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Biomedical subjects

F Ledda

Publications and source records attributed to F Ledda.

At least 73 records · Page 4Linked to original sources
PubMed1982

H1- and H2-receptors in the guinea-pig heart: an electrophysiological study.

The mechanical and electrophysiological effects of 2-pyridylethylamine (PEA) and 4-methylhistamine (4MeH) in different sections of guinea-pig heart were examined. 4MeH produced a dose-dependent increase in contractility in the right ventricle and the right atrium, and a decrease in functional refractory period (FRP) in all the sections studied; the action potential duration was decreased and the plateau phase was usually heightened in both atria and the ventricle. These effects were consistently antagonized by cimetidine. PEA-induced changes in contractility, FRP and the action potential profile were studied in the presence of cimetidine. Triprolidine antagonized PEA effects on FRP and the action potential profile only in the left atrium. The results obtained are discussed in terms of the functional role of both H1 and H2 receptors in the various guinea-pig heart sections.

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PubMed1981

An iridium-iridium oxide electrode for in vivo monitoring of blood pH changes.

An iridium-iridium oxide electrode for in vivo monitoring of blood pH changes is described. Because of its small size, sensitivity, flexibility, strength and fast response, this electrode is suitable for acute implantation even in the small vessels of animals such as rats or guinea pigs, allowing continuous pH monitoring anywhere in the central arteries or veins. Excellent noise-free records have been obtained in the in vivo experiments in animals.

Animals↗
PubMed1981

The influence of some cardiodepressant drugs on the histamine-induced restoration of contractility in potassium-depolarized heart preparations.

The ability of some drugs to affect calcium movements in cardiac fibers was tested using a simple method. Guinea-pig ventricular strips were depolarized by 22 mM K+ and their mechanical activity was restored by histamine (10(-5) M); in in these conditions, the effects on contractility of the classic calcium antagonistic drugs nifedipine, verapamil and D600, of the antiarrhythmic drugs lidocaine, quinidine and propafenon, and of a barbiturate, thiopental, were assessed. These drugs were chosen because all of them have been reported as affecting cardiac contractility. It was observed that the ED50 values obtained for the calcium antagonists were in good agreement with those calculated by other authors using different techniques. Moreover, it was found that at high concentrations either the antiarrhythmic drugs or thiopental showed a cardiodepressant activity; the likely explanation of their effects is discussed.

Animals↗
PubMed1980

alpha-Sympathomimetic amines and calcium-mediated action potentials in guinea-pig ventricular muscle.

1 The ability of amines, having alpha- or alpha- and beta-adrenoceptor stimulating activity, to restore excitability and contractility in heart preparations partially depolarized by potassium, was investigated in guinea-pig ventricular muscle in order to elucidate the mechanism of the positive inotropic effect mediated via alpha-adrenoceptors. 2 In preparations in which fast sodium channels were inactivated by K+-rich medium (22 mM) slow electrical responses as well as contractions were consistently induced by high concentrations of phenylephrine (10(-4) to 3 X 10(-4) M) and synephrine (3 X 10(-4) M). 3 The restorative effective effects of both phenylephrine and synephrine were unaffected by phentolamine (10(-5) M) but were readily abolished by practolol (10(-5) M) or sotalol (10(-5) M). 4 Methoxamine induced a dose-dependent positive inotropic effect in ventricular strips paced at 0.5 Hz in normal Tyrode solution; the maximum increase in contractile tension was obtained with methoxamine 10(-4) M. However, at the same concentration, the amine did not induce slow electrical responses in potassium-depolarized preparations. 5 It is concluded that the induction of slow responses by phenylephrine and synephrine is due to beta-adrenoceptor stimulation, and that the increase in cardiac contractility caused by alpha-adrenoceptor stimulation does not involve an increase in slow inward calcium current.

Action Potentials↗
PubMed1977

Studies on the positive inotropic effect of dopamine in the guinea-pig heart.

The positive inotropic effect of dopamine has been studied in isolated ventricular strips of guinea-pig heart. The concentration-inotropic response curve for dopamine was significantly shifted to the right by pretreatment with reserpine. In preparations obtained from animals pretreated with reserpine (2.5 mg/kg, 24 h prior to the experiment) the dose-response curve was not significantly affected by haloperidol, a dopamine vascular receptor antagonist (10(-6)-3X10(-6) M). The inotropic effect of dopamine was antagonized by practolol (3X10(-7)-10(-6) M), but not by phentolamine (3X10(-6)-10(-5) M); moreover the alpha-adrenoceptor blocking drug (10(-5) M) did not affect the curve for dopamine in the presence of practolol (3X10(-7) M). In preparations in which fast sodium channels were blocked by K+ -rich medium, slow electrical responses (calcium-mediated action potentials) as well as contractions were induced by high concentrations of dopamine (10(-4)-3X10(-4) M); again these responses were unaffected by phentolamine or haloperidol, but were blocked by practolol. It was concluded that in the guinea-pig ventricular muscle dopamine induced a positive inotropic effect through both indirect and direct action, and that the latter is due to the activation of beta-adrenoceptors.

Animals↗
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↗
PubMed1975

Studies on the positive inotropic effect of phenylephrine: a comparison with isoprenaline.

1. The effects of phenylephrine and isoprenaline on the isometric contraction of guinea-pig ventricle were compared over the whole range of their respective dose-response curves. 2. In preparations driven at 2.5 Hz the increase in contractile force induced by either isoprenaline of phenylephrine was linearly correlated to an increase in maximum velocity of force development. The relaxation time was shortened by isoprenaline but not by phenylephrine. 3. The negative inotropic effect induced by delta [N-(3,4-dimethoxyphenethyl)-N-methyl-amino]-alpha-(3,4,5-trimethoxyphenyl)alpha-isopropylvaleronitrile hydrochloride (D(600)) was reversed by isoprenaline, but little influenced by phenylephrine. 4. The study of the interval-force relationship shows that the increase in contractile force induced by phenylephrine (3 X 10(-5) M) was relatively greater at low frequencies of stimulation, and that the maximum effect was reached at the frequency of 1 Hz. 5. The positive inotropic effect of phenylephrine (10-4 M) was significantly higher at a frequency of 1 Hz than at 2.5 Hz; the effect of isoprenaline (3 x 10-8 M) was not significantly different at the two driving frequencies. 6. In preparations driven at 1 Hz the inotropic effect of the lower concentrations of phenylephrine was due to an increase in the time to peak tension without any change of the maximum velocity of force development; however an increase of this parameter became evident only after higher concentrations of the amine (10-5 M or more), associated with a progressive shortening of the time to peak. 7. A correlation between mechanical and electrophysiological effects of phenylephrine is attempted; the suggestion is advanced that the prolongation of the action potential and of the active state duration may be an important factor in the inotropic effect of phenylephrine.

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