Diabetes converts arterial regulation by perivascular adipose tissue from relaxation into H(2)O(2)-mediated contraction.

This study aims to reveal the reason for the increased force of 5-hydroxytryptamine-induced contraction of endothelium-denuded skeletal muscle arteries of diabetic rats in the presence of perivascular adipose tissue (PVAT). Our data on rat gracilis arteries show that i) PVAT of skeletal muscle arteries of healthy and diabetic rats releases hydrogen peroxide (H(2)O(2)), ii) higher concentrations of 5-hydroxytryptamine increase the production of H(2)O(2) in PVAT; iii) an enhanced PVAT production of H(2)O(2) is the main, if not the only, reason for the sensitization of arterial contraction to 5-hydroxytriptamine-induced contraction in diabetes and iv) endothelium antagonizes the effect of PVAT-derived H(2)O(2).

Ghrelin signaling in human mesenteric arteries.

The hypothesis is that the ghrelin signal pathway consists of new participants including a local second mediator in human mesenteric arteries. The contractile force of isometric artery preparations was measured using a wire-myograph. Whole-cell patch clamp experiments were performed on freshly isolated single smooth muscle cells from the same tissue. After the addition of ghrelin (100 nmol) the outward potassium currents conducted through iberiotoxin-sensitive calcium-activated potassium channels with a large conductance were almost entirely abolished. The effect of ghrelin on potassium currents was insensitive to selective inhibitors of cAMP-dependent protein kinase and soluble guanylate cyclase, but was eliminated in the presence of des-octanoyl ghrelin and O-(octahydro-4,7-methano-1H-inden-5-yl) carbonopotassium dithioate (D-609). Ghrelin dose-dependently increased the force of contraction of native, endothelium-denuded and mostly of endothelium-denuded and treated with tetrodotoxin human mesenteric arteries preconstricted with 1 nmol endothelin-1. This effect of ghrelin was blocked when the bath solution contained 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126), 4-amino-5-(4-methylphenyl)-7-(t-butyl) pyrazolo[3,4-d] pyrimidine (PP2), D-609, 2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl) maleimide (GF109203x), pertussis toxin, 2-aminoethyl diphenylborinate (2-APB), indomethacin, (5Z,13E)-(9S,11S,15R)-9,15,Dihydroxy-11-fluoro-15-(2-indanyl)-16,17,18,19,20,pentanor-5,13-prostadienoic acid (AL-8810) - a non-selective prostanoid receptor antagonist, 5-(4-Chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl pyrazolo (SC-560) - a selective cyclooxygenase 1 inhibitor, ozagrel - a selective thromboxane A(2) synthase inhibitor or T prostanoid receptor antagonist GR32191B. It is concluded that ghrelin increases the force of contraction of human mesenteric arteries by a novel mechanism that involves Src kinase, mitogen-activated protein kinase kinase (MEK), cyclooxygenase 1 and T prostanoid receptor agonist, most probably thromboxane A(2).

Ghrelin signalling in guinea-pig femoral artery smooth muscle cells.

AIM: Our aim was to study the new signalling pathway of ghrelin in the guinea-pig femoral artery using the outward I(K) as a sensor. METHODS: Whole-cell patch-clamp experiments were performed on single smooth muscle cells, freshly isolated from the guinea-pig femoral artery. The contractile force of isometric preparations of the same artery was measured using a wire-myograph. RESULTS: In a Ca2+- and nicardipine-containing external solution, 1 mmol L(-1) tetraethylammonium reduced the net I(K) by 49 +/- 7%. This effect was similar and not additive to the effect of the specific BK(Ca) channel inhibitor iberiotoxin. Ghrelin (10(-7) mol L(-1)) quickly and significantly reduced the amplitudes of tetraethylammonium- and iberiotoxin-sensitive currents through BK(Ca) channels. The application of 5 x 10(-6) mol L(-1) desacyl ghrelin did not affect the amplitude of the control I(K) but it successfully prevented the ghrelin-induced I(K) decrease. The effect of ghrelin on I(K) was insensitive to selective inhibitors of cAMP-dependent protein kinase, soluble guanylyl cyclase, cGMP-dependent protein kinase or a calmodulin antagonist, but was effectively antagonized by blockers of BK(Ca) channels, phosphatidylinositol-phospholipase C, phosphatidylcholine-phospholipase C, protein kinase C, SERCA, IP(3)-induced Ca2+ release and by pertussis toxin. The ghrelin-induced increase in the force of contractions was blocked when iberiotoxin (10(-7) mol L(-1)) was present in the bath solution. CONCLUSIONS: Ghrelin reduces I(K(Ca)) in femoral artery myocytes by a mechanism that requires activation of Galpha(i/o)-proteins, phosphatidylinositol phospholipase C, phosphatidylcholine phospholipase C, protein kinase C and IP(3)-induced Ca2+ release.