Antidiuretic action of angiotensin II in the river lamprey Lampetra fluviatilis: evidence for endocrine control of kidney function in cyclostomes

Intravenous infusion of angiotensin II ([Asn1 Val5]‐Ang II) at 10−9 mol min−1 kg−1 body mass produced a significant antidiuresis in river lamprey Lampetra fluviatilis, captured during upstream migration and maintained in fresh water. Although the renin‐angiotensin hormonal system (RAS) is now recognized in jawless fishes, until this study, the role of homologous Ang II in L. fluviatilis kidney function had not been examined. This study provides the first evidence for an antidiuretic action of Ang II in cyclostomes and, in evolutionary terms, suggests a renal function for the RAS in early vertebrates.