Effect of peripartal feeding strategy on colostrum yield and composition in sows

Research showed a positive association between back fat (BF) change the week before farrowing and colostrum yield (CY). This study tested the causality of this association, hence to optimize CY by altering the sows' peripartal feeding strategy. Sows were randomly divided into 2 treatment groups at d 108 of gestation. The first group (L, n = 28) received 1.5 kg feed·d(-1), the second group (H, n = 22) received 3 times 1.5 kg feed·d(-1) until farrowing. Daily feed intake and CY were measured. Colostrum was analyzed for nutrient composition, AA and fatty acids, IgG and IgA. Sow serum was obtained at d 108 of gestation and d 1 of lactation after overnight fasting and analyzed for NEFA, (iso)butyrylcarnitine (C4), creatinine, urea, 3-OH-butyrylcarnitine (3-OH-C4), IgG, and IgA. Based on BF at d 108, sows were divided into body condition (BC) groups: skinny (<17 mm, n = 15), moderate (17 to 23 mm, n = 21), fat (>23 mm, n = 14). We performed ANOVA with treatment and BC as fixed factors and Scheffé post-hoc test. The week before farrowing, the L group had the lowest daily feed intake (DFI; 1.5 kg), and within the H group, fat sows (3.8 kg) had a lower DFI than skinny sows (4.3 kg; p = 0.006). The H group tended to have a greater total CY (P = 0.074) and had a greater CY/kg liveborn piglet (P = 0.018) than the L group. Compared with sows in moderate BC, fat sows had a lower total CY (P = 0.044) and a lower CY/kg liveborn piglet (P = 0.005). The H group had a greater concentration of lactose (p = 0.009) and n-3 PUFA (p < 0.001) but a lower concentration of protein (p = 0.040) in colostrum than the L group. The concentration of IgG and IgA did not differ between treatment and BC groups. Serum parameters at d 108 were similar between the treatment groups and BC groups. At d 1, the H group mobilized less body fat (NEFA: p = 0.002) and protein (creatinine: p < 0.001, C4: p = 0.016) reserves but had a greater ratio urea:NEFA (p < 0.001) and less ketone bodies (3-OH-C4: p < 0.001) compared with the L group. This indicates a more balanced entry of metabolites in the citric acid cycle and thus a better support of the maternal peripartal metabolism in the H group. Serum parameters did not differ between BC groups. Both CY and composition can be influenced by the peripartal feeding strategy and BC. The highest CY and most beneficial colostrum composition were obtained when sows entered the farrowing unit in a moderate BC and were provided a high peripartal feeding strategy.

Lethal phenotype in conditional late-onset arginase 1 deficiency in the mouse

Human arginase deficiency is characterized by hyperargininemia and infrequent episodes of hyperammonemia, which lead to neurological impairment with spasticity, loss of ambulation, seizures, and severe mental and growth retardation; uncommonly, patients suffer early death from this disorder. In a murine targeted knockout model, onset of the phenotypic abnormality is heralded by weight loss at around day 15, and death occurs typically by postnatal day 17 with hyperargininemia and markedly elevated ammonia. This discrepancy between the more attenuated juvenile-onset human disease and the lethal neonatal murine model has remained suboptimal for studying and developing therapy for the more common presentation of arginase deficiency. These investigations aimed to address this issue by creating an adult conditional knockout mouse to determine whether later onset of arginase deficiency also resulted in lethality. Animal survival and ammonia levels, body weight, circulating amino acids, and tissue arginase levels were examined as outcome parameters after widespread Cre-recombinase activation in a conditional knockout model of arginase 1 deficiency. One hundred percent of adult female and 70% of adult male mice died an average of 21.0 and 21.6 days, respectively, after the initiation of tamoxifen administration. Animals demonstrated elevated circulating ammonia and arginine at the onset of phenotypic abnormalities. In addition, brain and liver amino acids demonstrated abnormalities. These studies demonstrate that (a) the absence of arginase in adult animals results in a disease profile (leading to death) similar to that of the targeted knockout and (b) the phenotypic abnormalities seen in the juvenile-onset model are not exclusive to the age of the animal but instead to the biochemistry of the disorder. This adult model will be useful for developing gene- and cell-based therapies for this disorder that will not be limited by the small animal size of neonatal therapy and for developing a better understanding of the characteristics of hyperargininemia.

