Increased pressor effect of repeated doses of rat or porcine endothelin in the anaesthetised rat.

Rat and porcine endothelin differ by 6 amino acids. Porcine and rat endothelin were equiactive at producing the transient fall in blood pressure in the anaesthetised rat but porcine endothelin was three times more potent at producing the subsequent sustained rise. Repeated doses of either peptide in the same rat produced a larger pressor response with each repetition, the peak response being reached more rapidly. The magnitude of the blood pressure fall did not change significantly but the first response in each rat was of longer duration than subsequent responses, especially with rat endothelin.