Search PubMed⌕ Search

Biomedical subjects

L Mantelli

Publications and source records attributed to L Mantelli.

64 records · Page 4Linked to original sources
PubMed1977

A histamine-induced decrease of action potential duration in cardiac muscle mediated by the H2 receptors.

The effects of histamine (10(-7)--10(-5) M) on the cardiac action potential have been studied in ventricular strips of guinea pig heart, electrically driven at a constant rate. A decrease of action potential was constantly observed at histamine concentrations above 10(-6) M. No significant variations of the other electrophysiological parameters were induced by the amine. The decrease in the duration of the action potential was blocked by burimamide at a concentration (10(-4) M) which induced only a slight changes in action potential outline. It is suggested that the shortening of the repolarization phase induced by histamine is due to the H2 receptor-mediated activation of the calcium inward current, which can increase the intracellular calcium concentration influencing the potassium permeability.

Action Potentials↗
PubMed1976

Frequency dependence of the alpha-adrenoceptor-mediated positive inotropic effect in guinea pig heart.

Evidence for the role of alpha-adrenoceptors in the production of a positive inotropic effect has been obtained chiefly in heart preparations stimulated at a low rate (1 or 1.4 Hz). However, our previous results suggested that the alpha-receptor-mediated positive inotropic effect could be frequency dependent. In the present study cumulative concentration-inotropic effect curves were obtained in guinea pig ventricle strips treated with adrenaline and stimulated at 1 and at 2.5 Hz. Phentolamine (3 X 10(-6) M) and practolol (10(-6) M) were employed as antagonists. Phentolamine antagonized the effect of low concentrations of adrenaline (10(-9)-10(-8) M) in preparations driven at 1 Hz, but did not modify the curve of the agonist at the higher stimulation rate. In preparations driven at 1 Hz, practolol antagonized the effect of adrenaline at concentration above 3 X 10(-8) M without affecting the curve at lower concentrations, the beta-blocker competitively anatagonized the effect of the agonist at 2.5 Hz. It was concluded that a shortening of the interval between beats abolishes the alpha-mediated positive inotropic effect.

Animals↗
PubMedDate not supplied

Enhancement of the vasoconstrictor response to KCL by nitric oxide synthesis inhibition: a comparison with noradrenaline.

The role of the vascular endothelium in the response to a vasoconstrictor agent acting through a non-receptorial mechanism, such as KCl, was tested in the isolated mesenteric vascular bed of the rat. It was confirmed that the vasoconstrictor response evoked by stimulation of sympathetic terminals was unaffected by 100 microM NG-nitro-D-arginine methyl ester (D-NAME), but was significantly potentiated by 100 microM NG-nitro-L-arginine methyl ester (L-NAME) and by removal of endothelium. Responses to exogenous noradrenaline (1-100 microM) were also enhanced by treatment with 100 microM NG-monomethyl-L-arginine (L-NMMA) and with L-NAME, but not with D-NAME. The potentiating effect of NO synthesis inhibitors was reversed by 1 mM L-arginine. Moreover, the noradrenaline-induced vasoconstriction was significantly increased by endothelium-deprivation. Potassium chloride (80 mM) induced a vasoconstrictor response which was not modified by pretreatment with prazosin (0.1 microM) and yohimbine (0.1 microM). The response to KCl was unaffected by D-NAME (100 microM) but the L-stereoisomer induced a significant increase in the perfusion pressure. In endothelium-denuded preparations the vasoconstrictor response to KCl was greater than in control conditions and was quantitatively similar to that observed in L-NAME-treated preparations. The responses to electrical field stimulation, noradrenaline and KCl in endothelium-denuded preparations were not modified by L-NAME. The results suggest that an increase in vascular tone, per se, may represent a trigger for the release of endothelium-derived relaxing factor from endothelial cells.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Induction by histamine of oscillatory activity in sheep Purkinje fibers and suppression by verapamil or lidocaine.

