Comparison of leptin levels in serum and follicular fluid during the oestrous cycle in cows

Leptin is mainly synthesised in white adipose tissue. Besides its effects on body weight and metabolic homeostasis, leptin also has effects on puberty, sexual maturation and reproduction. In this study the relationship between leptin, IGF-1, oestradiol (E2) and progesterone levels were investigated in serum and follicular fluid from cows. This study included 72 healthy, Brown Swiss cows aged 4-5 years. Samples from the jugular vein and follicular fluids were collected. Phases of the oestrus cycle of cows were classified according to their serum progesterone levels (< 3.18 nmol/l, follicular phase and the others as luteal phase). Follicles were grouped as large (> or = 8 mm) or small (< 8 mm). Leptin, IGF-1, oestradiol and progesterone levels were measured from serum and follicular fluid. Leptin concentrations were found to be significantly higher in luteal-phase follicular fluid of small follicles (P < 0.05). These were classified as atretic follicles. There was a positive correlation between serum and follicular fluid leptin levels in the luteal phase. Serum leptin was found to have a positive correlation with follicular fluid progesterone level (P = 0.01) in the preovulatory follicles. The present study shows that there is a relationship between the concentration of leptin in follicular fluid and atresia in small follicles.