Evidence for an extraneuronal location of monoamine oxidase in renal tissues

Abstract

(1) Homogenates of renal cortex and renal medulla of control and 6-hydroxydopamine-denervated cat kidneys were prepared. (2) Monoamine oxidase (MAO) activity was determined with [³H]-5-hydroxytryptamine ([³H]-5HT) and [¹⁴C]-β-phenylethylamine ([¹⁴C]-β-PEA) as preferential substrates for MAO-A and MAO-B, respectively. (3) The endogenous dopamine and noradrenaline tissue contents of control and chemicallydenervated kidneys were compared with the MAO activities. (4) The results show that a 70% depletion of monoamine content by chemical denervation resulted only in a 23% reduction of MAO-A activity in the renal cortex, whereas MAO-13 was unaffected either in the cortical or the medullary zones; in the renal medulla MAO-A activity was not changed by denervation. Most of the MAO activity in the cat kidney is of the B type (74%) and is located in the renal cortex.