Receptor binding and vasoconstrictor activity of big endothelin

We studied the effects of synthetic porcine big endothelin (ET), a putative 39-residue intermediate deduced from cDNA sequence analysis, on receptor binding activity in cultured rat vascular smooth muscle cells as well as its vasoconstrictive activity in rat pulmonary artery. Big ET was about two orders of magnitude less active than ET in the receptor binding and vasoconstriction assays. Our data are consistent with the contention that big ET is an intermediate which can be converted into fully bioactive 21-residue mature ET.