[Effect of opioid receptor blockade with naloxone on plasma renin activity and aldosterone levels in patients with kidney transplantation].

Function of the renin-angiotensin-aldosterone (RAA) system in kidney transplant patients (KTP) is often abnormal as in patients with chronic renal failure. On the other hand the importance of opioids in the regulation of function of endocrine organs is well established. These facts were the background of studies presented in this paper. They aimed to assess the role of opioid receptors in the regulation of the RAA in KTP. 12 patients with a stabilized renal graft function and on cyclosporin A + prednisone therapy and 15 healthy subjects were examined. In all subjects plasma renin activity (PRA), plasma aldosterone level (Ald) and blood pressure were assessed during a 4 hr bed-rest test. In each subject two tests were performed: the first one without naloxone administration, and the second one--after opioid receptor blockade. In KTP significantly elevated PRA and blood pressure and moderately elevated plasma Ald levels were found as compared with normals. After a 4 hr bed rest without naloxone no significant changes of the above mentioned parameters were noticed both in the patients and the controls. After opioid receptors blockade by naloxone a significant decrease of PRA and plasma Ald was observed in both examined groups. This decrease was significantly more marked in KTP than in controls. In addition only in KTP 4 hrs after naloxone administration a significant increase of systolic and diastolic blood pressure was found. Results obtained in this study suggest, that opioid receptors are involved in the regulation of the activity of the RAA system and of blood pressure more markedly in KTP than in healthy subjects.