Cilj: Glavni su ciljevi ovog istraživanja bili 1) testirati hipotezu da je mikrovaskularna osjetljivost na protokom (FID), kao i acetilkolinom (AChID), posredovanu dilataciju smanjena u krvnim žilama visceralnog (VAT) masnog tkiva u usporedbi s potkožnim (SAT); 2) istražiti mehanizme koji doprinose smanjenoj protokom posredovanoj vazodilataciji ljudskih krvnih žila potkožnog i visceralnog masnog tkiva u pretilosti. Metode: Krvne žile izolirane su iz bioptata potkožnog i visceralnog masnog tkiva pretilih žena (N=53) te su kanulirane na staklene mikropipete u sustavu za mjerenje vaskularne reaktivnosti. Mjerene su promjene promjera krvne žile u odgovoru na povećanje protoka (gradijent tlaka 10-100 cmH2O), te odgovoru na acetilkolin (ACh, 10-9-10-4 M). Mjeren je bazični odgovor žila, te u prisutnosti inhibitora dušik-oksid sintetaze, Nω-nitro-L-arginin metil ester (L-NAME, 10–4 M); indometacina, inhibitora ciklooksigenaze (INDO; 10-5M); katalaze, koja ukljanja H2O2 (PEG-CAT; 500 U/ml); i u prisutnosti neselektivnog ihhibitora citokroma P450, 17-octadecynoic acid (17-ODYA; 10-5 M). Također, fluorescentnim je mikroskopom mjereno stvaranje dušikovog oksida (NO) i vodikovog peroksida (H2O2) u krvnim žilama, prije i nakon povećanja protoka kroz žilu. Rezultati: Otporničke krvne žile VAT su manje osjetljive na povećanje protoka ili koncentracije acetilkolina u odnosu na one iz SAT. L-NAME, kao i INDO, značajno smanjuju FID potkožnih krvnih žila, dok dodani zajedno nemaju jači učinak na dilataciju. L-NAME ili INDO pojedinačno nemaju učinak na FID visceralnih krvnih žila, ali zajednički učinak im je značajan pri višim protocima. 17-ODYA djelomično smanjuje FID u krvnim žilama potkožnog, ali i visceralnog masnog tkiva uspoređujući ju s bazičnim odgovorom. PEG-CAT smanjuje FID žila potkožnog masnog tkiva, ali ne utječe na žile visceralnog. L-NAME, INDO i PEG-CAT značajno smanjuju AChID potkožnih krvnih žila, ali nemaju učinak u visceralnim žilama. U stanju bez protoka, proizvodnja NO-a je povećana u SAT uspoređujući ju s VAT. L-NAME u SAT smanjuje proizvodnju NO-a. U prisutnosti intraluminalnog protoka, proizvodnja NO-a je povećana i u SAT i VAT, a L-NAME smanjuje NO proizvodnju u SAT. Također, za vrijeme protoka, PEG-CAT značajno smanjuje DCF florescenciju u SAT, ali ne i u VAT. Zaključak: U pretilosti su krvne žile visceralnog masnog tkiva manje osjetljive na povećanje protoka i protkom posredovane proizvodnje NO-a, uspoređujući ih s krvnim žilama potkožnog masnog tkiva. Protokom potaknuta vaskularna reaktivnost otporničkih arteriola potkožnog i visceralnog masnog tkiva posredovana je različitim regulacijskim mehanizmima. Objective: The primary goals of the present study were to 1) test the hypothesis that microvascular flow-induced dilation (FID) and acetylcholine-induced dilation (AChID) are impaired in visceral (VAT) compared to subcutaneous adipose tissue (SAT) in obese patients and 2) determine the mechanisms contributing to reduced vasodilator sensitivity to flow in human visceral and subcutaneous adipose tissue arterioles in human obesity. Methods: Vessels from 53 morbidly obese women (BMI>40 kg/m2) were collected from SAT and VAT biopsies and were cannulated for vascular reactivity measurements in response to flow (pressure gradients of 10-100 cmH2O) and in response to acetylcholine (ACh, 10-9-10-4 M). Flow- and acetylcholine- mediated vasodilation was observed in the presence and absence of nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 10–4 M), cyclooxygenase inhibitor indomethacin (INDO; 10-5M), the H2O2 scavenger poly ethyleneglycol catalase (PEG-CAT; 500 U/ml), and non selective cytochrome P450 pathway inhibitor 17-octadecynoic acid (17-ODYA; 10-5 M).Also, nitric oxide (NO) and hydrogen peroxide (H2O2) generation in arterioles was detected with fluorescence microscopy, in the presence and absence of flow. Results: Dilator responses of VAT resistance arteries were less sensitive to increase flow, but also to ACh compared to SAT vessels. L-NAME significantly reduced FID in SAT microvessels. INDO reduced FID in SAT microvessels too, but had no additional effect in the presence of L-NAME. There was no effect of L-NAME or INDO alone on FID of VAT microvessels, but addition of L-NAME to INDO reduced FID at higher flow rates. The presence of 17-ODYA partially reduced FID of microvessels from both SAT and VAT, compared to baseline. PEG-CAT reduced FID of SAT microvessels, but had no effect on resistance arteries from VAT. There was a significant reduction in AChID in arterioles from SAT in the presence of L-NAME, INDO and PEG-CAT , but had no effect in microvessels from VAT. In the assence of intraluminal flow, NO production was increased in vessels from SAT compared to VAT, and presence of L-NAME reduced NO production in vessels from SAT, but not in vessels from VAT. In the presence of intraluminal flow, NO production was increased in both SAT and VAT microvessels, and was reduced in SAT by NOS inhibition with L-NAME. During flow PEG-CAT significantly reduced DCF fluorescence in SAT but not in VAT. Conclusion: During obesity, arterioles of visceral fat are less sensitive to flow-induced dilation and flow-induced NO generation compared to arterioles of subcutaneous adipose tissue. Microvascular reactivity to flow is mediated by different regulatory mechanisms in visceral and subcutaneous fat.