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

It has been postulated that gut peptides play a major role in the regulation of rectal gland secretion in elasmobranchs. An isolated perfused rectal gland preparation was developed for Scyliorhinus canicula that responded to dibutyryl 3',5'-cyclic monophosphate plus 3-isobutyl-1-methylxanthine, increasing chloride clearance rates threefold over basal levels. Activity was stimulated by an endogenous peptide, isolated in pure form by reverse-phase high-performance liquid chromatography from the intestine of S. canicula. The primary structure was established as Ser-Pro-Ser-Asn-Ser-Lys-Cys-Pro-Asp-Gly-Pro-Asp-Cys-Phe-Val-Gly-Leu-Met-NH2. This is a sequence identical to that of the tachykinin scyliorhinin II. Perfusion of synthetic scyliorhinin II increased secretion rate in the rectal gland 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 scyliorhinin II is the uncharacterized peptide rectin, previously identified from the intestine of S. canicula.