Vasomotor properties of immature canine coronary collateral circulation

This study examined the ability of the immature coronary collateral circulation to undergo vasodilation in response to nitroglycerin and vasoconstriction in response to α-adrenoceptor stimulation. Studies were performed in 12 anesthetized dogs. Collateral flow was estimated from measurements of retrograde flow from the acutely ligated and cannulated anterior descending branch of the left coronary artery. Antegrade flow into the collateral-dependent myocardium was mimimized by embolizing the anterior descending artery with 25-μm microspheres. Drugs to be tested were introduced into the left main coronary artery to reach collateral vessels arising from the left circumflex and septal arteries. Intracoronary administration of nitroglycerin (6 μg·kg^-1·min^-1) resulted in a 33 ± 7.7% increase in retrograde blood flow (P < 0.01) and a 23 ± 3.8% decrease in calculated collateral resistance (P < 0.01). No significant change occurred in retrograde blood flow or calculated collateral resistance during cardiac sympathetic nerve stimulation after β-adrenergic blockade with propranolol, selective α-adrenergic stimulation with phenylephrine (1 μg·kg^-1·min^-1), or selective α₂-stimulation with BHT 933 (2 μg·kg^-1·min^-1). Thus, the immature coronary collateral circulation was capable of active vasomotion, as demonstrated by vasodilation in response to nitroglycerin, but did not undergo vasoconstriction in response to α-adrenoceptor stimulation.