Insulin attenuates norepinephrine-induced venoconstriction. An ultrasonographic study.

To directly assess insulin-related venomotor changes objectively and quantitatively, we used a modified ultrasonographic technique to measure venous diameter. Ten healthy men and women were studied by use of an Acuson 128 XP ultrasonograph with a linear 7.5-MHz ultrasonographic transducer (sensitivity, +/- 0.1 mm). Venous diameter was measured with the arm kept at 30 degrees elevation and with a pneumatic cuff above the elbow inflated at 40 mm Hg for the last 2 minutes of each 5-minute observation period. Norepinephrine was infused at incremental concentrations of 12.5, 25, 50, and 100 ng/min (75, 150, 300, and 600 pmol/min, respectively) for 5 minutes each. Maximal venoconstriction was achieved by the dose of 100 ng/min norepinephrine, which was then combined with insulin doses of 8, 16, 24, and 32 microU/min (60, 120, 180, and 230 fmol/min, respectively) for 5 minutes each. In six different subjects, methylene blue, an inhibitor of guanylate cyclase, was infused simultaneously with 32 microU/min insulin and 100 ng/min norepinephrine. Mean resting diameter of the vein (1.8 +/- 0.6 mm [mean +/- SD]) increased (to 3.0 +/- 1.0 mm) after cuff inflation. Incremental doses of norepinephrine caused highly reproducible dose-dependent decrease in venous diameter (to 1.8 +/- 0.6 mm, P < .001). Incremental doses of insulin, when combined with the maximum dose of norepinephrine, caused highly reproducible dose-dependent increases in mean venous diameter (P < .001) compared with norepinephrine alone. Methylene blue, which had no independent effect on venous diameter, inhibited the venodilator effect of insulin (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)