Effect of Single Oral Dose of Melatonin on Plasma Concentration of Prolactin and Cortisol in Male Rhesus Monkeys

Background: Melatonin is a neurotransmitter involved in physiological regulation; it is thought that melatonin has a role in male reproductive physiology through effect on neuroendocrine axis. The present study was aimed to investigate the effect of melatonin on plasma levels of Prolactin and Cortisol (ηg/ml). Methods: Five adult male rhesus monkeys were used for the purpose. Monkeys were maintained at ad libitum. Melatonin 5 mg was administered orally to all five monkeys. Sequential blood samples were collected at 15 minute intervals in heparinised syringes. Plasma Prolactin and Cortisol were analysed by ELISA and RIA respectively. Results: Melatonin oral single dose (5 mg) increased the plasma prolactin concentration in all five monkeys after 15 minute of treatment and this increase remained until 60 min but this increase was not significant compared to before treatment concentration. The highest mean concentration of prolactin was observed at 15 to 60 minute (6.38±0.18 ηg/ml) and the lowest mean concentration was observed between 75 to 120 minute interval (5.43±0.22 ηg/ml). Decrease in the later was significant compared to former (p<0.001). Present study results showed significant effect of melatonin in terms of reduction on plasma prolactin concentration (F(2,52)=3.989; p<0.05). The study results showed no significant effect of melatonin on plasma Cortisol concentration (F(2,52)=0.074; p>0.05) in adult male rhesus monkeys. Conclusion: Our study suggests positive role of melatonin in reducing pathological effects of Prolactin, while it has been revealed that stress has no physiological coupling with melatonin administration.