Comparative studies on the effects of cholecystokinins, caerulein, bombesin 6–14 nonapeptide, and physalaemin on gastric secretion in the ascidian Styela clava

The effects of cholecystokinins (CCK), caerulein, bombesin 6–14 nonapeptide (bombesin), and physalaemin on gastric secretion in Styela clava were measured using a perfusion technique. Varying concentrations of both CCK 33 and CCK 8 produced a significant dose-dependent response. Dose for dose, CCK 33 was more potent than CCK 8, while the assay was unable to show any discrimination between sulphated and nonsulphated forms of CCK 8. The specific CCK inhibitor Bt 2cGMP significantly reduced the response to both CCK 33 and CCK 8. Both caerulein and physalaemin were effective although with a considerably reduced response compared with CCK. Bombesin was the most potent of all secretagogues tested while glucagon was without effect on gastric secretion. It is suggested that the primitive prepancreatic zymogen cells in Styela possess a receptor or receptors with an ability to recognise those peptides which are also active on vertebrate pancreatic acinar cells. It is further suggested that while the results indicate a receptor system less sophisticated than that found in vertebrates, they also imply the presence of an endogenous polypeptide hormone or hormones with a sequence which might be expected to show similarities to more than one vertebrate gastrointestinal peptide.