CARDIOVASCOLAR ACTIONS OF LUNGFISH BRADYKININ IN THE UNANAESHETISED AFRICAN LUNGFISH, PROTOPTERUS ANNECTENS.

Bradykinin ŽBK. isolated from plasma of the African lungfish, Protopterus annectens, contains four amino acid substitutions compared with BK from mammals ŽArg1 Tyr, Pro2 Gly, Pro7 Ala, Phe8 Pro.. Bolus intra-arterial injections of synthetic lungfish BK Ž11000 pmolkg body wt.. into unanaesthetised, juvenile lungfish Žn5. produced a dose-dependent increase in arterial blood pressure and pulse pressure. The maximum pressor response occurred 23 min after injection and persisted for up to 15 min. The threshold dose producing a significant ŽP0.01. rise in pressure was 50 pmolkg and the maximum increase, following injection of 300 pmolkg, was 9.32.3 mmHg. Injection of the higher doses of lungfish BK produced a significant ŽP0.05. increase in heart rate Ž2.80.8 beatsmin at 100 pmolkg.. In contrast, bolus intra-arterial injections of mammalian BK, in doses up to 1000 pmolkg, produced no significant cardiovascular effects in the lungfish. The data support the existence of a functioning kallikreinkinin system in the lungfish and demonstrate that the ligand-binding properties of the receptorŽs. mediating the cardiovascular actions of lungfish BK are appreciably different from mammalian B1 and B2 receptors. 2002 Elsevier Science Inc. All rights reserved.