Kassinin, a tachykinin dodecapeptide isolated from the skin of the African frog Kassina senegalensis was submitted to parallel bioassay with physalaemin, eledoisin and substance P, three major representatives of the tachykinin peptide family. Bioassay was carried out on blood pressure, salivary secretion and isolated or in situ smooth muscle preparations. 2. As expected, kassinin possessed the entire spectrum of biological activity peculiar to the tachykinins. However, among the examined tachykinins kassinin was the poorest stimulant of salivary secretion and the weakest hypotensive agent, while displaying very powerful stimulant effects on different smooth muscle preparations, especially on isolated preparations of urinary bladder. 3. Kassinin differed from the other tachykinins also for its more gradual and sustained action on several in situ and isolated preparations. The peptide most similar to kassinin in its spectrum of activity was eledoisin. 4. Emphasis is laid on the possibility to dissociate the effects of the tachykinins on different target systems through changes in the N-moiety of the tachykinin molecule.