L-arginine:glycine amidinotransferase deficiency protects from metabolic syndrome

Phosphorylated creatine (Cr) serves as an energy buffer for ATP replenishment in organs with highly fluctuating energy demand. The central role of Cr in the brain and muscle is emphasized by severe neurometabolic disorders caused by Cr deficiency. Common symptoms of inborn errors of creatine synthesis or distribution include mental retardation and muscular weakness. Human mutations in l-arginine:glycine amidinotransferase (AGAT), the first enzyme of Cr synthesis, lead to severely reduced Cr and guanidinoacetate (GuA) levels. Here, we report the generation and metabolic characterization of AGAT-deficient mice that are devoid of Cr and its precursor GuA. AGAT-deficient mice exhibited decreased fat deposition, attenuated gluconeogenesis, reduced cholesterol levels and enhanced glucose tolerance. Furthermore, Cr deficiency completely protected from the development of metabolic syndrome caused by diet-induced obesity. Biochemical analyses revealed the chronic Cr-dependent activation of AMP-activated protein kinase (AMPK), which stimulates catabolic pathways in metabolically relevant tissues such as the brain, skeletal muscle, adipose tissue and liver, suggesting a mechanism underlying the metabolic phenotype. In summary, our results show marked metabolic effects of Cr deficiency via the chronic activation of AMPK in a first animal model of AGAT deficiency. In addition to insights into metabolic changes in Cr deficiency syndromes, our genetic model reveals a novel mechanism as a potential treatment option for obesity and type 2 diabetes mellitus.

Guanidino compound levels in blood, cerebrospinal fluid, and post-mortem brain material of patients with argininemia

The paucity of hyperammonemic crises together with spasticity, only seen in human arginase I deficient patients and not in patients with other urea cycle disorders, forces a search for candidates other than ammonia to associate with the pathophysiology and symptomatology. Therefore, we determined arginine together with some catabolites of arginine in blood and cerebrospinal fluid of these patients as well as in extremely rare post-mortem brain material of two patients with argininemia. The levels of alpha-keto-delta-guanidinovaleric acid, argininic acid and alpha-N-acetylarginine correlate with the arginine levels in blood and cerebrospinal fluid of patients with imposed or spontaneous protein restriction. The levels in blood are higher than the upper limit of normal in all studied patients. In addition to the highly increased levels of these same compounds in blood of a child with argininemia, the increase of guanidinoacetic acid, 24h before death, is remarkable. However, the manifest increases of these studied catabolites of arginine are not seen in post-mortem brain material of the same pediatric patient. Otherwise a clear increase of guanidinoacetic acid in post-mortem brain material of an adult patient was shown. A similar, comparable increase of homoarginine in both studied post-mortem brain materials is observed. Therefore the study of the pathobiochemistry of arginine in argininemia must be completed in the future by the determination of the end catabolites of the nitric oxide and agmatine biosynthesis pathways in the knockouts as well as in the patients to evaluate their role, together with the here studied catabolites, as candidates for association with pathophysiology and symptomatology.

