Intracoronary endothelin-1 increases coronary retrograde pressure by constricting arterioles

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Abstract
Study objective – The aim was to determine the site of coronary vasoconstriction induced by endothelin, by investigating the response in terms of retrograde pressure and reactive hyperaemia. Experimental material – Twelve anaesthetised mongrel dogs, 12-14 kg, were used for the studies. Design – The left anterior descending coronary artery was cannulated and perfused with blood through an extracorporeal bypass. The effects of intracoronary endothelin-l (1-500 pmol) on coronary blood flow, coronary flow reserve (the peak reactive flow and the repayment after 15 s coronary occlusion), and retrograde coronary pressure during coronary occlusion were studied (n=7). The retrograde coronary flow was collected from the bypass at each dose (n=5). Measurements and main results – At doses of greater than 20 pmol the coronary flow decreased dose dependently and reached almost zero flow at 500 pmol. The coronary flow reserve also decreased; however, the retrograde pressure was raised dose dependently at doses of greater than 10 pmol. At a dose of 500 pmol, the retrograde pressure was increased to 61 mm Hg [82(SEM 12)% of the coronary perfusion pressure]. Retrograde flow remained unchanged throughout the experiment. Conclusions – The endothelin-1 induced rise in retrograde pressure is in accordance with a dose dependent reduction in coronary flow reserve, and collateral flow was not augmented by endothelin. It is concluded that the effect of endothelin-1 on coronary circulation in situ was mainly due to the constriction of small resistant vessels.

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