Endometrial cytosolic progesterone receptor dynamics during estrous cycle in buffalo (Bubalus bubalis)

Successful establishment and maintenance of pregnancy in buffalo (Bubalus bubalis) require precise synchrony between preimplantation embryo development and endometrial preparation. This coordination is primarily regulated by the ovarian steroid hormones, progesterone and estrogen through their respective receptors, which control uterine receptivity and establish a suitable environment for embryo survival. Despite their pivotal role in reproduction, information on cyclic changes in endometrial progesterone receptor (PR) concentrations in buffalo is limited. Therefore, the present study investigated variations in endometrial cytosolic PR concentrations during different stages of the estrous cycle. Reproductive tracts were collected from a local abattoir, and estrous cycle stages were classified according to corpus luteum morphology and plasma progesterone concentrations. Endometrial cytosolic fractions were prepared, and PR concentrations were quantified using radioligand binding assays. Cytosolic PR concentrations were lowest during the early luteal phase, increased progressively through the mid-luteal phase, and reached maximum levels during the late luteal phase associated with luteal regression. These stage-specific changes demonstrate that ovarian steroids dynamically regulate uterine PR availability throughout the estrous cycle, thereby modulating endometrial function and uterine receptivity. The findings provide valuable insights into endocrine regulation of the buffalo uterus and may contribute to a better understanding of the mechanisms underlying the high incidence of early embryonic loss in this economically important species.