Visualization of renal microcirculation and pharmacological analysis of renal vascular responses to vasoconstrictor peptide

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Glomerular filtration rate is determined by the balance of the tone of pre-glomerular and post-glomerular resistance vessels. The former includes interlobular artery and afferent arteriole and the latter efferent arteriole. Therefore, direct visualization of renal microvessels would help us to learn the control of glomerular filtration. In order to visualize these vessels directly, we have constructed optic system that consisted of a vital microscopy, CCD camera, video monitor, recorder and animal chamber suitable for transillumination of hydronephrotic rat kidney in vivo. By using this system, renal cortical microcirculation of hydronephrotic kidney can be visualized on the video-monitor at the magnification of 2,500-fold. Local application of endothelin isopeptide and analog elicited vasoconstriction of interlobular artery, afferent arteriole and the efferent arteriole where both ETA and ETB receptors were involved. Currently, we are developing a system for continuous measurement of … More erythrocyte velocity of renal microvessel, thereby single glomerular blood flow can be measured. In this research project, in addition to the microscopic examination of renal microcirculation, we also performed experiments to elucidate the role of endothelin and adenosine in the control of renal circulation at the whole organ level. The results suggested that activation of ETB receptors by endogenous ET acts as a physiological brake for the ETA-mediated renal vasoconstriction, and this effect is apparently mediated by stimulation of nitric oxide and/or vasodilatoiy prostaglandin(s) release. We also found that activation of renal adenosine A2 receptor had no effect on glomerular filtration despite marked renal vasodilatation, suggesting vasodilation of both afferent and efferent arteriole. Although 4-pentenoic acid, an inhibitor of fatty acid beta- oxidation, markedly stimulated renal production of adenosine and reduced glomerular filtration rate, adenosine Al receptor was not involved in the 4-pentenoic acid-induced fall in glomerular filtration rate. Less