ENDOCRINE RESPONSE TO PLASMA-VOLUME EXPANSION DURING THE EARLY POSTOPERATIVE PERIOD IN HEART-TRANSPLANT RECIPIENTS

The purpose of this study was to investigate the changes in endocrine control of blood pressure and electrolyte homeostasis during the early postoperative period after heart transplantation. Dynamic testing usi ng volume-expansion to increase cardiac filling pressures was performe d to determine changes in alpha atrial natriuretic peptide, renin, ald osterone, and vasopressin secretion in response to a physiologic stimu lus. Volume expansion was performed on five heart transplant patients each day from postoperative day 1 to postoperative day 5. Alpha atrial natriuretic peptide, renin, aldosterone, and vasopressin plasma level s were assessed by radioimmunoassay before and during the 6 hours afte r the beginning of infusion. No significant changes in the secretion o f any of the various hormones studied were found after volume expansio n. Moreover, we found that heart transplant recipients were unable to increase water and sodium renal excretion after volume expansion. The physiologic decrease in vasopressin release after volume expansion app ears to be altered by graft denervation. Furthermore, persistently ele vated alpha atrial natriuretic peptide plasma levels at rest despite i mproved patient hemodynamic status and the absence of enhanced hormone secretion after a physiologic stimulus are in favor of an intrinsic h ypersecretion of this hormone. Moreover, the absence of an appropriate renal response could be a major consequence of both the lack of furth er increased alpha atrial natriuretic peptide secretion and the heart denervation resulting from transplantation. This blunted renal respons e should be taken into account when managing patients in the early per iod after transplantation.