Effects of Unilateral and Bilateral
Ovarectomies on the Pituitary gland,
Uterine Horn, and remaining Ovary in
healthy Rats
By: Anil Sishta
BIO473 LAB
TA: David Moore
Introduction
Control of female reproductive hormones is deeply rooted within the
hypothalamus and anterior pituitary gland with multiple feedback loops present. Each
gland produces specific hormones that act on each other and various organs through
several direct and indirect pathways. The hypothalamus secretes gonadotropin
releasing hormone (GnRh) which stimulates the anterior pituitary gland to secrete
follicle stimulating hormone (FSH) and luteinizing hormone (LH) into the bloodstream.
FSH and LH both stimulate the development of a primary follicle within the ovary. LH
acts a synergist and stimulates theca interna cells to form androstenedione from
cholesterol. Androstenedione is a precursor to estrogen which is released by granulosa
cells under FSH stimulation. Estrogen helps maintain primary and secondary sex
characteristics while circulating throughout the body and together with this process,
FSH and LH stimulate ovulation. Inhibin, which is produced by the ovary in response to
the stimulation, and estrogen both act on the hypothalamus and anterior pituitary gland
to decrease activity; as a part of the negative feedback loop. Another important
hormone involved in the female reproductive system is progesterone. Produced after
ovulation by the granulosa cells and corpus luteum, progesterone helps to maintain the
endometrium. If fertilization of the egg occurs, the embryo will secrete hormones to
maintain the corpus luteum and progesterone levels. However in the absence of
fertilization, the corpus luteum will deteriorate roughly ten days after ovulation ending
progesterone production resulting in the deterioration of the endometrium. All of the
previously mentioned hormones combine to control the concentration of each other as
well as the activity of multiple glands to form a complex control system known as the
brain-ovarian axis.
The purpose of this experiment was to remove one or two ovaries from a healthy
rat and measure changes in weight of other parts of the brain-ovarian axis. This could
provide a vital insight into the process of compensation within the brain-ovarian axis and
eventually help people born with defects, hormone illnesses, and problems with
ovulation. These hormones and glands have very important jobs and understanding
how they interact with one another with variables could be very important to much
research.
Three different types of surgeries were performed: a control or “sham” surgery in
which nothing was removed, a unilateral ovarectomy, and a bilateral ovarectomy.
Results were based on the weights of the remaining ovary (if any), uterine horn, and
pituitary gland. Based on the control pathway described above, it is expected that the
remaining ovary’s weight would increase for the unilateral ovarectomy when compared
to the control due to compensation for the missing one ovary. Removing one ovary
would decrease estrogen levels leading to less feedback inhibition on the hypothalamus
and anterior pituitary gland. Therefore, these glands would produce more hormones to
stimulate the ovary causing hypertrophy and acting to compensate. The uterine horn
would not show any difference since the hormone levels would ultimately balance out.
There is no expected change for the pituitary gland in any of the surgeries because the
hypothalamus, which is most responsible for the pituitary action, is ignored in the
surgical and experimental procedure. For the bilateral ovarectomy, there should be a
substantial decrease in the weight of the uterine horn when compared to both the
control and unilateral surgery as the hormones from the anterior pituitary gland will not
be able to act without ovaries. This loss in estrogen production will come with loss of
maintenance of sex characteristics.
