In Vitro Differentiation of Bovine Theca and Granulosa Cells into Small and Large Luteal-like Cells: Morphological and Functional Characteristics1

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Abstract
This study was undertaken to investigate whether bovine granulosa and theca interna cells could be luteinized in vitro into luteal-like cells. Granulosa and theca cells were cultured for 9 days in the presence of forskolin (10 .mu.M), insulin (2 .mu.g/ml), insulin-like growth factor I (100 ng/ml), or a combination of these agents. During the first days of culture, granulosa and theca cells secreted estradiol and androstenedione, respectively; progesterone rose only after 3-5 days in culture and reached a maximum on the ninth day of culture. Cells incubated in the presence of forskolin plus insulin exhibited morphological and functional characteristics of luteal cells isolated from the corpus luteum. It was found that cell diameter, basal and stimulated porgesterone secretion, and pattern of cell replication for both cell types were comparable to those of luteal cells. Numerous lipid droplets and intensified mitochondrial adrenodoxin staining also indicated active steroidogenesis in luteinized cells. After 9 days in culture, stimulants were withdrawan, and the culture proceeded in basal medium for an additional 5 days; elevated progesterone that were maintained by luteinized granulosa cells (LGC), whereas in contrast a dramatic drop in progesterone production was observed in luteinized theca cells (LTC). On Day 9, cells were challenged for 3 h with LH (10 ng/ml), forskolin (10 .mu.M), or cholera toxin (100 ng/ml), resulting in a 4-fold; the same treatments failed to stimulate progesterone in LGC. These results demonstrate the regulation demonstrate that regulation of steroidogenesis in LGC and LCT appears to be different: LTC are highly dependent on and responsive to cAMP elevating agents. LGC, on the other hand, are unable to be stimulated but are nonetheless able to sustain steroidogenesis under basal conditions.

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