Intracoronary collagen: Effects on coronary collateral circulation and the role of thromboxane

This study investigated the effects of intravascular collagen on coronary collateral blood flow. Collateral vessel growth was stimulated in 11 dogs by embolizing the left anterior descending (LAD) coronary artery with a hollow stainless steel plug. Experiments were performed 41 ± 7 days after coronary embolization when collateral vessels were moderately well developed. Under α-chloralose anesthesia, the LAD was cannulated, and retrograde blood flow was used as a measure of collateral flow. Collagen (10-100 μg/kg) injected into the left main coronary artery caused a decrease of coronary collateral blood flow that became maximal at 3 min after injection and subsided within 9 min. At peak effect intracoronary collagen decreased retrograde flow by 53 ± 6% from 32.7 ± 8.2 to 16.8 ± 3.7 ml/min (p < 0.05) with no change in systemic hemodynamics. Selective thromboxane A₂ (TxA₂)- receptor blockade with SQ30,741 had no effect on collateral blood flow during basal conditions but attenuated the collateral constriction in response to collagen. Thus, after SQ30,741, collagen caused only a nonsignificant decrease retrograde flow from 35.9 ± 9.0 to 31.7 ± 9.62 ml/min. The findings indicate that intravascular collagen exerts a potent vasoconstrictor effect on coronary collateral vessels. Attenuation of this response by TxA₂- receptor blockade suggests that thromboxane released by activated platelets is the principal mediator of this response.