Immunoreactive beta-endorphin and met- and leu-enkephalin contents in pancreas and pituitary of corpulent (cp/cp) rats.

Previous reports have provided suggestive evidence for a role of endogenous opiates in modulating feeding behavior as well as insulin secretion from the pancreas. This evidence includes pharmacologic studies as well as studies of endogenous opioid peptides in tissues of genetically obese rodent models. In the present study, content of three opioid peptide immunoreactivities (beta-endorphin, met-enkephalin and leu-enkephalin) were measured in pituitary and pancreas of two recently described, genetically obese rats, the LA/N-cp and the SHR/N-cp. Although both of these inbred strains carry the same cp allele, the SHR-cp rat is obese and diabetic by 8 weeks of age, while the LA/N-cp is obese but remains euglycemic. There were no significant differences in content of immunoreactive beta-endorphin, met-enkephalin or leu-enkephalin in whole pituitary, posterior or anterior lobes of the pituitary, or pancreas which could be ascribed to the effect of the obese phenotype. These data are in contrast to previously reported studies in which significant alterations in opioid peptide immunoreactivities were found in genetically obese Zucker fa/fa rats, C57BL/6 ob/ob mice and C57BL/Ks db/db mice. The present work provides no support for pathological involvement of opioid peptides in the genetically obese cp/cp rat.