIGN.: 5/6 subtotal nephrectomy (SNX) by surgical ablation in maleSprague—Dawley rats. Comparison of ACE inhibitor Trandolapril(0.1 mg/kg/day), ET_AR antagonist BMS 182874 (30 mg/kg/day) andET_AR/ET_BR antagonist Ro 46-2005 (30 mg/kg/day) by gavage. Durationof the experiment eight weeks. METHODS.: Systolic blood pressure by tail plethysmography. Perfusion fixationof kidneys and morphometric analysis ET-1 and ET_A/ET_BR by quantitativePCR. RESULTS.: SNX caused a significant (P<0.01) increase of systolic bloodpressure (170±8.6 mmHg) compared to sham operated controls(131±5.3 mmHg). Blood pressure was significantly (P<0.001)lower with Trandolapril (128±5.3 mmHg), but not withBMS 182874 (153±5.9 mmHg) or Ro 46-2005 (167±7.6mmHg). Compared to sham operated rats (0.03±0.01) glomerulosclerosisindex (GSI) was significantly (P<0.01) higher in the untreatedSNX group (0.9±0.15). Significantly lower GSI was foundin Trandolapril treated (0.29±0.04), BMS 182874 treated(0.36±0.05), and Ro 46-2005 treated animals (0.45±0.11).The effect of BMS 182874 was accompanied by lower tubulointerstitialdamage index. Mean glomerular volume was dramatically increased(P<0.001) in SNX rats as compared to sham operated animals.This glomerular enlargement was partially prevented by Trandolapril(P<0.05), but not by either ETR antagonist. ET-1 mRNA tendedto be higher in SNX irrespective of treatment, while ET_AR andET_BR mRNA were significantly lower. CONCLUSION.: Both specific (ET_AR) and non-specific (ET_A/ET_BR) endothelinantagonists interfere with development of glomeruloscierosisby mechanisms which are, at least in part, independent of systemicblood pressure.     

Abnormal calcaemic response to PTH in the uraemic rat without secondary hyperparathyroidism

BACKGROUND: Skeletal resistance to the calcaemic action of parathyroid hormone(PTH) is an important pathogenic factor in the development ofsecondary hyperparathyroidism. Since parathyroidectomy normalizesthe calcaemic response to PTH in uraemic animals, the increasein PTH levels has been advanced as a cause of skeletal resistanceto the calcaemic action of PTH. This study was designed to evaluatein uraemic rats the effect of normal PTH levels on the calcaemicresponse to PTH. METHODS: To maintain normal PTH levels, rats were parathyroidectomized(PTX) and rat 1–34 PTH was infused at a rate of 0.022µg/100 g per hour via a subcutaneously implanted miniosmoticpump; this rate of infusion was considered to be the normalPTH replacement dose since it normalized serum calcium and phosphorusin PTX rats with normal renal function. Two separate studieswere performed. In the first study, rats were maintained ona moderate-phosphorus (0.6%) diet and rats were divided intofour groups: (I) normal; (II) uraemic; (III) PTX with normalPTH replacement; and (IV) uraemic with PTX and normal PTH replacement.In a second study, the groups were the same except that a high-phosphorus(1.2%) diet was given to increase the magnitude of hyperparathyroidismin rats with intact parathyroid glands; an additional group(V) identical to group IV except that rats received daily calcitriolwas included. After 14 days, rats received a 48-h infusion ofhigh-dose rat 1–34 PTH (0.11 µg/100 g per hour)to evaluate the calcaemic response to PTH. RESULTS: The calcaemic response to PTH was similar in normal rats andPTX rats with PTH replacement on both a moderate and high-phosphorusdiet. In uraemic rats, the calcaemic response to PTH was decreasedand the maintenance of normal PTH levels by PTH replacementdid not correct the decreased calcaemic response to PTH; moreover,calcitriol supplementation did not improve the calcaemic responseto PTH. Finally, hypocalcaemia was observed in uraemic ratswith PTH replacement and was more profound than in rats on ahigh-phosphorus diet. CONCLUSIONS: This study demonstrates that the maintenance of a normal PTHlevel in uraemic rats did not correct the impaired calcaemicresponse to PTH, suggesting that factors intrinsic to uraemia,independent of phosphorus, calcitriol, and PTH participate inthe decreased calcaemic response to PTH in uraemia.     

