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.

Frequency dependence of the alpha-adrenoceptor-mediated positive inotropic effect in guinea pig heart / A. Mugelli;F. Ledda;L. Mantelli. - In: EUROPEAN JOURNAL OF PHARMACOLOGY. - ISSN 0014-2999. - STAMPA. - 36:(1976), pp. 215-220.

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

MUGELLI, ALESSANDRO;
1976

Abstract

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.
1976
36
215
220
A. Mugelli;F. Ledda;L. Mantelli
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/674446
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