Author:
Bartlewski P. M.,Beard A. P.,Chapman C. L.,Nelson M. L.,Palmer B.,Aravindakshan J.,Cook S. J.,Rawlings N. C.
Abstract
The relationships between the development of antral follicles (growing from 3
to ≥5 mm diameter), hormone secretion (luteinizing hormone (LH),
follicle-stimlating hormone (FSH), oestradiol and progesterone), ovulation and
the formation of luteal structures in response to gonadotrophin-releasing
hormone (GnRH) were examined in 24 anoestrous Western White Face ewes
(May–July). Ewes were monitored by transrectal ovarian ultrasonography
for 34 days, commencing 15 days before the administration of GnRH. Following
treatment with GnRH, 83% (20/24) of ewes ovulated. Twenty-five per
cent of all ewes (6/24) subsequently had normal (full-life span) corpora
lutea (CL), 37% (9/24) had inadequate CL, 17% (4/24) had
both normal and inadequate CL, 17% (including three of four anovular
ewes and one ewe with inadequate CL) formed luteinized follicles and only
4% (1/24) did not ovulate or produce any luteal structure. None of
the variables of follicular growth (follicles reaching ≥5 mm diameter)
differed between follicles that either ovulated or failed to ovulate and there
was no evident correlation between the age or stage of development of
ovulatory sized antral follicles and the type of luteal structure formed,
except for luteinized unovulated follicles; these follicles all emerged within
3 days of GnRH injection. Mean serum concentrations of FSH and oestradiol
before treatment did not differ (P> 0.05) between
ewes with different ovarian responses, but peaks of fluctuations in serum
concentrations of FSH in daily samples were higher in ewes that produced
normal CL compared with ewes with inadequate CL. After GnRH treatment,
oestradiol secretion was higher in ewes that formed luteinized unovulated
follicles than in all ewes with inadequate CL (P>
0.05). The peak concentration of the GnRH-induced LH surge was higher and the
interval from GnRH to peak LH discharge was shorter in ewes with inadequate CL
compared with ewes that had normal CL after ovulation
(P> 0.05). In conclusion, ovulatory sized antral
follicles at a similar stage of their life span can give rise to either normal
or inadequate CL and a proportion of these follicles do not ovulate in
response to GnRH in seasonally anoestrous ewes. This suggests differences in
ovarian follicular responsiveness to gonadotrophic stimuli. Both the amplitude
of episodic elevations in daily serum FSH concentrations and the
characteristics of the pre-ovulatory LH surge may be important for
luteogenesis following ovulation.
Subject
Developmental Biology,Endocrinology,Genetics,Molecular Biology,Animal Science and Zoology,Reproductive Medicine,Biotechnology
Cited by
33 articles.
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