Relationship between ghrelin and estrogen in the ovary of pregnant sheep

BACKGROUND:Ghrelin, an endogenous ligand for the growth secretagogue receptor is predominantly produced in the stomach and an expression of ghrelin has recently been identified in placenta and ovary. OBJECTIVES: Therefore, we decited to measure ovarian ghrelin as quantitative and evaluate the correlation between ghrelin and estrogen during second half of ovine pregnancy. METHODS: The ovarian samples were collected from 40 pregnant sheep in 3, 3.5, 4, 4.5 and 5 months of pregnancy in a local abattoir. Follicles and active corpora lutea (CL) were dissected from surrounding tissues, separately. The samples were homogenized with phosphate buffer (0.1 M, pH=7.4) on liquid nitrogen to provide fluid samples. Ghrelin and estrogen concentrations were measured by ELISA method and expressed as milligram (mg) and picogram (pg) per mg of tissue protein, respectively. RESULTS: There was a linear correlation between ghrelin and estrogen in ovarian follicles (r=0.97 and p=0.004), but not in CL. Follicular ghrelin significantly increased in 4, 4.5 and 5 months (p<0.001) but CL ghrelin significantly decreased in the 4.5 month of ovine pregnancy (p<0.01). Estrogen concentration was also significantly higher in 4-5 months of pregnancy in ovarian follicles (p<0.001) but potent CL indicated higher estrogen level only in the 5th month of pregnancy (p<0.001). CONCLUSIONS: These results emphasize the role of ghrelin in the reproductive system and open a new window to future studies