238 EFFECTS OF LEPTIN SUPPLEMENTATION ON NUCLEAR AND CYTOPLASMIC IN VITRO MATURATION OF RABBIT OOCYTES

Abstract

Reproductive function is affected substantially by nutritional status. Leptin is a peptide secreted mainly by adipocytes that reflects the amount of body fat and acts as a modulator of oocyte quality. The aim of this study was to analyze, for the first time in the rabbit, the influence of leptin on meiotic and cytoplasmic maturation (cortical granule (CG) migration) of rabbit oocytes in vitro (IVM). Cumulus–oocyte complexes (COCs) were collected from 25 young New Zealand white female rabbits (<3 parturitions) in 3 replicates. COCs were aspirated from ovarian follicles >1 mm in size and were matured in TCM-199 medium, containing sodium pyruvate, sodium bicarbonate, BSA, and 10 ng mL^–1 epidermal growth factor (EGF), and supplemented with 0, 10, or 100 ng mL^–1 leptin. A total of 163 COCs were treated progressively with hyaluronidase (2 mm), 0.5% pronase, 4% paraformaldehyde, 0.02% Triton X-100, and 7.5% BSA after the maturation period. Oocytes were incubated with 100 mg mL^–1 fluorescein isothiocyanate (FITC)-conjugated Lens culinaris agglutinin (LCA) for CG staining and with 4′,6-diamino-2-phenylindole (DAPI) for nuclear staining, and observed under a confocal laser-scanning microscope. In addition, 17 ovulated oocytes recovered from oviducts at 20 h post- GnRH were used as in vivo-maturated controls for CG distribution. Most of the ovulated oocytes at metaphase II (MII, 100%) presented CGs located in the cortex beneath the plasma membrane (61.1 ± 11.8%). Addition of 10 ng mL^–1 leptin to IVM medium significantly increased the rate of oocytes reaching MII, compared to the 0 and 100 ng mL^–1 leptin concentrations (P < 0.05). The percentage of oocytes showing CG migration to the cortex was significantly increased in the 10 ng mL^–1 leptin treatment group (Table 1) compared to that in the 100 ng mL^–1 leptin group (P < 0.05) and tended to be higher than that in the 0 ng mL^–1 leptin group (P < 0.08). The rest of the oocytes showed homogeneous CG distribution, as they were not cytoplasmic maturated. Moreover, both in vivo- and in vitro-matured oocytes had a GC-free domain overlying the MII spindle. In conclusion, addition of leptin to IVM medium at physiological dose (10 ng mL^–1) improves both meiotic and cytoplasmic maturation of rabbit oocytes, whereas an excessive leptin concentration does not exert a beneficial effect. These findings suggest a physiological role for leptin in the relationship between nutritional status and regulation of oocyte maturation.

Table 1. Nuclear maturation and CG distribution of oocytes after IVM

This research was supported by AGL05-196 and UCM-CM research program (920249). MAA received a grant from CM and FSE. RMGG was supported by the Juan de la Cierva-MEC Program.