Relationship between internal diameter and vasoconstriction in human varicose veins

Varicose veins are common lower extremity venous disorders characterized by dilated veins and incompetent valves. Although maintaining the required vein wall tone for adaptive responses depends on a proper contractile function of the human saphenous smooth muscle, the contractile properties of varicose veins are mostly unknown. We investigated the relationship between contractile responses and the internal diameter of human saphenous varicose veins. The absolute contractile forces induced by potassium chloride (KCl, 60 mmol/l), serotonin (5-hydroxytryptamine [5-HT], 10 µmol/l), and noradrenaline (NAd, 10 µmol/l) were similar between normal saphenous veins (control) and varicose veins. When the contractile forces were normalized to the internal diameter in each preparation, the contractile responses to these stimuli were significantly lower in varicose veins than in the control veins. Furthermore, varicose veins were divided into three groups according to their internal diameter (group 1, 3–4.5 mm; group 2, 4.5–6 mm; group 3, >6 mm). The contractile responses induced by KCl, 5-HT, and NAd did not differ between groups 1 and 2 and the control group, while the contractile responses in group 3 were significantly lower than those in the control group. Moreover, the contractions induced by KCl and NAd in Group 3 were smaller than those in group 1 or group 2. This trend was also observed in 5-HT-induced contractions, although the results were not statistically significant. In conclusion, contractile responses in varicose veins may be altered by an increase in internal diameter, although adequate contractile responses are preserved in some diameters.