Differential profiles of GH, IGF-1, and fructosamine in follicular fluid and plasma of cyclic mares

Growth hormone (GH) influences follicular development mainly by stimulating insulin-like growth factor 1 (IGF-1), which acts systemically and locally within the ovary. However, the metabolic profile of follicular fluid (FF) in mares, particularly markers such as fructosamine (FRUCT), an indicator of glucose metabolism, remains poorly characterized. This study aimed to evaluate GH, IGF-1, and FRUCT concentrations in plasma and FF and their variation across follicle sizes. Sixty ovaries were collected during the breeding season from 30 clinically normal mares raised for meat production. Blood samples were obtained prior to slaughter. Follicles were classified as small (20–30 mm), medium (31–40 mm), and large (≥41 mm), and FF was aspirated individually. GH was measured by enzyme immunoassay, IGF-1 by ELISA, and FRUCT by spectrophotometry. GH concentrations did not differ significantly between plasma and FF across follicle sizes. IGF-1 remained low in small and medium follicles but increased in large preovulatory follicles ( p < 0.05). FRUCT concentrations in FF progressively rose with follicular development and were higher than plasma values ( p < 0.05). IGF-1 and FRUCT were positively correlated ( r = 0.65; p < 0.05). These findings suggest that IGF-1 plays a role in final follicular maturation, while FRUCT accumulation reflects enhanced local carbohydrate metabolism during follicular growth. Moreover, the positive correlation between IGF-1 and FRUCT indicates a potential link between metabolic activity and growth signaling within the follicular microenvironment.