Drug dosage in children with reduced renal function.

Drug dosing in paediatric nephrology requires multiple considerations and is therefore time-consuming and error-prone. This review combines dose adjustment guidelines for children with renal failure and information on the immature renal function of neonates and premature babies in order to help both paediatric nephrologists and neonatologists estimate drug doses for their patients.

Hypothalamic release of nitric oxide and interaction with amino acid neurotransmitters in chronically uraemic rats.

BACKGROUND: The activity of the hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator is diminished in uraemia. Since GnRH release is influenced by nitric oxide (NO) neurotransmission, we examined the integrity of hypothalamic NO neurotransmission in the chronically uraemic rat model. METHODS: Adult male castrated rats were rendered uraemic by two-stage 5/6 nephrectomy. Basal, N-methyl-D-aspartate (NMDA)-stimulated and DL-2-amino-5-phosphonovaleric acid (AP-5)-inhibited NO outflow was measured in uraemic and sham-nephrectomized control animals via a microdialysis probe in the medial preoptic area (MPOA). The influence of the noradrenergic system was evaluated by blocking noradrenergic neurons with N-(2-chloroethyl)-N-ethyl 2-bromobenzylamine (DSP-4). The activity of different NO synthase (NOS) isoforms was investigated by administration of the isoform-specific NOS inhibitors S-methyl-L-thiocitrulline (SMLT) and L-N6-(1-iminoethyl)-lysine (L-NIL). Moreover, hypothalamic mRNA expression of the individual NOS isoforms was quantitated by real-time reverse transcriptase-polymerase chain reaction. Effects of NO on amino acid outflow were assessed by addition of the NO donor S-nitroso-N-acetyl-penicillamine (SNAP). RESULTS: The expression of different NOS species and basal NO outflow did not differ between uraemic and control animals. Administration of the NO donor SNAP increased local NO production and amino acid outflow similarly in both groups. SMLT but not L-NIL, an inhibitor of the inducible NOS isoform, reduced NO outflow in both groups. AP-5 equally decreased, and noradrenergic blockade increased NMDA-stimulated NO outflow in both groups. CONCLUSIONS: NO is produced locally and may interfere with amino acid neurotransmission in the rat MPOA. Uraemia did not interfere with NO neurotransmission in our study.

Impaired autofeedback regulation of hypothalamic norepinephrine release in experimental uremia.

Chronic renal failure (CRF) is associated with multiple hypothalamic dysfunctions, including reduced secretion of gonadotropin-releasing hormone (GnRH). Because GnRH release is tightly controlled by sympathetic neuronal input, a possible alteration of local noradrenergic neurotransmission in experimental CRF was evaluated. Basal, stimulated, and autoinhibited norepinephrine (NE) release was assessed in hypothalamic and hippocampal tissue slices obtained from 5/6-nephrectomized and control rats. Autoinhibition-free NE release from brain slices, prelabeled with [3H]NE and superfused with physiologic buffer, was stimulated by six electrical pulses, 100 Hz (pseudo-one-pulse stimulation). Autoinhibited NE release was induced by 90 pulses at 3 Hz. The release of tritiated NE was measured upon addition of increasing concentrations of unlabeled NE to exogenously activate the inhibitory alpha2-autoreceptor. Although neither basal nor stimulated NE release differed between the groups, significantly lower pIC50 and Imax estimates of the concentration-response curves of exogenous NE on [3H]NE release were observed in CRF rats, suggesting a diminished autoinhibition of hypothalamic noradrenergic terminals in CRF. Western blotting of tissue homogenates disclosed a significantly reduced abundance of alpha2-autoreceptor protein in hypothalamic tissue from CRF rats. These abnormalities were selectively observed in the hypothalamus, whereas noradrenergic autoinhibition seemed unaltered in the hippocampus. The results suggest a diminished autoinhibition of hypothalamic NE release in CRF. Although impaired hypothalamic NE autoinhibition does not explain reduced GnRH secretion in CRF, it may be involved in the pathogenesis of sympathetic hyperactivity associated with this condition.

Molecular analysis of the SGLT2 gene in patients with renal glucosuria.

