The aim of this study was to investigate if a low concentration of endothelin-1 (ET-1; 8 × 10¹⁰ M) may amplify the skin vasoconstrictor effect of other vasoactive substances in the pathogenesis of skin vasospasm. Pig skin flaps (6 × 16 cm) were perfused with Krebs buffer equilibrated with 95% O₂ and 5% CO₂ at 37°C and pH 7.4. Skin perfusion pressure measured by a pressure transducer and skin perfusion assessed by the dermofluorometry technique were used for assessment of skin vasoconstriction. We observed that ET-1 (8 × 10¹⁰ M) significantly amplified the concentration-dependent (10⁷-10⁵ M) skin vasoconstrictor effect of norepinephrine. More importantly, we observed for the first time that this low concentration of ET-1 also amplified the concentration-dependent (10⁸-10⁶ M) skin vasoconstrictor effect of the thromboxane A₂ mimetic U-46619, and this amplification effect of ET-1 was completely blocked by the protein kinase C (PKC) inhibitor chelerythrine (5 × 10⁶ M). Conversely, the PKC activator phorbol 12,13-dibutyrate (10⁷ M) amplified the vasoconstrictor effect of U-46619. Furthermore, the sensitivity of the skin vasculature to the vasoconstrictor effect of extracellular Ca²⁺ in U-46619-induced skin vasoconstriction was significantly enhanced in the presence of 8 × 10¹⁰ M ET-1. Finally, the cyclooxygenase inhibitor indomethacin (5 × 10⁶ M) did not affect the amplification effect of ET-1 on U-46619-induced skin vasoconstriction. We conclude that a low concentration of ET-1 can amplify the skin vasoconstrictor effect of U-46619 independent of endogenous cyclooxygenase products, and the mechanism may involve activation of PKC and increase in sensitivity of the contractile apparatus to Ca²⁺ in smooth muscle cells.