Homeostatic plasticity of striatal neurons intrinsic excitability following dopamine depletion

The striatum is the major input structure of basal ganglia and is involved in adaptive control of behaviour through the selection of relevant informations. Dopaminergic neurons that innervate striatum die in Parkinson disease, leading to inefficient adaptive behaviour. Neuronal activity of striatal medium spiny neurons (MSN) is modulated by dopamine receptors. Although dopamine signalling had received substantial attention, consequences of dopamine depletion on MSN intrinsic excitability remain unclear. Here we show, by performing perforated patch clamp recordings on brain slices, that dopamine depletion leads to an increase in MSN intrinsic excitability through the decrease of an inactivating A-type potassium current, I(A). Despite the large decrease in their excitatory synaptic inputs determined by the decreased dendritic spines density and the increase in minimal current to evoke the first EPSP, this increase in intrinsic excitability resulted in an enhanced responsiveness to their remaining synapses, allowing them to fire similarly or more efficiently following input stimulation than in control condition. Therefore, this increase in intrinsic excitability through the regulation of I(A) represents a form of homeostatic plasticity allowing neurons to compensate for perturbations in synaptic transmission and to promote stability in firing. The present observations show that this homeostatic ability to maintain firing rates within functional range also occurs in pathological conditions, allowing stabilizing neural computation within affected neuronal networks.

Accumulation of methylguanidine and changes in guanidino compound levels in plasma, urine, and kidneys of furosemide-treated rats

Antidiuresis and renal diseases alter the levels of guanidino compounds (GCs) in various tissues. Therefore, we hypothesized that diuresis could also disturb GC metabolism, storage, and elimination. In this study, rats were made diuretic to analyze GC levels in plasma, urine, and kidneys. Furosemide was chosen because of its wide use in various human pathologies. Rats were injected intraperitoneally 5 or 10 mg furosemide spread over a 24-hour cycle. Urine was collected over a period of 24 hours before and during furosemide treatment. Plasma was obtained from arterial blood. Renal zones were dissected. The GCs were determined by liquid chromatography. Five milligrams of furosemide provoked a significant increase in plasma and urine levels of GCs compared with those of the controls. The renal distribution and content of GCs were weakly modified by furosemide except for methylguanidine (MG). The level of MG was enhanced by 10 to 16 times in all renal zones. The MG level was 60% higher in renal zones of rats treated with 10 rather than 5 mg furosemide. The fractional excretion of MG was decreased by furosemide. Our data suggest that MG accumulation in kidney and plasma was caused by furosemide, which might induce MG synthesis, and that MG washout from tissue cells into urine by furosemide through the kidney may cause an increase in MG in the kidney.

Increased plasma and tissue guanidino compounds in a mouse model of hyperargininemia

In humans, arginase I (AI)-deficiency results in hyperargininemia, a metabolic disorder with symptoms of progressive neurological and intellectual impairment, spasticity, persistent growth retardation, and episodic hyperammonemia. A deficiency of arginase II (AII) has never been detected and the clinical disorder, if any, associated with its deficiency has not been defined. Since the spasticity and paucity of hyperammonemic crises seen in human AI-deficient patients are not features of the other urea cycle disorders, the likelihood of ammonia as the main neuropathogenic agent becomes extremely low, and the modest elevations of arginine seen in the brains of our mouse model of hyperargininemia make it an unlikely candidate as well. Specific guanidino compounds, direct or indirect metabolites of arginine, are elevated in the blood of patients with uremia. Other guanidino compounds are also increased in plasma and cerebrospinal fluid of hyperargininemic patients making them plausible as neurotoxins in these disorders. We analyzed several guanidino compounds in our arginase single and double knockout animals and found that alpha-keto-delta-guanidinovaleric acid, alpha-N-acetylarginine, and argininic acid were increased in the brain tissue from the AI knockout and double knockout animals. Several compounds were also increased in the plasma, liver, and kidneys. This is the first time that several of the guanidino compounds have been shown to be elevated in the brain tissue of an arginase-deficient mammal, and it further supports their possible role as the neuropathogenic agents responsible for the complications seen in arginase deficiency.

