Reproductive Failure Associated with Cystic Rete Ovarii in Guinea Pigs

Vet. Pathol. 24335-339 (1987) Reproductive Failure Associated with Cystic Rete Ovarii in Guinea Pigs L. S. F. Keller, J. W. Griffith, and C. M. Lang The Pennsylvania State University, The Milton S. Hershey Medical Center, and Department of Comparative Medicine, Hershey, PA Abstract. Cystic ovaries were found at necropsy in 54 of 7 1 (76%) female guinea pigs between 18 and 60 months of age. Histologic appearance and location of the cysts within the ovary were consistent with cystic rete ovarii. Microscopic appearance of the large ovarian cysts suggested reproductive performance in these guinea pigs should be compromised. Breeding records indicated that fertility was markedly reduced in affected females over fifteen months of age. Cystic endometrial hyperplasia, mucometra, endometritis in appropriate placental tissue, or fibroleiomyomas were seen in 21 of 54 (39%) guinea pigs with cystic ovaries, but in only one of 17 (6%) guinea pigs without cystic ovaries. Ovarian cysts are common in aged rats,22 guinea pigs,24.26.33 cattle,27 and women.25 These cysts are usually derived from ovarian follicles, corpora lutea, ovarian surface epithelium, remnants of the mesonephric and paramesonephric ducts, or rete ovarii.9.17.22.24-27.31.33 The rete ovarii is a homologue of the rete testis and has been described as a normal structure in numerous species of mammal^.^^.^^ The rete system in most mammals consists of three parts: 1) the extraovarian rete, 2) the connecting rete, and 3) the intraovarian ~ete.~ The intraovarian rete tubules are lined by cuboidal epithelium while the connecting and extraovarian rete ovarii are lined by ciliated columnar epithelium.8 All rete cells contain dense rete bodies that resemble microperoxisomes'8~'9 and peroxisomes.' Cystic changes in the mammalian ovary need to be studied since they may cause infertility in aging laboratory and domestic animals and in Cystic ovaries were diagnosed at necropsy in female guinea pigs from a single breeding colony with low reproductive performance. The purpose of this report is to describe the ovarian gross and microscopic appearance, the incidence, age distribution, and reproductive performance of guinea pigs with cystic ovaries. Materials and Methods All of the animals were from a closed colony established in 1969 with 25 Abyssinian guinea pigs to study spontaneous diabetes mellitus. Due to declining reproduction, some Hartley guinea pigs were introduced into the colony to increase reproductive vigor from crossbreeding. These guinea pigs were housed in stainless steel cages at 72 -t 2 F, 50% f 20% relative humidity with a 12 hour light : dark cycle without twilight. They were fed commercial guinea pig chow, sup- 335 plemented with kale twice per week, and provided with water ad libitum. Guinea pigs of this study died of various causes or were euthanized because of severe health problems. At necropsy all organs were completely and systematically examined according to a written protocol. The cystic ovaries were sectioned through the cyst wall and thickest part of the parenchyma in an attempt to identify functional ovarian tissue. Tissues were collected from each organ, fixed in 10% neutral buffered formalin, and processed by standard histological methods. Is Written necropsy reports of female guinea pigs were reviewed to determine the incidence of cystic ovaries. Reproduction records were maintained on females in the colony who were bred at least once. Inbreeding was practiced whenever possible within certain family lines, and in many cases breeding was accomplished by placing one male and one female together until 24 hours postpartum so the female would be rebred as soon as possible. In some cases one male and one female or one male and two females were paired for 30 days. Oral glucose tolerance test values and blood and urine glucose values were recorded for the guinea pigs at specified intervals. The clinical diabetic status was determined using previously published methods. l4 Results Cystic ovaries were diagnosed in 54 of 71 (76%) female guinea pigs at necropsy. Smaller ovarian cysts were an incidental finding; however, larger cysts could be identified as an abdominal mass by palpation. Most guinea pigs with cystic ovaries were between 2 and 4 years old (Fig. 1). Both ovaries were cystic in 44 of 54 (81.5%) guinea pigs. In guinea pigs where only one ovary contained cysts, the right ovary was affected in eight of ten (80%) cases. Cysts ranged from 0.5 cm to 7 cm in diameter. The sizes of the cysts vaned among animals within the same age group and between age

