S-18149

Saphenous vein reactivity was recorded in the anaesthetized dog by use of an ultrasonic echo‐tracking device to measure the internal diameter of the vein and to calculate the venous compliance. This method was used to investigate the effects of a new partial α1/α2‐adrenoceptor agonist, S 18149, on the canine saphenous vein in vivo after intravenous (i.v.) or oral administration.Venoconstrictions induced by i.v. or local administration of compounds were evaluated by continuous recording of the internal diameter of the saphenous vein with the echo‐tracking method. Venous compliance was calculated in two ways: (1) as the slope of the diameter‐pressure curve obtained by increasing the venous pressure with an inflatable cuff and (2) in veins in which pressure was higher than 12 mmHg, pulsatile variations in the venous diameter and venous pressure were detected and used to calculate the pulsatile compliance of the vein.S 18149 administered i.v. at 0.5 μg kg−1 min−1 for 10 min induced a decrease in the saphenous vein diameter (−15±3%) and blood flow (−72±6%) associated with an increase in saphenous vein resistance; at the dose used, S 18149 did not modify venous pressure and caused only a weak increase in arterial pressure (+7±2 mmHg).The pulsatile compliance of the saphenous vein averaged 8.65±1.37 mm2×100 mmHg−1 in control dogs and was significantly decreased to 5.13±0.68 mm2×100 mmHg−1 in the same animals after treatment with S 18149 at 100 μg kg−1 per os (n=10). The saphenous vein compliance calculated with the increased external pressure method averaged 24.90±1.49 μm mmHg−1 in control dogs and was significantly reduced in the same animals after treatment with S 18149 at 100 μg kg−1 per os to 9.06±3.42 μm mmHg−1 (n=5). When constrictions of the vein were induced with increasing doses of (−)‐phenylephrine, injected locally at 1, 3 or 6 μg min−1, only the responses obtained with the lower dose of (−)‐phenylephrine were increased in dogs treated with S 18149 100 μg kg−1 per os (−16±4% versus −4±3%, n=5).These results show that the high resolution echo‐tracking device previously used for arterial compliance measurements, allows the detection of pulsatile changes in the canine saphenous vein and thus permits calculation of both the pulsatile and the static compliance of superficial veins in vivo. Using this technique, we have demonstrated that the novel α‐adrenoceptor agonist S 18149 constricts the canine saphenous vein in vivo and decreases the saphenous vein compliance after oral administration.