Follicular Fluid Leptin Concentrations and Expression of Leptin and Leptin Receptor in the Equine Ovary or in Vitro Matured Oocyte with Reference to Pubertal Development and Breeds

There is no published information about follicular fluid leptin concentrations or presence of 25 leptin and leptin-receptor in the equine ovary or oocyte. Three groups of mares: adult draft 26 mares, draft fillies and adult Standardbred mares were included in the study. Leptin and 27 leptin-receptor were detected in all immature oocytes by immunofluorescence with 28 intensity that was higher in oocytes from draft mares compared to draft fillies and 29 Standardbred mares. After in vitro maturation a higher proportion of oocytes reached 30 metaphase II in draft mares than in draft fillies and Standardbred mares, and in all groups 31 both leptin and leptin-receptor became localized in the oocyte cortex but with higher 32 immunopositivity in draft mares compared to draft fillies and Standardbred mares. These 33 intensities were confirmed by expression profile of leptin and leptin-receptor mRNA. 34 Moreover, leptin was detected in ovarian blood vessels in all kind of animals and within the 35 corpora lutea in adult mares. Serum and follicular fluid concentrations of leptin were 36 similar in draft and Standardbred mares but higher in draft mares than in draft fillies. This 37 study supports the hypothesis that expression of leptin and leptin-receptor mRNA and the 38 rate of maturation can be related either to adiposity or to puberty.