ANDROSTENEDIONE AND PROGESTERONE PRODUCTION IN-VITRO BY THE INNER OR THE OUTER THECA CELLS IN PREOVULATORY FOLLICLES OF GONADOTROPIN-STIMULATED CALVES

This study reports some of the steroidogenic characteristics of the in terna and externa theca cells taken from young and eCG primed calves. These cells were isolated from large healthy follicles. They were sepa rately cultured for 3 days in absence or in presence of steroid substr ates. Androstenedione (A4) and progesterone (P4) were measured by radi oimmunoassay (RIA). In control conditions, A4 levels, higher in intern a than in externa cells ( * P < 0.01), decreased during cultures ( * P < 0.01). In both cell types, A4 increased in presence of 17 alpha-hy droxypregnenolone (170HP5), pregnenolone (P5) and 22 R-hydroxycholeste rol (22 R-chol) ( P < 0.05) but not with P4 or 17 alpha-hydroxpproges terone (170HP4) (P > 0.05). The most efficient substrate was dehydroep iandrosterone (DHEA) ( P < 0.05). In control conditions, P4 levels in creased in both cell types. They were higher in externa than in intern a cells on day 1, the reverse was observed on day 3. P4 levels increas ed after addition of 22R-chol and P5 ( P < 0.05) but not with 170HP5, 170HP4 and DHEA(P > 0.05) from day 1 in externa cells and only on day 3 in interna cells. P4 levels measured on day 1 were lower than the q uantity of P4 added as a substrate. These results, obtained with theca cells from young calf follicles, indicate: 1/A4 is synthesized by the Delta 5 pathway and 17 alpha-hydroxylase activity decreases in vitro, 2/externa and interns cells differ by the quantities of A4 and P4 pro duced, 3/both lack precursors to produce A4 and P4 but their 3 beta-hy droxysteroid dehydrogenase activity subsists, 4/P4 could be metabolize d during the first 2 days in both cell structures. (C) 1998 Elsevier S cience B.V.