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The steroid hormones progesterone (P.), and testosterone (T.) were radio-immunologically determined in 108 medium samples, following co-culturing of bovine oocytes with granulosa cells. P. and T. values recorded from a control group were lower with significance than those recorded from co-culturing groups, that is 72 +/- 21 ng/ml and 264 +/- 84 pg/ml as compared to 208 +/- 138 ng/ml and 2,168 +/- 1,595 pg/ml in the oocyte plus fresh granulosa cell co-culturing group as well as 364 +/- 215 ng/ml and 825 +/- 233 pg/ml in the oocyte plus pre-incubated granulosa cell co-culturing group. These rises were accompanied by decline in maturation rate, increase in oocyte degeneration, and rises in the rates of fertilisation and segmentation.

Within the atretic follicles of Myxine glutinosa neither 3 beta-hydroxysteroiddehydrogenase, being in close relation to steroid production, nor cholesterol was found. The proofs of aryl sulphatase activity and acid phosphatase activity gave positive results in all cell types of the atretic follicle. A very strong reaction was observed in the granulosa cells and the migrating cells of the atretic follicle of the closed involutionary type.

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.

In a first paper, the structural and functional relationship of granulosa and theca of follicles during early development stages was reported. On the special question of whether and from which moment these two tissue formations are involved in the steroidbiosynthesis, our electronmicroscopic examinations have given a further insight to this. Neither the granulosa nor the theca folliculi of primordial, primary and secondary follicles show definite morphologic submicroscopic criteria of the steriodbiosynthesis. In the resting tertiary follicle, the electronmicroscopy defines the theca cells as steroidbiosynthetic active cells, whereas the granulosa cells of this stages of follicle demonstrate the morphologic characteristics of protein-synthetic active cells. Our, under physiological conditions, systematically conducted light and electronmicroscopic studies of preovulatory and freshly ruptured follicles showed remarkable structural changes in the granulosa, as well as in the theca folliculi. For the follicle granulosa cells of the preovulatory follicle, the studies could demonstrate a structural transformation process of proteinsynthetic active to steroidbiosynthetic active cells. This transformation process can be seen in the nucleus. Especially recognizable is the continuous change from rough to smooth endoplasmatic reticulum in the cytoplasm of most of the follicle granulosa cells, which apart from that, often displayed whorle-like formations. Furthermore, we noticed striking changes of the paraplasmatic structures, especially of the fat, present in various stages in the cytoplasm of the follicle granulosa cells. We also noticed large mitochondria, which showed a lot of vesicular cristae. Numerous existing Golgi-fields contained many little homogenous fat-like droplets, which were surrounded by a thin osmiophilic membrane. This recognizable transformation process of the proteinsynthetic active granulosa cells to the steroid cells is quite completed in freshly ruptured follicles, according to our examinations. Although the theca cells have already been defined submicroscopically in the resting tertiary follicle as steroidbiosynthetic active cells, we see in this cellgroup in the preovulatory, as well as in the freshly ruptured follicle a remarkable conspicuous size-increase of the mitochondria. Apart from that, there are wide areas which are solely occupied by smooth endoplasmatic reticulum, whereas other structures, for example fat, are scarely seen. As our examinations have shown, there is a close relationship between the transformation process in the granulosa and the theca of preovulatory follicles and the theca of preovulatory follicles that, the increasing concentration of progesteron in serum, which begins prior to the ovulation can be regarded as a product of the follicle granulosa cells being transformed to steroid cells.