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Inhibition by N‐acetyl‐5‐hydroxytryptamine of nitric oxide synthase expression in cultured cells and in the anaesthetized rat
Author(s) -
Klemm Peter,
Hecker Markus,
Stockhausen Hannelore,
Wu Chin Chen,
Thiemermann Christoph
Publication year - 1995
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1995.tb15021.x
Subject(s) - nitric oxide synthase , atp synthase , nitric oxide , chemistry , pharmacology , microbiology and biotechnology , biology , biochemistry , endocrinology , enzyme
1 Induction of the calcium‐independent isoform of nitric oxide (NO) synthase (iNOS) in various cell types has been implicated in the circulatory failure in experimental models of septic shock. Tetrahydrobiopterin (BH 4 ) appears to be an essential co‐factor for NO formation and therefore an inhibition of its biosynthesis represents a feasible therapeutic target. We have investigated the effects of an inhibitor of BH 4 synthesis, N‐acetyl‐5‐hydroxytryptamine (N‐acetylserotonin, NAS), on the expression of iNOS in cultured macrophages and smooth muscle cells in vitro , and on the hypotensive response to bacterial lipopolysaccharide (LPS) in the anaesthetized rat in vivo . 2 NAS (0.01–5 mM) caused a concentration‐dependent inhibition of the accumulation of nitrite in the conditioned medium of LPS/interferon‐γ (IFN γ )‐stimulated RAW 264.7 macrophages and interleukin‐1β (IL‐lβ)‐activated vascular smooth muscle cells (VSMC). This effect was paralleled by a similar decrease in the iNOS protein content of these cells, as determined by immunoblot analysis. 3 Pretreatment of RAW 264.7 macrophages with the BH 4 precursor, dihydrobiopterin (BH 2 , 0.1 mM) did not restore nitrite formation in the presence of NAS (1 mM). 4 Intravenous administration of NAS (1 mg kg −1 min −1 for 30 min) in anaesthetized rats significantly reduced the fall in mean arterial blood pressure, restored the pressor response to noradrenaline (1 μg kg −1 ), and ameliorated the increase in plasma nitrite following exposure to LPS (10 mg kg −1 ). 5 NAS pretreatment also attenuated iNOS activity in lung homogenates, as determined by the conversion of radiolabeled L‐arginine to L‐citrulline, and partially restored the constrictor effect of noradrenaline in aortic rings isolated from LPS‐treated rats. Moreover, NAS significantly reduced the rise in the plasma concentration of tumour necrosis factor α (TNFα) in response to LPS. 6 These findings suggest that NAS inhibits the expression rather than the activity of iNOS in cultured macrophages and smooth muscle cells. This effect of NAS appears to be independent of the availability of BH 4 , but may be related to an attenuation of the release of TNFα following LPS administration, as shown in the anaesthetized rat. This mechanism may also account for the beneficial haemodynamic effect of NAS in our experimental model of endotoxaemia.