Kynurenic acid inhibits intestinal hypermotility and xanthine oxidase activity during experimental colon obstruction in dogs.

Kynurenic acid (KynA), an endogenous antagonist of N-methyl-d-aspartate (NMDA) glutamate receptors, protects the central nervous system in excitotoxic neurological diseases. We hypothesized that the inhibition of enteric glutamate receptors by KynA may influence dysmotility in the gastrointestinal tract. Group 1 of healthy dogs served as the sham-operated control, in group 2, the animals were treated with KynA, while in groups 3 and 4 mechanical colon obstruction was maintained for 7 h. Group 4 was treated with KynA at the onset of ileus. Hemodynamics and motility changes were monitored, and the activities of xanthine oxidoreductase (XOR) and myeloperoxidase (MPO) were determined from tissue samples. Colon obstruction induced a hyperdynamic circulatory reaction, significantly elevated the motility index and increased the mucosal leucocyte accumulation and the XOR activity. The KynA treatment augmented the tone of the colon, permanently decreased the motility index of the giant colonic contractions and reduced the increases in XOR and MPO activities. These effects were concomitant with the in vitro inhibition of XOR activity. In conclusion, KynA antagonizes the obstruction-induced motility responses and XOR activation in the colon. Inhibition of enteric NMDA receptors may provide an option to influence intestinal hypermotility and inflammatory changes.

The roles of platelet function, thromboxane, blood lipids and nitric oxide in hypertension of children and adolescents.

The roles of platelet function, plasma lipids and nitric oxide (NO) were studied in adolescent patients with essential hypertension (JEHT group), with chronic renal failure (CRF) associated with hypertension (CRFH group), and CRF patients with normal blood pressure (CRF group), as compared with normal controls (cont. group). Platelet aggregation and the thromboxane B(2)(TxB(2)) level were significantly higher in the JEHT and CRFH groups as compared with the cont. group, whereas they were significantly lower in the CRF group. On the other hand, the platelet cAMP level was significantly lower in the JEHT and CRFH groups than in the cont. group. The plasma NO level was significantly higher only in the JEHT as compared with the cont. group (120 +/- 39 and 89 +/- 21 microM, respectively). The plasma total cholesterol, triglyceride and LDL cholesterol concentrations were normal in the JEHT group, but high in the CRF and CRFH group, the HDL cholesterol level was lower in the CRF and CRFH groups as compared with the cont. and JEHT groups. There was a positive correlation between the platelet aggregation and the TxB(2)level and between the BP and the platelet aggregation. In conclusion, hyperlipidaemia is commonly present in uraemia with haemodialysis, but is not specific for hypertension in children, while an increased platelet function is frequently associated with hypertension. The increased NO level might play a compensatory role in JEHT.

A putative tetrapeptide antagonist prevents beta-amyloid-induced long-term elevation of [Ca2+]i in rat astrocytes.

Comparative fluorimetric studies on the long-term (8-hour) action of beta[1-42]amyloid and its shorter fragments beta[1-40], beta[25-35] and beta[31-35] on the steady-state intracellular Ca2+ concentration in primary cultures of rat astroglial cells using the Ca2+-sensitive fluorescent probe Fura-2 AM revealed higher 340/380 fluorescence excitation ratios in the treated cells as compared to the untreated controls. All the peptides were found to induce similar cellular effects, suggesting the [31-35] region as the putative active centre of the molecule. No significant alteration was detectable in Fura-2 fluorescence using the Ca2+-insensitive excitation wavelength of 367 nm, indicating that the observed changes reflect a real alteration in the Ca2+ concentration of the cells. Moreover, no considerable difference was observed in the total protein content of treated and untreated cells. Co-treatment of the cells with Pr-Ile-Ile-Gly-Leu-NH2 (Pr-IIGL) peptide, an analogue of the [31-34] region of beta[1-42]-amyloid, was found to effectively antagonize the beta[1-42]-amyloid-induced elevation of the fluorescence excitation ratio, leaving the 367-nm fluorescence unaffected. To the best of the authors' knowledge, this is the first report on an analogue of beta-amyloid peptide capable of blocking one of its physiological effects, thereby raising the possibility that this sequence could prove to be a lead compound for designing effective beta-amyloid antagonists.

