Effect of a specific aromatase inhibitor on oestradiol secretion by porcine corpora lutea at various stages of the luteal phase.

The present study was undertaken to investigate the aromatization capability of pig corpora lutea at different stages of the luteal phase using the nonsteroidal aromatase inhibitor CGS 16949A. Luteal cells were collected during early (0-2 days after ovulation), mid- (7-10 days after ovulation) and late (13-16 days after ovulation) luteal phase. Cells were incubated either with or without 10(-7) MT (testosterone-supplemented culture). Six hours after starting the cultures, 0.1, 0.5 or 1.0 microM aromatase inhibitor was added to both culture types for the next 12 h period. Addition of the aromatase inhibitor to the luteal cells isolated during the early luteal phase had no effect on basal and testosterone-supplemented oestradiol secretion. The aromatase inhibitor added to cells isolated during the mid- and late luteal phase, however, caused a significant decrease in the basal and testosterone-stimulated secretion of oestradiol. This supports the hypothesis that luteal cells from these stages have active aromatase. The highest aromatization potential was observed in regressing corpora lutea. Oestradiol secreted by the regressing corpora lutea could play an active role in the regulation of oestrus cycle and could have a possible endocrine influence on gonadotropin secretion, a paracrine action on follicular growth or an autocrine influence on the luteal activity.