Surgical outcomes after pediatric kidney transplantation at the University of Heidelberg

BACKGROUND

Kidney transplantation (KTx) is the treatment of choice for children with end-stage renal disease (ESRD).

OBJECTIVE

An update of 48 years of surgical experience with pediatric KTx (PKTx) is presented, and the results between recipients of organs from deceased donors (DDs) and living donors (LDs) are compared.

STUDY DESIGN

All patients younger than 18 years who underwent KTx between 1967 and 2015 were evaluated. Data from 540 PKTx operations (409 DD and 131 LD) were obtained from the transplant center database. Peri-operative data and graft and patient survival were analyzed in the DD and LD groups.

RESULTS

Fewer recipients in the LD group underwent dialysis before PKTx than those in the DD group (50.8% in LD vs. 94.9% in DD, P < 0.001). The mean duration of dialysis (DD: 798 ± 525 days vs. LD: 625 ± 650 days, P = 0.03), time on the waiting list (DD: 472 ± 435 days vs. LD: 120 ± 243 days, P < 0.001), cold ischemia time (CIT) (DD: 1206 ± 368 min vs. LD: 140 ± 63 min, P < 0.001), operation time, and hospital stay were lower in the LD group. Except for arterial stenosis, the rates of postoperative vascular and urological complications were not different between the two groups. The cumulative 25-year graft and patient survival rates were 46.4% and 84.1% in the DD group and 76.5% and 96.1% in the LD group, respectively.

DISCUSSION

PKTx is the treatment of choice for children with ESRD. Graft quality has a direct impact on KTx outcome and rate of graft failure. Better HLA compatibility and shorter CIT reduce the impairment of graft function after LD PKTx. In addition, Establishment of an interdisciplinary approach using an individualized risk assessment and prevention model can improve PKTx outcomes.

CONCLUSION

Compared with DD PKTx, LD PKTx has better graft survival associated with a shorter duration of preceding dialysis, waiting time, and CIT and seems to be more beneficial for children.

Carnosine treatment in combination with ACE inhibition in diabetic rats

In humans, we reported an association of a certain allele of carnosinase gene with reduced carnosinase activity and absence of nephropathy in diabetic patients. CN1 degrades histidine dipeptides such as carnosine and anserine. Further, we and others showed that treatment with carnosine improves renal function and wound healing in diabetic mice and rats. We now investigated the effects of carnosine treatment alone and in combination with ACE inhibition, a clinically established nephroprotective drug in diabetic nephropathy. Male Sprague-Dawley rats were injected i.v. with streptozotocin (STZ) to induce diabetes. After 4 weeks, rats were unilaterally nephrectomized and randomized for 24 weeks of treatment with carnosine, lisinopril or both. Renal CN1 protein concentrations were increased under diabetic conditions which correlated with decreased anserine levels. Carnosine treatment normalized CN1 abundance and reduced glucosuria, blood concentrations of glycosylated hemoglobin (HbA1c), carboxyl-methyl lysine (CML), N-acetylglucosamine (GlcNac; all p<0.05 vs. non-treated STZ rats), reduced cataract formation (p<0.05) and urinary albumin excretion (p<0.05), preserved podocyte number (p<0.05) and normalized the increased renal tissue CN1 protein concentration. Treatment with lisinopril had no effect on HbA1C, glucosuria, cataract formation and CN1 concentration, but reduced albumin excretion rate more effectively than carnosine treatment (p<0.05). Treatment with both carnosine and lisinopril combined the effects of single treatment, albeit without additive effect on podocyte number or albuminuria. Increased CN1 amount resulted in decreased anserine levels in the kidney. Both carnosine and lisinopril exert distinct beneficial effects in a standard model of diabetic nephropathy. Both drugs administered together combine the respective effects of single treatment, albeit without exerting additive nephroprotection.

