Physiologia Bohemoslovaca最新文献

An assay was developed to characterize the kinetic parameters of the Na(+)-K+ pump of rat erythrocytes under conditions as physiological as possible. Changes in the red cell Na+ and Rb+ content were determined in Na+ media (containing 2.5 mM inorganic phosphate (PO4) as a function of cell Na+ (2-8 mmol/l) and extracellular Rb+ (0.2-5 mM). Evaluation of the data revealed that under these conditions the Na(+)-K+ pump mediates, in addition to forward running 3 Nai+: 2 Rbo+ exchange, 1 Ki+:Rbo+ exchange and pump reversal (3 Nao+:2 Ki+ exchange). The two latter modes of Na(+)-K+ pump operation are accelerated by PO4 and lowering of cell Na+. At physiological cation and PO4 concentrations, 1Ki+:Rbo+ exchange contributes by 30-60% to total ouabain-sensitive Rb+ uptake. Thereby, the stoichiometry of ouabain-sensitive Na+ net-extrusion to Rb+ uptake is reduced to values between 1.0 and 0.5. Only at cell Na+ contents above 20 mmol/l the Na+:Rb+ stoichiometry approaches the value of 3:2 = 1.5. At certain constellations of Nai+ and Rbo+ the Na(+)-K+ pump cannot perform any net-transport of Na+ and K+ (Rb+). These equilibrium points are not far from those expected from thermodynamic considerations. The results demonstrate that in normal rat erythrocytes the reversible reaction cycle of the Na(+)-K+ pump runs in several modes of operation. The "abnormal" modes complicate the interpretation of unidirectional fluxes mediated by the Na(+)-K+ pump.

Male Wistar strain rats and PHHC (Prague hereditary hypercholesterolaemic) rats received an intraperitoneal injection of 4-cholesten-3-one for five days. Lecithin-cholesterol acyltransferase activity and total cholesterol, triglyceride and phospholipid levels were determined in their serum. A significant drop in the total cholesterol level was found in normocholesterolaemic Wistar rats after the administration of cholestenone. The serum triglyceride content remained unaltered and the phospholipid concentration showed a downward trend. Lecithin-cholesterol acyltransferase activity was also significantly reduced. In PHHC rats, no significant changes occurred in total cholesterol, triglyceride and phospholipid levels, or in lecithin-cholesterol acyltransferase activity, after the administration of 4-cholesten-3-one. A comparison of serum 4-cholesten-3-one concentrations in the two groups of experimental animals shows that the turnover time for this substance in hypercholesterolaemic rats is only half as long as in normocholesterolaemic rats.

Male Wistar rats were subjected to 65-70% hepatectomy and either immediately or 18 h after surgery were given a 6-hour infusion containing 3 ml of either Ringer solution or aqua pro injectione alone or with L-carnitine in doses 8 mg (12.4 mumol), 40 mg (62 mumol) and 200 mg (310.2 mumol)/kg b.w. The rats were killed 6, 18, 24 and 30 h after surgery. The changes in the DNA specific activity and in the mitotic activity demonstrate that L-carnitine has a stimulating, dose-dependent effect on liver regeneration. This effect acts both during early post-hepatectomy, the prereplicative period and in the subsequent replicative period.

The protective effect of calcium entry blockers can be studied advantageously on the model of the calcium paradox, particularly on the basis of the preservation of haemodynamic and biochemical parameters as well as on the structure of the myocardium (Meno et al. 1984). Our aim in this study was to test the protective effect of the recently developed Czechoslovak drug diltiazem (LACHEMA) under conditions of the Ca2+ paradox.

The authors studied the question of the completeness of ventilation of an additional dead space in the form of a tube 3 cm in diameter and with a volume of 600 ml. Seven young volunteers were examined while breathing with and without the tube, seated at rest and during a two-grade exercise load on a bicycle ergometer. The criterion of ventilation of the tube was enlargement of the dead space by 600 ml during breathing through the tube. The functional dead space was always calculated from the tidal volume and the CO2 concentration in mixed expired air and in an end-tidal sample, using the Bohr equation. In every case, the tube was found to be completely ventilated by breathing, both under resting conditions and during exercise. In breathing during the bicycle exercise, the ratio of the functional dead space to tidal volume fell from 0.3 to 0.19 and a similar decrease was recorded in breathing through the tube.

