Abstract P154: Ultrasound Imaging for Serial Measurements of Venous Diameters in Rats

Abstract

The purpose of our study was to investigate serial ultrasound imaging in rats as a means to quantify the diameters of splanchnic veins in real time and the effect of drugs on venous capacitance. A 21 MHz probe ( Vevo 2100 imaging system,Visual Sonics Inc.) was used to collect images containing the portal vein (PV) and the superior mesenteric vein (SMV) in anesthetized male Sprague-Dawley rats maintained at 37°C. Stable landmarks were established and we were able to repeatedly locate specific cross-sections of PV and SMV. When controlled for respiratory and cardiac cycles during measurements, respective diameters of these vessels remained within 0.75±0.15% and 0.2±0.10% of baseline (PV: 2.02±0.15 mm; SMV: 1.67±0.05 mm) when located and measured every 5 minutes over 45 minutes (n=3 rats). PV and SMV remained within 1.0±0.6% and 0.38±0.9% from baseline, respectively, when measured on separate days over 10 weeks in a preliminary study using 2 rats. The consistency of raw vessel measurements allowed these vessels to serve as their own control during subchronic pharmacologic interventions. In a second study, the vasodilator sodium nitroprusside (2 mg/kg, i.v. bolus) was administered to anesthetized rats (n=3) following collection of baseline vessel measurements. PV and SMV diameters increased 37.23±2.4% and 29.77±8.8% from baseline by 30 minutes post drug administration while mean arterial pressure decreased 10.32±1.7 mmHg. Conversely, the administration of the venoconstrictor sarafotoxin (S6C) (5 ng/kg, i.v. bolus) to other anesthetized rats (n=3) decreased PV and SMV diameters 22.10±2.4% and 9.44±1.6% from baseline within 5 minutes, associated with an increase in mean arterial pressure of 12.85±3.2 mmHg. Together these results support serial ultrasound imaging as a reliable technique to accurately measure acute and subchronic changes in the diameter of splanchnic veins concurrent with blood pressure changes in intact rats. The ability to follow rat abdominal vein diameters in real time will assist in determining the role of the venous circulation in blood pressure regulation.