Determination of the effect of the interaction between Ghrelin and serotonin agonist (R)-8-OH-DPAT on the mean plasma concentrations of T3 & T4 in rat

Introduction: Previous studies have shown that ghrelin inhibits the activity of Hypothalamus –Pituitary – Thyroid (H–P-T) axis. It is also proved that ghrelin increases appetite via Agouti Related Protein and neuropeptide Y pathway, decreases T3 & T4 secretion and inhibits serotonin release from hypothalamic synaptosomes. Serotonin may interact with ghrelin in control of thyroid hormones secretion. Thus, the goal of this study was to determine the influence of the interaction between ghrelin and serotonin agonist on thyroid hormones concentration. This is a suugestive mechanism to determine the effect of serotonin agonist in decreasing the effect of ghrelin. Methods: Twenty four male Wistar rats weighing 230-250 g were randomly divided into 3 groups. The groups respectively received 5 nmol ghrelin ,20 nmol serotonin agonist (R)-8-OH-DPAT or 5 nmol ghrelin with 20 nmol (R)-8-OH-DPAT in the volume of 5μl during 3 days via lateral cerebral ventricle. The blood samples were collected from one day before to one day after injections and brain slices were taken to ensure the place of the canulae is right. The plasma were analysed by Radio Immuno Assay technique to determine T3 and T4 concentrations. Results: The results of this experience showed that the (.i.c.v) injection of ghrelin and (R)-8-OH-DPAT respectively decreased and increased the mean plasma concentrations of thyroid hormones significantly (p<0.05), while the interaction of these two substances showed that (R)-8-OH-DPAT can decease the inhibitory effect of ghrelin on thyroid hormones concentration, but this effect is not statistically significant. (p<0.05) Conclusion: This study showed that ghrelin decreased mean plasma concentration of T3 & T4 significantly and serotonin agonist while injected with ghrelin , because of the stronger effect of ghrelin, could not significantly inhibit this effect of ghrelin. (p<0.05)