Peritoneal dialysis tailored to pediatric needs

Consideration of specific pediatric aspects is essential to achieve adequate peritoneal dialysis (PD) treatment in children. These are first of all the rapid growth, in particular during infancy and puberty, which must be accompanied by a positive calcium balance, and the age dependent changes in body composition. The high total body water content and the high ultrafiltration rates required in anuric infants for adequate nutrition predispose to overshooting convective sodium losses and severe hypotension. Tissue fragility and rapid increases in intraabdominal fat mass predispose to hernia and dialysate leaks. Peritoneal equilibration tests should repeatedly been performed to optimize individual dwell time. Intraperitoneal pressure measurements give an objective measure of intraperitoneal filling, which allow for an optimized dwell volume, that is, increased dialysis efficiency without increasing the risk of hernias, leaks, and retrofiltration. We present the concept of adapted PD, that is, the combination of short dwells with low fill volume to promote ultrafiltration and long dwells with a high fill volume to improve purification within one PD session. The use of PD solutions with low glucose degradation product content is recommended in children, but unfortunately still not feasible in many countries.

Differential regulation of RGS-2 by constant and oscillating PTH concentrations

PTH has diverse effects on bone metabolism: anabolic when given intermittently, catabolic when given continuously. The cellular mechanisms underlying the varying target cell response are not clear yet. PTH induces RGS-2, a member of the Regulator of G-protein Signaling protein family, via cAMP/PKA, and inactivates PKC-mediated signaling. To investigate intracellular signaling pathways with different PTH concentration-time patterns, we treated UMR 106-01 osteoblast-like cells in a perfusion system. PTH was administered intermittently (4 min/h, 10(-7) M) or continuously at an equivalent cumulative dose (6.6 x 10(-9) M). cAMP was measured using radioimmunoassay, mRNA levels using real-time rtPCR and ribonuclease protection assay, and protein levels using Western immunoblotting. A single PTH pulse transiently increased cAMP levels by 2000% +/- 1200%. In contrast to continuous PTH exposure, cAMP induction remained unchanged with intermittent PTH, ruling out desensitization of the PTH receptor. In continuously perfused cells, RGS-2 abundance was three to five times higher than in cells intermittently exposed to PTH for up to 12 h. MKP-1 and -3 were significantly less induced with pulsatile PTH; exposure-mode-dependent differences in MMP-13 and IGFBP-5 were small. Pulsatile but not continuous PTH administration prevents PTHrP receptor desensitization and accumulation of RGS-2 in osteoblasts, which should preserve PKC-dependent signaling.

Multi-exon deletions of the PKHD1 gene cause autosomal recessive polycystic kidney disease (ARPKD)

BACKGROUND

Autosomal recessive polycystic kidney disease (ARPKD) is caused by mutations in the PKHD1 (polycystic kidney and hepatic disease 1) gene on chromosome 6p12, a large gene spanning 470 kb of genomic DNA. So far, only micromutations in the 66 exons encoding the longest open reading frame (ORF) have been described, and account for about 80% of mutations.

OBJECTIVE

To test the hypothesis that gross genomic rearrangements and mutations in alternatively spliced exons contribute to a subset of the remaining disease alleles.

METHODS

Using DHPLC for alternatively spliced exons and quantitative real time polymerase chain reaction to detect genomic imbalances, 58 ARPKD patients were screened, of whom 55 were known to harbour one PKHD1 point mutation in the longest ORF.

RESULTS

Three different heterozygous PKHD1 deletions and several single nucleotide changes in alternatively spliced exons were identified. The detected partial gene deletions are most likely pathogenic, while a potential biological function of the alterations identified in alternatively spliced exons must await the definition of transcripts containing alternative exons and their predicted reading frames.

CONCLUSIONS

Gross PKHD1 deletions account for a detectable proportion of ARPKD cases. Screening for major genomic PKHD1 rearrangements will further improve mutation analysis in ARPKD.

Structural organization and biological relevance of oscillatory parathyroid hormone secretion

Parathyroid gland secretory activity exhibits seasonal and circadian fluctuations, which are in synchrony with changes in serum calcium, phosphate, and bone turnover. In addition, an ultradian rhythm exists, which comprises seven pulses per hour, accounts for 30% of basal parathyroid hormone (PTH) release, and is highly sensitive to changes in ionized calcium. Acute hypocalcemia induces a selective, severalfold increase in pulse frequency and amplitude, whereas hypercalcemia suppresses the pulsatile secretion component, as does prolonged calcitriol therapy. Chronic renal failure is associated with a GFR dependent decrease in metabolic PTH clearance accounting for a two- to threefold increase in plasma PTH concentrations, a consistent increase of PTH burst mass and frequency, and a markedly reduced capacity to counteract changes in ionized calcium by modulation of pulsatile PTH release. Continuous PTH excess destroys bone, whereas intermittent administration of pharmacological doses of PTH improves bone morphology and strength in experimental and clinical settings. The molecular mechanisms of the exposure pattern dependent, contrasting biological effects of PTH may involve differential regulation of osteoblastic G protein signaling feedback circuits. In this context, calcimimetic and calcilytic agents are promising new therapeutic tools allowing for tight control of plasma PTH and restoration of circadian PTH rhythmicity.