Restoration of Bone Mineralization by Cinacalcet is Associated with a Significant Reduction in Calcitriol-Induced Vascular Calcification in Uremic Rats

The present study investigated to what extent normalization of bone turnover goes along with a reduction of high-dose calcitriol-induced vascular calcifications in uremic rats. Five groups of male Sprague–Dawley rats were studied: sham-operated controls (n?=?7), subtotally nephrectomized (SNX) uremic (CRF) animals (n?=?12), CRF?+?calcitriol (vitD) (0.25?μg/kg/day) (n?=?12), CRF?+?vitD?+?cinacalcet (CIN) (10?mg/kg/day) (n?=?12), and CRF?+?vitD?+?parathyroidectomy (PTX) (n?=?12). Treatment started 2?weeks after SNX and continued for the next 14?weeks. High-dose calcitriol treatment in hyperparathyroid rats went along with the development of distinct vascular calcification, which was significantly reduced by >50?%, in both CIN-treated and PTX animals. Compared to control animals and those of the CRF group, calcitriol treatment either in combination with CIN or PTX or not was associated with a significant increase in bone area comprising ±50?% of the total tissue area. However, whereas excessive woven bone accompanied by a dramatically increased osteoid width/area was seen in the CRF?+?vitD group, CIN treatment and PTX resulted in significantly reduced serum PTH level, which was accompanied by a distinct reduction of both the bone formation rate and the amount of osteoid. These data indicate that less efficient calcium and phosphorus incorporation in bone inherent to the severe hyperparathyroidism in vitamin D-treated uremic rats goes along with excessive vascular calcification, a process which is partially reversed by CIN treatment in combination with a more efficacious bone mineralization, thus restricting the availability of calcium and phosphate for being deposited in the vessel wall.     

Effects of ACE inhibition and bradykinin antagonism on cardiovascular changes in uremic rats

BACKGROUND: Cardiovascular death continues to be a major problem in renal failure. Structural abnormalities of the heart and the vasculature contribute to the increased cardiovascular risk. They are ameliorated by angiotensin-converting enzyme (ACE) inhibitors, but because of the nonspecifity of ACE inhibition, it is uncertain whether the beneficial effect is mediated by interfering with angiotensin II (Ang II) or by modulating other effector systems, for example, bradykinin. METHODS: To assess a potential role of bradykinin, subtotally nephrectomized Sprague-Dawley rats (SNX) received either the ACE inhibitor Ramipril (Rami, 0.2 mg/kg body weight p.o.), the specific B2 bradykinin receptor antagonist Hoe140 (0.2 mg/kg body weight, s.c.), or a combination of both, and were compared to sham-operated controls. To separately assess the effect of Ramipril on development and reversal of structural abnormalities, animals were either treated from the third day after SNX or from the fourth week after SNX onward (0.01 mg/kg body weight, p.o.). RESULTS: Heart and aorta were evaluated by morphometric and stereologic techniques. The weight of the perfused left ventricle, as an index of cardiac hypertrophy, was significantly higher in untreated SNX. While it was significantly lower in animals with early and late Ramipril treatment, the beneficial effect was completely antagonized by Hoe140. The wall-to-lumen ratio of intramyocardial arterioles was significantly higher in untreated SNX compared with controls, but failed to be modified by administration of either Ramipril or Hoe140. In the heart, the intercapillary distance was significantly higher in SNX, but it was not lowered by either early or late Ramipril or Hoe140 treatment. Treatment of SNX with Hoe140 alone, however, resulted in a marked further increase in intercapillary distance. The wall thickness of the aorta was significantly higher in SNX than in controls; early and late Ramipril treatment prevented such increase, and this effect was antagonized by Hoe140. CONCLUSION: These findings illustrate that bradykinin plays an important role for the beneficial effect of Ramipril in preventing (and potentially reversing) abnormal cardiovascular structure in uremic hypertensive rats.     

