[The control of the development of the corpus luteum and its maintenance in cattle]

During its limited lifespan the bovine corpus luteum secretes large amounts of progesterone. The function of lipoproteins in maintaining corpus luteum activity and the role of high density lipoprotein (HDL) in development of the corpus luteum have been examined using luteal and granulosa cell cultures. Results show that luteal cells require lipoproteins for steroidogenesis, low density lipoprotein (LDL) being 3.5 times more potent than HDL. It is likely, however, that HDL is of more importance in vivo since concentrations in the blood are considerably higher than those of LDL. The results also show that luteal cells may be maintained in culture in the presence of HDL. Granulosa cells in culture show an increasing basal progesterone production. In addition they respond to HDL and dibutyryl cyclic AMP with a marked increase in progesterone production. This data suggests that granulosa cells in pre-ovulatory follicles are prevented from responding to HDL, perhaps through lack of receptors. Luteinization must allow granulosa cells to respond to HDL and, in addition, it provides an increase in availability of both HDL and LDL through the marked angiogenesis occurring at this time.