Peritoneal dialysis in children: consider the membrane for optimal prescription

The peritoneal dialysis prescription was, for a long time, based on clinical experience and very empirical, especially for patients on continuous ambulatory peritoneal dialysis (CAPD). Better comprehension of the peritoneal membrane as a dynamic dialysis surface allows an individualized prescription, especially for children on automated peritoneal dialysis (APD). Fill volume prescription should be scaled for body surface area (mL/m(2)) and not in a too low amount to avoid a hyperpermeable exchange. Fill volume enhancement should be done under clinical control and is best secured by intraperitoneal pressure measurement (IPP; cm H2O). A peak fill volume of 1400-1500 mL/m(2) could be prescribed both in terms of tolerance and of efficiency. The dwell times should be determined individually with respect to two opposite parameters namely: short dwell times which provide adequate small solute clearance and maintain ultrafiltration capacity and long dwell times which enhance phosphate clearance but can contribute to dialysate reabsorption. The new peritoneal dialysis fluids which are free of GPD's, have neutral pH and are not exclusively lactate buffered, appear as the best choice in the context of peritoneal exchange membrane recruitment and of peritoneal vascular hyperperfusion preservation.

Vitamin D and dexamethasone inversely regulate parathyroid hormone-induced regulator of G protein signaling-2 expression in osteoblast-like cells

The PTH/PTHrP receptor stimulates both adenylate cyclase- and phospholipase C-dependent signaling pathways via different G proteins. The biological actions of PTH on bone are modified by steroid hormones. PTH induces expression of regulator of G protein signaling (RGS)-2, a putative preferential inhibitor of G(q)-mediated phospholipase C activation. We investigated whether steroid hormones interfere with PTH signaling by modulating PTH-induced RGS-2 expression in osteoblast-like UMR 106-01 cells. PTH (1-34) rapidly and transiently induced expression of RGS-2 mRNA and protein via the cAMP/protein kinase A pathway within 30 min, with maximal protein abundance after 2 h. PTH-induced RGS-2 preferentially bound to Galpha(q), compared with Galpha(s) protein. 1,25-(OH)(2)D(3) pretreatment enhanced PTH-induced RGS-2 mRNA and protein accumulation, whereas dexamethasone preincubation had an attenuating effect. These effects were due to modulation of the RGS-2 gene transcription rate, which increased by 35% with 1,25-(OH)(2)D(3) and decreased by 63% with dexamethasone pretreatment. RGS-2 mRNA half-life was not affected by either steroid. The transcriptional effects of dexamethasone and 1,25-(OH)(2)D(3) were independent of PTH/PTHrP receptor activation and were not explained by effects on cAMP accumulation, cAMP response element-binding protein expression or phosphorylation, or the abundance of the osteoblast-specific transcription factor core-binding factor alpha (CBFa1/Runx2), a known activator of RGS-2 expression. In conclusion, glucocorticoids and 1,25-(OH)(2)D(3) inversely modulate PTH-induced RGS-2 gene transcription. Regulation of RGS-2 may constitute a novel mechanism by which steroids modulate signaling via the PTH/PTHrP receptor and other G protein-coupled receptors in bone.

No difference in intestinal strontium absorption after oral or IV calcitriol in children with secondary hyperparathyroidism. The European Study Group on Vitamin D in Children with Renal Failure

BACKGROUND

Oral and intravenous calcitriol bolus therapy are both recommended for the treatment of secondary hyperparathyroidism, but it has been claimed that the latter is less likely to induce absorptive hypercalcemia. The present study was undertaken to verify whether intravenous calcitriol actually stimulates intestinal calcium absorption less than oral calcitriol and whether it is superior in suppressing parathyroid hormone (PTH) secretion.

