| Abstract: |
Recent data indicate that even brief exposure to anesthetics can influence expression of genes regulating transcription factors in the heart (1). This observation in conjunction with the fact that myocardial depression by volatile anesthetics may lead to increased ventricular end-diastolic volume, the primary stimulus for adaptive remodeling of the heart, lead us to hypothesize that prolonged anesthesia with halothane could elicit molecular changes within the myocardium consistent with remodeling. To test this hypothesis, the expression of sarcoplasmic endoreticular calcium ATPase subtype 2a (SERCA2a), an index of myocardial molecular remodeling (2), and its regulatory protein phospholamban (PLB) were determined in the hearts of halothane-treated rabbits and compared to control animals. Methods: Twelve adult, New Zealand white rabbits divided into 3 equal groups were used for the study. One group was immediately sacrificed and the hearts snap frozen in liquid nitrogen. In the other 2 groups, the rabbits were initially anesthetized with subcutaneous xylazine and intravenous ketamine. In one of these groups, the rabbits were allowed to recover from anesthesia before sacrifice after 5 hours (time control). In the other group, the trachea was intubated and the lungs ventilated with oxygen and 1% (0.7 MAC) halothane for 5 hours before sacrifice. Using Western blot, SERCA2a and PLB normalized to actin as an internal control were determined in the left ventricle of each heart. Data were compared by ANOVA and the Newman-Keuls test where applicable. Results. There was no difference in SERCA2a expression between the time control group (1.06+-0.03) and animals that were immediately sacrificed (0.96+-0.05), but following 5 hours of halothane SERCA2a expression was reduced nearly two-fold (0.57+-0.03, p<0.001). In contrast, there were no differences between any of the groups in regard to PLB expression. Accordingly, the ratio of SERCA2a to its regulatory protein PLB was reduced from 1.03+-0.06 in the immediate sacrifice group and 1.10+-0.05 in the time control group to 0.63+-0.05 in halothane treated rabbits (p<0.001). Discussion. Molecular remodeling of the heart in response to a variety of stimuli has been well described, with aspects of this process implicated in the transition from hypertrophy to failure (3). One area of primary interest has been alterations in calcium cycling proteins due to their importance for excitation-contraction coupling. In particular, decreased SERCA2a expression has been reported to be functionally significant in the failing heart (2). These preliminary data suggest that prolonged anesthesia with a clinically relevant concentration of halothane can lead to a decrease in SERCA2a protein without concomitant change in PLB. Whether this response is a direct effect of halothane on the myocyte or an indirect consequence of general anesthesia and mechanical ventilation remains unclear. Furthermore, functional significance of the alteration in SERCA2a expression remains to be determined. Nonetheless, the study provides the first data indicating that halothane can produce molecular changes within myocytes that may continue to influence excitation-contraction coupling after the drug has been discontinued. |
