Copper deficiency in rats increases pancreatic enkephalin-containing peptides and insulin

Free enkephalins (enk) and higher molecular weight enkephalin-containing peptides (enk-c-p) are present in the endocrine pancreas of rats, presumably in B cells. To determine whether these opioid peptides show dynamic alterations as insulin content of pancreas changes, we utilized a copper deficient rat model, in which the exocrine pancreas atrophies and the endocrine pancreas is “intact” and insulin (IRI) content increases. Dietary copper deficiency (−C) was produced in weanling male rats for 4 and 7 weeks. The deficient and copper supplemented (+C) groups were further subdivided to receive all dietary carbohydrate as either 62% fructose (F) or 62% starch (S). −CF rats showed the most severe deficiency. After 7 weeks, total units of pancreatic IRI in −CF were 7.5, +CF 2.1, −CS 7.9 and in +CS 2.8 (p<0.001). Pancreatic content of Met⁵- and Leu⁵-enk was measured in extracts which were purified on C-18 Seppaks with and without prior treatment with trypsin and carboxypeptidase B. −C animals showed progressive, significant increases in pancreatic content of Leu-enk-c-p, with a decrease in free Leu- and Met-enk (p<0.02-0.01). The pancreatic findings are compatible with a co-localization of enkephalins and insulin in the endocrine pancreas and are suggestive of co-regulation.