Premium
Oocyte structure and follicular steroid concentrations in superovulated versus unstimulated heifers
Author(s) -
Assey R. J.,
Hyttel P.,
Roche J. F.,
Boland M.
Publication year - 1994
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.1080390103
Subject(s) - medicine , endocrinology , biology , follicular phase , oocyte , estrous cycle , follicular fluid , follicle , ovulation , embryo transfer , andrology , follicle stimulating hormone , ovarian follicle , ovary , embryo , hormone , luteinizing hormone , microbiology and biotechnology
A highly variable yield of viable embryos in superovulated cattle is a major hindrance to the embryo transfer industry. To trace the cause of this problem, investigations were carried out on the intrafollicular steroids and structure of oocytes originating from follicles of follicular stimulating hormone (FSH)‐stimulated (superovulated) and unstimulated heifers. Unstimulated heifers were slaughtered at midcycle, or administered cloprostenol (PG) at midcycle and slaughtered after 24, 48, or 72 hr, while superovulated heifers were administered 4 injections of pFSH (2 injections per day) and slaughtered 12 hr later, or administered 6, 7, or 8 injections of FSH in combination with PG at the 5th and 6th injection, and slaughtered 24, 36, or 60 hr, respectively, after the first PG injection. The follicular fluid from the largest (presumptive dominant) follicle of the unstimulated heifers and from potentially ovulatory follicles (≥8 mm in diameter) of the superovulated heifers were assayed for estradiol‐17β (E2) and progesterone (P4), while the oocyte cumulus complexes from such follicles were processed for transmission electron microscopy. The mean E2 and especially P4 concentrations of the potentially ovulatory follicles of the superovulated heifers were lower than similar follicles of the unstimulated animals (83.7 ± 76.7 ng/ml vs. 208.1 ± 357.0 ng/ml, P > 0.05 and 31.1 ± 38.7 ng/ml vs. 150.3 ± 202, P < 0.05, respectively). The unstimulated oocytes had, in general, spherical oocyte nuclei and compact nucleoli before PG administration, while after PG, undulation of the nuclear envelope and nucleolus vacuolization was characteristic. The superovulated oocytes, in comparison, displayed the following deviations: premature perivitelline space formation, lack of nucleolar vacuolization, reduced amount of lipid droplets and lack of lipid‐mitochondria association, enlarged rough endoplasmic reticulum compartment, and increased condensation of chromatin and elongation, i.e., expansion of some cumulus cells. Degenerative oocytes were only found in the superovulated group. It is concluded that FSH‐stimulation is associated with reduced intrafollicular E2 and P4 concentrations and subcellular deviations in the oocytes that are established early in the superovulatory process. These deviations may contribute to the reduced developmental competence of superovulated oocytes. © 1994 Wiley‐Liss, Inc.