Hormonal control of the asymmetric uterus of the bat Molossus molossus during pregnancy and lactation: Emphasis on progesterone and estradiol.

Molossus molossus is an important species of Neotropical insectivorous bat of the family Molossidae. Despite its wide distribution, representativeness, and ecological importance, there are no detailed studies regarding the hormonal control of the female reproductive organs of this species, which presents accentuated morphofunctional asymmetry, with dextro-dominance. Thus, the present study aimed to evaluate the variations in hormone serum levels and in uterine hormonal control of M. molossus during its different reproductive phases, with an emphasis on estradiol and progesterone. Twenty sexually adult females were divided into four sample groups according to the reproductive status - non-reproductive, early pregnancy, late pregnancy and lactating - and subjected to histological, hormonal, and immunohistochemical analysis. The results showed that the uterine dextro-dominance asymmetry of M. molossus is strongly regulated and maintained by the interaction/cross-talk between estradiol and progesterone serum levels with their respective uterine receptors. The right uterine horn presents significantly higher estrogen receptor α and progesterone receptor expression and also greater proliferative activity in the endometrium than the left horn, which favors embryo implantation and development. Significant increases in the estradiol and progesterone serum levels are needed to regulate early pregnancy. The rapid formation of the diffuse portion of the placenta is essential to sustain the high demand for progesterone at the beginning of pregnancy, while the principal portion is not yet formed. Estrogen receptor α and progesterone receptor expression appear to be synchronized to coordinate most of the processes that occur within the uterus of M. molossus throughout the reproductive cycle.