Journal of Human Reproductive Sciences

: 2013  |  Volume : 6  |  Issue : 1  |  Page : 45--48

Ovulation and rate of implantation following unilateral ovariectomy in mice

Koushik Bhattacharya 
 Department of Physiology, Vidyasagar College for Women, University of Calcutta, Kolkata, India

Correspondence Address:
Koushik Bhattacharya
Department of Physiology, Vidyasagar College for Women, University of Calcutta, Kolkata 700 073


Objectives: Removal of an ovary of any side of the body is called the unilateral ovariectomy (ULO). ULO models are used to analyze the existence of functional and physiological asymmetries between the ovaries, including the ovum implantation. Materials and Methods: ULO was done in mice without any specification on their stages of the estrous cycle. The animals were mated between 3 rd and 15 th day after ULO to observe the consequence of ULO on ovulation and ovum implantation. Results: Ovulation and number of implantation were decreased in proportion to single contralateral ovary if the animals were mated within 36 hrs of ULO. It resulted in increased weight of contralateral ovary due to hypertrophy, and also in compensatory ovulation, formation of corpus luteum (CL) that reached a peak after 14 th and 15 th day of ULO (sacrificed on 5 th day of pregnancy i.e., 19 th and 20 th day of ULO) compared to animals undergone sham-surgery. Numbers of implantations were also increased progressively on the contralateral ovarian side and get to a peak after similar days of compensation. Discussion and Conclusion: Following ULO, the remaining ovary started to compensate within 5 th to 6 th day of ULO even during pregnancy. Ovarian histology also showed increased formation of CL which is a marker of rate of ovulation.

How to cite this article:
Bhattacharya K. Ovulation and rate of implantation following unilateral ovariectomy in mice.J Hum Reprod Sci 2013;6:45-48

How to cite this URL:
Bhattacharya K. Ovulation and rate of implantation following unilateral ovariectomy in mice. J Hum Reprod Sci [serial online] 2013 [cited 2022 Jan 27 ];6:45-48
Available from:

Full Text


Unilateral ovariectomy (ULO) is a time honored procedure which has been useful in elucidating follicular kinetics in species as disparate as pigs, chickens, Drosophila.[1] Some of these species normally always ovulates from right ovary, but following its removal the left ovary takes over. These studies permit certain conclusions, firstly the number of oocytes ovulated does not diminish after surgery since the rate of ovulation in the remaining ovary is doubled. For the rat, it has been shown that this compensatory ovulation has occurred by the first estrus after surgery, even if the latter is carried out as late as 1400 hr on the day before estrus. [2] The doubling of the ovulation rate is not a transient phenomenon, it can continue for at least 75 weeks in the mouse [3] and for at least 8 weeks in the hamster. [4] In the rat, it has been reported that compensatory ovulation has ceased by 6 months after surgery. [5] Secondly, the weight of the remaining ovary (or fragment of ovary) [6] progressively increases after surgery (compensatory hypertrophy) and may attain the combined weights of two ovaries in controls. This ovarian weight gain most likely results from the increased number of corpora lutea formed following compensatory ovulation, [7] although preovulatory follicles may also make a contribution.

The effect on mammals can be analyzed in terms of compensatory hypertrophy of the contralateral ovary (i.e., increased weight) representing persistence of increased number of corpora lutea (e.g.,, mice and rats) as well as enhanced follicular activity. The first species in which the immediate effects of ULO on compensatory ovulation established was hamster. [8] Removal of one ovary at morning for first 3 days of the 4-day estrous cycle was followed by doubling in the number of ovulations from the remaining ovary. It was believed that a reduction in atresia of larger follicles between day 3 and 4 spared follicles and resulted in compensatory ovulation. [8] Unilaterally ovariectomized mice, at random times during the cycle, invariably double the numbers of ova shed within 3 days after the procedure. [7] As there is no report on the effect of ULO on the occurrence of ovulation and implantation irrespective of the stages of the estrous cycle in mice, the present investigation was carried out to study the changes in these parameters subsequent to ULO.

 Materials and Methods

Adult virgin female mice (7-8 weeks old) of the Park strain weighing 20-25 g were maintained in the Departmental Animal house on Mouse Laboratory Diet and water ad-libitum, and at a temperature of 72-78°F and under a light regimen of 14 hrs of light: 10 hrs of darkness. ULO was done between 0800 hrs. and 0900 hrs. randomly in the experimental mice. The ectomized ovaries were fixed in Bouin's solution and processed for routine histology. The ovaries were sectioned by using microtome and stained with Hematoxylin and Eosin stain.

These unilaterally ovariectomized mice were placed with males in the evening on the 3 rd , 4 th , 5 th , 6 th , 7 th , 14 th , and 15 th days of ULO and vaginal plugs examined after overnight cohabitation with proven males. The day of observation of plug is considered as 1 st day of pregnancy (D1).

