ALPHA-ANP AND HEART-LUNG TRANSPLANTATION - CONSEQUENCES OF CARDIAC DENERVATION

Due to the discovery and elaboration of alpha ANP, the heart can be considered a veritable endocrine gland involved in fluid and electrolyte homeostasis as well as blood pressure regulation. Nevertheless, the mechanisms regulating the synthesis and release of this new hormone are far from being understood. Heart-lung transplantation provides an interesting research model for evaluating the consequences of allograft denervation on alpha ANP synthesis and release, without the disadvantage of significantly increasing the overall atrial tissue mass, as observed in orthotopic heart transplantation. To appreciate better these consequences, we studied the changes in alpha ANP release following heart-lung transplantation. Five patients were included in the study. It began during the immediate postoperative period and went on to the 8th postoperative day. Alpha ANP levels were determined using radioimmunoassay. The postoperative course was characterized by a rapid significant increase in hormone levels as of the 6th postoperative day (45.6 +/- 5.5 fmol/ml). These findings were comparable to those found in a previous study involving orthotopic heart transplantation alone. Thus, the heart-lung group was also capable of high levels of alpha ANP release from the onset. However, this rapidly increasing release was not found to be correlated with the changes in hemodynamic parameters observed postoperatively (blood and cardiac filling pressures). Moreover, we observed no episodes of rejection which might explain the increased release of this hormone. Finally, the fact that increased alpha ANP release occurs despite a smaller increase in the overall tissue mass is more than noteworthy. In conclusion, as we found in our initial study involving heart transplant recipients, the sustained high levels of alpha ANP observed following heart-lung transplantation are in favour of a possible modulating role played by cardiac innervation on the release of this hormone.