Differential regulation of the left and right coronary arteries of swine

Coronary artery disease is one of the leading causes of myocardial infarction. Despite the predominant role of the coronary arteries in the induction of myocardial infarction, the precise contribution of each artery to this process is not well established. The present work evaluates the histological characteristics and functional properties of the left (LCA) and right (RCA) coronary arteries in swine in order to establish if the arteries are differentially regulated. To investigate this possibility, concentration-response curves for serotonin (5-HT, from 0.1 nmol/l to 100 micromol/l) and KCl (from 5 to 40 mmol/l) were performed on both arteries to determine the receptor-dependent and independent responses, respectively. The specific subtype of the 5-HT receptor involved in the contraction of both arteries was evaluated using DL-propranolol hydrochloride (5-HT1 and nonselective beta-adrenergic receptor antagonist) and ketanserine (5-HT2 antagonist) and immunohistochemical assays. The Emax from the 5-HT concentration-response curves was 24% higher in the LCA than in the RCA (n = 59, p < 0.05). EC50 values from both curves were also significantly different (LCA 0.150 +/- 0.005 micromol/l and RCA 0.171 +/- 0.010 micromol/l, n = 59, p < 0.05). Similarly, the Emax for KCl was 36% higher in the LCA than in the RCA (n = 9, p < 0.05), and the EC50 values also differed (LCA 15.30 +/- 0.06 mmol/l and RCA: 14.30 +/- 0.11 mol/l, n = 9, p < 0.05). Ketanserine reduced the Emax by 63% in the LCA and by 67% in the RCA. DL-propranolol hydrochloride decreased Emax by 24% in the LCA and by 26% in the RCA. The dry weight and media area were larger in the LCA than in the RCA (17%, n = 40, p < 0.05, and 3%, n = 40, p < 0.05, respectively). Immunohistochemical assay results reveal that the average density of 5-HT2A receptor subtype was also higher in the LCA (41.24 +/- 1.35) than in the RCA (18.49 +/- 1.14; n = 20, p < 0.05). Together, the findings of this study suggest that a differential physiological regulation exists between the LCA and RCA in swine. This differential regulation may have arisen as a mechanism for maintaining an adequate perfusion pressure in the wall of the left ventricle, favoring a greater oxygen delivery to match the increased oxygen demand of the left ventricle.