Blood flow through the pancreas and within the islet is crucial to the physiological response and is regulated by complex and poorly understood processes. In this study we have visualised the pattern and arrangement of the islet microvasculature in anaesthetized mice (urethane, 1.8 g kg^-1 body weight; a high dose of anaesthetic was used to kill the animals humanely at the end of the experiments). The pancreas of CDI mice was exteriorised and viewed under the microscope using transmitted light. The carotid artery and femoral vein were cannulated. FITC-albumin was injected intra-arterially and images (1-4 µm optical sections) of the microvasculature were obtained with a Ω40 objective (WI, Olympus) using a MRC-600 laser scanning confocal microscope equipped with a Krypton argon laser (excitation at 488 nm). Estimates of islet blood flow were obtained from measuring fluorescently labelled 0.2 µm diameter microsphere flow velocity in single islet capillaries and from changes in red cell flux using a laser-Doppler flowmetry (Moor Instruments). Arterial pressure and body temperature were monitored continuously. Blood glucose was measured with a glucometer (Esprit, Bayer).

In the 2-3 min following blood glucose elevation (from 5-7 mM to 14-20 mM) the microsphere velocity increased from 113.3 ± 8.5 to 224.7 ± 12.9 µm s^-1 (mean ± S.E.M.). This increase was completely blocked (to 115.7 ± 8.9 µm s^-1) when L-NAME (10 mg kg^-1 body weight) was given 10-15 min before glucose infusion. L-Arginine (30 mg kg^-1 body weight) reversed the L-NAME inhibition of the glucose-induced blood flow response (250.7 ± 15 µm s^-1). Blood glucose elevation resulted in a significant increase in islet red blood cell flux (257.98 ± 32 % above control, n = 6, P ▓le│ 0.05, one-way ANOVA with Bonferroni correction). L-NAME pretreatment resulted in a smaller increase (135.04 ± 04 % above control, n = 6). L-NAME alone had no effect on islet red blood cell flux. Addition of L-arginine (15-20 min treatment) restored the glucose effect (302 ± 42 % above control, n = 5). Raised blood glucose had no significant effect on red blood cell flux in the exocrine pancreas. These data suggest that nitric oxide has an important role in the regulation of hyperglycaemic-induced increase in blood flow in islets of Langerhans.

This work was funded by The Wellcome Trust and approved by the University Animal Ethics Committee.