Luteolysis and luteostasis – the tripod of life or death for corpus luteum and its synthesis of progesterone in mammals

Corpus luteum (CL) is a transient organ with primary function of producing progesterone, which is essentially required for establishment and sustainance of pregnancy. Luteolysis and luteostasis are two major events that determine life span of corpus luteum within the anatomical space of the ovary and physiological time frame of oestrous cycle that is designated as oestrus to oestrus in a non-conceptive cycle or oestrus to parturition in a conceptive cycle. During oestrus cycle, corpus luteum usually undergoes degradation and hence, cessation of CL synthesis of progesterone so that the animal could return back to oestrus sequel to removal of progesterone inhibition on the release of the gonadotropins that initiate folliculogenesis and ovulation. During pregnancy, corpus luteum must not regress; rather it must be sustained for continual production of progesterone which is essentially required for establishment and maintainance of pregnancy. Therefore, luteolysis must be abrogated and it is called luteostasis. Abrogation of luteolysis during pregnancy to rescue corpus luteum is initiated via different mechanisms in different mammalian species in a phenomenon called maternal recognition of pregnancy. Luteolysis during pregnancy leads to abortion while failure of luteolysis to occur in a non-conceptive cycle keeps the animal in dioestrus stage of the cycle and non-return to oestrus. Luteolysis and luteostasis are reciprocally connected and represent well-orchestrated mechanisms strictly under hormonal regulation that occur throughout mammalian reproductive life. The molecular mechanisms underlying the two opposing reproductive phenomena are further discussed in this review.