The effects of interactions between testosterone and ghrelin on mean plasma thyroid hormones concentration in male rats

Ghrelin is an orexigenic peptide synthesized mainly by stomach and hypothalamus. Ghrelin decreases secretion of thyroid hormones. Testosterone is an esteroidogenic hormone that exerts stimulatory effects on Hypothalamus-Pituitary-Thyroid (HPT) axis activity. The aim of the present study was to investigate the effect of interactions between the central injection of ghrelin and testosterone on mean plasma thyroid hormones concentration. Twenty male Wistar rats (200-250 g) were randomly divided into four groups. The groups received saline, 5 nmol ghrelin, 1 μg testosterone and simultaneous injection of 5 nmol ghrelin and 1 μg testosterone in third cerebral ventricle in volumes of 3 μl. Blood samples were collected one day before injection and until 12 hours after that. Mean plasma thyroid hormones concentrations were determined by radio-immunoassay (RIA). The results indicated that testosterone significantly increased the mean plasma concentration of T3 and T4 hormones after injection compared to before injection, whereas ghrelin significantly decreased the mean plasma concentration of T3 and T4 compared to before injection. The results demonstrated that ghrelin significantly decreased the stimulatory effect of testosterone on mean plasma T3 and T4 concentrations.