Abstract. Prenatal stress has been seen as a reason for reproductive failures in pig offspring mostly originated or mediated by changed maternal functions. Experiments were conducted in pregnant gilts (n=32) to characterize effects of elevated maternal glucocorticoids on the secretion of reproductive hormones (LH, progesterone) during the 1 st (EXP 1), 2 nd (EXP 2) and 3 rd (EXP 3) trimester of pregnancy (TP). Transiently elevated cortisol release was repeatedly achieved by application of 100 IU adenocorticotropic hormone (ACTH) (Synacthen Depot®) six times every second day beginning either on day 28 (EXP 1), day 49 (EXP 2) or day 75 of pregnancy (EXP 3). Glucocorticoid concentrations were examined in umbilical blood vessels of fetuses which mothers were subjected to ACTH at 2 nd and 3 rd TP (EXP 4). Furthermore, the pituitary function of newborn piglets of EXP 2 was checked by a LH-RH challenge test. In sows, LH concentrations were at low basal level (0.1-0.2 ng/ ml) but with pulsatory release pattern during each TP. The number of LH pulses/6 h (LSM ± SE) of saline treated Controls increased with ongoing pregnancy and decreased to the 3 rd TP (1.3 ± 0.2 in EXP 1 vs. 2.0 ± 0.1 in EXP 2 vs. 1.4 ± 0.1 in EXP 3, p<0.05). After ACTH treatment the number of LH pulses left unchanged in Experiments 1 and 2 (1.3 ± 0.2 and 1.5 ± 0.1) and decreased in EXP 3 (0.8 ± 0.2, p<0.05). Differences (p<0.05) were obtained comparing the LH pulse number of ACTH and saline treated sows at the 2 nd and 3 rd TP. Moreover, areas under the curve (AUC) of each LH pulse and of LH over baseline were significantly reduced by treatment. Levels of progesterone increased (p<0.05) for 150 to 170 min after each ACTH application both in EXP 1 and EXP 2, but not in EXP 3. The mean progesterone concentration was different between trimesters, and ACTH and Controls (1 st TP: 30.0 ± 0.9 and 24.4 ± 0.7 ng/ml; 2 nd TP: 35.5 ± 0.9 and 29.1 ± 1.0 ng/ml; 3 rd TP: 13.6 ± 0.2 and 13.1 ± 0.1 ng/ml; p<0.05). In fetuses (n=87) recovered 3 h after ACTH or saline (EXP 4), the plasma cortisol concentrations were significantly increased in umbilical vein (93.7 ± 5.5 vs. 47.0 ± 5.3 nmol/l) and artery (95.7 ± 5.4 vs. 66.4 ± 5.4 nmol/l), and in periphery (46.8 ± 5.3 vs. 27.1 ± 5.3 nmol/l) compared to controls. Plasma ACTH concentrations, however, did not differ in fetuses of both treatment groups. Postnatal LH-RH challenge tests (1 st and 28 th day post partum) induced LH surges in female piglets (n=67) both of ACTH and saline treated sows, but did not differ between groups (1 st day: 7.2 ± 0.8 vs. 8.1 ± 0.7 ng/ml; 28 th day: 10.5 ± 1.7 vs. 13.6 ± 2.2 ng/ml). However, basal LH of piglets whose mothers were submitted to ACTH during 2 nd TP was lower on 1 st day (1.7 ± 0.2 vs. 2.3 ± 0.2 ng/ml, p<0.05) but not on 28 th day (1.0 ± 0.2 vs. 1.1 ± 0.2 ng/ml). However in both groups, the basal LH was always higher on 1 st as on 28 th day (p<0.05). Thus, chronic intermittent ACTH administration is able to influence the release pattern of maternal reproductive hormones. However, ...