Hyperphosphatemia aggravates cardiac fibrosis and microvascular disease in experimental uremia

BACKGROUND: Hyperphosphatemia is a known predictor of cardiovascular death and specifically of cardiac death in hemodialysis patients. The pathomechanisms involved have not been completely clarified. While a number of observations suggest an important role of hyperphosphatemia and positive calcium balance on atherosclerosis and calcification of the coronary conduit arteries, independent effects on postcoronary microvessels and on cardiac fibrosis have not been excluded. METHODS: Male Sprague-Dawley rats were sham operated (N = 14) or subtotally nephrectomized (SNX, N = 17) and subsequently placed on low phosphorus (0.08% w/w) and high phosphorus (1.2% w/w) diet under pair-feeding conditions. After 8 weeks, serum chemistry and inhibitory parathyroid hormone (iPTH) were measured, and the hearts were harvested using perfusion fixation. Arteriolar thickness and volume density of the interstitium (excluding vessels) were quantitated using stereologic techniques. RESULTS: In SNX animals with moderate renal failure serum phosphorus concentrations were higher than in sham-operated controls on low phosphorus diet (1.7 +/- 0.37 mmol/L) and were significantly higher in SNX + high phosphorus diet (2.33 +/- 0.23 mmol/L) compared to SNX + low phosphorus diet (1.95 +/- 0.32 mmol/L; P < 0.05). In sham-operated controls, dietary phosphorus content had no effect on cardiac morphologic indices. In contrast, in SNX + high phosphorus diet the index of interstitial cardiac fibrosis was significantly higher (3.22 +/- 0.44%) than in SNX + low phosphorus (2.75 +/- 0.46%) or in sham-operated controls (2.5 +/- 0.05% on high phosphorus and 2.4 +/- 0.89 on low phosphorus, respectively). In SNX + high phosphorus (14.0 +/- 9.0 microm), but not in SNX + low phosphorus (9.2 +/- 4.5 microm), arterial wall thickness was significantly higher compared to sham-operated controls (10.2 +/- 5.1 on high phosphorus and 9.8 +/- 5.0 micro;m on low phosphorus, respectively). The data were confirmed in an independent repeat experiment. CONCLUSION: High dietary phosphorus and hyperphosphatemia have significant effects on cardiac fibrosis and arterial wall thickening. Such abnormalities of cardiac architecture may be relevant for the increased cardiac risk in hyperphosphatemic uremic patients.     

Differential effects of intermittent PTH(1-34) and PTH(7-34) on bone microarchitecture and aortic calcification in experimental renal failure

PTH(1-84) and PTH(7-84) are elevated in chronic kidney disease (CKD). These peptides, as their shorter analogs PTH(1-34) and PTH(7-34) both promote PTH receptor (PTH1R) internalization but only PTH(1-34) and PTH(1-84) activate the receptor. Here, we examined the effects of intermittent administration of PTH(1-34) and PTH(7-34) on mineral ion metabolism, bone architecture, and vascular calcification in rats with experimental CKD. CKD with or without parathyroidectomy (PTX) was established by 5/6 nephrectomy (NPX) in rats. Animals were divided into 4 groups: Sham PTX+ sham NPX (Sham); PTX+ sham NPX (PTX); Sham PTX+NPX (NPX); PTX+NPX (PTX/NPX). Rats were treated with single daily doses of 40 microg/kg PTH(1-34), PTH(7-34), or vehicle. Creatinine was higher in NPX and Ca lower in PTX and PTX/NPX groups than in Sham or NPX rats. Plasma phosphate was higher in PTX, NPX and PTX/NPX than in Sham rats. PTH(1-34) was more hypercalcemic than PTH(7-34) in PTX rats. Fractional bone volume in rats treated with PTH(1-34) increased significantly in all groups compared to that of vehicle treatment. In addition, trabecular number, thickness and volumetric bone density increased in rats treated with PTH(1-34). In contrast, PTH(1-34) diminished vascular calcification. Bone and renal PTH1R mRNA expression was reduced as much or more in PTX/NPX rats as in NPX alone, whereas PTH(7-34) had no effect on PTH1R expression. Renal but not bone PTH1R mRNA increased in response to PTH(1-34). These findings suggest that PTH(1-34) exerts greater hypercalcemic and anabolic effects in parathyroidectomized and/or nephrectomized rats than does PTH(7-34). There was no evidence for significant bone or vascular actions of PTH(7-34). We conclude that PTH(1-34) protects against vascular calcification and bone demineralization in experimental renal failure.     

