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N Kolassa

Publications and source records attributed to N Kolassa.

At least 19 recordsLinked to original sources
PubMed1991

Vasodilatation elicited by 5-HT1A receptor agonists in constant-pressure-perfused rat kidney is mediated by blockade of alpha 1A-adrenoceptors.

The vasodilator mechanism of the putative serotonin1A (5-HT) receptor agonists, urapidil, 5-methyl-urapidil, ipsapirone, flesinoxan and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was investigated in constant-pressure perfused rat kidneys. The compounds (10(-12)-10(-7) mol bolus injection) neither enhanced basal flow nor evoked vasodilatation in kidneys preconstricted by 27 mM KCl, 1.5 mM BaCl2 or 10(-6) M prostaglandin (PG)F2 alpha, but evoked a dose-dependent, reversible and spiroxatrine-resistant increase in vasodilatation of organs preconstricted by 6 x 10(-7) M noradrenaline. 5-Carboxamidotryptamine and sumatriptan did not reverse the vasoconstriction induced by all stimuli or that induced by noradrenaline in the presence of 5-HT2 plus 5-HT3 receptor blockade. No correlation for the vasorelaxant drugs was found between their -log ED50 in rat kidney and pKi values at 5-HT1A binding sites in pig cortex as determined in radioligand experiments. The relaxation in rat kidney induced by 5-HT1A receptor agonists and alpha 1A-adrenoceptor-selective antagonists (WB 4101 and (+)-niguldipine) was significantly correlated with pKi values at alpha 1A binding sites in rat cortex and the pA2 values derived from contraction studies for competitive antagonism at alpha 1-adrenoceptors in prostatic portions of the rat vas deferens, but differed from pKi values for alpha 1B binding sites in rat cortex. Thus, the vasodilator effect of the 5-HT1A receptor agonists urapidil, 5-methyl-urapidil, ipsapirone, flesinoxan and 8-OH-DPAT in the noradrenaline-perfused rat kidney appears to be mediated by their concomitant alpha 1A-adrenoceptor blockade. No evidence for a vasodilator effect mediated through 5-HT1A receptors was found under our experimental conditions.

Adrenergic alpha-Antagonists↗
PubMed1991

Regional and laminar distributions of alpha 1-adrenoceptors and their subtypes in human and rat hippocampus.

The distributions of the alpha 1-adrenoceptor and its subtypes (alpha 1A and alpha 1B) in human and rat hippocampus are analysed by quantitative receptor autoradiography. alpha 1-Adrenoceptors are labelled by [3H]prazosin. The alpha 1A subtype is visualized by [3H]prazosin after irreversible blockade of alpha 1B adrenoceptors with chloroethylclonidine or directly by [3H]5-methyl-urapidil. The alpha 1B subtype is investigated by [3H]prazosin binding in the presence of the alpha 1A antagonist 5-methyl-urapidil. Considerable differences in the regional and laminar patterns of alpha 1-adrenoceptors are found between rat and human hippocampi. The rat hippocampus is characterized by a low overall density and a rather homogeneous regional and laminar distribution. This is in contrast to the human pattern, which shows a much higher overall level of alpha 1 receptor density and a restriction of alpha 1 receptors to the CA3 region of Ammon's horn and the dentate gyrus. Moreover, alpha 1A and alpha 1B receptors of the human hippocampus are differentially distributed with the alpha 1A subtype concentrated in the hilus and lucidum layer of CA3, and the alpha 1B subtype concentrated in the molecular layer of the dentate gyrus. Additionally, the distribution of alpha 1 receptors is compared with the distribution of 5-hydroxytryptamine 1A receptors. The subtype specific pattern is correlated with the distribution of glutamatergic systems in the human (but not in the rat) hippocampus. alpha 1A Receptor localization coincides with the target area of the mossy fibre system, and alpha 1B receptors are preferentially localized in the target area of the hippocampal associational fibres and partly of the perforant pathway. This result points to possible interactions between noradrenaline- and glutamate-mediated neurotransmission differentiated by topographically segregated alpha 1-adrenoceptor subtypes.

Adrenergic alpha-Antagonists↗
PubMed1990

Involvement of 5-HT1A receptors in blood pressure reduction by 8-OH-DPAT and urapidil in cats.