METHODS

Twenty children (16 males, age range of 5.1 to 16.9 years, mean creatinine clearance 21.9 +/- 11.5 mL/min/1.73 m2, range of 7.4 to 52.7) with chronic renal failure (CRF) and secondary hyperparathyroidism [median intact PTH (iPTH), 327 pg/mL; range 143 to 1323] received two single calcitriol boli (1.5 mg/m2 body surface area) orally and intravenously using a randomized crossover design. iPTH and 1,25(OH)2D3 levels were measured over 72 hours, and intestinal calcium absorption was measured 24 hours after the calcitriol bolus using stable strontium (Sr) as a surrogate marker. Baseline control values for Sr absorption were obtained in a separate group of children with CRF of similar severity.

RESULTS

The peak serum level of 1,25(OH)2D3 and area under the curve baseline to 72 hours (AUC0-72h) were significantly higher after intravenous (IV) calcitriol (AUC0-72h oral, 1399 +/- 979 pg/mL. hour vs. IV 2793 +/- 1102 pg/mL. hour, P < 0.01), but the mean intestinal Sr absorption was not different [SrAUC0-240min during the 4 hours after Sr administration 2867 +/- 1101 FAD% (fraction of the absorbed dose) vs. 3117 +/- 1581 FAD% with oral and IV calcitriol, respectively]. The calcitriol-stimulated Sr absorption was more then 30% higher compared with control values (2165 +/- 176 FAD%). A significant decrease in plasma iPTH was noted 12 hours after the administration of the calcitriol bolus, which was maintained for up to 72 hours without any differences regarding the two routes of administration.

CONCLUSIONS

These results demonstrate that under acute conditions, intravenous and oral calcitriol boli equally stimulate calcium absorption and had a similar efficacy in suppressing PTH secretion.

Calcitriol pulse therapy is not more effective than daily calcitriol therapy in controlling secondary hyperparathyroidism in children with chronic renal failure. European Study Group on Vitamin D in Children with Renal Failure

Calcitriol oral pulse therapy has been suggested as the treatment of choice for secondary hyperparathyroidism, but its efficacy and safety are still under discussion. The present randomized multicenter study compares the effect of an 8-week course of daily versus intermittent (twice weekly) calcitriol therapy on parathyroid hormone (PTH) suppression in 59 children (mean age 8.4+/-4.7 years) with chronic renal insufficiency (mean Ccr 22.4+/-11.6 ml/min per 1.73 m2) and secondary hyperparathyroidism. After a 3-week washout period, the patients were randomly assigned to treatment with daily oral calcitriol (10 ng/kg per day) or intermittent oral calcitriol (35 ng/kg given twice a week). The calcitriol dose was not changed throughout the study period of 8 weeks. At start of the study, the median intact PTH (iPTH) level was 485 pg/ml (range 83-2032) in the daily group (n=29) and 315 pg/ml (range 93-1638) in the intermittent group (n=30). After 8 weeks, the respective median iPTH concentrations were 232 pg/ml (range 63-1614) and 218 pg/ml (range 2-1785) (ns). The mean iPTH decrease from baseline was 19.2+/-57.8% and 13.7+/-46.7% respectively (not significant). Calcitriol reduced the iPTH concentration in 23/29 patients in the daily group and in 21/30 in the intermittent group. One episode of hypercalcemia (>11.5 mg/dl) was observed in both groups and a single episode of hyperphosphatemia (>7.5 mg/dl) was observed in the daily group. It is concluded that oral calcitriol pulse therapy does not control secondary hyperparathyroidism more effectively than the daily administration of calcitriol in children with chronic renal failure prior to dialysis.

Daily but not pulse calcitriol therapy improves growth in experimental uremia

Calcitriol (C) pulse therapy is widely used to suppress secondary renal hyperparathyroidism. However, high C serum concentrations may have an antiproliferative effect on growth cartilage cells and may suppress growth rate. The study was designed to evaluate whether daily C and pulse C therapy have differential effects on growth in uremic rats. Female Sprague-Dawley rats (150 g, n=5-10 per group) underwent two-stage subtotal nephrectomy (U). The duration of uremia was 14-18 days. The animals were fed a standard diet or a diet with a low-calcium content. Rats on a low-calcium diet were randomized for recombinant human growth hormone (rhGH) treatment (2.5 IU/kg per day) or solvent. C was injected subcutaneous twice daily (15 pmol/day) or intraperitoneal (105 pmol) twice per week. Weight gain and length gain was determined weekly. After sacrifice, total body calcium was determined by total body neutron activation analysis. Bone micromorphometric analysis of third lumbar vertebra and double staining with tetracycline for determination of mineralization rate were performed. Whereas daily C significantly increased total body length gain within 2 weeks, pulse C did not (U solvent 4.0+/-0.3 cm, UC bolus 4.3+/-0.4 cm, UC daily 5.3+/-0.3 cm, P<0.05). A low-calcium diet reduced and rhGH increased basal length gain and weight gain; regardless of these preconditions, daily but not bolus C increased length gain significantly. C both daily and in bolus form reduced bone osteoid content, but daily C improved mineral apposition rate more than C bolus. Total body calcium corrected for body weight decreased with a low-calcium diet, was lowest with concomitant rhGH treatment, and was not improved by C. In conclusion, daily but not bolus C treatment improves growth in uremic rats.

