Marleen Verbeke

The impaired renal vasodilator response attributed to endothelium-derived hyperpolarizing factor in streptozotocin – induced diabetic rats is restored by 5-methyltetrahydrofolate

Aims/hypothesis. Endothelial dysfunction contributes to the development of diabetic vascular complications. A better understanding of the pathophysiology of endothelial dysfunction in diabetes could lead to new approaches to prevent microvascular disease. Methods. Endothelium-dependent and endothelium-independent vasodilator responses were investigated in the renal microcirculation of streptozotocin-induced diabetic rats. We measured renal blood flow changes with an electromagnetic flow probe. In addition, the responses of the different segments of the renal microcirculation were evaluated with videomicroscopy using the hydronephrotic kidney technique. Because endothelial cells release different relaxing factors (nitric oxide, prostacyclin and an unidentified endothelium-derived hyperpolarizing factor), responses to acetylcholine were measured before and after treatment with the nitric oxide synthase inhibitor l-NG-nitroarginine methylester HCI (l-NAME) and the cyclooxygenase inhibitor indomethacin. We evaluated with the effect of 5-methyltetrahydrofolate, the active form of folate, on the responses. Results. The l-NAME- and indomethacin-resistant vasodilation to intra-renal acetylcholine was significantly reduced in the diabetic compared with control rats, suggesting impaired endothelium-derived hyperpolarizing factor-mediated vasodilation. The responses to the nitric oxide donor (Z)-1-[-2-(aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate) and to the K+-channel opener pinacidil were similar in diabetics and controls, indicating intact endothelium-independent vasodilator mechanisms. The contribution of endothelium-derived hyperpolarizing factor to vasodilation induced by acetylcholine was greatest in the smallest arterioles. In diabetic rats, the response to acetylcholine was increasingly impared as vessel size decreased. Defective vasodilation in diabetic kidneys was rapidly normalized by 5-methyltetrahydrofolate. Conclusion-interpretation. Endothelium-derived hyperpolarizing factor-mediated vasodilation is impaired in the renal microcirculation of diabetic rats, in particular in the smallest arteries. Treatment with folate restores the impaired endothelial function in diabetes. [Diabetologia (2000) 43: 1116–1125]

An organotypical in vitro model for vascular tissue remodelling and its application to study radiation effects.

An organotypic in vitro model, to study vascular tissueremodeling, was evaluated as a function of culture period. Inorder to validate the model as a tool for studying vascularresponses to damage, a dose-response analysis to ionizingirradiation was included.Rat aortic rings were explanted in vitro after being irradiatedwith single doses of 60Co γ-rays, namely 0, 5, 10, 15, 20or 25 Gy. Irradiated and sham-irradiated aortic rings werecultured for 3 weeks. Explant outgrowth on an adhesivesubstrate was evaluated by macroscopical scoring, and ringsderived from each irradiation group together with theoutgrowths were fixed and embedded in paraffin after 2, 7, 14and 21 days. Bromodeoxyuridine incorporation, α smoothmuscle actin and collagen types I and III were scored onimmunohistochemically stained sections. For each studiedparameter, irradiated and sham-irradiated rings were compared.In cultures of sham-irradiated rings, alterations from acontractile towards a synthetic/migratory smooth muscle cellphenotype were confirmed. After 3 weeks, fullgrown cultures hadformed. Irradiation slowed down the phenotypical modifications.After 15 Gy, irradiation explant outgrowth was already retarded;after 25 Gy, the outgrowth was completely blocked. On the otherhand, a dose of 15 Gy or more induced an increased collagen Iproduction in the tunica media.In conclusion, the present organotypical in vitro model fits toanalyse dynamics in the original vascular tissues as well as inthe primary outgrowth. It enables to confirm features oftissular reorganization and effects of ionizing radiationdescribed in vivo.

Biological effects of low intensity Helium-Neon and Gallium-Arsenide laser irradiation on embryonic chick heart fragments in vitro

The effect of pulsed Gallium-Arsenide and continuous Helium-Neon waves on embryonic chick heart fragments in vitro were investigated.Heart fragments were exposed for different irradiation times, varying from 1 s to 1500 s, to the laser beam. No differences could be observed between the irradiated and sham-irradiated fragments after an in vitro study of their 3 H-thymidine uptake, cell membrane permeability and cellular migration. This means that the effectiveness of low-intensity laser irradiation for wound healing can not be explained by an immediate influence on the mentioned characteristics of a living cell.