CHARACTERIZATION OF THE ENDOGENOUS INTESTINAL PEPTIDE THAT STIMULATESTHE RECTAL GLAND OF SCYLIORHINUS-CANICULA

It has been postulated that gut peptides play a major role in the regu lation of rectal gland secretion in elasmobranchs. An isolated perfuse d rectal gland preparation was developed for Scyliorhinus canicula tha t responded to dibutyryl 3',5'-cyclic monophosphate plus 3-isobutyl-1- methylxanthine, increasing chloride clearance rates threefold over bas al levels. Activity was stimulated by an endogenous peptide, isolated in pure form by reverse-phase high-performance liquid chromatography f rom the intestine of S. canicula. The primary structure was establishe d as s-Pro-Asp-Gly-Pro-Asp-Cys-Phe-Val-Gly-Leu-Met-NH2. This is a sequ ence identical to that of the tachykinin scyliorhinin II. Perfusion of synthetic scyliorhinin II increased secretion rate in the rectal glan d of S. canicula in a dose-dependent manner with a maximal response at 10(-6) M, whereas vasoactive intestinal peptide, a stimulator in the spiny dogfish, Squalus acanthias, had no effect. We propose that scyli orhinin II is the uncharacterized peptide rectin, previously identifie d from the intestine of S. canicula.