On D5, they were anesthetized and pontamine blue dye was injected. The animals were sacrificed by cervical dislocation and laparotomized to see the blue spots in the uterine horn. The blue spots were counted as number of implantation. The remaining ovary of the contralateral uterine horn containing blastocysts was also fixed in Bouin's solution and processed for routine histology. The ovary was sectioned by using microtome and stained with Hematoxylin and Eosin to study the compensatory hypertrophy. The data were statistically analyzed by Student's t-test (P < 0.05).


Number of implantations along with ovarian weight increased significantly in mice mated on day 3 onward [Table 1]. No mating was observed within 72 hours of ULO. The changes of ovarian weight were consistent from day 5 onward. After day 7 to day 15, the effect of compensatory hypertrophy of the remaining ovary was prominent. The single ovarian weight becomes 14.33 ± 0.33 mg after 20 days of compensation as compared to 5.33 ± 0.33 mg to 7.00 ± 0.12 mg in sham operated animals. Along with the ovarian hypertrophy, number of implantation sites were also be compensated; i.e., 10.5 ± 0.5 implantation sites were observed in sham operated animal whereas 9.00 ± 0.66 number of implantation [Table 1] occurred after 20 days of compensation after ULO The animals were ovariectomized randomly irrespective of their stages considering that it has no effect on the cyclicity. For all these reasons the animals did not mate before day 3 after ULO. Ovarian histology reveals that ovary could compensate its ovulation by D7 because there it is showing at least 7 corpus luteum (CL) [Figure 1].{Figure 1}{Table 1}


In the present study, the weight of the remaining contralateral ovary increased by compensatory hypertrophy, and by 3 weeks after surgery, it was equivalent to that of two ovaries in controls of the same age [Table 1]; it has been presumed that there is no effect of ULO on their cyclicity and all these changes have been attributed to hormonal alterations in the hypothalamus-pituitary-ovarian (HPO) axis caused by the elimination of a source of ovarian steroids due to ULO.

From the present investigation, it is assumed that the increased output of eggs by the remaining single ovary following surgery could be compensated either by increasing the rate at which follicles leave the pool, or by reducing the number of oocytes lost by atresia, which means compensatory ovarian functions have been explained as resulting from a hormonal alterations in the HPO axis. Following ULO the pituitary increases the release of follicle stimulating hormone (FSH), which in turn enhances the recruitment of small follicles and also decreases follicular atresia. [9] Aside from the hormonal participation in the compensatory responses observed after ULO, there are evidences suggesting that ovarian innervations arriving to the ovaries through the vagus nerves and the superior ovarian nerve (SON) play a role in compensatory ovarian responses. [9]

The contralateral uterine horn of unilaterally ovariectomized mice contains blastocysts after getting pregnant, having the increase in length during the early stages of implantation. At the same time, the implantation swellings of blastocysts were visible macroscopically before the implantation, after the administration of pontamine blue injection [Figure 2]. It is concluded that growth in length of the uterus occurs during the implantation reaction and this may assist in the accommodation of blastocysts along the length of the uterus. [10] A single horn of the mice uterus is provided for the development of as many as 12 young pups, after 3 weeks [11] and the single remaining ovary in unilaterally ovariectomized animals (assuming the number of corpora lutea to be an index of ovulation) produces as many ova as both ovaries in normal females.{Figure 2}

Implantation reduced in proportion to single ovary if the animals were mated within 24 hrs of ULO. There is an increase in ovarian weight along with an increase in implantation number continued in mated mice and reached at peak on 19 th -21 st day of ULO. [12] After ULO, the contralateral remaining ovary compensated within day 5-day 6 of ULO even during pregnancy. However, in the present study maximum ovulation and pregnancy was observed on D7 which did not increase significantly on D14 [Table 1]. This is to be noted that average number of implantation in this animal colony varies from 6 to10. Compensatory hypertrophy in the present experiment did not occur significantly until D15. But, the normal number of implantation can be corrected within D15. Ovarian histology showed stimulation of small antral follicles in mice mated on day 3 of ULO (sacrificed after 5 days i.e., day 8 of ULO) along with a decrease of large antral follicles and preantral follicles [Figure 1]. Preantral follicles were at peak during day 12-day 14, which may be again due to the increased release of FSH from pituitary. [9] ULO reported to cause a sharp, transient increase in serum levels of FSH with variable and less striking changes in Luteinizing hormone (LH). [13],[14],[15],[16],[17],[18],[19],[20],[21],[22] It has also been demonstrated that in rat second surge of FSH which is normally restricted to estrus, is extended to 2 nd day of the cycle and appears to be the signal that recruits additional follicles into ovulation range. [23] In mice, ovulation increased by two folds within 3 days after ULO at any stage of the cycle. [8] There is no report of implantation just after the ULO or even the short term effect of ULO on the subsequent implantation. During the normal pregnancy in mice, LH peaks on day 4 and day 11 of gestation with no significant changes in FSH; only on the day of parturition there is a sharp increase of both FSH and LH. [23] In ULO animals, implantation occurs when the FSH level is much higher than in normal conditions. Though, FSH level was not measured in the present study, it can be assumed that the occurrence of implantation in high FSH internal milieu.


