An analysis of the coronary vascular responses to catecholamines, using a modified Langendorff heart preparation

1. A modified Langendorff heart preparation from the guinea-pig was used to analyse catecholamine responses. Contractile force, heart rate and coronary perfusion pressure were recorded.2. Four components of the vascular response could be identified.(a) The initial phase was a vasoconstriction mediated by alpha-adrenoceptors which preceded any effects on heart rate and force.(b) A secondary constriction followed, which was due to the increased myocardial compression during positive inotropic and chronotropic responses.(c) The third, more predominant, effect was a prolonged dilatation probably associated with the increased metabolic activity of the heart.(d) A fourth component was a direct vasodilatation mediated by beta-adrenoceptors which was evident when small doses of catecholamines were used but was usually masked by the more pronounced metabolically linked dilatation.3. The actions of salbutamol were examined and since it caused direct vasodilatation by stimulation of beta-adrenoceptors without other myocardial effects, these adrenoceptors were classified as the beta(2)-type.4. I.C.I. 50,172 was employed to block selectively the myocardial effects due to stimulation of beta(1)-adrenoceptors and leave the vasodilator beta(2)-adrenoceptors unaffected.5. Adrenaline, noradrenaline and isoprenaline were compared at two dose levels, in the presence or absence of effects on heart rate and force.6. Constrictor or dilator effects were found in the absence of other effects and were shown to depend to some extent on the rate of coronary perfusion.