VASOACTIVITY AND IMMUNOREACTIVITY OF FISH TACHYKININS IN THE VASCULARSYSTEM OF THE SPINY DOGFISH

Tachykinin control of gut blood flow (measured by pulsed Doppler techn ique), dorsal aortic pressure, and heart rate were studied in unrestra ined spiny dogfish Squalus acanthias injected with the elasmobranch ta chykinins scyliorhinin I and II (SCY I and SCY II), the trout tachykin ins substance P (SP), and neurokinin A (NKA). Effects on somatic vascu lature 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 how. SCY II caused an initial hypertension in duced by a general vasoconstriction, followed eventually by an elevate d how in both gut arteries due to dilation of the vascular beds. Trout NKA evoked a short-lasting increase in celiac blood how due to a decr ease in vascular resistance, a late decrease in mesenteric flow due to vasoconstriction, and no effect on the somatic vasculature. None of t he peptides affected heart rate. The study demonstrates a significant vasoactive function of fish tachykinins in the vascular system of an e lasmobranch species and, in addition, the occurrence of tachykinin rec eptor subtypes. Immunohistochemistry revealed a NKA/SCY II-like peptid e in nerve fibers innervating many vessels, including the celiac and t he mesenteric arteries, the gastrointestinal canal, and the heart.