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 renal tissues to synthesize dopamine from added L-3,4-dihydroxyphenylalanine (l -DOPA); the deamination of newly-formed dopamine into 3,4-dihydroxyphenylacetic acid (DOPAC) was also studied. In some experiments, slices of renal cortex obtained from the human, dog and rat kidneys were used; tissues were incubated with increasing concentrations (5–5000 μM) of l -DOPA. The accumulation of newly-formed dopamine was, in all three species, found to be dependent on the concentration of l -DOPA, being the rat renal tissues endowed with a greater ability to produce dopamine, followed by the human and the dog tissues. In experiments performed in kidney homogenates, the decarboxylation of l -DOPA into dopamine was also found to be dependent, in all three species, on the concentration of l -DOPA used (10–5000 μm). AAAD activity as determined in kidney 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 differences were found between the K_m values of the three species (human, 62±8 μM; dog, 54±6 μM; rat, 82±12 μM). A considerable amount of newly-formed dopamine in both kidney slices and homogenates was converted into DOPAC; the DOPAC /dopamine ratios in these experimental conditions were greater in the human kidney, followed by the rat and dog. It is concluded that the decarboxylation of l -DOPA into dopamine is greater in the rat kidney followed by the human and dog, whereas the deamination of the amine into DOPAC appears to be greater in human renal tissues.