Pituitary contents of beta-endorphin, dynorphin, substance P, cholecystokinin and somatostatin in rats with streptozotocin-induced diabetes.

The effects of streptozotocin-induced diabetes on pituitary neuropeptides were studied. Substance P, dynorphin and beta-endorphin in both pituitary lobes and cholecystokinin and somatostatin in the neurointermediate lobe (NIL) were measured 4 weeks after streptozotocin treatment in adult male rats. There were significant decreases of substance P levels in both the anterior lobe (AL) and NIL, and of cholecystokinin, dynorphin and beta-endorphin in the NIL, whereas the dynorphin content in the AL increased, when values were expressed on a per-lobe basis. On a per-milligram-protein basis, however, only beta-endorphin in the NIL showed a significant decrease, while AL beta-endorphin and dynorphin were increased. Correlated with these changes were a drastic decrease in the serum insulin level and a marked increase in serum glucose and corticosterone levels. All these changes were reversible with insulin treatment. It is suggested that the decrease in NIL contents of neuropeptides demonstrated (except for beta-endorphin) might be due to mechanisms other than a change in synthesis.