بررسي اثر برهمكنش گرلين و آگونيست سروتونين (R)-8-OH-DPAT ) بر ميانگين غلظت پلاسمايي هورمون هاي T3 و T4 در موش صحرايي

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 the appetite via Agouti Related Protein and neuropeptide Y pathway, decreases T3 and T4 secretion and inhibits serotonin release from hypothalamic synaptosomes. Serotonin may interact with ghrelin over the 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. Methods: Twenty four male Wistar rats weighing 230-250 g were randomly divided into 3 groups. The groups received 5 nmol ghrelin, 20 nmol serotonin agonist (R)-8-OH-DPAT or 5 nmol ghrelin together with 20 nmol (R)-8- OH-DPAT in lateral cerebral ventricle in volumes of 5 (xl for 3 days . The blood samples were collected everyday, starting one day before and up to one day after injections. Brain slices were taken to ensure that the place of the canulae was right. The plasma was analysed by Radioimmunoassay technique to determine T3 and T4 concentrations. Results: The results showed that the i.c.v injection of ghrelin significantly decreased and (R)-8-OH-DPAT significantly increased the mean plasma concentrations of thyroid hormones (p < 0.05). Co-administration of these two substances showed that (R)-8-OH-DPAT can decrease the inhibitory effect of ghrelin on thyroid hormones concentration, but this effect was not statistically significant (p<0.05). Conclusion: This study showed that ghrelin significantly decreased mean plasma concentration of T3 and T4. Co­administration of a serotonin agonist partially blocked the inhibitory effect of ghrelin on thyroid hormones, but this effect did not reach significance. (p<0.05).