Assessment of changes in intrarenal blood flow in conscious rats using laser-Doppler flowmetry

Abstract

The present study was designed to develop, for the first time, a method that allows long-term repeated measurements of renal cortical blood flow (CBF) and medullary blood flow (MBF) in conscious unanesthetized rats. The use of fiber-optic probes (0.5 mm diam) for the chronic measurement of renal CBF and MBF was evaluated. Basal renal cortical and medullary laser-Doppler flow (LDF) signals and the responses to intravenous bolus injections of angiotensin II (ANG II, 12.5 ng) were determined every other day for 11 days in conscious Sprague-Dawley rats (n = 9). A recovery period of 5-7 days after surgery was required before stable signals were obtained from the implanted probes. Thereafter, the fiber-optic probes gave reproducible laser-Doppler measurements of CBF and MBF for 11 days. The CBF and MBF responses to intravenous bolus injections of ANG II (12.5 ng) were also constant during this period. Chronic implantation of the fiber-optic probes caused minimal tissue damage and did not significantly alter urine concentrating ability or renal function. These findings suggest that LDF technique with chronically implanted optical fibers provides a new tool for the continuous long-term monitoring of regional blood flow in the kidney of conscious rats.

Role of renal NO production in the regulation of medullary blood flow

“…Functional evidence that basal levels of NO contribute to MBF resulted from a series of studies in our laboratory that examined the effects of a variety of vasoactive compounds on MBF. These compounds were assessed by direct delivery into the medullary interstitial space of rats by use of a small implanted catheter (51,52), whereas MBF responses were determined using external and implanted optical fibers and laserDoppler flowmetry techniques (52). Substances infused into the medullary interstitium became trapped and concentrated by the countercurrent vasa recta circulation, enabling responses to be determined independent of the cortex.…”

Local Renal Medullary L-NAME Infusion Enhances the Effect of Long-Term Angiotensin II Treatment

“…16,17 Optical fibers were then implanted in the renal cortex (2-mm depth) and inner medulla (5.5-mm depth) by use of techniques developed in our laboratory. 15,17 All catheters and optical fibers were tunneled subcutaneously to the back of the neck, where they were exteriorized through a midscapular incision and passed through a spring for protection. Buprenorphine (0.3 mg/kg SC) was given during the recovery from anesthesia to provide postoperative analgesia.…”

“…Daily measurements of MAP, CBF, and MBF were then begun by use of an on-line data collection (rate, 100 Hz) and analysis system as previously described. 15 The flow signals from the renal cortex and medulla were measured and processed by a 2-channel laser-Doppler flowmeter (Transonics, Inc). Continuously recorded signals were transformed to minute averages for analysis.…”

“…If recirculation of L-NAME had occurred, one would have expected reductions in CBF during the first 4 hours of the medullary L-NAME infusion, changes that were not observed. The renal cortical vasculature is more sensitive than the medullary vessels to Ang II, 6,7,15 so blunting of NOS activity in the renal cortex should have amplified these differences. The enhanced vasoconstrictor effects of Ang II were confined strictly to the renal medulla.…”

“…Optical fibers implanted in the superficial cortex and inner medulla were used for daily measurements of changes in blood flow to these regions with laser-Doppler flowmetry. 15 The effects of long-term intravenous infusion of Ang II (3 ng ⅐ kg Ϫ1 ⅐ min…”