Intracellular free Ca2+ elevations in cultured astroglia induced by neuroligands playing a role in cerebral ischemia.

For better understanding of glial participation in cerebral ischemia, spectrofluorimetric analysis using the calcium indicator Fura-2AM was applied to examine the role of intracellular free Ca2+ ([Ca2+])i elevation induced by different neuroactive substances in cultured rat brain astrocytes. The activation by the general receptor agonist glutamate resulted in a biphasic cell response in [Ca2+]i. We couldn't observe N-methyl-D-aspartate-evoked [Ca2+]i response at all. Quisqualate triggered a complex [Ca2+]i response in astrocytes consisting of mobilization of Ca2+ from the intracellular stores and also Ca2+ influx from the extracellular space. Kainate elicited a markedly different Ca2+ signal an external Ca(2+)-dependent sustained [Ca2+]i rise resulting from the activation of the ionotropic glutamate receptor. According to our results two types of glutamate receptors, the quisqualate-specific metabotropic and kainate-specific ionotropic receptor, are involved in [Ca2+]i elevation in these cultures. We could monitor agonist-specific cell response to noradrenaline, serotonin, vasopressin and ATP as well in these cultured rat astrocytes.

The effect of erythropoietin on platelet function in uraemic children on haemodialysis.

The effect of 1-year erythropoietin (rHu-EPO) treatment on the bleeding time, platelet aggregation, ATP and thromboxane B2 (TXB2) release, cyclic AMP (cAMP) concentration and platelet surface positive charge were studied in 8 haemodialysed children with chronic uraemia and 8 controls. The pre-dialysis haematocrit (Hct) was 0.21 + 0.01 before and 0.36 + 0.01 following 1 year of rHu-EPO therapy. At the end of this period the pre-dialysis bleeding time became normal (P < 0.05); this was associated with a significant increase in platelet aggregability (P < 0.05), ATP release (P < 0.05) and TXB2 production (P < 0.01), and with a significant decrease in platelet cAMP concentration (P < 0.01). A further increase in platelet aggregation, ATP release and TXB2 production and a decrease in platelet cAMP concentration was observed following bicarbonate haemodialysis (BHD) (P < 0.01). There was a significant positive correlation between platelet aggregation and ATP release (r = 0.78, P < 0.05), as well as platelet aggregation and TXB2 production (r = 0.68, P < 0.05). A significant negative correlation was found between platelet aggregability and cAMP concentration (r = -0.7, P < 0.05). The platelet surface positive charge, which was significantly lower in the patients than in the controls (P < 0.01), did not change during rHu-EPO therapy, nevertheless BHD resulted in a significant increase (P < 0.05), suggesting the surface charge may influence platelet aggregation. In an in vitro and an in vivo study, rHu-EPO and the higher Hct did not increase platelet aggregation directly. Long-term administration of rHu-EPO stimulated complex functional and biochemical changes in the platelets of uraemic patients, which resulted in an improved aggregability.

Laser aggregometer studies, ATP release and thromboxane B2 release and cAMP concentration of the platelets in nephrotic syndrome.

Platelet function was studied in 56 children with nephrotic syndrome, 33 were on oral prednisolone (P) treatment (group 1), while 23 were in early (< 6 months) remission (group 2): 12 on P (group 2a) and 11 not on P (group 2b), and there were 18 controls (group 3). The following tests were used: platelet aggregation with collagen in a laser rheoaggregometer; adenosine triphosphate (ATP) release: during aggregation with luciferin-luciferase in a lumiaggregometer; thromboxane B2 (TXB2) release: by radioimmunoassay; platelet cAMP concentration: by binding assay. The changes in plasma cholesterol (C) and triglycerides (TG) were compared with the platelet aggregation results. Patients in group 1 and 2 exhibited significantly higher aggregability, TXB2 release and ATP release in response to collagen than those in group 3 (p < 0.01), but there was no difference between groups 1 and 2 or groups 2a and 2b. Some differences were observed between the histological groups. Patients with IgA and SLE nephropathy displayed higher aggregability than those with minimal change nephrotic syndrome in remission (p < 0.05). The highest level was in membranous nephropathy. The platelet cyclic adenosine monophosphate (cAMP) concentration was significantly lower in groups 1 and 2 than in group 3 (p < 0.001). No differences were observed between groups 1 and 2 or between groups 2a and 2b. Plasma C and TG levels did not show any correlation with the platelet aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of bicarbonate and acetate haemodialysis on platelet cyclic AMP concentration, thromboxane B2 release and aggregation.

