Increases responsiveness to stimulation of α- but not β-adrenoceptors in the hereditary cardiomyopathy of the Syrian hamster. Intact adenosine- and cholinoceptor-mediated isoprenaline antagonistic effect

Abstract

The effects of phenylephrine (in the presence of propranolol) or isoprenaline and of adenosine or carbachol (alone and in the presence of isoprenaline) were studied on the force of contraction in electrically driven papillary muscles isolated from the hearts of cardiomyopathic (strain BIO 8262) and age-matched, healthy Syrian hamsters. All experiments were performed in the so-called prenecrotic stage of the disorder within the first 30 days of life. Phenylephrine exerted a positive inotropic effect in all preparations from the cardiomyopathic hamsters. In contrast, in thirteen preparations from healthy Syrian hamsters, phenylephrine increased force of contraction in only four preparations. The positive inotropic effect of isoprenaline was similar in both cardiomyopathic and healthy Syrian hamsters. Adenosine and carbachol apparently reduced the isoprenaline-induced increase in force of contraction in both cardiomyopathic and healthy Syrian hamsters. We conclude that an increased responsiveness to α-adrenergic stimulation occurs in the hearts of cardiomyopathic Syrian hamsters and may be related to the myocardial injury occuring in this syndrome. An increased responsiveness to β-adrenoceptor stimulation or an impaired adenosine-mediated or cholinoceptor-mediated feedback inhibition is unlikely to play a role in the aetiology of this syndrome.