Effect of aluminium on the development of hyperparathyroidism and bone disease in the azotaemic rat

Aluminium toxicity in dialysis patients is associated with arelative parathyroid hormone (PTH) deficiency as well as osteomalacia.In-vitro studies of parathyroid cells have shown that aluminiuminhibits PTH secretion. However, only limited data are availableon how aluminium affects the development of hyperparathyroidismin the azotaemic animal. Four groups of azotaemic rats werestudied; in each group, renal failure was induced by a two-stage5/6 nephrectomy, after which rats were studied for 40 days.In three groups hyperparathyroidism was stimulated by the useof a high phosphorus (1.2%) diet (HPD). The four groups were(1) HPD; (2) HPD+high-dose aluminium (HDAL)—1.5 mg ofaluminium was adminis tered intraperitoneally (IP) 5 days perweek; (3) HPD+low-dose aluminium (LDAL)—0.5 mg of aluminiumwas administered IP 5 days per week; and (4) moderate phosphorus(0.6%) diet (MPD); the MPD group was used to control hyperparathyroidismand thus provide a comparison of PTH levels and azota emic bonedisease. After 40 days, the serum PTH level was higher (P<0.05)in the HPD+HDAL group (37±2pmol/l) than the HPD, HPD+LDAL,and MPD groups (24±3, 28±4, and 6±1 pmol/lrespect ively). The correlation between serum PTH and calcium,serum PTH and phosphorus, and serum calcium and phosphorus wassignificant for the four groups (P<0.02); however, the relationshipbetween serum PTH and calcium, and between serum calcium andphosphorus was altered in the HPD+HDAL group (serum aluminium30.8±2µmol/l). Aluminium administration induceda decrease (P<0.05) in the bone formation rate and the adjustedapposition rate, and an increase (P<0.05) in osteoid volumeand the min eralization lag time. Despite aluminium administration,diet-induced hyperparathyroidism resulted in an increase (P<0.05)in the osteoblast surface. In conclusion, in the azotaemic rat(1) aluminium did not slow the development nor decrease themagnitude of hyper parathyroidism; (2) aluminium appeared toalter the relationship between serum PTH and calcium, and betweenserum calcium and phosphorus; (3) hyperpara thyroidism changedthe expression of aluminium-induced bone disease and may affordthe bone some protection against the toxic effects of aluminium.     

Chronic effect of parathyroid hormone on NHE3 expression in rat renal proximal tubules

BACKGROUND: The most abundant Na+/H+ exchanger in the apical membrane of proximal tubules is the type 3 isoform (NHE3), and its activity is acutely inhibited by parathyroid hormone (PTH). In the present study, we investigate whether changes in protein abundance as well as in mRNA levels play a significant role in the long-term modulation of NHE3 by PTH. METHODS: Three groups of animals were compared: (1) HP: animals submitted to hyperparathyroidism by subcutaneous implantation of PTH pellets, providing threefold basal levels of this hormone (2.1 U. h-1); (2) control: sham-operated rats in which placebo pellets were implanted; (3) PTX: animals submitted to hypoparathyroidism by thyroparathyroidectomy followed by subcutaneous implantation of thyroxin pellets, which provided basal levels of thyroid hormone. After eight days, we measured bicarbonate reabsorption in renal proximal tubules by in vivo microperfusion. NHE3 activity was also measured in brush border membrane (BBM) vesicles by proton dependent uptake of 22Na. NHE3 expression was evaluated by Northern blot, Western blot and immunohistochemistry. RESULTS: Bicarbonate reabsorption in renal proximal tubules was significantly decreased in HP rats. Na+/H+ exchange activity in isolated BBM vesicles was 6400 +/- 840, 9225 +/- 505, and 12205 +/- 690 cpm. mg-1. 15 s-1 in HP, sham, and PTX groups, respectively. BBM NHE3 protein abundance decreased 39.3 +/- 8.2% in HP rats and increased 54.6 +/- 7.8% in PTX rats. Immunohistochemistry showed that expression of NHE3 protein in apical BBM was decreased in HP rats and was increased in PTX rats. Northern blot analysis of total kidney RNA showed that the abundance of NHE3 mRNA was 20.3 +/- 1.3% decreased in HP rats and 27. 7 +/- 2.1% increased in PTX. CONCLUSIONS: Our results indicate that the chronic inhibitory effect of PTH on the renal proximal tubule NHE3 is associated with changes in the expression of NHE3 mRNA levels and protein abundance.     

