Constriction of native coronary collaterals
Authors: L Becker
Journal: Cardiovascular Research (2000)

See article by Mansaray et al. [5] ( pages 359 -366) incollaterals, partially opened by application of a critical this issue.coronary artery stenosis, can acutely constrict during formation of an intracoronary thrombus at the site of the Interconnections between adjacent coronary arteries, stenosis.Although they attribute this effect to release of known as ''collateral vessels,'' were discovered as early as vasoconstrictors from aggregating platelets (based on the the 17th century [1].Anatomically, collaterals provide fact that platelet aggregation is strongly implicated in the conduits through which blood can flow from normal to Folts model used by the authors), the experiments do not jeopardized myocardial regions, following obstruction of definitively identify platelets as the responsible source, nor the antegrade blood supply.However, controversy has do they identify the specific molecules or receptors responexisted for decades about the true functional significance sible for the constrictor effect.Interestingly, collateral of the coronary collateral system.Native collateral vessels, constriction did not occur during thrombus formation when consisting of thin walled vascular structures with a the antegrade coronary artery was completely occluded rudimentary smooth muscle coat, were thought for many rather than merely critically narrowed.The authors hypothyears to be passive tubes through which blood flowed as a esize that the vasoconstrictor stimulus resulting from result of a mechanical pressure gradient between the thrombus formation was not sufficiently potent to overnormal and occluded vascular beds.The concept that come ''maximal'' collateral dilatation caused by a comnative collaterals were capable of significant vasomotion, plete coronary artery occlusion.Although it is well aceither dilatation or constriction, was not widely accepted.cepted that platelet aggregation within the coronary arteries In recent years, however, a number of studies in at the site of an ulcerated atherosclerotic plaque can different animal models have consistently demonstrated produce local arterial constriction, or downstream microthat collaterals dilate over the first several minutes follow-vascular constriction, the finding that coronary collaterals ing an acute coronary artery occlusion, resulting in a may also be affected is a new observation.significant increase in blood flow.The mechanism for Because the experimental model required a patent rather acute collateral enlargement, however, remains unknown.than an occluded antegrade vessel, the authors could not Collateral dilatation could potentially be mediated by measure collateral blood flow and collateral resistance mechanical stretching, endothelium-dependent relaxation using standard approaches.Instead, they employed a clever of vascular smooth muscle, or possibly other mechanisms.modification of the microsphere technique in which colla-Native collaterals have been shown to respond to various teral flow was estimated as the difference between total vasodilator stimuli, supporting the concept that receptor-flow to the jeopardized region (measured with micromediated mechanisms are operative in such vessels.For spheres) and antegrade flow (measured with an electroexample, nitrates, prostaglandins E and I , and adenosine magnetic flowmeter), with antegrade flow converted to a