Human umbilical cord vessels (HUCV) release dopamine and nitric oxide (NO). This study aims to verify whether HUCV release nitrocatecholamines such as 6-nitrodopamine (6-ND).
Liquid chromatography ...coupled to tandem mass spectrometry (LC-MS/MS) was used to identify 6-ND release from HUCV rings incubated in Krebs-Henseileit's solution. Vascular reactivity of HUCV rings was tested (with and without endothelium integrity) by suspension of the rings in an organ bath under isometric tension and application of 6-ND and other known mediators.
LC-MS/MS revealed a basal release of 6-ND from endothelium intact from both human umbilical artery (HUA) and vein (HUV). The endothelium intact release was inhibited by the pre-treatment with NO synthesis inhibitor L-NAME (100 μM). In contrast to dopamine, noradrenaline and adrenaline, 6-ND did not contract HUCV, even in presence of L-NAME or ODQ. 6-ND (10 μM) produced a rightward shift of the concentration-response curves to dopamine (pA2: 5.96 in HUA and 5.72 in HUV). Contractions induced by noradrenaline and adrenaline were not affected by pre-incubation with 6-ND (10 μM).
In U-46619 (10 nM) pre-contracted endothelium intact tissues, 6-ND and the dopamine D2-receptor antagonist haloperidol induced concentration-dependent relaxations of HUA and HUV. Incubation with the dopamine D1-receptor antagonist SCH-23390 (10 nM) abolished relaxation induced by fenoldopam but did not affect those induced by 6-ND.
6-ND is released by HUCV and acts as a selective dopamine D2-receptor antagonist in this tissue. This represents a novel mechanism by which NO may modulate vascular reactivity independently of cGMP production.
•HUCV releases 6-ND but only in endothelium intact sections. The endothelium intact release was inhibited by the pre-treatment with L-NAME.•Unlike dopamine, noradrenaline and adrenaline, 6-ND did not contract HUCV, nor in the presence of L-NAME nor ODQ.•6-ND caused a rightward shift of the concentration-response curves to dopamine but did not affect the responses of noradrenaline and adrenaline.•6-ND caused a concentration-dependent inhibition of the contractions induced by the dopamine D2-receptor agonist sumanirole in HUCV.•6-ND is suggestibly acting as a dopaminergic antagonist, with selectivity for the D2-receptor.•6-ND represents a novel mechanism by which NO may modulate vascular reactivity independently of cGMP production.
•For the first time, nucleotide level is measured in washed platelet by LC-MS/MS.•This method shows high precision with the lowest LLoQ to date for cAMP and cGMP.•6-Nitrodopamine does not affect ...platelet nucleotide levels when stimulated.
Cyclic Nucleotides are important in regulating platelet function. Increases in 3′5′-cyclic adenosine monophosphate (cAMP) and 3′5′-cyclic guanosine monophosphate (cGMP) inhibit platelet aggregation and are pharmacological targets for antiplatelet therapy. Here we report an improved method for determining cAMP and cGMP concentrations and, for the first time, in washed platelet supernatants by combining high-performance liquid chromatography and tandem mass spectrometry (LC-MS/MS). Characteristic peaks of the substrates, cGMP or cAMP and their internal standards were identified in negative-ion electrospray ionisation using multiple reaction monitoring. Compared with previously reported methods, the method presented here shows high precision with the lowest lower limit of quantification (LLoQ) to date (10 pg/mL). The effect of a novel catecholamine, 6-nitrodopamine, on cyclic nucleotide levels was quantified. Our results showed that this new method was fast, sensitive, and highly reproducible.
Absolute growth rates change with tree size and age, shifting throughout species ontogeny. The study on interspecific variation in plant traits has generated important insights into the life-history ...strategies and their consequences for ecosystem functioning. However, it remains unknown to what extent – and even if – species’ functional traits are related to the variation in their growth trajectories. We set out to model growth trajectories of 45 woody species from the Brazilian Atlantic Forest in a secondary subtropical forest under regeneration, aiming to understand if species can be grouped by their growth patterns throughout ontogeny and if these groups could be classified in distinct ecological strategies based on key plant traits. We used a maximum likelihood estimation approach to predict growth trajectories using three ecologically relevant parameters maximum growth rate (G
max
), diameter at maximum growth rate (D
opt
), and the ontogenetic variability in growth rate (K) followed by multivariate analyses to detect associations among phylogenetic relationships, plant traits, and growth parameters and classify species into growth pattern groups. Across species, growth trajectory parameters varied widely. The cluster analysis identified three distinct groups based on growth trajectories parameters, which were not functionally or ecologically well defined. Our findings supports the idea that traits describing plant size and tree shape, such as maximum height, canopy volume and height to diameter ratio, were generally the best predictors of species growth parameters throughout ontogeny, even though traits representing resource-use and reproductive strategies also played a significant role. Growth-trait framework can be understood as a continuum of multi-trait combinations where, at one end of the gradient, we find trees with higher growth rate and larger diameters supporting a voluminous canopy combined with lower investment in leaf tissue and smaller diaspore; at the other end, taller trees supporting a smaller canopy with higher investment in leaf tissue and longer diaspore. Ultimately, we have shown that tree architecture, leaf and reproductive traits significantly influence growth trajectory along tree ontogeny, which may be the reason why objectively grouping species based on growth-trajectories parameters is ineffective, at least in highly diverse secondary subtropical forests undergoing regeneration.
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