THE PHYSIOLOGY OF THE OVARY - MATURATION OF OVARIAN GRANULOSA-CELLS AND A NOVEL ROLE FOR ANTIOXIDANTS IN THE CORPUS-LUTEUM

During folliculogenesis the granulosa cells divide whilst in contact w ith each other, and so exhibit some of the characteristics of stem cel ls. In vitro we have shown that bovine granulosa cells from 3-7 mm fol licles, like stem cells, divide without the need for a substratum, and produce colonies of cells. Growth factors, bFGF and IGF's, stimulate their division. These cells secrete and assemble a basal lamina, sugge sting that the follicular basal lamina is produced by the granulosa ce lls. They have the morphological characteristics of follicular granulo sa cells. Thus this system is ideal for studying the functions of imma ture granulosa cells because the cells do not spontaneously differenti ate or luteinize into luteal cells, as occurs in culture on a substrat um. On differentiation into luteal cells in vivo the cells express the steroidogenic enzymes for progesterone production and accumulate beta -carotene. During culture of bovine luteal cells we observed that a pr oportion of the steroidogenic enzyme cholesterol side-chain cleavage c ytochrome P450 enzyme became chemically cross-linked to its electron d onor, adrenodoxin. P450 enzymes produce oxygen free radicals and oxyge n free radicals can cause cross-linking between proteins in close prox imity. Cell protect against this damage by the use of antioxidant vita mins. Repleting the cultured luteal cells with beta-carotene reduced t he amount of cross-linking. We conclude that the high levels of beta-c arotene in corpora lutea are to protect against damage due to oxygen f ree radicals generated in the course of progesterone synthesis.