M. J. Bosc

Adrenal maturation of the sheep fetus during late pregnancy

The mechanism by which adrenal growth is achieved and steroidogenesis is stimulated in the fetal lamb during late pregnancy has been studied. Fetal plasma ACTH levels remained roughly constant between 14 and 3 days pre partum (298 +/- 38 pg/ml), then increased to a mean of 634 +/- 89 pg/ml. The rise in ACTH did not occur before the pre partum rise in cortisol. The increase in adrenal weight was achieved in three periods, one of DNA duplication between two phases of cellular hypertrophy. Cellular hypertrophy was accompanied by an important biosynthesis of membrane proteins. This development might partly explain the increased production rate of cortisol by the fetal adrenals during late pregnancy. At the same time, the number of ACTH receptors per 2 adrenals increased 5-fold. There was a close correlation between the levels of fetal plasma corticosteroids and the number of ACTH receptors during late pregnancy. It has been suggested that receptor modulation is one of the factors responsible for the enhanced sensitivity of the fetal adrenals to ACTH just before parturition. Preliminary results on the endocrine regulation of that development are also presented.

Steroid productions by co-cultures of granulosa cells with inner and outer theca cells in preovulatory follicles of gonadotropin stimulated calves.

Granulosa, interna and externa theca cells were isolated from large follicles of equine-chorionic-gonadotropin (eCG)-primed calves and co-cultured during 3 days in the absence or in the presence of dehydroepiandrosterone (DHEA). Co-cultures were performed by adding defined numbers of theca and/or granulosa cells which represented 0, 10, 20, 50 or 100% of total cells per well. Secretion of oestradiol-17beta (E2), androstenedione (A4) and progesterone (P4) depended on the type of theca cells (P < 0.001), on the percentage of seeded granulosa cells (P < 0.001) and on the day of culture (P < 0.001). DHEA increased (P < 0.001) E2 and A4, but not P4 (P > 0.05) productions. Interactions existed between these factors (P < 0.01). On day 1, A4 production was nil in granulosa cells alone. E2 production was negligible in theca cells alone but it increased when granulosa cells were added. E2 and A4 varied in an opposite manner according to the percentage of granulosa cells and with the type of theca cells. On day 3, without DHEA, E2 and A4 were low. On day 3 with DHEA, E2 production was maintained in granulosa cells alone but not with any combination of theca cells. In these conditions, A4 production was maintained in the presence of theca cells but not in granulosa cells alone. Granulosa cells alone secreted more P4 than theca cells. P4 increased as a function of the percentage of granulosa in co-cultures with externa but not interna theca cells with which it remained low. In conclusion, theca cells in culture have two effects in relation to the granulosa cells, which differ according to the steroid concerned and to the cell combination. Both types of theca cells have an inhibitory effect on E2 secretion whereas only interna theca cells are able to alter P4 production.

Evaluation of progesterone, estrogens and placental lactogen in pregnant ewes following experimental infection with an abortive agent chlamydia psittaci “Var-Ovis”

The plasma levels of progesterone, free and conjugated estrone and of placental lactogen have been determined in three groups of pregnant ewes inoculated with an abortive agent (Chlamydia psittacci var. ovis) on day 66 of gestation. In the control group, ewes were immunized against this abortive agent, and lambed after a normal duration of pregnancy; the blood levels of the three studied hormones showed normal patterns. In the two other groups, the ewes which were not immunized, had a shortened gestation and gave birth in most cases to dead lambs. In some animals, plasma levels of estrone followed an apparently normal evolution; in others the amplitude of the prepartum rise was lower than in the control group. Moreover, plasma levels of progesterone and of placental lactogen were lower in the animals which aborted than in the controls. This effect on the secretion of these two placental hormones probably reflects the action of the abortive agent on the placenta.

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 interna and externa theca cells taken from young and eCG primed calves. These cells were isolated from large healthy follicles. The were separately cultured for 3 days in absence or in presence of steroid substrates. Androstenedione (A4) and progesterone (P4) were measured by radioimmunoassay (RIA). In control conditions, A4 levels, higher in interna than in externa cells (P < 0.001), decreased during cultures (P < 0.01). In both cell types, A4 increased in presence of 17 alpha-hydroxypregnenolone (17OHP5), pregnenolone (P5) and 22R-hydroxycholesterol (22R-chol)(*P < 0.05) but not with P4 or 17 alpha-hydroxyprogesterone (17OHP4)(P > 0.05). The most efficient substrate was dehydroepiandrosterone (DHEA) (P < 0.005). In control conditions, P4 levels increased in both cell types. They were higher in externa than in interna cells on day 1, the reverse was observed on day 3. P4 levels increased after addition of 22 R-chol and P5 (P < 0.005) but not with 17OHP5, 17OHP4 and DHEA (P > 0.05) from day 1 in externa cells and only on day 3 in internal cells. P4 levels measured on day 1 were lower than the quantity of P4 added as a substrate. These results, obtained with theca cells from young calf follicles, indicate: 1/A4 is synthesized by the delta5 pathway and 17 alpha-hydroxylase activity decreases in vitro, 2/externa and interna cells differ by the quantities of A4 and P4 produced, 3/both lack precursors to produce A4 and P4 but their 3 beta-hydroxysteroid dehydrogenase activity subsists, 4/P4 could be metabolized during the first 2 days in both cell cultures.