It is known that
melatonin has important immunomodulatory properties in the Japanese quail. However, the mechanism of
melatonin action on the immune system is not clearly understood in avian species. In mammals, the immunostimulatory properties of
melatonin are mediated by the release of
opioid peptides from activated T-lymphocytes. The present study was performed to determine if these same
melatonin-induced
opioids (MIO) are involved with the immunoenhancing effects of
melatonin in quail. Three treatment groups were given
melatonin (50 microg/ml) in the
drinking water ad libitum along with
naltrexone, a known
opioid receptor-blocking agent.
Melatonin was administered throughout the 3 week study and each bird received a daily
intramuscular injection of
naltrexone at a dose of 0.1, 1.0, or 10.0 mg/kg. In addition, three control groups were established that received only
melatonin,
naltrexone, or diluent. Evaluation of the cellular and humoral immune responses was initiated after 2 weeks of treatments. A cutaneous basophil
hypersensitivity reaction to
phytohemagglutinin (
PHA-P) was measured to evaluate the cellular immune response. To evaluate the humoral immune response, primary antibody titers were determined 7 days post-
intravenous injection with a Chukar red blood cell (CRBC)
suspension. Both the cellular and humoral immune responses were significantly increased by 22 and 34%, respectively, upon
melatonin exposure as compared to quail receiving diluent only. Concomitant administration of
naltrexone and
melatonin significantly reduced the immunoenhancing effect of
melatonin across all
naltrexone doses. We conclude that
melatonin enhances a cellular and humoral immune response in Japanese quail via an opiatergic mechanism.