Progesterone, androgen and estradiol production by porcine luteal cell subpopulations: dependence on cell composition and periods of luteal phase.

The size and number small (Sc) and large (Lc) luteal cells and the steroids they secrete were determined in porcine corpora lutea (CL) collected on days 1-3, 8-10 and 14-16 of the estrus cycle. The cells were separated with the aid of Ficoll linear gradient. The size of Sc increased in middle-luteal phase (MLP) in comparison with early luteal phase (ELP) and retained consistent value until the end of the luteal phase (LLP). Lc increased in size with advancing luteal phase, their number per CL being greater in MLP than in ELP but decreased in LLP. In contrast, the number of Sc decreased in MLP in comparison with ELP and did not change in LLP. At the initial luteal phase the majority of small cells did not show any histochemical reactivity for delta5-3ß-hydroxysteroid dehydrogenase which then increased with luteal phase progress. Lc collected during ELP showed 5.7 times higher androgen secretion than Sc. A decrease of androgen secretion by Lc was observed as the luteal phase progressed but it was three times higher in Sc than in Lc collected during LLP. Both types of luteal cells produced estradiol even without the addition of substrates. Endogenous estradiol content was always higher in Lc than in Sc. Moreover, estradiol secretion by both cell types was higher in LLP than in MLP and ELP. These findings suggest that the view on granulosa origin of Lc and theca origin of Sc as raised by others may be oversimplified. In appears that Sc most likely undergo hypertrophy, but retain their prior phenotype and also that some Lc gradually dedifferentiate to Sc as the corpus luteum ages.