Guanidino compounds after creatine supplementation in renal failure patients and their relation to inflammatory status

BACKGROUND

Specific guanidino compounds have been described as uraemic toxins and their concentrations are increased in renal failure due to dimished glomerular filtration, whereas the guanidino compound creatine is used as a performance-enhancing substance in athletes. The present study investigates the effects of creatine supplementation on plasma guanidino compounds in a chronic haemodialysis population.

METHODS

Twenty male haemodialysis patients were included in a placebo-controlled cross-over trial. Patients were treated with creatine (2 g/day) or placebo during two treatment periods of 4 weeks, separated by a washout of 4 weeks. Plasma guanidino compounds and routine biochemical parameters were determined, as well as the prognostic inflammatory and nutritional index (PINI).

RESULTS

Upon creatine supplementation, guanidinoacetate concentrations decreased by 15%, due to inhibition of creatine synthesis. Concentrations of alpha-keto-delta-guanidinovaleric acid increased three-fold and argininic acid concentrations doubled. Guanidinosuccinate concentrations did not change, but correlated inversely with CRP (r = -0.736; P = 0.001), PINI-score (r = -0.716; P = 0.002) and correlated positively with plasma urea concentration (r = 0.54; P = 0.02).

CONCLUSIONS

Creatine supplementation in haemodialysis patients significantly altered the concentration of specific guanidino compounds. Guanidinosuccinate correlated positively with plasma urea and negatively with inflammation markers.

Complex Compartmental Behavior of Small Water-Soluble Uremic Retention Solutes: Evaluation by Direct Measurements in Plasma and Erythrocytes

BACKGROUND

Although scanty data suggest that large solutes show kinetic behavior different from urea, there are virtually no data comparing the kinetics of urea with those of other small water-soluble uremic compounds, which are believed to behave similarly.

STUDY DESIGN

Cross-sectional study of kinetics of urea and guanidino compounds in plasma and erythrocyte compartments during a single hemodialysis session.

SETTING & PARTICIPANTS

Six stable hemodialysis patients on standard low-flux dialysis therapy.

PREDICTORS

Reduction ratios (RRs) of urea calculated from plasma and erythrocyte concentrations.

OUTCOMES

RRs for guanidino compounds calculated from measurements of both plasma and erythrocyte concentrations.

MEASUREMENTS

Blood samples were collected from the dialyzer inlet and outlet at 0, 5, 15, 30, and 120 minutes and at the end of the session. Plasma and erythrocyte concentrations of urea and guanidino compounds (creatinine [CTN], guanidinosuccinic acid [GSA], guanidinoacetic acid [GAA], guanidine [G], and methylguanidine [MG]) were determined.

RESULTS

Postdialysis plasma RR was higher for GSA (82% +/- 3%) compared with urea (77% +/- 2%; P < 0.01), whereas CTN (69% +/- 4%), GAA (49% +/- 14%), G (55% +/- 7%), and MG (55% +/- 7%) showed smaller RRs (P < 0.01). In erythrocytes, GSA (45% +/- 1%), G (10% +/- 13%), and MG (27% +/- 10%) showed markedly smaller RRs than urea (59% +/- 6%; P < 0.05). Finally, significant differences were found between plasma and erythrocyte RRs for urea, GSA, G, and MG (P < 0.01).

LIMITATIONS

Discrepancies were found between the biochemical and mathematical approaches. Hence, the erythrocyte compartment does not necessarily conform to the kinetic nonperfused compartment.

CONCLUSIONS

Our data indicate by means of direct estimations that the compartmental behaviors of guanidino compounds and urea are substantially different. Hence, we should consider that not all changes in concentrations in uremia and dialysis are representatively reflected by urea kinetics, even when considering other small water-soluble substances, such as the guanidino compounds.