The effects of chronic uraemia and serial acetate (HDA) or bicarbonate (HDB) haemodialysis on the aggregation, thromboxane B2 (TXB2) release and cyclic AMP (cAMP) concentration of platelets from arterial blood were studied in 14 uraemic patients (6 dialysed and 8 conservatively treated) and 10 controls. Platelets from uraemic patients, either dialysed or treated conservatively, exhibited a significantly higher cAMP level (P less than 0.005), a lower TXB2 level (P less than 0.01), and a lower aggregability (P less than 0.001) than the controls. The platelet cAMP level was more markedly decreased after HDB than after HDA (P less than 0.05). Greater increases in platelet aggregation (P less than 0.05) and TXB2 formation were observed after HDB than after HDA. The concentration of platelet cAMP and aggregability, and also the platelet cAMP and the TXB2 level showed a significantly negative correlation (r = -0.7, P less than 0.05 and r = -0.60, P less than 0.05, respectively). There was a positive correlation between the platelet-derived TXB2 and the aggregability (r = 0.67, P less than 0.05). Although most patients had secondary hyperparathyroidism, the serum parathyroid hormone level did not correlate closely with the cAMP, TXB2 or aggregation results. The dysfunction of uraemic platelets accompanied by a reduced TXB2 release may be explained by an increased cAMP and a decreased arachidonic acid availability. HDB improves the platelet function to a greater degree than does HDA.

Sodium and potassium uptake in primary cultures of rat astroglial cells induced by long-term exposure to the basic astroglial growth factor (AGF2).

Astroglial cell cultures were derived from newborn rat forebrain and cultured for 5 days in serum containing-, and for an additional 4 days in a serum-free, defined medium. At the end of this 9-day-long period, basic astroglial growth factor (AGF2) was administered to the culture medium (10 ng per ml). Cells were subsequently cultured in AGF2 containing serum-free, defined medium for further two weeks. At definite intervals of culturing, unidirectional influx of both Na+ and K+ (INa and IK, respectively) was determined by applying 22Na and 42K. The AGF2-treated cultures showed highly increased, amiloride-sensitive INa at the early exposure period (2-8 hours), similar to that we have reported about cultured astroglia exposed to AGF2 for minutes. They also exhibited significant furosemide-sensitive-, while relatively poor ouabain-sensitive component of INa. However, at later periods of exposure to AGF2, INa was significantly reduced, particularly due to the decrease of its amiloride-sensitive component, while its furosemide-sensitive component further increased with the time of AGF2 treatment. In contrast to INa, the IK in the cultures exposed to AGF2 increased significantly in the course of the long-term exposure period, particularly the ouabain-, and furosemide-sensitive-components, while its amiloride-sensitive component, similarly to that of INa, decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of plasma from IgA nephropathy patients on vascular prostacyclin and platelet cyclic AMP production.

The effects of plasma from 10 IgA nephropathy patients and from ten controls were studied on vascular prostacyclin (PGI2) production, the cyclic AMP (cAMP) level and the aggregation of normal platelets. The ability of the plasma to support PGI2-like activity (PSA) was significantly lower in the group of patients (18.0 +/- 13.3%) than in the controls (52.6 +/- 12.9%). The concentration of 6-keto-PGF1 alpha in the supernatant of the vascular tissue was also lower following incubation with patient plasma than with control plasma (p less than 0.001). The reduced PGI2 released by the patient plasma led to a significantly lower platelet cAMP than that following the control plasma (p less than 0.01). There was a significantly positive correlation between the 6-keto-PGF1 alpha and the plasma PSA, and also between both the plasma PSA and 6-keto-PGF1 alpha concentrations and the platelet cAMP level. These findings suggest that a vascular PGI2 defect may cause a reduced cAMP production and an uninhibited aggregation of platelets, which might play a role in the pathogenesis of IgA nephropathy.

Sodium and potassium uptake in primary cultures of proliferating rat astroglial cells induced by short-term exposure to an astroglial growth factor.

