Histological Characteristics of the Uterine Endometrium and Corpus Luteum during Early Embryogenesis and the Relationship to Embryonic Mortality in the Domestic Cat1

Abstract

Pregnancy rates are low and litter sizes generally small when assisted reproduction techniques are used in gonadotropin-treated felid (cat) species. A prerequisite to determining whether or not abnormal morphological changes in the uterine lumen or corpus luteum (CL) are related to this reproductive failure is the documentation of normal histological kinetics during natural embryogenesis. This study characterized the histological changes of the endometrium and ovarian CL during the early stages of preimplantation embryonic development in the naturally estrous, mated queen. The purpose was to 1) develop a system for dating the cat endometrium and CL of early pregnancy; 2) document the frequency of abnormal uterine and CL history under natural mating conditions; and 3) compare histological traits of queens producing good- vs. poor-quality embryos. Naturally estrous, mated queens were ovariohysterectomized at 64 h (n = 8), 76 h (n = 11), 100 h (n = 8), 124 h (n = 7), 148 h (n = 6), or 480 h (n = 8) after first copulation. Embryos collected from oviductal and uterine flushings were graded for quality, and uteri and ovaries were fixed in formalin. Fixed tissue sections were stained and multiple histological traits described for each uterine (endometrial height, endometrial vacuolation, percentage of glandular cells with subnuclear vacuoles, number of mitoses, nuclear-to-cytoplasmic ratio) and ovarian (presence of tertiary follicles, vacuolation of luteal cell cytoplasm, luteal cell shape) sample. Modest histological changes were observed at each time point, and these were documented in detail. The most prominent modifications occurred at 124 h after first copulation and included thickening of the endometrium, straightening of the glands, increased cytoplasmic vacuolation, and increased epithelial height. Of 15 queens failing to produce good-quality embryos, only 4 expressed unusual histological characteristics; and 3 of 25 queens producing only high-quality embryos exhibited abnormal uterine or CL cellular integrity. Therefore, aberrant histological changes are not primarily responsible for failure of the naturally estrous, mated queen to produce good-quality embryos. Furthermore, a normative database now is available to date the endometrium and CL of early pregnancy and to examine the impact of exogenous gonadotropins and assisted techniques on uterine/CL structure and function.

Endometrial Hyperplasia and Mineralization in Zoo Felids Treated with Melengestrol Acetate Contraceptives

“…Proliferative changes in the endometrium that were typical for stages of the estrous cycle were not considered hyperplasia. 20 Cystic hyperplasia was distinguished from endometrial cysts by the crowding, pseudostratification, and hyperchromasia of glandular epithelium and the involvement of multiple glands. For the purpose of grading, cystic and adenomatous hyperplastic changes were combined to determine the overall cumulative increase in endometrial thickness because these changes were presumed to have a similar effect on fertility.…”

“…Stage of estrous cycle was estimated by glandular length, tortuosity, and epithelial morphology. 20 Uteri with variation in the severity of EH were graded based on the most severe lesion. Adenomyosis was defined as the presence of well-differentiated endometrial glands and stroma in the myometrium discontiguous with but morphologically similar to the endometrium.…”

Indução De Ovulação Com Swab Vaginal Em Gatas Domésticas E Seus Efeitos Sobre a Morfologia Uterina

“…A resposta uterina à crescente estimulação de progesterona ocorre lentamente no início, com apenas algumas mudanças discerníveis às 76 h após a ovulação, tornandose mais notáveis após 100 h (20) . A máxima concentração de progesterona durante a pseudogestação na maioria das gatas domésticas ocorre próximo aos 40 dias pós-ovulação (21) , isto explica as diferenças histológicas observadas nos animais em fase lútea, em que alguns apresentaram maior proliferação e enovelamento glandular que outros, denotando a influência de diferentes níveis sanguíneos de progesterona.…”

“…Células colunares com citoplasma pálido e vacuolizado e glândulas endometriais extensamente espiraladas foram visualizadas em uma gata deste estudo, semelhantes às células observadas 100 h após a cópula (23) e similares em animais no final de diestro (20) . A máxima espiralização e secreção glandular seriam respostas ao aumento no nível da concentração de progesterona (24) .…”

The Normal Genital Tract of the Female California Sea Lion (Zalophus californianus): Cyclic Changes in Histomorphology and Hormone Receptor Distribution

“…Similarly, marked progestational changes have been noted in uterine epithelium of fur seals shortly after ovulation (Craig, 1964). Subnuclear vacuoles are considered indicative of increased secretory activity of endometrial glands and, similar to sea lions, have been noted in fur seals and harbor seals starting in estrus and early diapause (Bigg and Fisher, 1974;Boshier, 1981;Roth et al, 1995).…”