This study investigated the effects of (-)-pindolol, a putative 5-HT1A receptor antagonist, upon the central hypotensive action of the antihypertensive drug urapidil and of the purported 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) in cats. Chloralose/urethane-anesthetized cats were thoracotomized and artificially ventilated. Blood pressure was monitored in the iliac artery, and the drugs were injected into the vertebral artery. Urapidil (1-300 nmol/kg) or 8-OH-DPAT (0.01-1 nmol/kg) dose-dependently reduced blood pressure. (-)-Pindolol (30 and 100 nmol/kg) shifted the dose-response curves of both drugs significantly and in a similar manner to the right. Doses of urapidil of 30 nmol/kg or higher also reduced the elevation of blood pressure following the intravenous injection of the alpha 1-adrenoceptor agonist cirazoline whereas 8-OH-DPAT was ineffective. Yet, the hypotensive response to the directly acting vasodilator nitroglycerin remained unchanged after urapidil. The results support the hypothesis that the centrally mediated component of the antihypertensive action of urapidil is due to stimulation of 5-HT1A receptors in the brainstem. Peripheral alpha 1-adrenoceptor blockade comes into play with higher doses of the drug administered via the vertebral artery.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1979

Ionized and bound calcium inside isolated sarcoplasmic reticulum of skeletal muscle and its significance in phosphorylation of adenosine triphosphatase by orthophosphate.

Calcium loading of skeletal muscle sarcoplasmic reticulum performed passively by incubation with high calcium concentrations (0.5--15 mM) on ice gives calcium loads of 50--60 nmol/mg sarcoplasmic reticulum protein. This accumulated calcium is not released by EGTA [ethyleneglycol bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid], but almost completely released by ionophore X-537A plus EGTA or phospholipase A plus EGTA treatment and is therefore assumed to be inside the sarcoplasmic reticulum. This calcium is distributed in one saturable and one non-saturable calcium compartment, as derived from the dependence of the calcium load on the calcium concentration in the medium. These compartments are assigned to bound and ionized calcium inside the sarcoplasmic reticulum, respectively. Maximum calcium binding under these conditions was 33 nmol/mg protein with an apparent half-saturation constant of 5,8 nmol/mg free calcium inside, or between 1.2 and 0.6 mM free calcium inside, assuming an average vesicular water space of 5 or 10 microliter/mg protein, respectively. Calcium-dependent phosphorylation of sarcoplasmic reticulum calcium-transport ATPase from orthophosphate depends on the square of free calcium inside, whilst inhibition of phosphorylation depends on the square of free calcium in the medium. Calcium-dependent phosphorylation appears to be determined by the free calcium concentrations inside or outside allowing calcium binding to the ATPase according to the two classes of calcium binding constants for low affinity calcium binding or high affinity calcium binding, respectively. It is further suggested that the saturation of the low-affinity calcium-binding sites of the ATPase facing the inside of the sarcoplasmic reticulum membrane is responsible for the greater apparent orthophosphate and magnesium affinity in calcium-dependent phosphorylation than in calcium-independent phosphorylation from orthophosphate. Maximum calcium-dependent phosphoprotein formation at 20 degrees C and pH 7.0 is about 4 nmol/mg sarcoplasmic reticulum protein.

Adenosine Triphosphatases↗
PubMed1979

Pharmacological properties of taglutimide, a new sedative-hypnotic drug.

2-[Bicyclo(2,2,1)heptane-2-endo-3-endo-dicarboximido]-glutarimide (taglutimide, K-2004) proved to be a new sedative-hypnotic drug which did not produce any toxic effects when administered orally to mice even at a very high dosage. Central-nervous depression was demonstrated by a reduction in spontaneous motor activity, potentiation of the central-depressant effect of pentobarbital, antagonism of the central-stimulant effect of amphetamine after oral administration and by narcotic activity after i.v. administration of the drug. Furthermore, oral administration of taglutimide potentiated the analgesic action of morphine without being effective on its own. Only weak potentiation of chlorpromazine-induced catalepsy, but not of reserpine-induced catalepsy was observed after taglutimide pretreatment. The drug influenced neither motor co-ordination nor the toxicity of ethanol. Taglutimide exhibited no anticonvulsant activity with respect to maximum electroshock or strychnine-induced seizures. No effect on heart rate or blood pressure was demonstrable after taglutimide treatment in conscious dogs.

Animals↗
PubMed1979

Plasma level of the prodrug midodrine and its active metabolite in comparison with the alpha-mimetic action in dogs.

Midodrine, i.v. or orally administered, causes a prolonged elevation of blood pressure and a reduction in heart rate. These cardiovascular changes are not correlated to the plasma levels of the intact drug. On administration of either midodrine or its metabolite, ST-1059, formed by cleavage of the glycine residue, the elevation of blood pressure and the reduction in heart rate were significantly correlated to the plasma level of ST-1059. The results are in agreement with the assumption that the pressor activity of midodrine is mainly exerted by its metabolite ST-1059.

Adrenergic alpha-Agonists↗
PubMed1978

pH and temperature dependence of adenosine uptake in human erythrocytes.

Kinetic analysis of the saturable adenosine uptake in human erythrocytes suggests the existence of two saturable components, distinguished by different Km values (1.4 and 260 micron, respectively, at pH 7.4 and 25 degrees C). Both components were abolished by p-nitrobenzylthioguanosine or dipyridamole. Total uptake was significantly higher at pH 8 than at pH 7 at adenosine concentrations above 2 micron. The increase in uptake at the higher pH was brought about mainly by an increase in the maximum rate of transport of the low-affinity uptake system. With rising temperature the Km and the V of both uptake components increased. No transition temperature was observed between 12 and 37 degrees C.

