A comparison of the sensitivities of neonatal ovine pulmonary and femoral arteries to l-norepinephrine stimulation.

We compared the concentration-response relationship of intralobar pulmonary arteries to l-norepinephrine with that of femoral arteries from newborn lambs. In addition, the effect of inhibition of the neuronal and extra-neuronal uptake mechanisms on these concentration-response relationships was examined. Concentration-response curves on 10 intralobar pulmonary arteries were performed with and without inhibition of the uptake mechanisms. Uptake inhibition shifts the curve to the left; thus, the -log EC50 with uptake inhibition (6.63 +/- 0.15) is greater than that without uptake inhibition (6.13 +/- 0.14). Similar curves on 10 femoral arteries demonstrated that the -log EC50 with and without uptake inhibition (6.20 +/- 0.13 and 6.00 +/- 0.04, respectively) are not statistically different. Because, in the presence of intact uptake mechanisms the concentration of l-norepinephrine in the alpha-receptor microenvironment is less than that placed in the organ bath, the appropriate comparison of pulmonary and femoral arterial response to l-norepinephrine stimulation requires uptake inhibition in both vessels. The concentration-response curve with uptake inhibition for the intralobar pulmonary artery is significantly to the left of that for the femoral; the -log EC50 for the pulmonary vessel (6.63 +/- 0.15) is greater than that of the femoral vessel (6.20 +/- 0.13). The intralobar pulmonary artery in vitro is more sensitive to l-norepinephrine stimulation than is the femoral.