Relationship between growth hormone concentrations in bovine oocytes and follicular fluid and oocyte developmental competence

Abstract

In the last few years, several works suggest that Growth Hormone (GH) is involved in follicular development and oocyte maturation. These actions may reflect endocrine roles of pituitary GH and also account for local autocrine or paracrine activities of GH produced in reproductive tissue. This study was aimed to verify whether the developmental competence of bovine female gametes might be related to ovarian GH.We evaluated the localisation and distribution of GH in the cumulus oocytes complexes (COCs) and the concentration of GH in the oocytes and in the follicular fluids (FF) from ovaries classified on the basis of the follicles number. Oocytes retrieved from ovaries with more than 10 follicles of 2 to 5 mm in diameter (High ovaries, Hi) show higher rate of maturation and blastocyst formation than those retrieved from ovaries with less than 10 follicles (Low ovaries, Lo). At the same time we measured Estrogen (E2) and Progesterone (P4) concentrations in FF, to relate oocytes quality, GH concentration and follicle health. GH localization in COCs and oocytes was performed by indirect immunofluorescence and its concentration within the ooplasm was evaluated by microspectrophotometer analysis. GH, E2 and P4 concentrations in FF were measured by an Enzyme Linked ImmunoSorbent assay (ELISA).We observed a positive, diffuse signal at cytoplasmic level in most of the cumulus cells, with no differences between COCs collected from Hi and Lo ovaries. On the contrary, GH level was significantly higher in the oocytes collected from Lo ovaries than in those recovered from Hi ovaries. Finally we found that also GH level in the FF was inversely related to the oocytes developmental capability. We suggest that the increase of GH in the oocytes and in the FF derived from Lo ovaries might be interpreted as attempt of the follicular environment to improve ovarian activity and in turn oocytes developmental competence in a autocrineparacrine manner. Moreover, E2, and P4 levels in FF suggest that, in our model, atresia processes are also involved in oocyte developmental capability and that the highest level of GH may represent a local reaction to these phenomena.