A COMPARATIVE-STUDY ON THE SYNTHESIS OF DOPAMINE IN THE HUMAN, DOG AND RAT-KIDNEY

The present work has examined the ability of human, canine and rat ren al tissues to synthesize dopamine from added L-3,4-dihydroxyphenylalan ine (L-DOPA); the deamination of newly-formed dopamine into 3,4-dihydr oxyphenylacetic acid (DOPAC) was also studied. In some experiments, sl ices of renal cortex obtained from the human, dog and rat kidneys were used; tissues were incubated with increasing concentrations (5-5000 m uM) of L-DOPA. The accumulation of newly-formed dopamine was, in all t hree species, found to be dependent on the concentration of L-DOPA, be ing the rat renal tissues endowed with a greater ability to produce do pamine, followed by the human and the dog tissues. In experiments perf ormed in kidney homogenates, the decarboxylation of L-DOPA into dopami ne was also found to be dependent, in all three species, on the concen tration of L-DOPA used (10-5000 muM). AAAD activity as determined in k idney homogenates was found to be in the rat kidney (V(max) = 7.7 +/- 0.8 nmol mg-1 protein h-1) higher than that occurring in the human (V( max) = 5.8 +/- 0.6 nmol mg-1 protein h-1) and the dog kidney (V(max) = 3.9 +/- 0.5 nmol mg-1 protein h-1). No statistically significant diff erences were found between the K(m) values of the three species (human , 62 +/- 8 muM; dog, 54 +/- 6 muM; rat, 82 +/- 12 muM). A considerable amount of newly-formed dopamine in both kidney slices and homogenates was converted into DOPAC; the DOPAC /dopamine ratios in these experim ental conditions were greater in the human kidney, followed by the rat and dog. It is concluded that the decarboxylation of L-DOPA into dopa mine is greater in the rat kidney followed by the human and dog, where as the deamination of the amine into DOPAC appears to be greater in hu man renal tissues.