The rodent corpus luteum

ACCIALINI PAULA; HERNANDEZ FATIMA; ABRAMOVICH DALHIA; TESONE MARTA

The life cycle of the corpus luteum

Spinger

Año: 2017; p. 117 - 132

Rats and mice have not only a short lifespan but also a poor offspring survival. For these reasons, rodents have evolved a reproductive system that is able to maximize the number of offspring per time period. To achieve this goal, rodents developed different strategies that range from divergences in follicular development to divergences in corpus luteum physiology. Moreover, the corpus luteum is one of the points that present more differences among species and rodents have particular features in corpus luteum formation, function and regression that make them different from other groups of mammals. According to corpus luteum lifespan and steroidogenic capacity, the different types of mammalian corpora lutea can be classified in four groups. Corpus luteum of the pregnancy that is present in all species, corpus luteum of the cycle, corpus luteum of the lactation and corpus luteum of the pseudopregnancy. Rodents are the only mammals that present the four types of corpus luteum. Rodents belong to the species that have an ultrashort lifespan of the corpus luteum. The estrous cycle in these mammals lasts 4 to 5 days and lacks a true luteal phase. The follicular cells that remain in the ovary after ovulation take some of the features of luteal cells. However, the resulting corpus luteum is not well developed and is considered not functional because it is not able to secrete enough quantities of progesterone to stimulate a uterine response to implantation signal. Moreover, progesterone is rapidly converted to its inactive analogue 20-hydroxyprogesterone. This lack of a fully secretory corpus luteum allows the occurrence of follicular recruitment and ovulation within a few days. Cervical stimulation during estrous without pregnancy, results in a condition called pseudopregnancy that in fact does not exist in nature because in wild conditions mating always results in pregnancy. Pseudopregnancy is characterized by a formation of a true corpus luteum that secretes progesterone for 12 to 14 days. In the case of pregnancy, progesterone is required throughout the whole gestation. At the end of gestation the corpus luteum regresses and the drop in progesterone levels is an important signal that triggers parturition.In the present chapter we review the characteristic of the rodent corpus luteum, the formation process, the regulation of its function and the mechanisms that regulate its regression, emphasizing the similarities and differences among species.