Vasoactivity and immunoreactivity of fish tachykinins in the vascular system of the spiny dogfish.

Tachykinin control of gut blood flow (measured by pulsed Doppler technique), dorsal aortic pressure, and heart rate were studied in unrestrained spiny dogfish Squalus acanthias injected with the elasmobranch tachykinins scyliorhinin I and II (SCY I and SCY II), the trout tachykinins substance P (SP), and neurokinin A (NKA). Effects on somatic vasculature were measured by in vitro perfusion of the isolated tail. SCY I and trout SP produced hypotension due to a general vasodilation. This caused a transient increase in mesenteric blood flow and a prolonged increase in celiac blood flow. SCY II caused an initial hypertension induced by a general vasoconstriction, followed eventually by an elevated flow in both gut arteries due to dilation of the vascular beds. Trout NKA evoked a short-lasting increase in celiac blood flow due to a decrease in vascular resistance, a late decrease in mesenteric flow due to vasoconstriction, and no effect on the somatic vasculature. None of the peptides affected heart rate. The study demonstrates a significant vasoactive function of fish tachykinins in the vascular system of an elasmobranch species and, in addition, the occurrence of tachykinin receptor subtypes. Immunohistochemistry revealed a NKA/SCY II-like peptide in nerve fibers innervating many vessels, including the celiac and the mesenteric arteries, the gastrointestinal canal, and the heart.