Different steroidogenic response of young and aged porcine small and large luteal cells to prostaglandin F2 alpha, oxytocin and estradiol.

The role of oxytocin (OXT) and prostaglandin F2 alpha (PGF2 alpha) in the process of luteal regulation, particularly their function in the early luteal phase is poorly understood. Therefore the effects of both compounds on in vitro steroid release of porcine luteal cells harvested from young/middle-aged (day 4-6, day 0 = 1st estrous day) or old (day 12-14) corpora lutea were tested. As corpora lutea (CL) contain at least two different steroidogenic cell populations, fractions of the so called small (SLC) and large (LLC) luteal cells were prepared and tested in separate experiments. In SLC as well as LLC from young CL OXT and PGF2 alpha inhibited progesterone (P) production but induced a strong increase of estradiol (E2) release. In old SLC and LLC OXT and PGF2 alpha were still inhibitory to P release but OXT was ineffective and PGF2 alpha had a moderate stimulatory effect on luteal E2 secretion. In SLC cultures from young but not from old CL E2 exerted a powerful stimulatory effect on progesterone (P) secretion, i.e. E2 has strong luteotrophic effects in the early luteal phase. Indeed, the pronounced inhibitory effect of OXT and PGF2 alpha on P release from SLC could be counteracted by the addition of exogenous E2 to the culture media. Therefore, we suggest that in the early luteal phase OXT as well as PGF2 alpha have an indirect, E2-mediated luteotrophic effect on P release which is stronger than the direct inhibitory action on P secretion.(ABSTRACT TRUNCATED AT 250 WORDS)