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 using volume-expansion to increase cardiac filling pressures was performed to determine changes in alpha atrial natriuretic peptide, renin, aldosterone, and vasopressin secretion in response to a physiologic stimulus. 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 levels were assessed by radioimmunoassay before and during the 6 hours after the beginning of infusion. No significant changes in the secretion of any of the various hormones studied were found after volume expansion. 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 appears to be altered by graft denervation. Furthermore, persistently elevated alpha atrial natriuretic peptide plasma levels at rest despite improved patient hemodynamic status and the absence of enhanced hormone secretion after a physiologic stimulus are in favor of an intrinsic hypersecretion of this hormone. Moreover, the absence of an appropriate renal response could be a major consequence of both the lack of further increased alpha atrial natriuretic peptide secretion and the heart denervation resulting from transplantation. This blunted renal response should be taken into account when managing patients in the early period after transplantation.