Amplification effect and mechanism of action of ET-1 in U-46619-induced vasoconstriction in pig skin

The aim of this study was to investigate if a low concentration of endothel in-1 (ET-1; 8 X 10(-10) M) may amplify the skin vasoconstrictor effect of o ther vasoactive substances in the pathogenesis of skin vasospasm. Pig skin flaps (6 X 16 cm) were perfused with Krebs buffer equilibrated with 95% O-2 and 5% CO2 at 37 degreesC and pH 7.4. Skin perfusion pressure measured by a pressure transducer and skin perfusion assessed by the dermofluorometry t echnique were used for assessment of skin vasoconstriction. We observed tha t ET-1 (8 X 10(-10) M) significantly amplified the concentration-dependent (10(-7)-10(-5) M) skin vasoconstrictor effect of norepinephrine. More impor tantly, we observed for the first time that this low concentration of ET-1 also amplified the concentration-dependent (10(-8)-10(-6) M) skin vasoconst rictor effect of the thromboxane A(2) mimetic U-46619, and this amplificati on effect of ET-1 was completely blocked by the protein kinase C (PKC) inhi bitor chelerythrine (5 X 10(-6) M). Conversely, the PKC activator phorbol 1 2,13-dibutyrate (10(-7) M) amplified the vasoconstrictor effect of U-46619. Furthermore, the sensitivity of the skin vasculature to the vasoconstricto r effect of extracellular Ca2+ in U-46619-induced skin vasoconstriction was significantly enhanced in the presence of 8 x 10(-10) M ET-1. Finally, the cyclooxygenase inhibitor indomethacin (5 X 10(-6) M) did not affect the am plification effect of ET-1 on U-46619-induced skin vasoconstriction. We con clude that a low concentration of ET-1 can amplify the skin vasoconstrictor effect of U-46619 independent of endogenous cyclooxygenase products, and t he mechanism may involve activation of PKC and increase in sensitivity of t he contractile apparatus to Ca2+ in smooth muscle cells.