Vascular actions of neurohypophysial peptides in the flounder

Free swimming, chronically cannulated flounder have been used to study the blood pressure effects of arginine vasotocin (AVT) and isotocin. The initial fall in dorsal aortic blood pressure following AVT injection coincided with an increase in ventral aortic blood pressure, suggesting AVT caused constriction of the arterio-arterial pathway. Ventral aortic blood pressure increased in a dose dependent manner with increasing AVT dose. Dorsal aortic blood pressure also increased following the initial fall but not in a dose dependent manner, the effect at higher doses being off set by branchial vasoconstriction. Isotocin also caused dorsal aortic blood pressure to fall due to branchial vasoconstriction, but no subsequent pressor effect was seen. Branchial vasoconstriction caused by both teleost neurohypophysial peptides suggests the presence of neurohypophysial peptide receptor(s) in the gill, although it is unclear as to whether this is a single common receptor or different populations for each peptide. The dorsal aortic pressor effect of AVT and its absence following isotocin injection suggests there may be other types of neurohypophysial receptors in post-branchial vascular beds. The vascular actions of AVT and isotocin suggest that these peptides may play some role in the regulation of blood pressure or regional blood flow distribution.