Dopamine production by the isolated perfused rat kidney

We used isolated perfused rat kidneys to examine dopamine (DA) production and its relation to renal function. Both innervated and chronically surgically denervated kidneys perfused with a solution containing neither albumin nor tyrosine, excreted 0.2 ± 0.1 ng DA∙min−1∙g wet weight−1 during the 10-min collection period between 30 and 40 min after starting perfusion. When perfused with 6.7% albumin, without tyrosine, innervated kidneys excreted 1.0 ± 0.06 ng DA∙min−1∙g−1 and denervated kidneys excreted 1.0 ± 0.07 DA∙min−1∙g−1. When 0.03 mM tyrosine was included in the albumin perfusate, innervated kidneys excreted 1.2 ± 0.1 ng DA∙min−1∙g−1 (p < 0.1). Under these conditions DA excretion continued for at least 100 min at which time it was 0.6 ng∙min−1∙g−1 and 86 ng/g kidney weight had been excreted. Denervated kidneys perfused with albumin + tyrosine excreted 0.9 ± 0.13 ng DA∙min−1∙g−1. Renal stores of free DA, conjugated DA, and dihydroxyphenylalanine (DOPA) could have provided at the most 30 ng/g of DA. Carbidopa inhibited DA excretion completely. DA excretion did not correlate with renal vascular resistance, inulin clearance, or fractional sodium excretion. In summary, nonneural tissue in isolated perfused kidneys produced DA at the same rate as denervated kidneys in vivo. Less than one-third of the DA produced by isolated kidneys could have come from intrarenal stores of DOPA, free DA, and conjugated DA; the rest was synthesized from unknown precursors. Circulating DOPA and tyrosine were not the DA precursors, but albumin was required to obtain production rates similar to those in vivo. Nonneuronal DA production did not influence renal hemodynamics, glomerular filtration rate (GFR), or sodium excretion.