A regulatory defect of constitutive no-synthase in islet endothelial cellscorrelates with probability of disease manifestation in BBdp rats

Aims/hypothesis. Type I (insulin-dependent) diabetes mellitus is characteri sed by leucocyte infiltration of pancreatic islets and a progressive destru ction of insulin-producing beta cells. As endothelial nitric oxide producti on is known to regulate adhesion molecule expression and leucocyte permeati on, we examined the activity and expression of the constitutive nitric oxid e synthase (ecNOS) of islet endothelial cells from prediabetic BBdp rats. Methods. Cultures of aortic endothelial cells and islet capillary endotheli al cells were established from young normoglycaemic BBdp rats, Wistar rats and diabetes-resistant BBdr rats, all matched for age. Nitrite and citrulli ne production was measured in all culture supernatants as indicators for ec NOS activities. Expression of ecNOS mRNA was assessed by reverse transcript ion-polymerase chain reaction. Results. In contrast to those of the aorta, the Wistar rat islet derived en dothelial cells exhibited a strong positive correlation of ecNOS activity w ith the culture medium glucose concentration but none of the BE Pat-derived islet endothelial cells showed a similar glucose-responsiveness. Furthermo re, at physiological as well as at increased glucose concentrations islet e ndothelia from all BBdp rats exhibited a considerable decrease in ecNOS act ivity by a factor of 3 to 6, indicating a specific dysfunction which is als o found for the inducible nitric oxide synthase activity after cytokine cha llenge but effects were less (2.5 to 3 times) dramatic. In contrast, aorta endothelia from all fats exhibited identical ecNOS activities and no glucos e responsiveness. We also found a correlation between ecNOS activities and ecNOS-mRNA expression and can exclude the involvement of the inducible isof orm. Conclusion/interpretation. A reproducible and highly significant dysfunctio n of islet ecNOS expression and activity in young normoglycaemic BBdp rats, which strongly correlates with the probability for disease manifestation i s shown.