Experiments using a cytochemical method showed the presence of a specific precipitate of the adenylate cyclase (AC) reaction on the sarcolemma and in the subsarcolemmal cisternae and junctional sarcoplasmic reticulum in rat cardiomyocytes. The localization of AC in the given organelles draws attention to the mutual association between Ca2+ ions and cAMP in the modulation of cardiac contractions. Trifluoperazine (TFP) and chlorpromazine (CHP) are known as phenothiazine derivatives inhibiting cellular enzymatic processes dependent on calmodulin and Ca2+. AC is one of these enzyme systems. The administration of TFP and CHP (both in a dose of 0.1 and 3 mmol.1(-1)) did not affect the cytochemical localization of the enzyme. Quantitative determination of 125I-cAMP by RIA showed that CHP inhibited AC activity in both concentrations. TFP, on the other hand, did not inhibit AC activity in 0.1 mmol.1(-1) concentration and actually stimulated its activation in 3 mmol.1(-1) concentration. The different action of the phenothiazine derivatives on AC activity can be attributed partly to the different affinity of TFP and CHP for calmodulin and partly to interaction of the inhibitor-calmodulin complex with the phosphodiesterase (PDE) system.

The ratio of total concentrations or molar ratios (moles/1,000 amino acid residues) of three non-essential amino acids (glycine, alanine, serine-GAS) and three essential-branched chain amino acids (valine, isoleucine, leucine-BCAA) were investigated in rat systemic and portal vein plasma and jejunal and ileal gut contents after feeding normoprotein (NP) or protein-free (PF) diets for 7 days. Amino acid analysis of gut content showed that the GAS:BCAA ratio was not significantly altered by the PF diet either in the jejunum or in the ileum. On the contrary, the PF diet, caused a three and four-fold increase in this ratio in the portal and systemic plasma, respectively. The situation was produced by the higher concentrations of GAS, which remained near control levels (portal plasma) or exceeded these values (systemic plasma), in contrast to the decreasing levels of BCAA found in both plasmas of the PF group.

The Prague hypertensive rat is a unique strain exhibiting genetic hypertension in which a hypertensive line (PHR) was bred in parallel with a normotensive one (Prague normotensive rat--PNR) from the same parental pair. Sodium efflux from Na(+)-loaded erythrocytes into Mg2(+)-sucrose medium was measured in these two strains as well as in spontaneously hypertensive rats (Okamoto-Aoki, SHR) and in normotensive outbred Wistar rats. Kinetic parameters--maximal velocity and apparent dissociation constant (reflecting the affinity for internal sodium)--were calculated. It was found that PHR as well as SHR had a higher Na+ leak and a decreased activity of the ouabain-sensitive Na+ transport as compared to Wistar rats. Furosemide-sensitive Na+ transport was substantially lower in erythrocytes of both hypertensive strains (PHR and SHR) than in the respective normotensive strains (PNR and Wistar).

A group of 44 patients with chronic glomerulonephritis (GN) and 20 healthy subjects were investigated under the conditions of normal dietary NaCl intake and after one week of salt load with a daily addition of 5 g NaCl per os. After the salt load, the mean blood pressure increased significantly in 47% subjects (salt-sensitive) and their natriuretic response was accompanied by an increase of glomerular filtration rate. The rates of ouabain-sensitive (OST) and furosemide-sensitive transport (FST) were decreased in patients with chronic GN even before salt loading which did not change these values. The lower OST rate can be explained by a reduced affinity for internal Na+. A decreased affinity of the Na(+)-K+ cotransport system for internal Na+ was detected only in hypertensive GN patients. In our study, no relationship between salt-sensitivity and red cell sodium transport either in normotensive or in hypertensive GN patients was found.