Intragonadal evaluation of sexual steroid hormones during three reproductive events in two species of Peromyscus (Rodentia: Cricetidae)

ABSTRACT

The ovary of sexually mature females involves oogenetic process for follicular development, ovulation, and luteinization (gametogenic function), which in turn relate to stages of the estrous cycle (EC), as well as the production and biotransformation (steroidogenic function) of sexual steroid hormones (SSH) during EC, pregnancy, and lactation. Depending on their concentrations, SSH play different functions to elicit such reproductive events, but little is known about this in free-living wild species. Here we used ELISA to assess intraovarian concentrations of progesterone, androstenedione, testosterone, and estradiol, during EC, pregnancy, and lactation in wild adult females of Peromyscus melanotis J.A. Allen & Chapman, 1897 and Peromyscus difficilis (J.A. Allen, 1891), immediately after their capture. Results of intraspecific ANOVA showed statistical differences between concentrations of different SSH in the same reproductive stage or event and between the stages or events for each SSH, according to the steroidogenic Δ ₄ pathway. Although ANOVA analyses showed no interspecific differences of the same SSH in the same event, except for more testosterone in P. melanotis during heat, profiles of production curves suggest intraspecific peculiarities and interspecific differences that need to be further investigated. Our results contribute to physiological-endocrine evidence during the four stages of EC and first and second part of pregnancy in species of Peromyscus, and are the first documentation for overall lactation in wild rodents.

KEY WORDS:
Estrous cycle; female mice; lactation; ovarian function; pregnancy; sexual steroid hormones; rodents