Residual peritoneal volume and body size in children on peritoneal dialysis. [Members of the Mid European Pediatric Peritoneal Dialysis Study Group (MEPPS)]

Residual peritoneal volume may play an important role in dialysis efficacy and abdominal compliance in patients on chronic peritoneal dialysis (CPD). In children on CPD, the relationship between residual peritoneal volume and different measures of body size, as well as the day-to-day variability of residual volume, have not been established. We therefore investigated, on two consecutive days, residual peritoneal volume in 25 children on CPD, using the dextran dilution technique. Residual volume was linearly correlated with body size. Residual volume was independent of body size when normalized to body surface area, but decreased with increasing body size when normalized to body weight (r = -0.62, p < 0.001). Mean residual volume was 79 +/- 25 mL/m2, with an intra-individual day-to-day coefficient of variation of 21% +/- 15%. Residual volume was not correlated with the duration of PD, frequency of peritonitis, or peritoneal permeability as estimated by D/P creatinine or D/D0 glucose. In conclusion, residual peritoneal volume is constant across the pediatric age range when normalized to body surface area. It accounts for approximately 8% of the usual fill volume in patients on CPD. Residual volume is not a major confounder of the transport status estimation obtained by peritoneal equilibration test.

Intermittent administration of parathyroid hormone (1-37) improves growth and bone mineral density in uremic rats

BACKGROUND

Parathyroid hormone (PTH) is secreted in a pulsatile fashion. Continuous infusion of PTH(1-84) resulted in a net decrease in trabecular bone volume. Differential effects have been reported following an intermittent application of PTH. We investigated the effects of a continuous infusion and of an intermittent (2 times daily subcutaneously) administration of PTH(1-37) on growth and bone mineral density (BMD) in healthy and uremic rats.

METHODS

Two-stage subtotal nephrectomy was performed on 130 g female Sprague-Dawley rats. PTH(1-37) or solvent was administered through minipumps in sham-operated and uremic rats (60 microg/kg x day for 2 weeks). The effect of intermittent administration was tested with a subcutaneous injection of solvent: 30 microg/kg PTH(1-37) two times per day, 100 pmol calcitriol (C)/kg two times per day, or both. The length (snout-tailtip) and BMD were measured at the start of uremia and at sacrifice. BMD was measured by peripheral quantitative computer tomography at the proximal tibia, 6 and 12 mm distal of the kneejoint space. Femur bone morphology was assessed by x-rays, and calcium content was measured by atomic absorption spectrophotometry.

RESULTS

Length gain was not altered by the continuous infusion of PTH. In contrast, it was significantly increased by intermittent PTH (control solvent 5.35 +/- 0.37 cm vs. control PTH 6.19 +/- 0.47 cm; uremia solvent 4.78 +/- 0.20 cm vs. uremia PTH 6.17 +/- 0.36 cm; P < 0.05). Intermittent PTH but not C increased BMD in uremic rats (Delta total BMD 134 + 13.3 vs. 76.3 +/- 11.5 mg/mL; P < 0.05). X-rays revealed increased bone mass following treatment with PTH but not with C. Uremia decreased bone calcium content (64 +/- 0.3 vs. 73. 3 +/- 2.5 mg/mL), which was normalized by PTH (80 +/- 3.6 mg/mL, P < 0.05) but not by C (69 +/- 1.9 mg/mL).

CONCLUSION

Pulsatile administration of PTH does not adversely affect, but improves longitudinal growth independent of concomitant treatment with C. At the same time PTH increases BMD and the calcium content of bone.