Biochemical validation of a rat model for polycystic kidney disease: Comparison of guanidino compound profile with the human condition

Polycystic kidney disease (PKD) accounts for 7-10% of all dialyzed renal insufficient patients. Accumulation of specific guanidino compounds (GCs) has been related to neurological, cardiovascular, hematological, and immunological complications of renal failure. In this study, we investigate whether the PKD/Mhm rat model can be used as a biochemical model for human PKD. For the validation of the rat model, we performed the first detailed evaluation of the concentrations of GCs in serum and urine of patients with PKD in addition to the GC patterns in the plasma, urine, and tissues of the PKD/Mhm rat model. The GCs were determined after separation on a cation exchange resin and fluorescence detection. The GC levels and changes observed in blood and urine of patients with PKD are comparable with those found in patients with renal insufficiency due to different etiologies. The PKD/Mhm rat model can be used as a biochemical model for human PKD as the obvious increases of urea, guanidinosuccinic acid, creatinine, guanidine, methylguanidine, and N(G)N(G)-dimethylarginine (symmetrical dimethylarginine) seen in blood of oldest heterozygous and younger homozygous PKD rats were largely within the same range as those found in the studied human PKD population, especially in patients with a glomerular filtration rate below 60 ml/min/1.73 m(2). The decreased levels of plasma guanidinoacetic acid seen at end-stage renal disease in homozygous and oldest heterozygous rats were also observed in serum of patients with a glomerular filtration rate below 20 ml/min/1.73 m(2). The PKD/Mhm rat model has, besides similar disease characteristics with human PKD, comparable GC alterations.

Regional distribution of biogenic amines, amino acids and cholinergic markers in the CNS of the C57BL/6 strain

A reliable extrapolation of neurochemical alterations from a mouse model to human metabolic brain disease requires knowledge of neurotransmitter levels and related compounds in control mouse brain. C57BL/6 is a widely used background strain for knockout and transgenic mouse models. A prerequisite for reliable extrapolation from mouse brain to the human condition is the existence of analogous distribution patterns of neurotransmitters and related compounds in control mouse and human brain. We analysed regional distribution patterns of biogenic amines, neurotransmitter and non-neurotransmitter amino acids, and cholinergic markers. Distribution patterns were compared with known neurotransmitter pathways in human brain. The present study provides a reference work for future analyses of neurotransmitters and related compounds in mouse models bred in a C57BL/6 background strain.

Kinetic behavior of urea is different from that of other water-soluble compounds: The case of the guanidino compounds

BACKGROUND

Although patients with renal failure retain a large variety of solutes, urea is virtually the only currently applied marker for adequacy of dialysis. Only a limited number of other compounds have up until now been investigated regarding their intradialytic kinetics. Scant data suggest that large solutes show a kinetic behavior that is different from urea. The question investigated in this study was whether other small water-soluble solutes, such as some guanidino compounds, show a kinetic behavior comparable or dissimilar to that of urea.

METHODS

This study included 7 stable conventional hemodialysis patients without native kidney function undergoing low flux polysulphone dialysis (F8 and F10HPS). Blood samples were collected from the inlet and outlet bloodlines immediately before the dialysis session, after 5, 15, 30, 120 minutes, and immediately after discontinuation of the session. Plasma concentrations of urea, creatinine (CTN), creatine (CT), guanidinosuccinic acid (GSA), guanidinoacetic acid (GAA), guanidine (G), and methylguanidine (MG) were used to calculate corresponding dialyzer clearances. A two-pool kinetic model was fitted to the measured plasma concentration profiles, resulting in the calculation of the perfused volume (V(1)), the total distribution volume (V(tot)), and the intercompartmental clearance (K(12)); solute generation and overall ultrafiltration were determined independently.

RESULTS

No significant differences were observed between V(1) and K(12) for urea (6.4 +/- 3.3 L and 822 +/- 345 mL/min, respectively) and for the guanidino compounds. However, with respect to V(tot), GSA was distributed in a smaller volume (30.6 +/- 4.2 L) compared to urea (42.7 +/- 6.0L) (P < 0.001), while CTN, CT, GAA, G, and MG showed significantly higher volumes (54.0 +/- 5.9 L, 98.0 +/- 52.3 L, 123.8 +/- 66.9 L, 89.7 +/- 21.4 L, 102.6 +/- 33.9 L, respectively; P= 0.004, = 0.033, = 0.003, < 0.001, = 0.001, respectively). These differences resulted in divergent effective solute removal: 67% (urea), 58% (CTN), 42% (CT), 76% (GSA), 37% (GAA), 43% (G), and 42% (MG).