Primary cultures of rat astroglial cells were maintained in a serum-free medium. After 8-10 days of cultivation the cells were exposed to an astroglial growth factor (AGF2) for short periods (1-120 min). Subsequently, uptake of 22Na+ and 42K+ into control and AGF2-pretreated cells was studied. Assay of the Na+ and K+ values in the cells was also performed by atomic absorption spectrometry. Treatment of rat astroglial cells with AGF2 resulted in a significant increase of the uptake of both Na+ and K+ depending on the duration of the exposure period. To reach the maximum increase of cation uptake, 6-10 min and 30 min of AGF2 pretreatment were needed for Na+ and K+, respectively. Amiloride blocked this increase of Na+ and K+ uptake elicited by AGF2 pretreatment, but the control cells were amiloride resistant. Treatment with AGF2 increased the ouabain sensitivity of the K+ uptake as that: 10(-4) M ouabain inhibited K+ uptake of the AGF2-treated cells to the same degree as 5 X 10(-3) M ouabain with the control cells. The Na+ uptake of AGF2-treated cells, however, exhibited no relevant changes in the presence of ouabain. A significant part of the AGF2-induced K+ uptake could be inhibited by both ouabain and amiloride, but a ouabain-resistant and amiloride-sensitive component also was revealed. The furosemide sensitivity of both Na+ and K+ uptake into cultured astroglial cells was also significantly increased by AGF2. Our findings suggest that short-term exposure of cultured glial cells to AGF2 induces these very early ionic events: 1) The appearance of a relevant amiloride-sensitive Na+/H+ exchange, and as a consequence of increased Na+ entry into the cells, secondary activation of the ouabain-sensitive K+ uptake via the Na+,K+-pump. 2) A direct effect of AGF2 on the Na+,K+-pump assembly in the membrane, resulting in increased Na+ sensitivity of the inner pump sites and enhanced ouabain sensitivity of the external K+-binding sites. 3) An increase of ouabain-resistant but amiloride- or furosemide-sensitive Na+ and K+ uptake.

Manifestation of K+ transport alterations in cultured tumour cells of mice.

Sarcoma was induced by injection of human adenovirus type 12 into newborn, isogeneic CBA mice and maintained in adult female CBA mice by serial passages. Cells obtained from the tumours were cultivated by 3-4 passages in vitro. Normal fibroblastic cell cultures were gained by the same manner from isogeneic CBA mouse embryos. Characteristics of potassium transport in cultures of malignant cells and of normal fibroblastic cells were analysed. As a chemical tracer of K+ movements, 86Rb+ was applied. No significant difference could be detected either in the potassium concentration, or in the 86Rb+ uptake of the two types of cultured cells. However, when the cells were exposed to ouabain, the malignant cells showed a significantly reduced response, thus, the malignant cells accomplished a much less decrease in either cellular potassium concentration or in that of 86Rb+ uptake rate than the normal cells. These findings well fit the hypothesis advanced by several authors that malignant cells have a reduced density of ouabain receptor on the membrane.

Control of cation transport in cultured glial cells by external Ca++: a possible signal in glial-neuronal interaction.

In cultured glial cells from chick embryonic brain, both influx and efflux of 42K+ and 22Na+ are dependent on the external Ca++ and concentration ([Ca++]0) between 2 and 0.1 mM although intracellular concentrations of K+ ([K+]i) and Na+ ([Na+]i) do not change. Only a reduction of [Ca++]0 below 0.1 mM results in both a decrease of [K+]i and an increase of [Na+]i. Ouabain significantly decreases the [Ca++]0 sensitivity of uphill cation movements (K+ influx and Na+ efflux), while the [Ca++]0 sensitivity of downhill cation movements (K+ efflux and Na+ influx) is almost not affected by the presence of ouabain. Additionally, a decrease in [Ca++]0 triggers an increase in intracellular concentration of adenosine 3':5'-cyclic monophosphoric acid (cAMP). These findings suggest that changes of [Ca++]0, which take place in vivo in the microenvironment of the glia after neuronal firing, represent a signal in the glial-neuronal interaction controlling cation transport and that this control is achieved by a co-operation between the cAMP-generating and the cation transport system.