The PTH-Calcium Relationship During a Range of Infused PTH Doses in the Parathyroidectomized Rat

To establish the PTH dosage that maintains normal mineral homeostasis in the PTX rat, a series of doses of rat 1-34 PTH were infused via a subcutaneously implanted miniosmotic pump. The doses were 0, 0.011, 0.022, 0.044, and 0.11 μg/100 g/hour. After 48 hours, serum calcium ranged from 5.56 ± 0.02 to 16.29 ± 0.25 mg/dl, ANOVA P < 0.001, and serum phosphorus from 12.49 ± 0.03 to 5.33 ± 0.34 mg/dl, ANOVA P < 0.001. By post hoc test, the serum calcium level was different (P < 0.05) at every PTH dose; the serum phosphorus level was different (P < 0.05) at every PTH dose except between the two highest doses. The PTH dosage that produced a normal serum calcium (10.09 ± 0.10 mg/dl) and phosphorus (6.90 ± 0.18 mg/dl) was 0.022 μg/100 g/hour. The relationship between increasing doses of PTH and both serum calcium and phosphorus was curvilinear and the calcium-phosphorus product was remarkably constant from a serum calcium of 7–13 mg/dl. The increase in serum calcium and the decrease in serum phosphorus were more rapid at lower than at higher PTH doses so that for both, an asymptote was reached. At the highest serum calcium values, the calcium-phosphorus product increased and in individual rats, an increase in serum phosphorus was associated with a decrease in serum calcium. In summary, this study shows that (1) for rat 1-34 PTH, the normal replacement dose in the PTX rat with normal renal function on a normal diet is 0.022 μg/100 g/hour; (2) the relationship between PTH and both serum calcium and phosphorus is curvilinear, and an asymptote is reached for both; and (3) the calcium-phosphorus product is remarkably constant as the serum calcium increases from 7 to 13 mg/dl and only increased during marked hypercalcemia when serum phosphorus did not decrease further or even tended to increase. Received: 30 May 1997 / Accepted: 15 October 1997     

Compensatory parathyroid hypertrophy after hemiparathyroidectomy in rats feeding a low calcium diet

Summary The functional and anatomic compensatory response of the parathyroid gland was examined in hemiparathyroidectomized (HPTx) rats whose parathyroid hormone (PTH) secretion was stimulated by a low calcium diet. These responses were compared with those observed in the thyroid gland of hemithyroidectomized (HTx) rats. Rats kept on a low calcium diet for 10 days were subjected to HPTx, HTx, or sham operations. Throughout the experiment (up to 28 days after surgery), serum calcium levels of HPTx rats were lower than the basal, with Δ values (mg/dl, mean±SEM) of −0.66±0.17 and −0.84±0.17, (P<0.05) 3 and 28 days after surgery, respectively. Serum PTH decreased significantly from 7 to 21 days after HPTx, reaching normality at day 28 after surgery. In HTx rats, serum thyroxine (T4) levels diminished significantly 7 days after surgery, and attained normality thereafter. The mitotic index (number of metaphases/1,000 cells) in parathyroid glands of colchicine-treated HPTx rats increased significantly in comparison to sham-operated controls, when examined 2 or 40 days after surgery. The mitotic index of thyroid follicular cells was significantly higher than that of their respective controls, 2 but not 40 days after HTx. These results indicate that after HPTx, a delayed compensatory response is found when the animals are kept under a low calcium diet. Parathyroid response is both delayed and of a minor degree compared to that found in the thyroid gland after HTx.     

Effects of parathyroidectomy on blood pressure in spontaneously hypertensive rats

The long-term effects of parathyroidectomy (PTX) on blood pressure, intravascular volume, pressor hormones, and on acute vascular effects of intravenous parathyroid hormone (PTH) were evaluated in spontaneously hypertensive (SH) and normotensive Wistar-Kyoto (WK) rats. PTX or sham operation (CO) were done at 4-5 weeks of age, and a high calcium diet was offered to PTX rats to study them at eucalcemic calcium levels. The cardiovascular effects of PTX, determined after 11-13 weeks, were qualitatively similar in SH and WK rats: mean arterial blood pressure (conscious unrestrained rats) was lower, intravascular volume was higher, total body sodium was slightly higher, and plasma angiotensin II or norepinephrine levels were not different from CO groups. The acute hypotensive and chronotrophic effect of intravenous PTH was unchanged in PTX groups. When parathyroid intact SH rats and PTX SH rats were both examined on an 1.6% Ca diet, blood pressure was significantly lower in PTX than in parathyroid-intact SH rats. The results are compatible with the hypothesis that PTH has a permissive action on blood pressure maintenance in eucalcemic SH and WK rats by mechanisms unrelated to volume status or circulating pressor hormone concentrations.     

