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 .
C0027061
myocardial
C0018787
heart