salicylates and esculetin

Cholecystokinin (CCK) has been shown to stimulate insulin secretion through an effect which involves mediation by phospholipase C (PLC) and protein kinase C (PKC). However, data exist suggesting involvement also of other transduction pathways. We investigated possible involvement of phospholipase A2 (PLA2) and arachidonic acid (AA) in mechanisms of insulin secretion, induced by the C-terminal octapeptide of CCK (CCK-8) in isolated rat islets. At 5.6 mM glucose, the specific PLA2 inhibitor p-amylcinnamoylantranilic acid (ACA; 50 microM) diminished CCK-8 (100 nM)-stimulated insulin secretion (by 57 +/- 16%; P = 0.001). Furthermore, at 5.6 mM glucose, CCK-8 significantly increased the efflux of [3H]arachidonic acid from prelabelled islets (by 130 +/- 25%; P < 0.001). These results imply that CCK-8 activates PLA2 to form AA in islets. To study whether the insulinotropic effect of CCK-8 is due to AA per se or to its metabolites, the oxidative pathways of the AA metabolism were inhibited. However, the cyclooxygenase inhibitors, indomethacin (30 microM) and salicylate (1.25 mM) as well as the lipoxygenase inhibitors baicalein (1-100 microM) and esculetin (0.5-50 microM), did not affect CCK-8-induced insulin secretion. We conclude that CCK-8-induced insulin secretion is partially mediated by a pathway involving PLA2, and that the formed AA, rather than its metabolites, is of importance.

Topics: Animals; Arachidonic Acid; Cyclooxygenase Inhibitors; Enzyme Inhibitors; Flavanones; Flavonoids; Glucose; Indomethacin; Insulin; Insulin Secretion; Islets of Langerhans; Lipoxygenase Inhibitors; Male; Phospholipases A; Phospholipases A2; Rats; Rats, Sprague-Dawley; Salicylates; Salicylic Acid; Sincalide; Umbelliferones

Our previous studies had suggested a link between bile salt stimulation of colonic epithelial proliferation and the release and oxygenation of arachidonate via the lipoxygenase pathway. In the present study, we examined the role of reactive oxygen versus end products of arachidonate metabolism via the cyclooxygenase and lipoxygenase pathways in bile salt stimulation of rat colonic epithelial proliferation. Intracolonic instillation of 5 mM deoxycholate increased mucosal ornithine decarboxylase activity and [3H]thymidine incorporation into DNA. Responses to deoxycholate were abolished by the superoxide dismutase mimetic CuII (3,5 diisopropylsalicylic acid)2 (CuDIPS), and by phenidone or esculetin, which inhibit both lipoxygenase and cyclooxygenase activities. By contrast, indomethacin potentiated the response. Phenidone and esculetin suppressed deoxycholate-induced increases in prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and 5, 12, and 15-hydroxyeicosatetraenoic acid (HETE), whereas CuDIPS had no effect. Indomethacin suppressed only PGE2. Deoxycholate (0.5-5 mM) increased superoxide dismutase sensitive chemiluminescence 2-10-fold and stimulated superoxide production as measured by cytochrome c reduction in colonic mucosal scrapings or crypt epithelium. Bile salt-induced increases in chemiluminescence were abolished by CuDIPS, phenidone, and esculetin, but not by indomethacin. Intracolonic generation of reactive oxygen by xanthine-xanthine oxidase increased colonic mucosal ornithine decarboxylase activity and [3H]thymidine incorporation into DNA approximately twofold. These effects were abolished by superoxide dismutase. The findings support a key role for reactive oxygen, rather than more distal products of either the lipoxygenase or cyclooxygenase pathways, in the stimulation of colonic mucosal proliferation by bile salts.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Bile Acids and Salts; Cell Cycle; Deoxycholic Acid; DNA; Female; Free Radicals; Indomethacin; Intestinal Mucosa; Lipoxygenase; Luminescent Measurements; Ornithine Decarboxylase; Oxygen; Prostaglandin-Endoperoxide Synthases; Pyrazoles; Rats; Salicylates; Superoxide Dismutase; Superoxides; Umbelliferones; Xanthine Oxidase