PARENT SESSION
BIOLOGY OF MALE AND FEMALE GAMETES
Harborside C
7:30 AM-10:00 AM

(168) ASSESSMENT OF OOCYTE QUALITY FOLLOWING REPEATED GONADOTROPIN STIMULATION IN THE MOUSE.

Combelles, Catherine^1,2, Albertini, David¹, ¹ Department of Anatomy and Cellular Biology, Boston, MA² Program in Cellular, Molecular, and Developmental Biology, Boston, MA

ABSTRACT- Whether folliculogenesis and oogenesis are compromised in adult females subjected to repeated rounds of ovarian stimulation remain uncertain. The present study was designed to assess whether defects arising from repeated stimulation occur at the level of somatic cells, oocytes, or both. CF-1 female mice were stimulated with 5 I.U. eCG followed 48 hours later by 5 I.U. hCG at one week intervals for four weeks. After each week of stimulation, immature oocytes were collected from ovaries of eCG stimulated mice, and ovulated oocytes from oviducts of eCG/hCG stimulated mice. Germinal vesicle (GV) stage oocytes were evaluated in relation to size, cumulus morphology, and incidence across weeks of stimulation. In addition, expression of meiotic competence markers (% NSN/SN, phosphoproteins, microtubules, centrosomes) and ATP content were monitored in GV, in vivo (IVO) and in vitro (IVM) matured oocytes. Lastly, the developmental competence of ovulated oocytes was determined after in vitro fertilization (IVF) and embryo culture. Inner cell mass and trophectoderm differential cell counts were performed on resulting blastocysts. Deficiencies in cumulus morphology and premature transcriptional repression of GVs were observed in ovaries subjected to repeated gonadotropin stimulation. Moreover, meiotic competence expression was unaffected for IVO oocytes but IVM oocytes exhibited a progressive decrease in meiotic competence with repeated stimulation. The ATP content of immature oocytes decreased with repeated rounds of stimulation, in parallel with measurement on IVO oocytes; in contrast, IVM oocytes exhibited stable levels of ATP across groups. Finally, the developmental competence of oocytes retrieved after repeated stimulation was not significantly different because both rates of IVF and development of blastocysts were similar between weeks. Together, these findings augment our understanding of the influence of gonadotropin priming on oocyte developmental competence. Thus, despite measurable consequences of repeated stimulation on ovarian oocytes, compensatory mechanisms may exist to optimize the developmental competence of ovulated oocytes in the mouse. Supported by NIH Training Program in Developmental Biology HD07403 and Research Grant FY01-248 from March of Dimes Birth Defects Foundation.

KEY WORDS: oocyte, quality, gonadotropin, mouse