Chronotropic and inotropic effects of atrial peptides on the isolated systemic heart ofOctopus vulgaris

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Abstract
The chronotropic and inotropic effects of four atrial peptides (cardiodilatin 1–16, atrial natriuretic factor 8–33 and atriopeptin I and III) on the isolated systemic heart ofOctopus vulgaris were studied. Using a preparation that produces a physiological stroke volume at physiological input pressures, it was found that ANF, atriopeptin I and atriopeptin III exerted both negative chronotropic and inotropic effects. In contrast, cardiodilatin produced a positive inotropic effect. A dose-response curve of ANF is reported, showing a threshold concentration of about 10−12 M. The pharmacological and physiological implications of these results are discussed in relation to some characteristics of the cephalopod systemic heart.