Effects of clonidine, isoflurane, and the clonidine+isoflurane association in isolated hearts.

Abstract

Background: Isoflurane has been consecrated as an anesthetic drug of choise in heart surgeries, as it presents characteristics that ensure the preservation of cardiac indexes and myocardial stability. Recently, alpha-adrenergic agents, mainly Clonidine, have been added to this anesthetic arsenal in an attempt to prevent adrenergic discharges, increase cardiac stability, reduce myocardial ischemia and improve anesthetic induction and recovery. Objective: The aim of this study was to evaluate the cardiovascular effects of Clonidine, Isoflurane, and Clonidine+Isoflurane association in isolated hat hearts preparations, as well as to evaluate direct heart effects of the clonidine, possibly masked by its central action. Method: This study used twenty four, male, albino, Wistar rats from the Biotherium of the Federal University of Minas Gerais (UFMG). The animals were anesthetized with 100 mg of ketamine + 10 mg of xylazine intraperitoneally, and, after a full thoracotomy, their hearts were isolated and placed in coronary perfusion using a Krebs-Henseleit nutrient-rich solution, according to the Langerdorff method. The parameters of Heart Rate, Systolic Blood Pressure, Coronary Flow, and Myocardial Contractility were evaluated at times of O, 1, 2, 3, 5, 10, and 15 minutes. Results: Heart rate – No statistically significant difference was observed among the Clonidine, Isoflurane, Clonidine+Isoflurane, and Control groups. Systolic Blood Pressure – No statistically significant difference was identified among the Clonidine, Clonidine+Isoflurane, and Control groups. In the group that received only Isoflurane, the systolic blood pressure proved to be equal to the control group and presented, on average, 18.3 more units than did the Clonidine group. In the groups that received Clonidine+Isoflurane, the systolic blood pressure was, on average, 22.5 units less than thecontrol group and, on average, 32.7 units less than the group that received only Isoflurane. Coronary Flow – No statistically significant difference was found regarding the coronary flow among the Clonidine, Isoflurane, Clonidine+Isoflurane, and Control groups. Myocardial Contractility – No statistically significant change was found in this parameter among the Clonidine, Isoflurane, Clonidine+Isoflurane, and Control groups. Conclusion: Clonidine, when used in an isolated manner, produced no significant effect on the hemodynamic behavior of the isolated rat hearts. When used in association with Isoflurane, Clonidine was capable of diminishing the effects of this drug, demonstrating an apparent protective effect upon the heart. The observed effects occurred directly upon the heart, considering that this study was conducted on isolated hearts, that is, with no connection to the central nervous system.