CONCLUSION

The kinetics of the guanidino compounds under study are different from that of urea; hence, urea kinetics are not representative for the removal of other uremic solutes, even if they are small and water-soluble like urea.

Biochemical and behavioural phenotyping of a mouse model for GAMT deficiency

Deficiency of guanidinoacetate N-methyltransferase (GAMT) is the first described creatine (CT) deficiency syndrome in man, biochemically characterized by accumulation of guanidinoacetic acid (GAA) and depletion of CT. Patients exhibit severe developmental and muscular problems. We created a mouse model for GAMT deficiency, which exerts biochemical changes comparable with those found in human GAMT-deficient subjects. CT and creatinine (CTN) levels are significantly decreased and GAA is increased in knockout (KO) mice. In patients, other guanidino compounds (GCs) appear to be altered as well, which may also contribute to the symptomatology. Extensive evaluation of GCs levels in the GAMT mouse model was therefore considered appropriate. Concentrations of 13 GCs in plasma, 24-h urine, brain and muscle of GAMT mice were measured. We also report on the detailed behavioural characterization of this model for GAMT deficiency. Besides an increase of GAA and a decrease of CT and CTN in plasma, 24-h urine, brain and muscle of KO mice, we observed a significant increase of other GCs in brain and muscle that was sometimes reflected in plasma and/or urine. KO mice displayed mild cognitive impairment. In general, it could be concluded that the GAMT mouse model is very useful for biochemical research of GAMT deficiency, but shows only a mild cognitive deficit.

Analysis of cholinergic markers, biogenic amines, and amino acids in the CNS of two APP overexpression mouse models

Two transgenic mouse models expressing mutated human amyloid precursor protein and previously found to display cognitive and behavioural alterations, reminiscent of Alzheimer patients' symptomatology, were scrutinised for putative brain region-specific changes in neurochemical parameters. Brains of NSE-hAPP751m-57, APP23 and wild-type mice were microdissected to perform brain region-specific neurochemical analyses. Impairment of cholinergic transmission, the prominent neurochemical deficit in Alzheimer brain, was examined; acetylcholinesterase and choline acetyltransferase activity levels were determined as markers of the cholinergic system. Since Alzheimer neurodegeneration is not restricted to the cholinergic system, brain levels of biogenic amines and metabolites, and amino acidergic neurotransmitters and systemic amino acids were analysed as well. Cholinergic dysfunction, reflected in reduced enzymatic activity in the basal forebrain nuclei, was restricted to the APP23 model, which also exhibited more outspoken and more widespread changes in other neurotransmitter systems. Significant changes in compounds of the noradrenergic and serotonergic system were observed, as well as alterations in levels of the inhibitory neurotransmitter glycine and systemic amino acids. These observations were clearly in occurrence with the more pronounced histopathological and behavioural phenotype of the APP23 model. As transgenic models often do not represent an end-stage of the disease, some discrepancies with results from post-mortem human Alzheimer brain analyses were apparent; in particular, no significant alterations in excitatory amino acid levels were detected. Our findings of brain region-specific alterations in compound levels indicate disturbed neurotransmission pathways, and greatly add to the validity of APP23 mice as a model for Alzheimer's disease. Transgenic mouse models may be employed as a tool to study early-stage neurochemical changes, which are often not accessible in Alzheimer brain.

