Contrast angiography of the rat renal microcirculation in vivo using synchrotron radiation

Departments of 1 Physiology and 2 Mechanical and Aerospace Engineering, Monash University, Melbourne, Australia; 3 Department of Clinical Radiology, Hiroshima International University, Hiroshima; 4 Japan Synchrotron Radiation Research Institute, Hyogo, Japan; and 5 Monash Centre for Synchrotron Science, Monash University, Melbourne, Australia Submitted 20 August 2008 ; accepted in final form 27 February 2009 We have developed a new method for contrast microangiography of the rat renal circulation using synchrotron radiation. The method was applied to determine responses of the renal arterial vasculature to angiotensin II and electrical stimulation of the renal nerves (RNS). Iodinated contrast agent was administered directly into the renal artery of pentobarbital-anesthetized rats before and during 1 ) intravenous infusion of angiotensin II (1.6 µg·kg –1 ·min –1 ) or 2 ) its vehicle, or 3 ) RNS at 2 Hz. Images were obtained at 30 Hz, before and during these treatments, and vascular caliber was determined by use of a newly developed algorithm described herein. Up to four levels of branching could be observed simultaneously along the arterial tree, comprising vessels with resting diameter of 28–400 µm. Vessel diameter was not significantly altered by vehicle infusion (+3.1 ± 3.5% change) but was significantly reduced by angiotensin II (–24.3 ± 3.4%) and RNS (–17.1 ± 3.8%). Angiotensin II-induced vasoconstriction was independent of vessel size, but RNS-induced vasoconstriction was greatest in vessels with a resting caliber of 100–200 µm and least in vessels with a resting caliber 40–100 µm. In conclusion, the method we describe herein provides a new approach for assessing responses of the renal arterial circulation to vasoactive factors along several orders of branching. angiography; angiotensin II; vascular caliber; kidney circulation; renal nerves Address for reprint requests and other correspondence: G. Eppel, Dept. of Physiology, PO Box 13F, Monash Univ., VIC 3800, Australia (e-mail: gabriela.eppel{at}med.monash.edu.au )