No difference in intestinal strontium absorption after an oral or an intravenous 1,25(OH)2D3 bolus in normal subjects. For the European Study Group on Vitamin D in children with renal failure

It has been suggested that 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) stimulates intestinal calcium absorption less via the intravenous (iv) than the oral route, because the first avoids direct contact of the drug with the enterocytes. However, no study has addressed the issue directly. This investigation was designed to measure the effect of a single oral or iv dose of 1,25(OH)2D3 on calcium absorption, using stable strontium (Sr) as a surrogate for calcium, and measuring the Sr fractional absorbed dose (FAD%) over 240 minutes after Sr administration. In 10 healthy volunteers, five tests were performed in a cross-over design, with a wash-out period between two consecutive tests: Sr absorption without 1,25(OH)2D3 (test A); Sr absorption immediately after either oral (test B) or iv (test C) 1,25(OH)2D3 (1.5 microg/m2 of body surface area [BSA]); Sr absorption (24 hr after either oral (test D) or iv (test E) 1, 25(OH)2D3 (1.5 microg/m2 BSA). The concurrent administration of 1, 25(OH)2D3 and Sr (tests B and C) did not significantly change the area under the Sr FAD%-time curve with respect to test A (test A: 4090 +/- 345; test B: 4510 +/- 345; test C: 4210 +/- 345), whereas Sr absorption was significantly increased (p < 0.001) when Sr was given 24 hr after either oral or iv 1,25(OH)2D3 (test D: 5710 +/- 345; test E: 5510 +/- 345). It was concluded that 1,25(OH)2D3 is likely to influence calcium absorption significantly only via its genomic effect, independent of its administration route.

Altered instantaneous and calcium-modulated oscillatory PTH secretion patterns in patients with secondary hyperparathyroidism

The relative contributions of increased parathyroid cell mass and altered control mechanisms of parathyroid hormone (PTH) secretion in secondary hyperparathyroidism are still controversial. In this study, endogenous pulsatile PTH secretion was analyzed by the multiparameter deconvolution technique to differentiate alterations in cell mass-dependent (PTH burst mass) and regulation-dependent (frequency, synchrony, calcium responsiveness) PTH release in uremic patients. PTH concentration versus time profiles were obtained in 13 uremic and 16 healthy adults under baseline conditions and during acute hypo- and hypercalcemia. Plasma PTH half-life was increased in patients compared with control subjects (4.7+/-1.9 versus 2.6+/-0.1 min, P < 0.005). The baseline PTH secretion rate was elevated eightfold in the patients as a result of an increased PTH mass secreted per burst (17.1+/-4.7 versus 2.0+/-0.4 pM, P = 0.0001), higher burst frequency (8.0+/-0.3 versus 6.8+/-0.3 h(-1), P < 0.01), and a higher tonic secretion rate (343+/-99 versus 30+/-4 pM/h, P = 0.0001). Acute hypocalcemia elicited an immediate, frequency- and amplitude-mediated selective increase in the pulsatile secretory component, which was fractionally weaker in patients (+595%) than control subjects (+1755%, P < 0.001). The acceleration and the amplification of PTH bursts were 35 and 60% lower in the patient group. Acute hypercalcemia suppressed total PTH secretion by 79% in control subjects but only by 63% in patients (P < 0.002). PTH burst frequency was reduced during hypercalcemia by 30% in control subjects, but remained unchanged in patients. In conclusion, uremic hyperparathyroidism is mediated by a marked increase in glandular secretion, but also by reduced PTH elimination. The increased spontaneous PTH burst frequency and the blunted responsiveness to changes in Ca2+ indicate partial uncoupling of hyperplastic parathyroid glands from the physiologic regulatory mechanisms that direct pulsatile PTH release.

