Luteotropic and luteolytic responsiveness of ovine luteal cells in long-term culture

Isolation of granulosa-like cells from the bovine secretory corpus luteum and their characterization in long-term culture

BACKGROUND

The isolation of cells termed type 5 from the bovine corpus luteum was recently reported. Since these cells were reminiscent of immature granulosa cells, their morphological and functional relationship requires further investigation in view of the novel concept of corpus luteum growth. It suggests that putative stem cells of unknown origin supply the pool of small luteal cells.

METHODS

Bovine corpora lutea were mechanically dispersed, cell suspensions separated over a Percoll density gradient, and type 5 cells purified by colony transfer. Granulosa cells were harvested from small-sized antral follicles. Observations were carried out at the light and electron microscopical level. 3 beta-Hydroxy-steroid-dehydrogenase was localized histochemically in addition to intracellular lipid droplets stained with nile red. Immunolocalization was used to study Factor VIII antigen presence, the architecture of the cytoskeleton, as well as the occurrence of neuronal cell adhesion molecules, and of neuronal cadherin-like molecules. The uptake of acetylated low density lipoprotein was examined. As for progesterone concentration, cells were seeded at low density on day zero. Cell numbers and progesterone levels of supernatants were determined on day 10 in culture.

RESULTS AND CONCLUSIONS

Type 5 cells behaved morphologically like immature granulosa cells, yet the total cell number and the progesterone concentration differed for type 5 cells compared to granulosa cells. The addition of LH had no influence on the progesterone concentration as seen for either type 5 cells or for granulosa cells. It is concluded that type 5 cells, which were originally mistaken for microvascular endothelial cells, display similarities with immature granulosa cells. Type 5 cells may play a role in renewal of luteal cells.

Evaluation of the physiological value of porcine luteal cells isolated in various stages of the luteal phase: Tissue culture approach

Porcine luteal cells were collected from corpora lutea in four different stages of the luteal phase and cultured as monolayers. Progesterone (P4) secretion was assayed using radioimmunoassays (Gregoraszczuk, 1991). Luteal cells cultured from porcine corpora lutea collected in the early luteal phase maintained steroidogenic capacity for 6 days in culture until the time comparable with midluteal corpora lutea. Luteal cells collected from mature and regressing corpora lutea did not dedifferentiate during 2 days of culture. After this time secretion of progesterone decreased to undetectable amounts characteristic of old corpora lutea. The regression in the culture progressed. The results demonstrate that the degree of the decline of progesterone depends on the type of corpus luteum, which is connected to particular time intervals of the luteal phase. Before starting experiments it is necessary to take into consideration the stage of the luteal phase from which the material is collected for culture. This study provides evidence that long term culture is useful for investigating a variety of aspects of luteal function only if cells are collected in the early luteal phase. Short term culture is suitable for investigation of cells collected from mid and late luteal phase. Regulation of luteal function is dependent on stage of the luteal phase.