Submitted November 9, 2006
Returned for revision December 12, 2006
Accepted March 13, 2007
Ovary
Differential Effects of Various Estradiol-17beta
Treatments on Follicle-Stimulating Hormone Peaks,
Luteinizing Hormone Pulses, Basal Gonadotropin
Concentrations, and Antral Follicle and Luteal Development
in Cyclic Ewes
David M.W. Barrett ,
Rajesha Duggavathi ,
Kate L. Davies ,
Pawel M. Bartlewski ,
Edward T. Bagu ,
and
Norman C. Rawlings *
* To whom correspondence should be addressed. E-mail: norman.rawlings{at}usask.ca.
Abstract
In a previous study, 10-day estradiol implant treatment
truncated FSH peaks that precede follicular waves in
sheep, but subsequent ovine FSH (oFSH) injection
reinitiated wave emergence. The present study's objectives
were to examine the effects of a 20-day estradiol and
progesterone treatment on FSH peaks, follicle waves, and
responsiveness to oFSH injection. Also, different
estradiol doses were given to see if a model could be
produced that differentially suppressed FSH peaks, LH
pulses, or basal gonadotropin secretion, to study effects
of these changes on follicular dynamics. Mean estradiol
concentrations were 11.8±0.4 pg/mL, FSH peaks were
truncated, wave emergence was halted, and number of small
follicles (2-3mm diameters) was reduced (P<0.05) in cyclic
ewes given estradiol and progesterone implants (Experiment
1). On Day 15 of treatment, oFSH injection failed to
induce wave emergence. With three different estradiol
implant sizes (Experiment 2), estradiol concentrations
were 5.2, 19.0, 27.5, and 34.8 (±4.6) pg/mL in
control and treated ewes, respectively. All estradiol
treatments truncated FSH peaks, except that which created
the highest estradiol concentrations. Experiment 2
treated ewes had significantly reduced mean and basal FSH
concentrations and LH pulse amplitude and frequency. We
concluded that 20-day estradiol treatment truncated FSH
peaks, blocking wave emergence, and reduced the small
follicle pool, rendering the ovary unresponsive to oFSH
injection in terms of wave emergence. Varying the steroid
treatment created differential FSH peak regulation
compared to other gonadotropin secretory parameters; this
provides a useful model for future studies of the
endocrine regulation of ovine antral follicular dynamics.
Key words:
Corpus luteum •
Estradiol •
Follicle-stimulating hormone •
Follicular development •
Luteinizing hormone
