OPIOID ANTAGONIST MODULATION OF DNA-SYNTHESIS IN MOUSE TONGUE EPITHELIUM IS CIRCADIAN DEPENDENT

In addition to neuromodulation, endogenous opioids also serve as growth factors. To investigate the possible involvement of opioid peptides in the renewal of epithelium, mice were given systemic injections of the opioid antagonist, naltrexone (NTX) (10 mg/kg). Disruption of opioid-receptor interaction by NTX resulted in an elevation (43-150% from control levels) of the number of basal epithelial cells undergoing DNA synthesis in the tip, dorsal, and ventral surfaces of the tongue. This stimulatory effect lasted up to 8 h following drug exposure, and was recorded at 1700 h but not 0700 h. These results are the first indication that endogenous opioids function in cellular renewal processes, and do so in a circadian rhythm-dependent manner.