336 Keller, Griffith, and Lang UI 16 14 12.P 10 n m.- g 8 3 0 % 6 k p 4 f 2 2 Fx\sIx \N\N \W 1 4 2 2% 3 3% 4 4% 5 Age (years) Guinea Pigs with Cystic Ovaries Fig. 1. Age distribution and incidence ofguinea pigs with cystic ovaries. groups. The average size of the cysts increased with advancing age (Table 1). Forty-eight of 54 (85%) of the affected animals had cystic ovaries visible by both gross and microscopic examination. The ovarian cysts observed in most of the guinea pigs were multilocular, clear, fluid-filled dilated structures (Fig. 2). The diameter and number of cysts per ovary varied. Sectioning and histologic examination revealed that 80 to 90% of the ovarian parenchyma was replaced by epithelial lined cysts (Fig. 3). The cysts were centered in the hilar region of the ovary and were lined with flattened, cuboidal, or columnar epithelial cells, some of which contained cilia (Fig. 4). Focal papillary hyperplasia was noted in cysts from 13 of 54 (24%) animals. Twelve of the 13 (92.3%) guinea pigs with papillary hyperplasia were more than 18 months old. Eight of the 13 (61.5%) guinea pigs with papillary hyperplasia in the cysts and 21 of 54 (39%) guinea pigs with cystic ovaries had extraovarian reproduction-related lesions (Table 2). One ovary contained a large teratoma. A detailed description of these lesions is beyond the scope of this paper. The average age of guinea pigs with cystic ovaries and other concurrent reproductive lesions was 38.9 months while guinea pigs with no cystic ovaries averaged 30.4 months old. Analysis of reproductive records revealed that fertility was similar between guinea pigs with and without cystic ovaries up to 15 months of age. However, after 15 months of age there was a marked decrease in the proportion of affected guinea pigs delivering as compared to guinea pigs without cystic ovaries (Table 3). Litter size did not differ significantly between the groups nor did diabetic status. Approximately 50% of guinea Table 1. Approximate age and average cyst size in guinea pigs with cystic ovaries. Number of Age Average Cyst Size Affected Animals* _ ~ ~ 18 months Microscopic 8 24 months 1.08 cm 3 30 months 2.29 cm 7 36 months 2.50 cm 5 42 months 2.90 cm 5 48 months 3.38 cm 13 60 months 3.58 cm 6 * Cyst size was not recorded in seven guinea pigs. pigs in each group were classified as diabetic. No correlation could be found between the reproductive lesions described and lesions seen in any of the endocrine organs. Discussion Five types of cysts can be found in the ovaries of various laboratory animal species and are classified according to tissue of origin within the ovary, and include: 1) follicular cysts, 2) luteal cysts, 3) inclusion cysts, 4) parovarian cysts, and 5) cysts of rete ovarii. Follicular cysts are derived from secondary follicles that fail to ovulate or undergo atresia and are the most common. The follicular cysts seen in cattle, swine, and aged rats frequently secrete estrogen in normal or excessive amounts leading to irregular estrous cycles, persistent estrus, and infertility. 13,22,23 Although the pathogenesis of follicular cysts is uncertain, investigators believe that luteinking hormone levels are not sufficiently elevated to luteinize the follicle, thus creating a mature follicle that becomes cystic. Histologically, follicular cysts are large with a thin wall made up of several layers of granulosa cells, have an increased amount of fluid, and do not contain an oocyte. Luteal cysts are corpora lutea that develop a central cavity and fail to regress. These cysts persist and serve as a progesterone source. The pathogenesis of luteal cysts is unknown but may involve an abnormality in hypothalamic-hypophyseal function or a failure of the endometrium to produce a luteolytic substance.13 Microscopically, the cystic corpus luteum has a wall made up of large, polyhedral granuloluteal cells with abundant eosinophilic, foamy cytoplasm. These cells are surrounded by smaller thecal-luteal cells that are derived from the ovarian stroma. Inclusion cysts arise from segments of the ovarian surface epithelium. They are variable in size and consist of a unilocular, fluid-filled space which is usually lined by a single layer of flattened epithelial cells. In-

