Submitted February 13, 2004
Returned for revision March 3, 2004
Accepted April 1, 2004
Ovary
Aberrant Blood Flow Area and Plasma Gonadotropin
Concentrations During the Development of Dominant-Sized
Transitional Anovulatory Follicles in Mares
T. J. Acosta ,
M. A. Beg ,
and
O. J. Ginther *
* To whom correspondence should be addressed. E-mail: ginther{at}svm.vetmed.wisc.edu.
Abstract
Color Doppler transrectal ultrasound was used to evaluate
blood flow area in the wall of dominant anovulatory
follicles versus ovulatory follicles in mares, during the
transition between anovulatory and ovulatory seasons.
Daily examinations were done in 11 control mares toward
the end of the anovulatory season. In 13 separate mares,
follicular fluid was collected from 30-mm follicles and
blood flow areas from control mares were used as a basis
for designating the sampled follicle as anovulatory or
ovulatory. Blood flow area in the controls ranged from
0.18 to 0.35 cm2 in six mares on the day of a 30-mm
anovulatory follicle and from 0.25 to 0.86 cm2 in 11 mares
on the day of a 30-mm ovulatory follicle; the ranges did
not overlap except for one follicle. In the controls, mean
blood flow area was lower (P < 0.05) in the anovulatory
group than in the ovulatory group for each day beginning
at the first Doppler examination at 25 mm. For plasma LH
in controls, an effect of follicle group (P < 0.0001) and
an interaction (P < 0.0001) of group by day reflected
lower (P < 0.05) concentrations in the anovulatory group
on Days -6, -2, 5, 6, 7, and 8 (Day 0 = 30-mm follicle).
For plasma FSH, an interaction (P < 0.0001) reflected
higher (P < 0.05) concentrations in the anovulatory group
on Days -3, 1, 2, 3, and 4. There were more (P < 0.05)
statistically identified FSH surges in the anovulatory
group during Days -7 to 8. In the sampled mares,
follicular-fluid concentrations of estradiol, free
insulin-like growth factor-1, inhibin-A, and vascular
endothelial growth factor were lower (P < 0.05) in 30-mm
designated anovulatory follicles than in 30-mm designated
ovulatory follicles. Results were interpreted as follows:
1) the future anovulatory dominant-sized follicle
developed under an LH deficiency; 2) the LH deficiency led
to reductions in blood flow area and in concentrations of
follicular-fluid factors; and 3) the reduction in follicle
production of FSH suppressors resulted in higher plasma
FSH concentrations.
Key words:
Ovary •
Follicular development •
Growth factors •
Seasonal reproduction •
Steroid hormones
