The biological activity of endothelin-1 analogues in three different assay systems.

Endothelin (ET) is a vasoconstrictor peptide with 21-amino acid residues. In this study, we determined the relative potencies of ET-1 analogues to investigate the essential moiety of ET-1 for expression of its biological effect. We synthesized ET-1 analogues with the substitution of one amino acid at positions 2-18 and 21. All ET-1 analogues had the proper intramolecular disulfide bonds. We have conducted a systematic survey to compare the biological activity of ET-1 analogues in three different assay systems: the vasoconstrictor activity in the rat pulmonary artery, the nonvascular smooth muscle contracting activity in the rat trachea, and the pressor activity in the conscious rat. In the pulmonary arterial preparation, the carboxyl groups of Asp8, Glu10, and Asp18, the aromatic groups of Phe14, His16, and Trp21, and the hydrophobic group of Leu17 contributed to the expression of the vasoconstrictor activities. However, the contracting activities in the tracheal preparations were retained even upon replacement of these amino acid residues by alanine or other amino acids. Moreover, substitution of the amino acid residue of ET-1 at positions Ser5, Lys9, and Tyr13 for alanine was found to increase the potency of ET-1 by a factor of about 2. With respect to vasopressor effects, the activities were retained, and all ET-1 analogues showed relative potencies ranging from 5 to 90% of ET-1. These findings suggest that different types of receptors may be present in different organs.