Premature progesterone rise in ART-cycles.

Premature rise of progesterone during the late follicular phase in stimulated IVF cycles is a frequent event and its effect on the endometrial receptivity and on the ART (Assisted Reproductive Technique) - outcome has become a matter of intense debate and research. An emerging body of evidence demonstrates that premature progesterone rise does have a negative impact on the outcome of the ART-success. Until now, the exact cause of progesterone elevation is not fully clear, however lately published studies points to the fact, that premature progesterone elevation might be caused by enhanced FSH stimulation. The impact of elevated peripheral progesterone levels seems to be mainly on the endometrium and the window of implantation, leading to an asynchrony between the endometrium and the developing embryo. Hence, new data show additional an influence on the embryo quality. This review aims to summarize the up-to-date knowledge on the causes of premature progesterone rise during hormonal stimulation, on its influence on endometrial receptivity and embryo quality, on the impact on pregnancy and live birth rates as well as on the possible strategies to prevent this event or to deal with premature progesterone elevation in case it could not be avoided.

Misregulated progesterone secretion and impaired pregnancy in Cyp11a1 transgenic mice.

Normal pregnancy is supported by increased levels of progesterone (P4), which is secreted from ovarian luteal cells via enzymatic steps catalyzed by P450scc (CYP11A1) and HSD3B. The development and maintenance of corpora lutea during pregnancy, however, are less well understood. Here we used Cyp11a1 transgenic mice to delineate the steps of luteal cell differentiation during pregnancy. Cyp11a1 in a bacterial artificial chromosome was injected into mouse embryos to generate transgenic mice with transgene expression that recapitulated endogenous Cyp11a1 expression. Cyp11a1 transgenic females displayed reduced pregnancy rate, impaired implantation and placentation, and decreased litter size in utero, although they produced comparable numbers of blastocysts. The differentiation of transgenic luteal cells was delayed during early pregnancy as shown by the delayed activation of genes involved in steroidogenesis and cholesterol availability. Luteal cell mitochondria were elongated, and their numbers were reduced, with morphology and numbers similar to those observed in granulosa cells. Transgenic luteal cells accumulated lipid droplets and secreted less progesterone during early pregnancy. The progesterone level returned to normal on gestation day 9 but was not properly withdrawn at term, leading to delayed stillbirth. P4 supplementation rescued the implantation rates but not the ovarian defects. Thus, overexpression of Cyp11a1 disrupts normal development of the corpus luteum, leading to progesterone insufficiency during early pregnancy. Misregulation of the progesterone production in Cyp11a1 transgenic mice during pregnancy resulted in aberrant implantation, anomalous placentation, and delayed parturition.

Effect of feeding level on luteal function and progesterone concentration in the vena cava during early pregnancy in gilts.

This study assessed the effect of feeding level on progesterone concentration in the caudal vena cava during early pregnancy in gilts. Twenty-four Landrace gilts were allocated to either a high (2.8±0.02) or a low (1.5±0.01 kg day⁻¹) feeding level at Day 0 of pregnancy. Serial blood samples were collected every 15 min for 3 h before and 3 h after feeding on Days 6 and 9 of pregnancy. Embryo survival and development as well as in vitro luteal progesterone production were assessed at Day 10 of pregnancy. Progesterone concentration in the vena cava was pulsatile with gilts on the high feeding level having more pulses compared with Low gilts on Day 9 of pregnancy (P<0.05). On Day 6 the number of pulses did not differ significantly between treatments; however, the average progesterone concentration in the vena cava tended to be higher in the gilts on the high feeding level (P<0.10). Embryo survival at Day 10 was 92±3% for High gilts compared with 77±3% for Low gilts (P<0.05). No difference in embryo development between the treatments was seen. There was no difference between treatments in in vitro secretion of progesterone by luteal tissue. In conclusion, a high plane of nutrition positively affects progesterone secretion by the ovaries in early pregnancy.

Escherichia coli lipopolysaccharide administration transiently suppresses luteal structure and function in diestrous cows.

The objective was to characterize the effects of Escherichia coli lipopolysaccharide (LPS) endotoxin (given i.v.) on luteal structure and function. Seven nonlactating German Holstein cows, 5.1 ± 0.8 years old (mean ± s.e.m.), were given 10  ml saline on day 10 (ovulation=day 1) of a control estrous cycle. On day 10 of a subsequent cycle, they were given 0.5 µg/kg LPS. Luteal size decreased (from 5.2 to 3.8 cm², P≤0.05) within 24 h after LPS treatment and remained smaller throughout the remainder of the cycle. Luteal blood flow decreased by 34% (P≤0.05) within 3 h after LPS and remained lower for 72 h. Plasma progesterone (P4) concentrations increased (P≤0.05) within the first 3 h after LPS but subsequently declined. Following LPS treatment, plasma prostaglandin (PG) F metabolites concentrations were approximately tenfold higher in LPS-treated compared with control cows (9.2 vs 0.8 ng/ml, P≤0.05) within 30 min, whereas plasma PGE concentrations were nearly double (P≤0.05) at 1 h after LPS. At 12 h after treatment, levels of mRNA encoding Caspase-3 in biopsies of the corpus luteum (CL) were increased (P≤0.05), whereas those encoding StAR were decreased (P≤0.05) in cattle given LPS vs saline. The CASP3 protein was localized in the cytoplasm and/or nuclei of luteal cells, whereas StAR was detected in the cytosol of luteal cells. In the estrous cycle following treatment with either saline or LPS, there were no significant differences between groups on luteal size, plasma P4 concentrations, or gene expression. In conclusion, LPS treatment of diestrus cows transiently suppressed both the structure and function of the CL.

