Analysis on regulation of renal microcirculation with an in-vivo visualisation system

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Visualisation studies on renal microcirculation so far have been limited on isolated nephron samples, pathological hydronephrotic kidney models or cheek pouch transplant models. It is because making an access to the renal microcirculation under physiological conditions is technically very difficult. We have overcome this obstacle by developing a CCD intravideomicroscope. To investigate glomerular functions further, we have started applying fluorescence for visualisation. The purpose of this study is to visualise renal microcirculation by intravital videomicroscopy and two-photon microscopy in two-week STZ-induced diabetic rats. With 60 mg per kilogramme of STZ, rats become diabetic to the moderate degree. Blood glucose level after 2 weeks is about 400 mg/dl.We found with our intravital videomicroscope that diameters of glomerular arterioles in early diabetic rats (afferent (aff) 14.0 ± 1.9, efferent (eff) 9.4±0.7μ m) were larger than those of normal control (aff 11.9±0.8, eff 8.8±0.7μ m (p<0.05). Renal flow per 100 g kidney weight was larger for diabetic rats, which was measured with a transonic ultrasound flowmeter. From these results, diabetic rats were under hyperfiltrated state.Such renal filtration was visualised with a two-photon microscope administering FITC dextran (500k) and Rhodamine dextran (20k, size less than 5 nm). FITC dextran stayed in the glomerular circulation, while rhodamine dextran was filtered out of the glomeruli. The renal tubules were visualized about 60 seconds after rhodamine B dextran injection. The brightness is greater for diabetic rats than normal control rats. Taken together, hyperfiltration observed in early diabetes will be elucidated physiologically and molecular biologically by intravital videomicroscopy and two-photon microscopy.