Springer Online Journal Archives 1860-2000
Summary In 12 female dogs renal excretion and catabolism of 14C-(±)-adrenaline, 14C-(±)-noradrenaline, 14C-dopamine and 3H-(±)-normetanephrine were investigated using a modified stop-flow technique. Radioactive compounds were infused, together with inulin, into the left renal artery for 10 min. During the first 2 min of the infusion period the left ureter was occluded. Urine samples were serially collected from both kidneys up to the end of the infusion. In the urine the total radioactivity and the pattern of radioactive metabolites were measured. On average, the infused kidney excreted from the infused dose of 14C-adrenaline 9.4% as adrenaline, 27.9% as metanephrine and 5.8% as deaminated or conjugated metabolites. From infused 14C-noradrenaline 7.4% was excreted as noradrenaline, 3.5% as normetanephrine and 1% as deaminated or conjugated compounds. When 3H-normetanephrine was infused the urine contained only radioactive normetanephrine (22.2%). From the infused dose of 14C-dopamine 9.6% was excreted as dopamine, 16.2% as 3-O-methyldopamine and 3.7% as deaminated or conjugated compounds. — Urine from the other kidney contained 1/25 to 1/5 the radioactivity of that from the infused side, but the pattern of radioactive compounds was similar. From the excretion rate of simultaneously infused inulin the filtration fraction of the infused kidney was determined. That part of the infused 14C-catecholamines which was excreted unmetabolized in the urine, corresponds to the filtration fraction in this kidney. Therefore, it is suggested, that in mammals the unmetabolized catecholamines of the urine are mainly excreted by glomerular filtration and not by tubular secretion. On the other hand, the urinary O-methylated radioactive catecholamines, which were excreted by the infused kidney at a high rate, were formed in this organ from the infused catecholamines and were excreted by tubular secretion. Thus, in mammals tubular secretion is linked to an inactivation of these compounds by O-methylation.
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