1,25(OH)2-vitamin D3 reduces spontaneous and hypocalcemia-stimulated pulsatile component of parathyroid hormone secretion

To investigate the effects of 1,25(OH)2-vitamin D3 (1,25(OH)2D3) on pulsatile parathyroid hormone (PTH) release, minute-to-minute intact PTH secretion was examined in nine healthy adults under baseline conditions and during hypocalcemia (sodium citrate clamp) before and after 5 d of oral 1,25(OH)2D3 treatment (1 microgram/d). In addition, acute effects of 1,25(OH)2D3 were examined by a single intravenous bolus of 2 micrograms of 1,25(OH)2D3. Pulsatile and tonic PTH secretion rates were calculated by the multiparameter deconvolution technique. During baseline, 68% of circulating PTH was attributable to tonic, and 32% to pulsatile, secretion. During induction of hypocalcemia, a selective increase in pulsatile secretion (+1100%), mediated by a combined increase in burst frequency and burst mass, was observed. During the subsequent steady-state hypocalcemic period, burst frequency and mass decreased and tonic secretion increased to 3 times the baseline level. Intravenous 1,25(OH)2D3 did not affect the temporal pattern of PTH secretion. In contrast, oral 1,25(OH)2D3 decreased baseline plasma PTH by 30% without a detectable change in Ca2+. This suppression was accounted for mainly by a decrease in PTH burst frequency. During hypocalcemia induction, a significantly lower (30%) increase in burst mass occurred compared with the pretreatment study. During steady-state hypocalcemia, PTH burst mass (-45%) and pulsatile (-50%) and total (-35%) secretion rate were lower than before treatment. In conclusion, acute hypocalcemia selectively increases pulsatile PTH release by stimulating both burst frequency and mass via a Ca2+ rate-sensitive mechanism. Oral 1,25-(OH)2D3 suppresses pulsatile baseline PTH release and reduces the pulsatile secretory capacity of the parathyroids during a hypocalcemic stimulus.

Urinary excretion of urodilatin in healthy children and children with renal disease

Urodilatin (URO) is a natriuretic peptide isolated from human urine which is thought to be produced by distal tubular cells. We measured urinary URO excretion in 50 healthy children and 23 children with acute (ARF), chronic renal failure (CRF), or hereditary tubular disorders, using a specific radioimmunoassay. The mean URO excreted in these four groups was 56, 45, 94, and 121 fmol/min per 1.73 m2, respectively (differences between first three groups not significant). The variation in URO excretion was larger in patients with kidney disease than in controls. There were significant correlations between urinary URO and sodium excretion in controls and CRF, but not in ARF. URO excretion also correlated with urine flow rate in CRF. Although no correlation was found between URO excretion and creatinine clearance, urinary URO was increased in some patients with advanced CRF, which suggests stimulated tubular production to compensate for reduced sodium excretion. In view of the therapeutic potential of URO in renal insufficiency, further study of the renal handling of URO is warranted.

Subacute infusion of physiological doses of parathyroid hormone raises blood pressure in humans

BACKGROUND

Acute administration of parathyroid hormone (PTH) causes vasodilation and blood pressure decrease in experimental animals. This effect contrasts with the putative role of secondary hyperparathyroidism in the pathogenesis of hypertension of patients with renal failure. Uraemia is characterized by insulin resistance and hyperinsulinaemia. We therefore investigated whether subacute administration of physiological doses of human 1,34-PTH affects blood pressure under conditions of controlled insulin levels (euglycaemic clamp technique) in humans.

METHODS

In a double-blind cross-over design 10 healthy male subjects received, on two occasions, in random order, for 2 h, either a sham infusion or an infusion of 200 units of 1,34-PTH.

RESULTS

Mean ionized calcium concentration increased significantly (P < 0.01) within the normal range during euglycaemic hyperinsulinaemia, both with sham infusion (from 1.25 +/- 0.04 to 1.29 +/- 0.02 mmol/l) and with infusion of 1,34-PTH, but the increase was more marked with 1,34-PTH administration (from 1.26 +/- 0.05 to 1.33 +/- 0.07). In addition, mean platelet intracellular calcium concentration (by fluorescence spectroscopy) was unchanged with sham infusion (49.9 +/- 4.1 versus 50.3 +/- 5.0 nmol), but increased significantly (P < 0.05; paired t-test) after 1,34-PTH infusion (from 49.8 +/- 5.0 to 52.8 +/- 5.8). The infusion of 1,34-PTH resulted in a significant (P < 0.01) increase in mean MAP (from 84 +/- 5 to 88 +/- 5 mmHg) as compared with sham infusion (85 +/- 4 versus 86 +/- 4). The intra-individual changes in intracellular calcium concentration (delta[Ca2+]i) were significantly correlated to the changes in mean MAP (delta MAP) (r = 0.87, P < 0.001). In contrast to blood pressure, insulin sensitivity was not affected by 1,34-PTH infusion (M-value: 7.2 +/- 1.6 mg/kg per min) as compared with sham infusion (7.3 +/- 1.4).

