ASSESSMENT OF RENAL DOPAMINERGIC SYSTEM ACTIVITY DURING THE RECOVERY OF RENAL-FUNCTION IN HUMAN KIDNEY-TRANSPLANT RECIPIENTS

Background. The urinary excretion of free dopamine has been used as an index of the renal synthesis of amine. However, it is now well recogn ized that in the kidney, newly-formed dopamine is significantly inacti vated through deamination to 3,4-dihydroxyphenylacetic acid (DOPAC) by monoamine oxidase (MAO). The aim of the present study was to assess t he renal dopaminergic system activity during the recovery of renal fun ction in kidney transplant recipients and to assess which parameters a re appropriate for the evaluation of renal amine synthesis under these conditions. Methods. Twenty-four-hour urinary excretion of L-DOPA, do pamine and its metabolites (DOPAC; 3-MT; HVA) were continuously monito red in 19 renal transplant recipients from the first day of surgery un til the twelfth day post-transplantation. Results. In 11 patients (Gro up 1), renal function consistently recovered throughout the study (pla sma creatinine levels decreased from 6.2+/-0.4 to 2.1+/-0.1 mg/dl). Ei ght patients presented with acute tubular necrosis (Group 2) and minim al renal function was maintained until the twelfth post-operative day. The urinary excretion of L-DOPA did not differ throughout the study b etween the two groups of patients. In contrast, the 24-h urinary level s of dopamine, DOPAC and HVA were significantly higher throughout the study in patients of Group 1: dopamine (Group 1, 179+/-26 to 422+/-51 nmol/24 h; Group 2, 25+/-3 to 57+/-13 nmol/24 h), DOPAC (Group 1,698+/ -57 to 3487+/-414 nnol/24 h; Group 2, 158+/-22 to 1014+/-193 nmol/24 h ) and HVA (Group 1, 13058+/-1199 to 20387+/-1559 nmol/24 h; Group 2, 4 140+/-848 to 15219+/-1037 nmol/24 h). Conclusions. The recovery of ren al function in renal transplant recipients is accompanied by an enhanc ed ability to synthesize dopamine and inactivate it to DOPAC and HVA. It is suggested that the urinary levels of DOPAC may be a useful param eter for the assessment of dopamine formation in renal tissues.