Variations of serum estradiol and progesterone levels during consecutive reproductive states in Mongolian gerbils (Meriones unguiculatus).

Serum estradiol (E2) and progesterone (P4) levels were measured by chemiluminescence immunoassay (CLIA) during consecutive reproductive states in Mongolian gerbils. The results show that E2 and P4 levels throughout the estrous cycle in Mongolian gerbils peaked at proestrus and estrus, respectively. During gestation in primiparous and multiparous gerbils, E2 levels reached a small peak on day 6 and a maximum peak on day 21, followed by a slight decline until parturition. Thereafter, they dropped sharply during the first 3 days of lactation and remained stable until lactation ended. P4 levels reached a peak on day 12 during gestation in primiparous gerbils, while they peaked on day 6 in multiparous gerbils. The levels of P4 then decreased until parturition. During lactation, P4 levels peaked on day 9 in primiparous gerbils, while they peaked on day 6 in multiparous gerbils, and then the levels declined gradually until lactation ended. The findings suggest that the variations of E2 levels during the estrous cycle, gestation and lactation in Mongolian gerbils are similar to those observed in rats and mice. Changes in E2 levels during different reproductive states were the same in the primiparous and multiparous gerbils, but the variations in P4 levels did not display this tendency. Changing patterns of E2 and P4 levels are suitable for the reproductive stages of Mongolian gerbils.