Methods
An ovarectomy is the removal of an ovary through surgical procedures. This
experiment involved a sham control surgery, and two ovarectomies; one unilateral and
one bilateral. These were performed on multiple rats and three weeks later, the rats
were euthanized. Immediately following this, the remaining ovaries, pituitary glands, and
uterine horns were removed and weighed to display the effects of the surgeries. In order
to put the rat in a stage of painless unconsciousness to perform surgery, two drugs
were administered in doses based on the rat’s weight. Ketamine is an anesthetic and
knocks the rat out without providing pain relief. Xylazine is an analgesic and would act
as a muscle relaxant and a pain reliever. Bupivacaine was also administered following
the sewing of the muscle wall to provide topical pain relief. The surgery was performed
using sterile technique to prevent infections in the rat. This included keeping certain
items and people out of contact with the rat combined with only surgeons performing
tasks on the rat as well. The procedure for the entire surgery including details about
sterile technique can be found in the "Rodent Survival Surgery Protocol Handout".1
Results
Table #1: Average weights of organ/glands post operation
Control
Unilateral
Bilateral
Gonad
.109±.011
.148±.005 *
N/A
Uterine Horn
0.60±.041
.57±.049
.15±.031 *
0.0165±.0019
.0169±.0021
.014±.001
Pituitary
Data represented as [mean ± standard error of mean]. (*) indicated a significant difference from control
value (p<.01 for gonads, p<.05 for uterine horn and pituitary gland). No gonad data can be reported for
the bilateral ovarectomy since both ovaries were removed during surgery.
Table #1 shows the results of the autopsy on the rats that underwent
ovarectomies or control surgeries. Data was complied for the average weight of the
remaining gonad(s) as well as the uterine horn and pituitary gland. Averages are
displayed with standard errors calculated using the values from each surgery group.
There was a significant difference in the size of the ovaries removed from rats that
underwent unilateral ovarectomies when compared to rats involved in control surgeries.
However this was the only statistical difference for unilateral rats when compared to
control rats. The data also shows one other statistical difference when looking at the
uterine horn; the rats that underwent bilateral ovarectomies showed a significant drop in
uterine horn weights. The two significant differences are represented in Table #1 by a
(*) and were determined by the p-values calculated from two-tailed t-tests.
Discussion
The data from the results matched the expectations perfectly. The statistical
differences in the unilateral ovary and bilateral uterine horn were expected based on
hormone responses to the surgeries. Unilateral surgeries had an ovary which
underwent hypertrophy to compensate for the other missing ovary. In addition there was
no change in uterine horn weight for unilateral ovarectomy rats. This was expected
since estrogen levels would balance out as the compensating ovary maintained
estrogen levels to preserve sex characteristics and reproductive organs. The pituitary
gland should be left intact since the main control gland, the hypothalamus, was
unaltered during the surgery. Data for the bilateral treatment also met expectations. The
uterine horn had deteriorated, in most cases, by almost 75%. Removing both ovaries
prevented estrogen production which prevented perpetuation of the sex characteristics.
This in turn led to the degeneration of the uterine horn. Also, the pituitary gland was
unaffected by the lack of estrogen from the ovaries similar in the end to the glands
removed from the unilateral rats. In conclusion, there was a strong data correlation with
the hypothesis. The only statistical differences lied with the unilateral gonad and
bilateral uterine horn weight. These differences were expected and are viable when
looking at the brain-ovarian axis. There is no evidence to show that the data does not
strongly match the hypothesis.
Although the experimental procedure was standardized for all surgeries and all
rats were healthy absent in major differences, some error could have occurred while
measuring the different organs or glands. This especially holds true for the uterine horn.
The procedure stated that the uterine horn was to be removed just below where both
join to the uterus. Although explained and demonstrated, it is very possible a few of the
uterine horns removed would not be consistent with the procedure. All types of error
were minimized and taking an average of all of the removed horns will help to reduce
this error.
This experiment’s data clearly shows the repercussions of removing a part of the
brain-ovarian axis. The decrease in estrogen led to a severe deterioration of the uterine
horn in bilateral ovarectomies and hypertrophy of the remaining ovary in unilateral
ovarectomies. By showing how hormone levels in the female reproductive system
change based on the experimental variables, this information will prove critical in
helping patients with hormone level problems and missing parts. Hormone treatment is
becoming increasingly important and this experiment provides an important insight into
the body’s control over them.
References
1. "Rodent Survival Surgery Protocol Handout." ANGEL CMS. Pennsylvania State
University, n.d. Web. 12 Apr 2013.
<https://cms.psu.edu/section/default.asp?id=MRG-121218-114302-JRW8>.