Parathyroidectomy for Renal Hyperparathyroidism in Children and Adolescents

Background Renal hyperparathyroidism (rHPT) almost inevitably develops in pediatric patients with end-stage chronic kidney disease (CKD) and may require parathyroidectomy (PTX) despite intensified conservative therapy. Long-term duration of uncontrolled rHPT may result in disabling osteodystrophy and vascular calcifications. Only a few reports on children undergoing PTX for rHPT are available and mainly consist of case reports with short follow-up periods. To study this entity, we analyzed the course of 23 pediatic patients who underwent PTX for rHPT. Methods Twenty-three patients with a mean age of 15 years and who underwent PTX for rHPT between 1986 and 2006 were evaluated. Surgical indications and techniques, specific postoperative management, and follow-up courses are described. Results Preoperative mean serum (s-) calcium was 2.7 ± 0.05 mmol/L (normal range = 2.2–2.7 mmol/L); s-phosphate was 1.8 ± 0.1 mmol/L (normal range = 0.8–1.6 mmol/L), and mean intact parathyroid hormone (PTH) level was 1240.1 ± 160.1 pg/ml (normal range = 11–65 pg/ml). Twenty-one patients underwent initial PTX and two patients underwent reoperative PTX. Total PTX with parathyroid autotransplantation (AT) was performed in 18 patients. In three patients less than four parathyroid glands were identified and no AT was performed consecutively. Postoperatively, no complications with respect to bleeding or vocal cord damage were recorded. The postoperative values of s-calcium, s-phosphate, and PTH decreased to or below normal range (s-calcium = 2.0 ± 0.1 mmol/L, s-phosphate = 1.2 ± 0.1 mmol/L, PTH = 50.1 ± 11.2 pg/ml). All 15 children below the age of 15 years required calcium intravenously. Follow-up was obtained in all patients 69.6 ± 11.4 months after PTX. Bone pain resolved in all previously symptomatic patients. S-calcium was 2.2 ± 0.2 mmol/L, s-phosphate was 1.4 ± 0.3 mmol/L, and PTH was 90.2 ± 21.5 pg/ml. No patient required repeated parathyroid autografting, and only one underwent an explantation of his AT six years after initial PTX. Conclusion Total PTX with AT in pediatric patients with rHPT is a safe and effective procedure. It should be considered if rHPT is refractory to conservative treatment, in view of the risk of potentially lethal vascular calcifications developing in the majority of adults with childhood onset of CKD. K. Schlosser and C. P. Schmitt contributed equally to this work.     

Effect of ammonium chloride and dietary phosphorus in the azotaemic rat. Part II--Kidney hypertrophy and calcium deposition.

BACKGROUND: Kidney hypertrophy is stimulated by both partial nephrectomy and NH(4)Cl administration. Also, parathyroidectomy (PTX) has been reported to prevent kidney hypertrophy induced by a high protein diet. Our goal was to determine in the azotaemic rat: (i) the combined effects of NH(4)Cl administration and dietary phosphorus on the development of kidney hypertrophy and calcium deposition in the kidney and (ii) whether the absence of parathyroid hormone (PTH) affected the development of kidney hypertrophy and calcium deposition. METHODS: High (HPD, 1.2%), normal (NPD, 0.6%) or low (LPD, <0.05%) phosphorus diets were given to 5/6 nephrectomized rats for 30 days. In each dietary group, one-half of the rats were given NH(4)Cl in the drinking water. The six groups of rats were: (i) HPD + NH(4)Cl; (ii) HPD; (iii) NPD + NH(4)Cl; (iv) NPD; (v) LPD + NH(4)Cl and (vi) LPD. In a separate study, PTX was performed to determine whether PTH affected renal hypertrophy in 5/6 nephrectomized rats given NH(4)Cl. RESULTS: Both with and without NH(4)Cl (+/-NH(4)Cl), kidney weight was greatest (P<0.05) in the HPD groups. In each dietary phosphorus group, kidney weight was greater (P<0.05) in the NH(4)Cl group. In both the +/-NH(4)Cl groups, kidney calcium content was greatest (P<0.05) in the HPD group, but was less (P<0.05) in the NPD and HPD groups given NH(4)Cl. An inverse correlation was present between creatinine clearance and kidney calcium content (r = -0.51, P<0.001). When factored for kidney weight, creatinine clearance was less (P<0.05) in the HPD group in both the +/-NH(4)Cl groups, but was greater in the HPD + NH(4)Cl than in the HPD group. In PTX rats, kidney weight was greater (P<0.05) and kidney calcium deposition was less (P<0.05) in rats given NH(4)Cl. CONCLUSIONS: In azotaemic rats studied for 30 days, NH(4)Cl administration induced kidney hypertrophy. A HPD also induced kidney hypertrophy. The effects on kidney calcium deposition were divergent for which NH(4)Cl administration decreased and a HPD increased calcium deposition. The inverse correlation between kidney calcium content and creatinine clearance suggests that kidney calcium deposition is harmful to renal function. When factored for kidney weight, the lower creatinine clearance in the high phosphorus group suggests that kidney hypertrophy does not completely compensate for the harmful effects of a HPD. This result also suggests that a longer study would probably result in more rapid deterioration in the high phosphorus group. In PTX rats, the absence of PTH did not prevent NH(4)Cl from inducing kidney hypertrophy and reducing kidney calcium deposition. In conclusion, NH(4)Cl and dietary phosphorus each independently affect kidney growth and calcium deposition in the growing rat with renal failure.     