The role of SGLT2 (the gene for a renal sodium-dependent glucose transporter) in renal glucosuria was evaluated. Therefore, its genomic sequence and its intron-exon organization were determined, and 23 families with index cases were analyzed for mutations. In 21 families, 21 different SGLT2 mutations were detected. Most of them were private; only a splice mutation was found in 5 families of different ethnic backgrounds, and a 12-bp deletion was found in two German families. Fourteen individuals (including the original patient with 'renal glucosuria type 0') were homozygous or compound heterozygous for an SGLT2 mutation resulting in glucosuria in the range of 14.6 to 202 g/1.73 m(2)/d (81 - 1120 mmol/1.73 m(2)/d). Some, but not all, of their heterozygous family members had an increased glucose excretion of up to 4.4 g/1.73 m(2)/d (24 mmol/1.73 m(2)/d). Likewise, in index cases with glucosuria below 10 g/1.73 m(2)/d (55 mmol/1.73 m(2)/d) an SGLT2 mutation, if present, was always detected in the heterozygous state. We conclude that SGLT2 plays an important role in renal tubular glucose reabsorption. Inheritance of renal glucosuria shows characteristics of a codominant trait with variable penetrance.

Circulating inhibitor of gonadotropin releasing hormone secretion by hypothalamic neurons in uremia.

BACKGROUND: Previous studies have suggested a neuroendocrine defect underlying uremic hypogonadism, characterized by a reduced secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). METHODS: We studied the GnRH-producing GT1-7 cell line and the LH-producing LbetaT-2 pituitary cell line under uremic conditions to investigate whether substances circulating in uremic plasma directly affect hypothalamic or pituitary hormone secretion. The cells were incubated with serum from 5/6-nephrectomized or sham-nephrectomized castrated rats, respectively. Furthermore, GT1 cells were incubated with delipidated sera, serum subfractions separated by molecular weight, or several peptide hormones. Cellular viability, apoptosis rate and extracellular hormone degradation were assessed separately. GnRH and LH were measured by RIA in supernatants and cell lysates. GnRH gene expression was assessed by Northern blot. RESULTS: Uremic serum caused a reduction of extracellular GnRH concentration by 31%, whereas intracellular GnRH increased by 12%. This effect was independent of serum lipids and enzymatic GnRH degradation but was abolished by trypsin digestion. Cellular viability, apoptosis rates and GnRH gene expression did not differ between the two groups. The inhibitory activity was recovered from the high-molecular weight fraction, whereas the fraction <5 kD had stimulatory activity. In contrast, uremic serum did not affect LH secretion from LbetaT-2 cells, indicating that the hypoactivity of the hypothalamo-pituitary gonadotrope unit results from an inhibition at the hypothalamic rather than the pituitary level. CONCLUSIONS: Our results suggest that uremic serum contains macromolecular and hydrophilic peptide(s) able to specifically suppress the neurosecretion of GnRH from GT1-7 cells.

Biotin-dependent carboxylase activities in different CNS and skin-derived cells, and their sensitivity to biotin-depletion.

The validity of various transformed and untransformed CNS and skin-derived cell cultures as a model for studying effects of biotin deficiency was tested. In biotin-sufficient conditions (0.1-10 mumol/L) all cell types showed considerable activities of the four biotin-dependent carboxylases. Notably, pyruvate carboxylase activity was also present in the different neuronal cells. One passage in low-biotin medium (6-130 pmol/L) lowered mitochondrial carboxylase activities in all cell types, but to varying degrees. Sensitivity to biotin depletion was greatest in three neuronal cell types, Roc-1 oligodendroglia, and three keratinocyte cell types (carboxylase activities decreased to 2-11% of maximal); intermediate in primary astrocytes and C6 glioma (decreased to 12-28%), and least in SAOS2 sarcoma and skin fibroblasts (decreased to 32-85%). Transformed and untransformed cell lines of the same cell type showed similar sensitivity. We conclude that cultures of different transformed CNS and keratinocyte cell types allow the study of effects of biotin deprivation. Carboxylase activities of neurons, oligodendroglia, and keratinocytes were much more sensitive to biotin depletion than fibroblasts. This may be an important factor in the pathogenesis of neurological and cutaneous abnormalities in congenital biotinidase deficiency where recycling of biotin is deficient.

