LUTEAL FUNCTION - THE ESTROUS-CYCLE AND EARLY-PREGNANCY

A number of morphological and biochemical changes occur as the cells o f the recently ovulated follicle luteinize and develop into a function al CL. There are two distinct steroidogenic luteal cell types that app ear to differentiate from thecal and granulosal cells in the follicle. The control of progesterone secretion is quite different in the two c ell types. Prostaglandin F-2 alpha (PGF(2 alpha)) is the primary luteo lytic hormone in most mammals. PGF(2 alpha) appears to exert its antis teroidogenic actions via activation of the protein kinase C system, wh ile its cytotoxic effects appear to be mediated via a dramatic increas e in intracellular levels of free calcium. The mechanisms involved in maternal recognition of pregnancy are very diverse between species and may involve direct luteotropic stimulation of the CL, reduced uterine secretion of PGF(2 alpha), and/or inhibition of actions of PGF(2 alph a) at the level of the CL.