Effect of parathyroidectomy on aluminum toxicity and azotemic bone disease in the rat

In maintenance dialysis patients, low-turnover osteomalacia and aplastic bone disease are generally attributed to aluminum toxicity. Both groups of patients have a relative deficiency of PTH. The reason for the development of osteomalacia versus aplastic bone disease is unclear. The present study was performed to evaluate whether parathyroidectomy (PTX) modifies the effect of aluminum administration on bone histology in renal failure. Seven groups of pair-fed rats were studied: normals (N); renal failure (RF); RF + PTX; PTX; RF + aluminum (AL); RF + PTX + AL; and PTX + AL. Aluminum was administered intraperitoneally 5 days/week for 6 weeks. All groups were sacrificed at 6 weeks. Renal failure increased the serum calcium in both the parathyroid intact (RF versus N, 11 +/- 0.1 versus 10 +/- 0.3 mg/dl, X +/- SEM, P less than 0.05) and calcium-supplemented PTX groups (PTX + RF versus PTX, 9.7 +/- 0.2 versus 9.2 +/- 0.2 mg/dl, P less than 0.05). After PTX, aluminum administration increased the serum calcium (PTX + AL versus PTX, 9.8 +/- 0.3 versus 9.2 +/- 0.2, P less than 0.05, and PTX + RF + AL versus PTX + RF, 10.8 +/- 0.1 versus 9.7 +/- 0.2 mg/dl, P less than 0.05). In rats with renal failure receiving aluminum, PTX decreased osteoid volume and surface but not osteoid thickness. Rats receiving aluminum did not mineralize bone. Additionally, in PTX rats receiving aluminum, renal failure per se increased osteoblast surface, osteoid surface, osteoid volume, and osteoclast number.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduced left ventricular hypertrophy in type 1 diabetic patients with end-stage renal failure. A comparison between groups investigated 1977-80 and 1991-93

BACKGROUND.: During the last decade, control of hypertension, oedema, anaemia,uraemia, and blood glucose has improved in patients with diabeticnephropathy. We have investigated whether this has influencedcardiac function at the time of end-stage renal failure. STUDY DESIGN.: Echocardiographic investigations were performed in 26 type 1diabetic patients evaluated for kidney transplantation and theresults compared with those obtained in healthy controls andin a similar group of patients investigated in 1977–1980. RESULTS.: Blood pressure was 153 ± 21/85 ± 12mmHg versus174±17/91±9 (recent group versus early group).The left ventricular (LV) diameter index, ameasure of volaemia,was increased in systole and diastole in the early but not inthe recent group. Both groups had LV hypertrophy, but this wasmuch less pronounced in the recent group; posterior wall thicknesswas 1.1 ± 0.16 cm versus 1.3 ± 0.26 cm (P = 0.0001)and LV mass index 132±43 g/m² versus 166 ± 44g/m² (P = 0.009). Blood pressure correlated significantly withindices of LV hypertrophy in the recent group. Systolic functionwas normal in both groups but diastolic function was disturbedin both and to the same extent, atrial systole contributingby 27±14% to ventricular filling. CONCLUSION.: Better treatment of hypertension, fluid overload, and uraemiahas led to less pronounced LV hypertrophy. The remaining correlationwith blood pressure suggests that more could be gained by intensifiedantihypertensive treatment.     

