Neurointermediate lobe transplanted under the kidney capsule modifies the activity of the neurointermediate lobe in situ, but does not respond to opiate treatment.

To investigate the possibility of a direct effect of morphine on the pars intermedia cells of the pituitary gland, rat neurointermediate lobes (NIL) were transplanted under the kidney capsule. At 2 and 8 days posttransplantation the NIL transplant had maintained its morphological integrity. However, at 15 days posttransplantation the morphological integrity of the NIL transplant had started to deteriorate. The NIL transplant contained, synthesized, and released beta-endorphin-like peptides. It was noticed that there was very little beta-endorphin in the radiolabelled biosynthesized products, suggesting that either the maturation processing of proopiomelanocortin was modified, or that beta-endorphin was released immediately as soon as it was formed and did not accumulate in the tissue. In support of the latter possibility was the elevated content of beta-endorphin-like immunoreactivity in the sera of rats with a NIL under the kidney capsule. Furthermore, the NIL transplant seemed to produce a substance or substances which could decrease the content, the biosynthesis and the release of beta-endorphin-like peptides by the NIL in situ. Treatment with either morphine or naloxone for 5 days did not change the beta-endorphin-like immunoreactivity content in the NIL transplanted under the kidney capsule. However, a distinct decrease in the beta-endorphin-like immunoreactivity in the NIL in situ of animals with or without a NIL transplant was observed following the morphine treatment. Naloxone treatment induced a decrease in the beta-endorphin-like immunoreactivity content in the hypothalamus, but had no effect on the beta-endorphin-like immunoreactivity content in the anterior lobe and NIL of the pituitary gland in situ or in the NIL transplant.