ISSN:
1432-1912
Keywords:
Phenylephrine
;
Isolated Organs
;
Competitive Dualism in Action
;
Local Anaesthesia
;
Antiarrhythmic Activity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The β-sympathomimetic effect of phenylephrine was investigated on the electrically driven atrium, as well as on the tracheal chain of the guinea pig. 1. Phenylephrine (PE) was found to be less effective than isoprenaline (IPN) with regard to its positive inotropic effect on the guinea-pig atrium and to its relaxing action on the tracheal chain. The intrinsic activity for PE amounted to 0.75 on the tracheal chain and to 0.45 on the atrium, when compared with IPN. 2. From these low intrinsic activities, PE was assumed to be a partial β-agonist, exerting a competitive dualism in action to IPN. This dualism could be confirmed by dose-response curves for PE in the presence of IPN and vice versa: PE behaved as a β-agonist as well as a β-antagonist. 3. The intrinsic activity of PE steadily decreased with prolongation of the incubation period. After 1 h PE had almost lost its intrinsic activity. Under these conditions the dose-response curves for IPN on the tracheal chain, as well as on atrium, were shifted to the right in a parallel manner, i.e. PE behaved as a competitive β-antagonist. 4. High concentrations of PE (10−3 M) protected the electrically driven guineapig atrium against arrhythmias induced by k-strophanthoside. The onset of both the first extrasystoles and of heart standstill, which occurred after infusion of k-strophanthoside, were delayed after preincubation with PE. 5. Phentolamine was without any influence on these antiarrhythmic properties of PE. Therefore, it could be excluded that the antiarrhythmic effect of phenylephrine is due to a stimulation of myocardial α-adrenoceptors. 6. The local anaesthetic activity of phenylephrine, as tested on the rabbit cornea, was 4 times higher than that of propranolol. 7. The effective concentrations for the β-adrenolytic, antiarrhythmic, and local anaesthetic activities of PE were clearly different. We concluded, therefore, that the different actions produced by phenylephrine were not associated with each other.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00500345
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