Reactivity of Canine Isolated Epicardial Collateral Coronary Arteries

To study the relation between structure and vascular reactivity in mature coronary collateral arteries, we prepared 17 dogs with a casein occluder near the origin of the circumflex coronary artery. At least 24 weeks later, we examined the reactivity of surface collateral arteries (-500 ,um i.d.) to a range of constrictor and dilator agents and compared them with normal left anterior descending coronary arteries of similar size branching away from the collateral zone. Pairs of normal and collateral arteries 2 mm long were mounted in a double-vessel myograph for isometric force recording. Arteries were contracted by K' (124 mM) or by cumulative addition of endothelin-1 (1-100 nM) or U46619 (1-300 nM), a thromboxane A2 mimetic drug. In each case, the collateral vessels contracted to approximately half the force generated by the normal arteries. When partially contracted by K' (25-30 mM), the collateral vessels had a greater range of relaxation and similar sensitivity to acetylcholine, sodium nitroprusside, and cromakalim compared with normal arteries. Morphological and morphometric analyses revealed that the collateral arteries had thickened adventitia, thinner media, ruptured internal elastic laminae, and a thick neointima lined by endothelium. Theoretical calculations of luminal area were made for isotonic conditions in response to constrictor stimuli. Despite the