Effect of the mode of calcitriol administration on PTH-ionized calcium relationship in uraemic patients with secondary hyperparathyroidism

To assess the effect of the different modes of calcitriol administrationon PTH-ionized calcium relationship we conducted a prospectiveclinical trial in 33 patients on chronic haemodialysis withsecondary hyperparathyroidism (four times upper normal limitintact PTH) who were randomly assigned, with stratificationto PTH levels, to receive daily oral, intermittent oral, orintermittent intravenous calcitriol at the same dose of 0.045µg/kg/weekly. PTH-iCa curves were generated by inducinghypo- or hypercalcaemia in sequential haemodialysis 1 week apart,before and after 10 weeks on treatment. All patients were dialysedagainst a dialysate calcium concentration of 2.5 mEq/l throughoutthe study period. After drop-outs, 26 patients completed the study: 11 on intravenouscalcitriol (mean basal PTH±SD: 666±280 pg/ml),eight on intermittent oral calcitriol (mean basal PTH: 831±361),and seven on daily oral calcitriol (mean basal PTH: 719±280).Serum ionized calcium and phosphorus significantly increasedin intravenous and daily oral groups after calcitriol treatment,but not in the intermittent oral group. Basal PTH did not significantlychange in the three groups after 10 weeks on treatment. MaximalPTH significantly decreased in intravenous group (1449±660versus 1122±691 pg/ml, P=0.0085) and at the limit ofstatistical significance in the intermittent oral group (1701±774versus 1445±634, P=0.12), but it did not change in thedaily oral group. Minimal PTH did not modify in the three groups.In all three groups, a shift to the right in the PTH-iCa relationshipswere observed, with significant changes in the set point ofcalcium. The slope of the post-treatment curves only becameless steep in the intermittent oral and intravenous groups. In conclusion, intermittent administration of calcitriol seemsto be more effective in reducing maximal PTH than daily oraladministration, but at the conditions under which this studywas carried out all the modes of calcitriol administration shiftedPTH-iCa relationships to the right.     

Remodeling of resistance arteries in renal failure: effect of endothelin receptor blockade

Remodeling of vessels is a known feature of renal failure, but it is unclear whether this represents an appropriate or inappropriate response to the known changes in blood flow, shear stress, and wall tension. To investigate remodeling in response to variations in blood flow, first-order mesenteric arteries were exposed to high- and low-flow conditions via the ligation of second-order branches, according to the technique described by Pourageaud and De Mey. The resulting changes in vessel geometric features, relative proportions of intima and media, submicroscopic structure, and immunostaining for proliferating cell nuclear antigen (PCNA), endothelin-1 (ET-1), and ET(A) receptors were assessed in first-order mesenteric arteries under low-flow and high-flow conditions. Subtotally nephrectomized (SNX) animals were compared with sham-operated rats. Animals either were left untreated or were treated with the ET(A) receptor antagonist (ET-RA) LU-135252, because of suggestions in the literature that ET is involved in vascular remodeling in uremia. A highly significant increase in intimal thickness was noted in low-flow arteries (4.21 +/- 1.39 microm) of SNX animals, compared with normal-flow arteries (2.06 +/- 0.61 microm), but this increase was not observed in sham-operated rats (1.38 +/- 0.77 in low-flow arteries versus 2.40 +/- 0.35 microm in normal-flow arteries). The increase in intimal thickness in low-flow arteries was abrogated by ET-RA. The medial thickness was increased in untreated SNX animals (19.5 +/- 3.61 microm), compared with sham-operated rats, and this increase was also prevented by ET-RA. The medial thickness was not affected by low flow in either sham-operated or SNX animals. In parallel, the number of PCNA-positive intimal cells was higher in low-flow, but not high-flow, arteries of SNX rats, compared with sham-operated rats. No significant change was observed in sham-operated animals. In the media, the number of PCNA-positive cells was higher in untreated SNX animals than in sham-operated rats. The number was even more markedly increased in high-flow, but not low-flow, vessels. This increase was abrogated by ET-RA. It is concluded that, in uremic animals, the response of the intima to low flow and the response of the media to high flow are exaggerated. Both responses are apparently mediated by ET.