In vivo visualization of angiotensin II- and tubuloglomerular feedback-mediated renal vasoconstriction

Background. A noninvasive technique to monitor renal microcirculation would be a useful tool for investigation of renal disease and the effects of drugs on the renal system. We have developed a novel, less invasive technique to visualize renal microcirculation in vivo using an intravital tapered-tip (1 mm ø) lens-probe (pencil lens-probe) videomicroscopy, which only requires insertion of the probe into superficial renal cortex in situ. Methods. To assess validity of this technique, the effects of angiotensin II (Ang II) and intrarenal sodium chloride loading (activator of tubuloglomerular mechanism) were examined. The renal microvasculature was successfully visualized and monitored. Results. Administration of Ang II (1, 3, 10 and 30 ng/kg/ min) produced a dose-dependent constriction of afferent and efferent arterioles in similar degrees; at 30 ng/kg/min, Ang II elicited 52 ± 3 (N = 9) and 53 ± 3% decreases in diameter (N = 9), respectively. The Ang II-induced arteriolar constriction was completely prevented by losartan, an Ang II type 1 (AT1) antagonist. The intrarenal hypertonic saline administration elicited transient increments (from 98 ± 8 to 122 ± 7 mL/ min, N = 6, P < 0.05), followed by a marked reduction in renal blood flow (RBF; 78 ± 7 mL/min, P ± 0.05). This response was accompanied by prominent constriction of afferent (from 15.0 ± 1.1 to 8.5 ± 1.1 μm, N = 6, P < 0.05), but not efferent (from 14.3 ± 1.2 to 13.8 ± 1.0 μm, N = 3) arterioles. Furthermore, this response was completely inhibited by furosemide, a tubuloglomerular feedback inhibitor. Conclusion. The intravital pencil lens-probe videomicroscopy can be a powerful tool for in vivo observation of renal microcirculation, with intact renal microvascular responses to two important renal homeostatic mechanisms, angiotensin II and tubuloglomerular feedback.