Histamine (1--2 x 10(-5) M) induced or enhanced oscillatory activity in four of five sheep Purkinje fibers depolarized by a low-potassium medium. These effects of histamine were readily antagonized by 2 x 10(-5) M burimamide but were unaffected by 10(-5) M practolol. Oscillatory activity was consistently induced or enhanced by 5 x 10(-6) M adrenaline in five preparations. Oscillatory activity, whether induced by histamine or adrenaline, was always abolished by verapamil (0.22--2.2 x 10(-6 M) but in only one of five experiments by lidocaine (4.2 x 10(-5) M). We conclude that induction of oscillatory responses may be added to the other arrhythmogenic mechanisms produced by histamine through the stimulation of H2 receptors. We confirmed that oscillatory activity is very effectively suppressed by verapamil.

Action Potentials↗
PubMedDate not supplied

Electrophysiological and antiarrhythmic properties of propafenon in isolated cardiac preparations.

Propafenon, a new antiarrhythmic drug, caused a 30% decrease in maximal driving frequency and a 65 ms net increase in functional refractory period of isolated guinea pig atria at a concentration as low as 0.5 microgram/ml. The spontaneous rate of isolated atria and the contractility of electrically driven ventricular strips were reduced after treatment with propafenon 1 microgram/ml. Propafenon 0.5 microgram/ml also altered action potentials of sheep Purkinje fiber. It reduced the action potential and overshoot amplitudes, decreased the maximum rate of depolarization of the action potential upstroke in a frequency-dependent fashion, shortened the action potential and effective refractory period, and depressed the membrane responsiveness. Moreover, propafenon antagonized the chronotropic and inotropic effects of isoprenaline in isolated guinea pig heart preparations; the pA2 value was about 6.4. Finally, propafenon possessed very weak calcium antagonist properties, being about 100 times less potent than verapamil in this respect. We conclude that propafenon is an antiarrhythmic drug with beta-adrenoceptor blocking and "membrane stabilizing" activities in the same range of concentrations and that it has a calcium antagonistic activity only at much higher concentrations.

Action Potentials↗
PubMedDate not supplied

The potent relaxant effect of adenosine in rabbit corpora cavernosa is nitric oxide independent and mediated by A2 receptors.

In the present study the effect of adenosine and adenosine analogues on rabbit isolated cavernosal smooth muscle has been evaluated in comparison with the effect of acetylcholine and electrical field stimulation. In the presence of guanethidine and indomethacin, acetylcholine and electrical field stimulation relaxed the rabbit corpus cavernosum, which was precontracted with phenylephrine. The nitric oxide synthesis inhibitor, N omega-nitro-L-arginine-methylester (L-NAME), greatly reduced the relaxation induced by electrical stimulation and completely abolished the relaxant effect of acetylcholine. A concentration-dependent relaxation of the rabbit corpus cavernosum was produced by adenosine; this effect was not modified by L-NAME, but was reduced by adenosine deaminase. On the other hand, the adenosine-induced relaxation was potentiated by the inhibitor of adenosine deaminase, erythro-9-(2-hydroxy-3-nonyl)adenine and by the adenosine uptake inhibitor dipyridamole. Moreover, the effect of adenosine was antagonized by the unspecific adenosine receptor antagonist 8-phenyltheophylline. The receptor subtypes involved in cavernosal relaxation were characterized by using selective receptor antagonists: 1,3-dipropyl-8-cyclopentylxanthine, a blocker of A, receptors, did not modify adenosine-induced relaxation. This effect was, however, antagonized by the A2-receptor antagonist CGS15943. A relaxant effect was also obtained with nanomolar concentrations of two synthetic adenosine analogues, the preferential A2 receptor agonist 5'-N-ethylcarboxamidoadenosine and the A2a selective agonist CGS21680. These results demonstrated that adenosine has potent relaxant activity on the corpus cavernosum, acting through a mechanism different from the nitric oxide pathway, and that receptors involved in the effect of adenosine belong to the A2a subtype.

Acetylcholine↗