Key result
Inhibition of MAO-A or COMT fails to alter urinary dopamine, sodium, or phosphate excretion.
Why the study?
The effects of chronic selective or combined inhibition of type A monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) on daily urinary excretion of dopamine and metabolites, natriuresis, and phosphaturia in 3/4 nephrectomized and Sham rats were examined.
Answers are grounded in this paper and cite their sources.
Chronic MAO-A/COMT inhibition did not alter natriuresis or phosphaturia in 3/4nx rats; leaves open their role in dopamine-dependent renal sodium handling.
BACKGROUND/AIMS: The present study examined the effects of chronic selective or combined inhibition of type A monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) on daily urinary excretion of dopamine and metabolites and on natriuresis and phosphaturia in 3/4 nephrectomized (3/4nx) and Sham rats. METHODS: The 3/4nx and Sham rats were placed in metabolic cages and received the MAO-A-selective inhibitor Ro-411049 (7.5 mg x kg(-1) bid) and/or the COMT-selective inhibitor BIA 3-202 (30 mg x kg(-1) bid) orally for 3 days during high sodium diet. RESULTS: Selective COMT inhibition increased the urinary excretion of the deaminated metabolite (3,4-dihydroxyphenylacetic acid, DOPAC) and decreased the urinary excretion of the methylated (3-methoxytyramine, 3-MT) and deaminated plus methylated metabolite (homovanillic acid, HVA) in both groups. Selective MAO-A inhibition increased the urinary excretion of 3-MT and reduced the urinary excretion of both DOPAC and HVA in either 3/4nx or Sham rats. Combined inhibition of MAO-A and COMT did not significantly change the urinary excretion of DOPAC and markedly decreased the urinary excretion of 3-MT and HVA in both groups. Selective or combined inhibition of MAO-A and COMT did not alter the daily urinary excretion of dopamine, sodium or phosphate in either 3/4nx or Sham rats. CONCLUSIONS: Chronic selective or combined inhibition of MAO-A and COMT is not of major importance in regulating the dopamine-dependent natriuresis and phosphaturia in either 3/4nx or Sham rats.
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Sampaio‐Maia et al. (2006) studied Remnant kidney (3/4 nephrectomized rats). Ro-411049 (MAO-A-selective inhibitor) and/or BIA 3-202 (COMT-selective inhibitor) vs. Sham-operated rats and untreated/single-inhibitor groups was evaluated on Daily urinary excretion of dopamine and metabolites (DOPAC, 3-MT, HVA), sodium (natriuresis), and phosphate (phosphaturia). Selective or combined oral inhibition of MAO-A (Ro-411049) and COMT (BIA 3-202) for 3 days altered urinary dopamine metabolites but did not change urinary dopamine, sodium, or phosphate excretion.
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