Cystic Ovaries in Guinea Pigs 331 Fig. 2. Urogenital tract from guinea pig with cystic ovaries. The right ovary (arrowheads) is enlarged and cystic. Fig. 3. Rete cysts. Remaining ovarian parenchyma (p) compressed laterally. Bar = 225 pm. clusion cysts cause pressure atrophy of adjacent ovarian parenchyma, do not routinely secrete any hormones, and are commonly found in the mare.11.31 Parovarian cysts are vestigial remnants of the mesonephric and paramesonephric ducts that give rise to vesicular structures located in the mesosalpinx or mesovarium. During ovarian development, cords of epithelial and primordial germ cells develop and grow in the stroma of the ovarian blastema. In the hilar region of the ovary the cords that are derived from the mesonephric tubules are devoid of germ cells and are known as rete ovarii.i6 Cystic rete ovarii have been previously reported in guinea heifers, I cats,8 sheep,io swine,32 prairie deer mice,24 a camel,28 dogs,30 and women.25 Hyperplasia and metaplasia of the rete ovarii have also been described in aging women.25 Cysts of the rete ovarii in guinea pigs are usually concentrated in the hilar region of the ovary and are in continuity with one another. The rete ovarii of young animals may contain dilated regions lined by epithelium similar to that in larger cysts of older animals.24 A previous study found no evidence to indicate that Table 2. Extraovarian lesions associated with cystic ovaries in guinea pigs. Guinea pigs Guinea Pigs Without Extraovarian Lesion with Cystic Cystic Ovaries Ovaries Uterine or cervical leiomyoma 6/54 0/17 Cystic endometrial hyperplasia 7/54 0/17 Endometritis 3/54 1/17 Mucometra 2/54 0/17 Inappropriate placental tissue 3/54 0/17 Fig. 4. Ciliated epithelium which lines portions of rete cysts. Bar = 20 pm.

338 Keller, Griffil :h, and Lang Table 3. Age range and fertility of guinea pigs with and without cystic ovaries (C.O.). Num- Num- Percent ber Deliv- Deliv- Bred ered ered Under 15 months age with C.O. 50 24 48% Under 15 months age without C.O. 13 6 46% Over 15 months age with C.O. 30 4 13% Over 15 months age without C.O. 6 3 50% guinea pigs with cystic ovaries had altered estrous cycles or reprod~ction.~~ However, in this study a reduction in fertility was seen in guinea pigs with ovarian cysts as compared to unaffected animals over 15 months of age, suggesting that cystic ovaries may be a cause of infertility in older guinea pigs. From this, one may speculate that the cysts progressively enlarge with age and eventually destroy normal ovarian function. The pathogenesis of rete ovarii cysts has been postulated to be related to the secretory activity of the cells lining the rete tubules. The tubules apparently have no outlet for the fluid accumulation and expand into cysts which cause pressure atrophy of the adjacent ovarian parenchyma.8 A hormone may activate these cells to and excessive secretions may result in the cyst development. Secretory activity in the rete tubules has been reported in the cat,8 heifer, ferret,5 mink,5 and dog. Periodic acid-schiff (PAS)-positive cytoplasmic granules have been described in the connecting and extraovarian rete, and PAS-positive secretions have been seen in the tubule lumens when meiosis begin^.^ Investigators have suggested that estrogens in the feed may cause ovarian cysts and infertility in guinea pigs but no cause-effect relationship has been proved.26 Similarly, endometrial gland hyperplasia has been reported in swine and laboratory rodents that accidentally received an excessive amount of estrogens in their feed. I I One investigator considered the rete ovarii an ontogenic male remnant with no functional importance in the female.25 However, various studies have suggested that the rete ovarii system is essential for the onset of meiosis and ovarian development in many species. Researchers do not know if the rete ovarii influence germ cells by direct cellular contact or by means of a secretory component. 