Difference in glucose dependency of insulin and somatostatin release.

The splenic Brockmann body of channel catfish (Ictalurus punctatus) was isolated and perfused in vitro. It has been shown previously that the hormone release from the catfish pancreas in response to various stimuli resembled that of a mammalian pancreas. The release of insulin and somatostatin was measured at various concentrations of glucose in the perfusate, and the corresponding dose-response curves were derived. As in a variety of mammalian pancreases, insulin release was stimulated half-maximally at ca. 9 mM glucose. In contrast, half-maximal somatostatin release occurred already at ca. 5 mM glucose. Although a comparable finding with mammalian D cells has not yet been reported, histological and physiological resemblances of the mammalian and the fish pancreas suggest that mammalian D cells may also have a glucose sensitivity in the 5 mM range.