CONCLUSION

Subacute administration of physiological doses of parathyroid hormone under hyperinsulinaemic conditions significantly affects intracellular calcium and blood pressure in healthy subjects, but does not affect the action of insulin.

Control of pulsatile and tonic parathyroid hormone secretion by ionized calcium

To investigate the effect of changes in ionized calcium on instantaneous PTH secretion, we examined seven young healthy volunteers by 1-min blood sampling under conditions of normo-, hypo-, and hypercalcemia. After a baseline period of 75 min, ambient ionized calcium was either increased or decreased by 0.2 mmol/L for 105 min by clamped infusion of calcium gluconate or sodium citrate. The characteristics of PTH secretion were analyzed by a deconvolution technique, accounting for subject-specific plasma PTH disappearance half-life, as measured during the first 15 min of calcium infusion (range, 2.04-2.93 min). The process regularity of pulsatile PTH secretion was evaluated by an approximate entropy statistic. Under baseline conditions, 32% of total PTH secretion was released in a pulsatile fashion, with a burst frequency of 6.9 +/- 0.8 h-1 and a PTH mass per burst of 2.6 +/- 0.9 pmol/L. The remaining 68% of total secretion was attributed to tonic hormone release. During the initial 30 min of induced hypocalcemia, pulsatile secretion increased by 1140%, whereas tonic secretion did not change. The preferential increase in pulsatile PTH secretion was mediated by a combined rise in burst frequency and mass released per burst. During subsequent steady state hypocalcemia, the tonic secretion rate increased (255% of baseline), whereas burst frequency and burst mass decreased (to 103% and 189% of the baseline values), restoring the baseline ratio of tonic to pulsatile PTH secretion. The regularity of PTH release increased during steady state hypocalcemia. During hypercalcemia, tonic secretion, burst mass, and burst frequency decreased by 75%, 82%, and 32%, respectively, and remained constant throughout the clamp period. We conclude that acute hypocalcemia elicits an immediate pulsatile and a delayed tonic secretory response of the parathyroid gland with increased regularity of PTH release. Acute hypercalcemia suppresses both the pulsatile and the tonic component of PTH secretion.

Clonal analysis of the effect of TGF-beta on the apoptosis-inducing activity of normal cells

We have recently described induction of apoptosis in transformed fibroblasts by transforming growth factor type beta (TGF-beta)-treated normal fibroblasts, which leads to the specific elimination of transformed cells. Here we investigate whether the ability to eliminate transformed cells is the property of a specialized subpopulation of normal fibroblasts or whether all cells within the population are able to respond to exogenous TGF-beta by induction of elimination of transformed cells. Clonal analysis of the eliminative capacity of normal fibroblasts showed that all cells are able to induce elimination after addition of optimal concentrations of exogenous TGF-beta. In the absence of exogenously added TGF-beta, a minority of clones exhibited complete eliminative activity. Neither the ability nor the inability to perform elimination in the absence of exogenous TGF-beta was a stable characteristic of the respective cell clones. The number of cell clones with the ability to respond to suboptimal concentrations of TGF-beta increased with the passage number of the normal cells, whereas the number of clones inducing apoptosis in the absence of exogenous TGF-beta remained constant.

Transforming growth factor beta-treated normal fibroblasts eliminate transformed fibroblasts by induction of apoptosis

Transforming growth factor beta (TGF-beta) induces normal fibroblasts to perform an inhibitory effect directed against transformed cells (P. Höfler, I. Wehrle, and G. Bauer, Int. J. Cancer, 54: 125-130, 1993). Coculture of normal fibroblasts with transformed cells, either resistant to G 418 or expressing Mx antigen detectable by specific immunofluorescence, allowed discrimination between three theoretical mechanisms of inhibition: irreversible inhibition of proliferation; reversion to the nontransformed phenotype; or elimination of transformed cells. Our data demonstrate that normal fibroblasts treated with TGF-beta are able to eliminate transformed cells by induction of apoptosis. Sensitivity against TGF-beta-induced elimination seems to be a general feature of in vitro-transformed cell lines. TGF-beta-induced elimination of transformed fibroblasts by their untransformed counterparts is proposed as a potential potent control point in carcinogenesis, which may lead to the suppression of transformed cells.