In vivo release of adrenal catecholamines in rats by fusaric acid

We studied the effect of fusaric acid, an inhibitor of dopamine beta-hydroxylase (D beta H), on plasma and peripheral tissue catecholamine (CA) content and on urinary excretion of CA in the rat. We found that fusaric acid treatment resulted in a rapid decline of adrenal epinephrine (E) and norepinephrine (NE) and an increase of adrenal dopamine (DA); the kidney and heart NE and DA contents were affected in a pattern similar to that of the adrenals. In contrast, the E concentrations in the kidneys and heart were markedly elevated after a single intraperitoneal dose of fusaric acid (100 mg/kg); the maximum response was observed at 60 min, when kidney E increased from 9.3 +/- 4.4 to 101 +/- 24 pmol/g tissue and heart E in both atrium and ventricle rose from 92 +/- 8 to 607 +/- 85 pmol/g tissue and from 70 +/- 4 to 632 +/- 50 pmol/g tissue, respectively. In addition, a large increase of CA (predominantly of E) was found in the plasma of treated rats, where E, NE and DA were 27, 6.6 and 2.7 times higher than control values, respectively. The excretions of urinary E and NE were also significantly elevated during treatment. Fusaric acid-treated bilaterally adrenalectomized rats did not exhibit any increase in plasma, heart and kidney E concentrations. The results suggest that fusaric acid stimulates adrenal CA release in vivo, resulting in large increases of the main adrenal CA, E in peripheral tissues, plasma and urine. The decline in the adrenal E content is thus not only due to its decreased synthesis but also increased release.