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

Abstract

Changes in reproductive tract histomorphology, and estrogen (ERa) and progesterone receptor (PR) expression throughout the breeding cycle were evaluated in free-ranging stranded female California sea lions (Zalophus californianus). Hormone receptor expression in the ovaries, uterus, cervix, and vagina was evaluated using an immunohistochemical technique with monoclonal antibodies. During a large portion of the cycle, ovaries contained both a corpora lutea (CL) and follicles in varying stages of development. In the periods of pupping and estrus during June and July, and in the spring morphologic features of the endometrium suggested estrogen influence. There were areas of squamous differentiation in the pseudostratified columnar epithelium of the cervix and vagina in some animals during estrus and in the spring. Estrogen receptor immunohistochemical scores were highest during pupping and estrus and in the spring and lowest during embryonic diapause. Cyclic changes in uterine PR expression throughout the cycle were minimal. Both ERa and PR were expressed in epithelial and stromal cells throughout the cervix and vagina, however, receptor expression was typically higher in the stroma. Stromal cell hormone receptors may play an important role in epithelial responses to circulating sex hormones. The results of this investigation add to the general knowledge of California sea lion reproduction and establish baseline information on reproductive tract hormone receptors that will aid in determining the factors involved in urogenital cancer development in sea lions.

Embryonic diapause: development on hold

“…Semiquantitative analysis by immunohistological staining suggests that both are substantially lower in the endometrium during diapause, relative to post-implantation gestation. No variation was evident in progesterone receptor abundance in the surface and glandular epithelium between diapause and later gestation in this species (Colegrove et al, 2009). Clearly, further investigation of steroid receptors during gestation and diapause in carnivores is warranted.…”

“…The same authors demonstrated progesterone receptors to be present in the post-implantation uterus, but no comparisons between diapause and later gestation were made. Progesterone receptors, along with both ESR1 and ESR2 are present in the uterus of the California sea lion (Zalophus calforianus), a pinniped carnivore (Colegrove et al, 2009). Semiquantitative analysis by immunohistological staining suggests that both are substantially lower in the endometrium during diapause, relative to post-implantation gestation.…”

Genital morphology of the male South American fur seal (Arctocephalus australis) and biological implications

“…The relationship between morphology and seasonal functionality of the reproductive organs in the Otariidea family has been scientifically demonstrated (Colegrove et al 2009a, Colegrove et al 2009b. Based on the possibility that the anatomy of male genital organs relates to the environment and influences reproductive success and conservation status of the species, we hypothesize that special features found in the morphology of A. australis genital organs are related to the unique annual mating season.…”

Ectopic pregnancy with associated gestational choriocarcinoma in a California sea lion (Zalophus californianus)

“…The main differential diagnosis for this tumor was California sea lion urogenital carcinoma. However, the pattern of growth and cellular morphology were distinctly different from any of the patterns described for that well-characterized entity (Gulland et al 1996, Colegrove et al 2009a. Additionally, no neoplastic transformation was seen grossly or histologically in the lower urinary or genital tracts, which are the usual primary sites of the urogenital carcinoma.…”