Abstract
Background: Perivascular adipose tissue (PVAT) can decrease vascular contraction to NE. We tested the hypothesis that metabolism and/or uptake of vasoactive amines by mesenteric PVAT (MPVAT) could affect NE-induced contraction of the mesenteric resistance arteries.Methods: Mesenteric resistance vessels (MRV) and MPVAT from male Sprague-Dawley rats were used. RT-PCR and Western blots were performed to detect amine metabolizing enzymes. The Amplex® Red Assay was used to quantify oxidase activity by detecting the oxidase reaction product H2O2 and the contribution of PVAT on the mesenteric arteries' contraction to NE was measured by myography.Results: Semicarbazide sensitive amine oxidase (SSAO) and monoamine oxidase A (MAO-A) were detected in MRV and MPVAT by Western blot. Addition of the amine oxidase substrates tyramine or benzylamine (1 mM) resulted in higher amine oxidase activity in the MRV, MPVAT, MPVAT's adipocyte fraction (AF), and the stromal vascular fraction (SVF). Inhibiting SSAO with semicarbazide (1 mM) decreased amine oxidase activity in the MPVAT and AF. Benzylamine-driven, but not tyramine-driven, oxidase activity in the MRV was reduced by semicarbazide. By contrast, no reduction in oxidase activity in all sample types was observed with use of the monoamine oxidase inhibitors clorgyline (1 μM) or pargyline (1 μM). Inhibition of MAO-A/B or SSAO individually did not alter contraction to NE. However, inhibition of both MAO and SSAO increased the potency of NE at mesenteric arteries with PVAT. Addition of MAO and SSAO inhibitors along with the H2O2 scavenger catalase reduced PVAT's anti-contractile effect to NE. Inhibition of the norepinephrine transporter (NET) with nisoxetine also reduced PVAT's anti-contractile effect to NE.Conclusions: PVAT's uptake and metabolism of NE may contribute to the anti-contractile effect of PVAT. MPVAT and adipocytes within MPVAT are a source of SSAO.
Highlights
Perivascular adipose tissue (PVAT) makes up the fourth layer of most blood vessels (Chaldakov et al, 2007)
Inhibition of monoamine oxidase (MAO)-A/B or sensitive amine oxidase (SSAO) individually did not alter contraction to NE. Inhibition of both MAO and SSAO increased the potency of NE at mesenteric arteries with PVAT
mesenteric PVAT (MPVAT) and adipocytes within MPVAT are a source of SSAO
Summary
Perivascular adipose tissue (PVAT) makes up the fourth layer of most blood vessels (Chaldakov et al, 2007). PVAT is appreciated for its effects on the vasculature, from mediating relaxation (Brandes, 2007; Fesus et al, 2007) to stimulating contraction of arteries by the release of catecholamines (Gao et al, 2006; Ayala-Lopez et al, 2014). Investigating mesenteric PVAT’s mechanisms of handling NE, the sympathetic neurotransmitter, is relevant in understand the pathology in this disease because sympathetic nervous system activity is increased in obesityrelated hypertension (Hall et al, 2010). Mesenteric and aortic PVAT can take up NE applied exogenously, which could contribute to PVAT’s anticontractile effect on mesenteric and aortic arteries exposed to NE (Ayala-Lopez et al, 2015). Perivascular adipose tissue (PVAT) can decrease vascular contraction to NE. We tested the hypothesis that metabolism and/or uptake of vasoactive amines by mesenteric PVAT (MPVAT) could affect NE-induced contraction of the mesenteric resistance arteries
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