6 Some authors have suggested that the dense rete bodies present in rete cells may influence the regulation of steroid synthesis2 or may be involved in lipid metabolism.20 Cystic dilatation of the rete ovarii in guinea pigs appears to be a function of aging in this study, but very small rete ovarian cysts have been reported in guinea pigs as young as a few months of age.24 More work is necessary to investigate the pathogenesis of rete ovarii cysts, to determine the fluid composition within the cysts, and to determine if there is a relationship between these cysts and other reproductive tract lesions observed in these guinea pigs. Acknowledgement Supported in part by grants RR00469 and RR07006 from the Division of Research Resources, National Institutes of Health, Bethesda, Maryland. 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Vet Pathol21:304-307, 1984 9 Gustafsson BK Testicular and ovarian pathology in swine. In: Current Therapy in Theriogenology, ed. Morrow DA, pp. 1099-1 103. WB Saunders Co, Philadelphia, 1980 10 Hadek R: Morphological and histochemical study on the ovary ofthe sheep. Am J Vet Res 19:873-881, 1958 11 Jones TC, Hunt RD: The genital system. In: Veterinary Pathology, 5th ed., pp. 1512-1515. Lea and Febiger, Philadelphia, 1983 12 Julian CG, Goss J, Blanchard K, et al.: Biologic behavior of primary ovarian malignancy. Obstet Gynecol44: 873-884, 1974 13 King NW: The reproductive tract. In: Pathology of Laboratory Animals, ed. Benirschke K, Garner FM, Jones TC, pp. 524-526. Springer-Verlag, New York, 1978 14 Lang CM, Munger BC: Diabetes mellitus in the guinea pig. Diabetes 25434443, 1976 15 Luna LG: Manual of Histologic Staining Methods of the Armed Forces Institute of Pathology. 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Cystic Ovaries in Guinea Pigs 339 19 Novikoff AB, Novikoff PM, Davies C, et al.: Studies on microperoxisomes. V. Are microperoxisomes ubiquitous in mammalian cells? J Histochem Cytochem 21: 737-755, 1973 20 Novikoff AB, Shin WY: The endoplasmic reticulum in the Golgi zone and its relations to microbodies, Golgi apparatus and autophagic vacuoles in rat liver cells. J Microsc 3: 187-206, 1964 21 O Shea JD: Histochemical observation on mucin secretion by subsurface epithelial structures in the canine ovary. J Morphol120:347-358, 1966 22 Peluso J J, England-Charlesworth C Formation of ovarian cysts in aged irregularly cycling rats. Biol Reprod 24: 1183-1190, 1981 23 Peluso JJ, Steger RW, Huang J, et al.: Pattern of follicular growth and steroidogenesis in the ovary of aging cycling rats. Exp Aging Res 5319-333, 1979 24 Quattropani SL: Serous cysts of the aging guinea pig. I. Light microscopy and origin. Anat Rec 188:351-360, 1977 25 Sauramo H: Development, occurrence, function and pathology of the rete ovarii. Acta Obstet Gynecol Scand 33:29-46, 1954 26 Schoenbaum M, Klopfer U: Cystic changes in the ovaries of guinea pigs. Refuah Vet 26: 118-121, 1969 27 Sequin B: Ovarian cysts in dairy cows. In: Current Therapy in Theriogenology, ed. Morrow DA, pp. 199-204. WB Saunders Co, Philadelphia, 1980 28 Shehata R: Medullary tubes in the ovary of the camel and other mammals. Vet Rec 76:750-753, 1964 29 Talbert GB: Effect of aging of the ovaries and female gametes on reproductive capacity. In: The Aging Reproductive System, ed. Schneider EL, pp. 59-83. Raven Press, New York, 1978 30 Tanaka K: Morphological study on the canine ovary. Jpn J Vet Res 10:80-81, 1962 3 1 Vaughan JT: Surgery of the equine reproductive system. In: Current Therapy in Theriogenology, ed. Morrow DA, pp. 783-824. WB Saunders Co, Philadelphia, 1980 32 Wilkerson WV The rete ovarii as a normal structure of the adult mammalian ovary. Anat Rec 26:75-78, 1923 33 Young WC, Dempsey EW, Myers HI, et al.: The ovarian condition and sexual behavior in the female guinea pig. Am J Anat 63:457-483, 1938 Request reprints from Dr. Lynn S. F. Keller, Department of Comparative Medicine, The M. S. Hershey Medical Center, Pennsylvania State University, PO Box 850, Hershey, PA 17033 (USA).