Peripheral vascular response to norepinephrine at temperatures from 2 to 40 degrees C

The response to norepinephrine (NE) was studied in the perfused whole vascular bed and perfused arteries in situ and on helical strips of arteries and veins from the isolated duck leg. NE consistently produced vasoconstriction but the sensitivity was 3-50 times greater in the whole vascular bed than in artery segments. The drug effect was maximal at temperatures near 25 degrees C and diminished considerably at low temperatures (2-5 degrees C). Isolated helical strips of arteries and veins, when exposed to NE, showed maximal developed force at 25-30 degrees C. Tibial vessels developed only slight force at 5 degrees C while the tarsal-metatarsal and digital vessels responded even at 2 degrees C. The sensitivity to NE of both vessel types from the same region was similar. Flow in whole vascular bed perfused at constant pressure (40 cmH2O) was maximum at 30-35 degrees C. At both higher and lower temperatures flow declined and was about the same at 2 degrees C as at 40 degrees C. Our findings indicate that the vasoconstrictor effect of NE is exerted on both large and small veins and arteries; yet peripheral vessels respond more than do proximal segments at low temperatures. These findings suggest that peripheral vascular compartments may be capable of regulating regional blood flow at temperatures approaching freezing.