Endothelin B receptors on vascular smooth muscle cells of the human umbilical vein mediate vasoconstriction.

Objective: To test the hypothesis that smooth muscle cells of the human umbilical vein have vasoconstricting endothelin B (ETB) receptors.

Methods: In strip preparations of human umbilical veins isometric tension after exposure to the selective ETB receptor agonist sarafotoxin S6c (S6c) was compared to the tension before S6c exposure (set as 100%).

Results: In intact preparations S6c induced vasoconstriction only at the highest concentration applied (10(-8)M; 149.

Nitric oxide and endothelin in oxygen-dependent regulation of vascular tone of human umbilical vein.

We investigated the possible contribution of nitric oxide (NO) and endothelin (ET) to oxygen-dependent regulation of human umbilical vein vascular tone by simultaneous registration of intracellular membrane potential and isometric tension of vessel strips with and without NO synthase inhibition [10-4 M N omega-nitro-L-arginine methyl ester (L-NAME)], ETA receptor blockade (10(-5) M BQ-123), or ETB receptor blockade (10(-7) M BQ-788) at Po2 values in the bath solution between 5 and 104 mmHg. Increasing PO2 above the physiological intrauterine range resulted in depolarization and an increase of isometric tension, whereas lowering PO2 resulted in hyperpolarization and a decrease in isometric tension. Removal of the endothelium reversed these effects.