AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 3 645-R652, Copyright © 1994 by American Physiological Society
Opioid growth factor inhibits DNA synthesis in mouse tongue epithelium in a circadian rhythm-dependent manner
I. S. Zagon, Y. Wu and P. J. McLaughlin
Department of Neuroscience and Anatomy, Pennsylvania State University College of Medicine, Hershey 17033.
In addition to neuromodulation, endogenous opioids also serve as growth
factors. To investigate the involvement of the naturally occurring opioid
peptide [Met5]enkephalin [termed opioid growth factor (OGF)] in the renewal
of epithelium, adult mice were given systemic injections of OGF (1 mg/kg)
and examined 2 h later at 0700 or 1700 h. DNA synthesis in the tongue was
investigated using [3H]thymidine and autoradiography. OGF depressed DNA
synthesis of the basal epithelial cells in the tip, and dorsal and ventral
surfaces of the tongue (42-44% of control levels) only at 0700 h. This
decrease in DNA synthesis was blocked by concomitant administration of the
opioid antagonist naloxone (10 mg/kg); naloxone alone had no influence on
cell replicative processes. Both OGF and its receptor, zeta (zeta), were
detected in the stratified squamous epithelium of the ventral and dorsal
surfaces of the tongue by immunocytochemistry. Photodensitometric
measurements of immunocytochemical preparations revealed almost twofold
more OGF and zeta-receptor immunoreactivity at 1700 h than at 0700 h. These
results indicate that an endogenous opioid peptide and its receptor are
present and govern cellular renewal processes in the tongue and regulate
DNA synthesis in a circadian rhythm-dependent fashion.
