Abstract 1185: A Novel In Vivo Method for Measurement of Nitric Oxide Synthase-Dependent Vasodilation in Living Rodents using High Resolution Ultrasound
Background: In humans, endothelial function can be measured by monitoring changes in arterial diameter with ultrasound after temporary ischemia (flow mediated dilation; FMD). However, in rodent models of vascular disease, direct measurements of changes in diameter have been limited to studying isolated vessel fragments ex vivo. Here, we aimed at assessing the feasibility of an FMD-related approach to study NOS-dependent vasodilation of peripheral arteries in living rats.
Methods and Results: Sprague Dawley rats (n=5/ group, 4 groups) were anesthetized with isoflurane and a loop occluder was positioned around the common iliac artery. Body core temperature was kept stable and continuously monitored. Ultrasound diameter and Doppler-flow measurements were obtained from longitudinal sections of the femoral artery using a stationary 30 MHz probe and not changed throughout the investigations. Data analysis was performed off-line using automated edge detection and flow analysis software (1.2% coefficient of variation for repeated readings). After five minutes of hindlimb ischemia, a hyperemic flow increase and significant vasodilation was observed (13±2%, delta percent diameter). Following NOS-inhibition by L-NMMA (8 mg/100 mg body weight IV), vasodilation was completely inhibited (to -1±2%) but not hyperemic flow. A saline control injection did not change baseline readings. In contrast, 10 min of ischemia induced a similar vasodilation (13±4%) that was not completely inhibited by L-NMMA (5±3%), suggesting that longer ischemia invokes an additional NOS-independent vasodilation mechanism. Pharmacological stimulation of NOS by acetylcholine injected locally into the common iliac artery via an aortic catheter (10−9-10−4 μM) led to comparable dose-dependent vasodilation.
Conclusions: We have developed a novel, feasible, and reproducible in vivo method to assess NOS-dependent vasodilation in rodents. The ability to measure vascular reactivity in living rats considerably enhances the usefulness of rat models for research on vascular disease and potential interventions.