Intracoronary collagen: Effects on coronary collateral circulation and therole of thromboxane

This study investigated the effects of intravascular collagen on coronary c ollateral blood flow. Collateral vessel growth was stimulated in 11 dogs by embolizing the left anterior descending (LAD) coronary artery with a hollo w stainless steel plug. Experiments were performed 41 +/- 7 days after coro nary embolization when collateral vessels were moderately well developed. U nder alpha-chloralose anesthesia the LAD was cannulated, and retrograde blo nd flow was used as a measure of collateral flow. Collagen (10-100 mu g/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 subs ided within 9 min. At peak effect intracoronary collagen decreased retrogra de flow by 53 +/- 6% from 32.7 +/- 8.2 to 16.8 +/- 3.7 ml/min (p < 0.05) wi th no change in systemic hemodynamics. Selective thromboxane A(2) (TxA(2))- receptor blockade with SQ30,741 had no effect on collateral blood flow duri ng basal conditions but attenuated the collateral constriction in response to collagen. Thus, after SQ30,741, collagen caused only a nonsignificant de crease retrograde flow from 35.9 +/- 9.0 to 31.7 +/- 9.62 ml/min. The findi ngs indicate that intravascular collagen exerts a potent vasoconstrictor ef fect on coronary collateral vessels. Attenuation of this response by TxA(2) -receplor blockade suggests that thromboxane released by activated platelet s is the principal mediator of this response.