Follicle and oocyte morphology in ewes after treatment with insulin in the late follicular phase.
Stress reduces fertility in ruminants. Various experimental models, such as insulin-induced hypoglycaemia, have been used to investigate the mechanisms involved, and have revealed abnormal LH profiles (both pulse and surge secretion). This disruption affects follicular function and it is proposed there may be negative consequences on subsequent oocyte morphology. Insulin (5iu/kg), administered to ewes in the late follicular phase, induced hypoglycemia for 10h, decreased estradiol concentrations for 8-12h and delayed the LH surge by 15h. Although the diameters of dominant follicles just before ovulation were not affected, granulosa cells had fewer pycnotic nuclei, less apoptosis and increased proliferation 16-17h after the LH surge. Nevertheless, we did not observe gross ultra-structural differences in nuclear, cytoplasmic or cumulus maturity between oocytes from insulin-treated and control animals. This suggests that reduced LH pulsatility and a delay in the LH surge may only produce very subtle changes in gross oocyte morphology, imperceptible by electron microscopy.
Scherzer
J
J
Department of Veterinary Clinical Science, University of Liverpool, Leahurst Campus, Chester High Road, Neston, Wirral CH64 7TE, UK. jakobs@uga.edu
Ghuman
S P S
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Pope
M
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Routly
J E
JE
Walter
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Smith
R F
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Dobson
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D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001786:Blood Glucose / Q000032:analysis; D002455:Cell Division / Q000187:drug effects; D002467:Cell Nucleus / Q000648:ultrastructure; D004958:Estradiol / Q000097:blood; D030762:Estrous Cycle / Q000187:drug effects*; D005260:Female; D005498:Follicular Phase / Q000187:drug effects; D006107:Granulosa Cells / Q000648:ultrastructure; D006854:Hydrocortisone / Q000097:blood; D007328:Insulin / Q000008:administration & dosage*; D007986:Luteinizing Hormone / Q000097:blood; D046529:Microscopy, Electron, Transmission; D009865:Oocytes / Q000648:ultrastructure*; D006080:Ovarian Follicle / Q000033:anatomy & histology*; D012756:Sheep
D001786:Blood Glucose; D007328:Insulin; D004958:Estradiol; D007986:Luteinizing Hormone; D006854:Hydrocortisone