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Catecholamine-induced vasodilator metabolite release from guinea-pig hearts is not due to increased myocardial
Insights
Sympathomimetic drugs like isoprenaline trigger coronary vasodilation by releasing a metabolite. This occurs independently of increased heart activity, as shown in guinea-pig hearts.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Biochemistry
Background:
- Sympathomimetic drugs impact cardiac function and coronary blood flow.
- The precise mechanisms of sympathomimetic-induced coronary vasodilation are not fully understood.
- Investigating the role of metabolites in mediating these effects is crucial.
Purpose of the Study:
- To elucidate the mechanism of sympathomimetic-induced coronary vasodilation.
- To determine if mechanical cardiac hyperactivity is necessary for this vasodilation.
- To identify the role of vasodilator metabolites.
Main Methods:
- Series perfusion of isolated guinea-pig hearts.
- Administration of isoprenaline to donor hearts.
- Assessment of recipient heart response to donor perfusate.
- Pharmacological blockade of beta-adrenoceptors with propranolol.
Main Results:
- Isoprenaline increased donor heart rate, contractility, and oxygen consumption, causing coronary vasodilation.
- Donor heart perfusate induced recipient heart vasodilation, blocked by propranolol, indicating metabolite release.
- Isoprenaline released vasodilator metabolite and increased oxygen consumption even during donor heart arrest, without mechanical changes.
- Beta-adrenoceptor blockade prevented metabolite release.
Conclusions:
- Sympathomimetic-induced coronary vasodilation is mediated by the release of a vasoactive metabolite.
- The release of this metabolite is triggered by the drug, not by increased cardiac mechanical activity.
- Beta-adrenoceptors play a key role in this metabolite-mediated vasodilatory pathway.
Abstract:
Guinea-pig isolated hearts were perfused in series, the donor heart perfusate supplying the recipient heart. Isoprenaline increased the rate and force of contraction and oxygen consumption of donor hearts and produced a coronary vasodilatation. This was accompanied by the release of vasodilator metabolite as demonstrated by vasodilatation of the recipient heart, the beta-adrenoceptors of which were antagonized by propranolol. During arrest of donor hearts by either carbachol or application of a fibrillating current, isoprenaline still released vasodilator metabolite and increased oxygen consumption but without changes in rate or tension. This release was prevented by beta-adrenoceptor blockade. It is concluded that the sympathomimetic-induced coronary vasodilatation is mediated via the release of a vasoactive metabolite, the trigger for which is not the concomitant mechanical hyperactivity.