Unilateral ovariectomy does not affect the sexual activities as well as sexual behaviors in female (as in lordosis), it has no impact on reproductive cyclicity too. Number of ova production hampered immediately after ULO but became normal just after few days of compensation. Ovulation and implantation are not affected by ULO due to the compensatory hypertrophy, and thus, it also has no effect on process of fertilization. The fertilized ova do not cross over and implant in the horn of the uterus opposite the side of their origin.


1Peppler RD. Method and mechanism of ovulatory compensation following unilateral ovariectomy in the rat (Dissertation). Lawrence: University of Kansas; 1968.
2Peppler RD, Greenwald GS. Effects of unilateral ovariectomy on ovulation and cycle length in 4- and 5-day cycling rats. Am J Anat 1970;127:1-8.
3Biggers JD, Finn CA, McLaren A. Long-term reproductive performance of female mice. I. Effect of removing one ovary. J Reprod Fertil 1962;3:303-12.
4Sengupta P, Chaudhuri P, Bhattacharya K. Screening obesity by direct and derived anthropometric indices with evaluation of physical efficiency among female college students of Kolkata. Ann Med Health Sci Res. In press.
5Peppler RD. Effects of unilateral ovariectomy on follicular development and ovulation in cycling aged rats. Am J Anat 1971;132:423-7.
6Mandl AM, Zuckerman S, Patterson HD. The number of oocytes in ovarian fragments after compensatory hypertrophy. J Endocrinol 1952;8:347-56.
7McLaren A. Regulation of ovulation rate after removal of one ovary in mice. Proc R Soc Lond B Biol Sci 1966;166:316-40.
8Greenwald GS. Quantitative study of follicular development in the ovary of the intact or unilaterally ovariectomized hamster. J Reprod Fertil 1961;2:351-61.
9Morales-Ledesma L, Ramirez DA, Vieyra E, Trujillo A, Chavira A, Cardenas M, et al. Effects of acute unilateral ovariectomy to pre-pubertal rats on steroid hormones secretion and compensatory ovarian responses. Reprod Biol Endocrinol 2011;9:41.
10Finn CA. Increase in length of the uterus at the time of implantation in the mouse. J Reprod Fertil 1968;17:69-74.
11Baker TG, Challoner S, Burgoyne PS. The number of oocytes and the rate of atresia in unilaterally ovariectomized mice up to 8 months after surgery. J Reprod Fertil 1980;60:449-56.
12Sengupta P, Sahoo S. A Cross Sectional Study to Evaluate the Fitness Pattern among the Young Fishermen of Coastal Orissa. Indian J Public Health Res Dev 2013;4:171-5.
13Sengupta P. The laboratory rat: relating its age with human's. Int J Prev Med. In press.
14Welschen R, DuUaart J, DeJong F. Interrelationships between circulating levels of estradiol-17 beta, progesterone, FSH and LH immediately after unilateral ovariectomy in the cyclic rat. Biol Reprod 1978;18:421.
15Chandra A, Sengupta P, Goswami H, Sarkar M. Excessive dietary calcium in the disruption of structural and functional status of adult male reproductive system in rat with possible mechanism. Mol Cell Biochem 2012;364:181-91.
16Chandra A, Sengupta P, Goswami H, Sarkar M. Effects of dietary magnesium on testicular histology, steroidogenesis, spermatogenesis and oxidative stress markers in adult rats. Indian J Exp Biol 2013; 51: 37-47.
17Johnson SK, Smith MF, Elmore RG. Effect on unilateral ovariectomy and injection of bovine follicular fluid on gonadotropin secretion and compensatory ovarian hypertrophy in prepuberal heifers. J Anim Sci 1985;60:1055-60.
18Sengupta P. Environmental and occupational exposure of metals and their role in male reproductive functions. Drug Chem Toxicol 2013;36:353-68.
19Baird DT, Backstrom T, McNeilly AS, Smith SK, Wathen CG. Effect of enucleation of the corpus luteum at different stages of the luteal phase of the human menstrual cycle on subsequent follicular development. J Reprod Fertil 1984;70:615-24.
20Chandra AK, Goswami H, Sengupta P. Dietary calcium induced cytological and biochemical changes in thyroid. Environ Toxicol Pharmacol 2012;34:454-65.
21Sengupta P, Chaudhuri P, Bhattacharya K. Male reproductive health and yoga. Int J Yoga.In press.
22Sengupta P. Health impacts of yoga and pranayama: A state-of-the art review. Int J Prev Med 2012;3:444-58.
23Sengupta P. Challenge of infertility: How protective the yoga therapy is? Ancient Sci Life. In press.