Insight into luteolytic effects of repeated administration of LH in pregnant rats Analysis of cAMP PKA pathway during LH induced luteolysis

Abstract

The Corpus luteum (CL) is a dynamic endocrine structure that develops in the ovary from the remnants of the ovulated follicle and plays a critical role in the control of estrous/menstrual cycle as well as in establishment and maintenance of pregnancy. Its main function is to secrete a steroid hormone progesterone (P4). During non-fertile reproductive cycles, CL undergoes regression but its life span gets extended during fertile cycles including pseudopregnant condition. The growth and function of CL are regulated by luteotropic and luteolytic factors. The luteotropic factors mainly include prolactin, luteinizing hormone (LH), P4 and growth hormone, whereas the luteolytic factors include oxytocin and prostaglandin F2and#945; (PGF2and#945;). LH plays a critical role in the growth and maintenance of CL function in pregnant rats. However, it appears that the effects of LH on CL vary with the stage of pregnancy. Accordingly, it has been observed that LH functions as a luteotropic factor during the first half of pregnancy, but during the second half of pregnancy its luteolytic effects may predominate. While the luteotropic role of LH in several species has been widely accepted and extensively investigated, its luteolytic role has received scant attention. In this work, studies have been carried out to examine the luteolytic actions of LH with a view to elucidate the molecular mechanism/s involved in the initiation of LH-mediated luteolysis in pregnant rats. It has been reported by others that administration of repeated injections of LH leads to initiation of luteolytic events during late pregnancy. In the current studies, the same method has been standardized to initiate luteolysis and to examine the mechanism/s by which repeated administration of LH causes luteolytic effects. Two stages of pregnancy were chosen for the studies; late stage (gestation day 19 to 20) and mid stage (gestation day 8 to 10) of pregnancy...