Amplifying effect of endothelin-1 on serotonin-induced vasoconstriction of human umbilical artery

OBJECTIVE: The purpose of this study was to evaluate the role of endothelin-1 in serotonin-induced vasoconstriction in human umbilical artery. STUDY DESIGN: Umbilical arteries collected from 41 normal subjects at term were cut helically and suspended in an organ bath for recording isometric mechanical activity. In study 1 we measured the concentration-contraction response to serotonin or endothelin-1 according to a cumulative concentration schedule. In study 2 vessels were preincubated with a subthreshold concentration of endothein-1 (100, 250, or 500 pg/ml), and then serotonin was added cumulatively. In study 3 vessels were preincubated with H-7 (3 × 10−6 mol/L), an inhibitor of protein kinase C, or with 12-tetradecanoylphorbol-13 acetate (10−9 to 10−7 mol/L), an activator of protein kinase C; then serotonin was added cumulatively. In study 4 vessels were suspended in a calcium-free solution contaiing 2 mmol/L ethylene glycol-bis(β-aminoethyl ether) N,N,N′,N′-tetraacetic acid and 60 mmol/L potassium chloride, and then a cumulative concentration-response curve to calcium chloride (10−7 to 10−3 mol/L) was constructed for vessels pretreated with endothelin-1, 500 pg/ml or 5 ng/ml. RESULTS: The threshold concentrations of serotonin and endothelin-1 were 5 and 1 ng/ml, respectively. A subthreshold concentration of endothelin-1 (250 or 500 pg/ml) potentiated significantly the concentration response to serotonin (p< 0.084, p< 0.009, by analysis of variance). Pretreatment with H-7 significantly suppressed the amplifying effect of endothein-1 on serotonin-induced contraction. Treatment with 12-tetradecanoylphorbol-13 acetate (10−7 or 10−8 mol/L) significantly potentiated the contractile response to serotonin (p< 0.0003, p< 0.015). The sensitivity of the arterial segments to calcium chloride in the presence of a subthreshold concentration of endothelin-1 did not differ from that in the control group. CONCLUSION: Endothelin-1 at a subthreshold concentration amplified the smooth muscle contraction induced by serotonin. The mechanism of action may be mediated by activation of intracellular protein kinase C.