Laparoscopic Tenckhoff catheter implantation in children.

OBJECTIVE: To assess the suitability of a laparoscopic Tenckhoff catheter implantation (TCI) technique in children. DESIGN: Prospective nonrandomized controlled study. SETTING: Laparoscopic and conventional TCIs in children were performed in a tertiary-care hospital. PATIENTS: Between 1998 and 2001, 25 laparoscopic and 23 conventional TCIs were performed in 42 children. Patients in unstable clinical conditions were excluded. The laparoscope was inserted via transumbilical incision, and a forceps by percutaneous puncture. After catheter insertion, the tip was positioned in the Douglas space, and the inner cuff placed adjacent to the peritoneum, without sutures. Peritoneal dialysis was initiated immediately after surgery. MAIN OUTCOME MEASURES: Catheter-related complications during the first 4 weeks after TCI. RESULTS: After laparoscopic TCI, dialysate leakage occurred in 2 of 25 cases, one of which could be managed conservatively. In 1 patient in whom dwell volume was increased immediately after laparoscopic TCI, subcutaneous leakage occurred at the site of forceps insertion. In 2 patients with severe pre-existing intra-abdominal adhesions, outflow obstruction persisted after laparoscopic TCI. Simultaneous herniotomy was performed in 2 male infants. After conventional TCI, dialysate leakage occurred in 5 of 23 cases, 1 of which could be managed conservatively. Outflow obstruction occurred in 2 cases. CONCLUSION: Laparoscopic TCI is feasible in children of all age groups, with at least equivalent functional results compared to conventional TCI. An additional advantage is the option to identify and eliminate anatomical risk factors, such as intra-abdominal adhesions or preformed inguinal hernias in male infants.

Emergency dialysis in neonatal metabolic crises.

Metabolic crises in children with inborn errors of metabolism are caused by the accumulation of neurotoxic metabolites. Rapid elimination of these metabolites is apparently crucial to prevent irreversible neuronal damage; long-term outcome is correlated with the rate of toxin removal during the crisis. The usefulness of different blood purification techniques for removing accumulated neurotoxins is reviewed in this manuscript.

Experimental uremia affects hypothalamic amino acid neurotransmitter milieu.

Chronic renal failure is associated with delayed puberty and hypogonadism. To investigate the mechanisms subserving the reported reduced pulsatile release of gonadotropin-releasing hormone (GnRH) in chronic renal failure, this study examined the amino acid neurotransmitter milieu in the medial preoptic area (MPOA), the hypothalamic region where the GnRH-secreting neurons reside, in 5/6-nephrectomized male rats and in ad libitum-fed or pair-fed controls. All rats were castrated and received either a testosterone or a vehicle implant to evaluate additional effects of the prevailing sex steroid milieu. Local excitatory (essential amino acids: aspartate, glutamate) and inhibitory (gamma-aminobutyric acid [GABA], taurine) amino acid transmitter outflow in the MPOA was measured by microdialysis via stereotactically implanted cannulae in the awake, freely moving rats. In addition to basal extracellular concentrations, the neurosecretory capacity was assessed by the addition of 100 mM KCl to the dialysis fluid. The mechanisms of neurosecretion were evaluated further by inhibition of vesicular release with the use of Ca(2+)-free, Mg(2+)-enriched dialysis fluid and by local perfusion with inhibitors of voltage-dependent synaptic release (1 microM tetrodotoxin) and of GABA reuptake (0.5 mM nipecotic acid). In the uremic rats, basal outflow of GABA, glutamate and aspartate, and K(+)-stimulated aspartate outflow were increased. K(+)-stimulated GABA and glutamate release was less sensitive to Ca(2+) depletion in the uremic than in the control rats. The elevated basal GABA and essential amino acid outflow in the uremic rats was due to a voltage- and Ca(2+)-independent mechanism. GABA reuptake was inhibited proportionately by nipecotic acid in uremic and pair-fed control rats. Testosterone supplementation had no independent effects on neurotransmitter outflow. In summary, the amino acid neurotransmitter milieu is altered in the MPOA of uremic rats by a nonsynaptic, nonvesicular mechanism. These abnormalities may contribute to the impaired function of the GnRH pulse generator.