Adenosine↗
PubMed1978

Calcium gradient-dependent and calcium gradient-independent phosphorylation of sarcoplasmic reticulum by orthophosphate. The role of magnesium.

Phosphorylation of the calcium-transport ATPase of skeletal muscle sarcoplasmic reticulum by inorganic phosphate was investigated in the presence or absence of a calcium gradient. The maximum phosphoprotein formation in the presence of a calcium gradient at 20 degrees C and pH 7.0 is approximately 4 nmol/mg sarcoplasmic reticulum protein, but only between 2.4 and 2.8 nmol/mg protein in the absence of a calcium gradient, using Ionophore X-537 A or phospholipase-A-treated sarcoplasmic reticulum vesicles. Maximum phosphoprotein formation independent of calcium gradient at 20 degrees C and pH 6.2 is in the range of 3.6--4 nmol/mg protein. Half-maximum phosphoprotein formation dependent on calcium gradient was achieved with 0.1--0.2 mM free orthophosphate at 10 mM free magnesium or at 0.1--0.2 mM free magnesium at 10 mM free orthophosphate. Phosphoprotein formation independent of calcium gradient is in accordance with a model which assumes, firstly, the formation of a ternary complex of the ATPase protein with orthophosphate and magnesium (E . Pi . Mg) in equilibrium with the phosphoprotein (E-Pi . Mg) and, secondly, an interdependence of both ions in the formation of the ternary complex. The apparent equilibrium constant was 0.6 and the apparent dissociation constants KMg, KMg', KPi and KPi' were 8.8, 1.9, 7.2 and 1.5 mM respectively, assuming a total concentration of the phosphorylation site per enzyme of 7 nmol/mg protein.

Animals↗
PubMed1978

Influence of hexobendine, dipyridamole, dilazep, lidoflazine, inosine and purine riboside on adenosine uptake by the isolated epithelium of guinea pig jejunum.

The uptake of (14C)adenosine by isolated epithelium of guinea pig jejunum, administered on the blood side, was inhibited by hexobendine, dipyridamole, dilazep and lidoflazine. On the lumen side, however, weak inhibition was observed with lidoflazine only and no significant change was recorded with hexobendine, dipyridamole or dilazep. This difference was not altered when the degradation of hexobendine by the jejunal epithelium was blocked by physostigmine. When adenosine uptake was already reduced by purine riboside, further addition of hexobendine, dipyridamole, dilazep or lidoflazine caused divergent changes depending on the side of administration. Adenosine uptake was further diminished on the blood side, but raised towards control values on the lumen side. By contrast, inosine inhibited adenosine uptake on both sides of the epithleium. The results suggest that the mechanism of adenosine uptake is different on either side with respect to inhibition characteristics, corresponding to differences in morphology and function of the two sides of the intestinal epithelium.

Adenosine↗
PubMed1977

Relaxation of coronary artery strips by adenosine and acidosis.

Cumulative dose-response curves of Ca2+-induced tension increments were studied in K+-depolarized helical strips of dog coronary arteries. Adenosine 10(-4) M reduced the Ca2+ sensitivity of the strips without altering the maximal tension with full Ca2+ activation. In contrast, acidosis of pH 7.05 significantly diminished the maximal tension with full Ca2+ activation. The relaxing effect of acidosis was almost completely abolished by 10(-4) M adenosine. It is concluded that adenosine inhibits Ca2+ influx, whereas acidosis depresses the contractile process of vascular smooth muscle directly.

Acidosis↗
PubMed1977

Weak electrolyte transfer in the guinea pig jejunum: secretion of trimethoxybenzoic acid.

In isolated epithelia of guinea pig jejunum the transcellular permeation of 10(-4) M (carboxyl-14C)-3,4,5-trimethoxybenzoic acid (TMBA) in the direction blood-lumen was more than 10 times greater the transcellular permeation of 10(-4) M (carboxyl-was reduced to less than 2 by anaerobiosis or by increasing TMBA concentrations of up to 10(-2) M. Under aerobic conditions the cellular uptake of TMBA (10(-4) M) from the blood side was twice as high as that from the lumen side. In anaerobiosis the percentage of TMBA taken up into the epithelium was enhanced, when TMBA was administered on the lumen side, while the percentage was unchanged after administration on the blood side; thereby the difference in cellular TMBA concentrations was abolished. Similar results were obtained under aerobic conditions, if the TMBA concentration was increased up to 10(-2) M. The results are consistent with a three-compartment model with an intermediate compartment distinguished by a high pH as compared to that of the outer compartments and by a luminal boundary highly permeable for the ionized form of the substrate in contrast to the contraluminal boundary.

Aerobiosis↗