Effects of norepinephrine infusion (iv) on microvascular pressures and capillary blood flow in the mesentery

Abstract The purpose of these studies was to characterize the effects of intravenous infusion of norepinephrine on pressure and flow adjustments within the mesenteric microcirculation of the rat. The servo-null method of Wiederhielm was used to measure pressures within selected arterioles and venules and the dual-slit photometric method of Wayland and Johnson was used to measure RBC velocity in mesenteric capillaries during iv infusion of 4 μg/Kg/min of norepinephrine for periods of 5–7 min. Systemic arterial pressure increased over the first 2–3 min of infusion following which pressure gradually declined towards preinfusion levels. At the microvascular level the effects of norepinephrine were evident but highly variable among single vessels. However, pooling of the data showed that average pressure at all levels of the mesenteric vasculature and average mesenteric capillary RBC velocity paralleled the systemic pressure response. Pressure to velocity ratios (an index of vascular resistance) indicated little change in net mesenteric vascular resistance throughout norepinephrine infusion.