GSA: behavioral, histological, electrophysiological and neurochemical effects

Renal insufficient patients suffer from a variety of complications as direct and indirect consequence of accumulation of retention solutes. Guanidinosuccinic acid (GSA) is an important probable uremic toxin, increased in plasma, urine, cerebrospinal fluid and brain of patients with uremia and supposed to play a role in the pathogenesis of some neurological symptoms. GSA, an NMDA-receptor agonist and GABA-receptor antagonist, is suggested to act as an excitotoxin and shown to be convulsive. The effect of hippocampal (i.h.) GSA injection on behavior and hippocampal volume in mice is presented here. In addition, hippocampal cGMP concentration after systemic injection of GSA was measured. The effect of co-application of NMDA-receptor antagonist CGP37849 with GSA was tested, in vivo, after hippocampal GSA injection and, in vitro, on GSA evoked currents in spinal cord neurons. A significant dose-dependent effect of i.h. injection of GSA on cognitive performance, activity and social exploratory behavior was observed. There was a protective effect of CGP37849 on GSA induced behavioral alterations. Volume of hippocampal cornu ammonis region decreased significantly and dose-dependently after GSA injection. Systemic GSA injection increased cGMP concentration in hippocampal formation. It can be concluded that GSA is an important neurotoxin. As GSA is increased in patients with uremia, it probably contributes to their neurological symptoms. Knowledge of neurotoxic effects and mechanisms of action of GSA and other uremic retention solutes could help in the development of more efficient treatment of uremic patients. Animal models like the 'GSA mouse model' are useful tools for research in this context.

Plasma guanidino compounds are altered by oral creatine supplementation in healthy humans

Although creatine is one of the most widely used nutritional supplements for athletes as well as for patients with neuromuscular disorders, the effects of oral creatine supplementation on endogenous creatine synthesis in humans remains largely unexplored. The aim of the present study was to investigate the metabolic consequences of a frequently used, long-term creatine ingestion protocol on the circulating creatine synthesis precursor molecules, guanidinoacetate and arginine, and their related guanidino compounds. For this purpose, 16 healthy young volunteers were randomly divided to ingest in a double-blind fashion either creatine monohydrate or placebo (maltodextrine) at a dosage of 20 g/day for the first week (loading phase) and 5 g/day for 19 subsequent wk (maintenance phase). Fasting plasma samples were taken at baseline and at 1, 10, and 20 wk of supplementation, and guanidino compounds were determined. Plasma guanidinoacetate levels were reduced by 50% after creatine loading and remained ∼30% reduced throughout the maintenance phase. Several circulating guanidino compound levels were significantly altered after creatine loading but not during the maintenance phase: homoarginine (+35%), α-keto-δ-guanidinovaleric acid (+45%), and argininic acid (+75%) were increased, whereas guanidinosuccinate was reduced (−25%). The decrease in circulating guanidinoacetate levels suggests that exogenous supply of creatine chronically inhibits endogenous synthesis at the transamidinase step in humans, supporting earlier animal studies showing a powerful repressive effect of creatine on l-arginine:glycine amidinotransferase. Furthermore, these data suggest that this leads to enhanced utilization of arginine as a substrate for secondary pathways.

Effect of NaCN on currents evoked by uremic retention solutes in dissociated mouse neurons

Uremic retention solutes possibly contribute to neuronal hypoxia/ischemia and its consequences in patients with renal failure. We examined the in vitro effects of several uremic retention solutes on murine central neurons under chemically induced metabolic hypoxia by application of sodium cyanide (NaCN). Whole cell currents were recorded using the tight-seal whole-cell voltage clamp technique. Application of NaCN caused an inward whole-cell current. From all tested toxins, which included several indoles, guanidino compounds, polyamines, purines, phenols, DL-homocysteine, orotate and myoinositol, only creatinine (CTN), guanidine (G) and guanidinosuccinic acid (GSA) produced a significant current in control and hypoxic neurons. Current evoked by GSA was significantly increased in the chemical hypoxic condition, and a synergistic effect of GSA and spermine was observed in hypoxic neurons.