Role of the double luteinizing hormone peak, luteinizing follicles, and the secretion of inhibin for dominant follicle selection in Asian elephants (Elephas maximus).

Elephants express two luteinizing hormone (LH) peaks timed 3 wk apart during the follicular phase. This is in marked contrast with the classic mammalian estrous cycle model with its single, ovulation-inducing LH peak. It is not clear why ovulation and a rise in progesterone only occur after the second LH peak in elephants. However, by combining ovarian ultrasound and hormone measurements in five Asian elephants (Elephas maximus), we have found a novel strategy for dominant follicle selection and luteal tissue accumulation. Two distinct waves of follicles develop during the follicular phase, each of which is terminated by an LH peak. At the first (anovulatory) LH surge, the largest follicles measure between 10 and 19.0 mm. At 7 ± 2.4 days before the second (ovulatory) LH surge, luteinization of these large follicles occurs. Simultaneously with luteinized follicle (LUF) formation, immunoreactive (ir) inhibin concentrations rise and stay elevated for 41.8 ± 5.8 days after ovulation and the subsequent rise in progesterone. We have found a significant relationship between LUF diameter and serum ir-inhibin level (r(2) = 0.82, P < 0.001). The results indicate that circulating ir-inhibin concentrations are derived from the luteinized granulosa cells of LUFs. Therefore, it appears that the development of LUFs is a precondition for inhibin secretion, which in turn impacts the selection of the ovulatory follicle. Only now, a single dominant follicle may deviate from the second follicular wave and ovulate after the second LH peak. Thus, elephants have evolved a different strategy for corpus luteum formation and selection of the ovulatory follicle as compared with other mammals.

Transforming growth factor-beta (TGFbeta) and its signaling components in peri-ovulatory pig follicles.

The present studies investigated the hypothesis that TGFbeta plays a role in mediating LH/hCG-induced maturation, ovulation and/or luteinization of follicles in the pig. In Experiment 1, the temporal and spatial gene expression patterns of TGFbeta signaling components were examined in pig follicles which had been induced to ovulate and luteinize in vivo by hCG treatment, or by the LH-surge. Pre-pubertal pigs were injected with PG-600 followed by hCG, and ovaries were collected surgically at 0, 1, 12, 24 and 48h post-hCG. Post-ovulatory follicles were also collected from cycling gilts on Day 4 (D4) of the estrous cycle. Pre- and post-ovulatory follicles were used for the measurement of mRNA (PCR) and protein (Western blots) abundance and for protein localization by immunohistochemistry (IHC). Steady state amounts of mRNA for TGFbeta3 and TGFbetaR2 were increased (P<0.05, as compared to 0h) at 12h and on D4, respectively, while TGFbeta2 protein showed a tendency to increase on D4. TGFbeta signaling components did not change significantly. By IHC, the localization of TGFbeta components was as follows: pre-ovulatory follicles; TGFbeta1 - granulosa cells (GC), TGFbeta2 - theca cells (TC), TGFbetaR1 and 2 - GC and TC: post-ovulatory follicles; TGFbeta1 and 2 and TGFbetaR1 and 2 - luteinizing TC and GC. In Experiment 2, TGFbeta1 (1-100ng/ml) alone had no significant effect on progesterone (P4) secretion by pig GC in culture. Furthermore, while LH+IGF-1 (positive control) stimulated P4 approximately 10-fold, TGFbeta at 10 and 100ng/ml added in combination with LH+IGF-1, had no effect on P4 accumulation. In conclusion, data from the present study on temporal and spatial patterns of expression of the TGFbeta-system suggest that TGFbeta may play a role in the overall process of luteinization, but it appears not to influence steroidogenesis in luteinizing pig follicles.

Luteal function induced by transvaginal ultrasonic-guided follicular aspiration in mares.

Ultrasonic-guided transvaginal follicle aspiration was performed in 58 crossbreed mares in order to determine whether aspiration of various dominant follicle diameters resulted in luteal tissue capable of producing progesterone (P(4)). The mares were randomly assigned to three groups according to follicular diameter (25-29 mm; 30-35 mm and >35 mm). Mares that had ovulations naturally served as controls. The serum progesterone (P(4)) concentrations in the aspirated mares were greater (P < 0.0001; r(2) = 0.6687; CV = 21.52) in mares with natural ovulation compared to mares with aspirated follicles regardless of groups. Serum P(4) concentration in aspired mares with follicular diameter of 25-29 mm declined 0.365 ng/ml/day (P = 0.0065) from the day of aspiration (D0) up to D8. In mares with follicle diameter of 30-35 mm, serum P(4) concentration increased (0.258 ng/ml/day; P = 0.001), as well as in the mares with follicles >35 mm diameter (0.481 ng/ml/day; P < 0.0001), and in mares with natural ovulation (1.236 ng/ml/day; P < 0.0001). Out of the 25 mares with follicular aspirations that formed Corpora hemorragica (P(4) >1 ng/ml), 23 (92%) had greater (>2 ng/ml) serum P(4) concentrations on Day 8 after aspiration. Of these 23 mares, 75% were in the 25-29 mm group, 9/10 (90%) in the 30-35 mm group, and 11/11 (100%) of the mares in the >35 mm follicular diameter group had luteinization (P(4) >2 ng/ml). These results suggest that a functional Corpus luteum can be induced in mares using follicular aspiration and that a minimum 35 mm follicular diameter is needed to reach a progesterone serum concentration compatible with that of a Corpus luteum produced by natural ovulation.

Luteal blood flow is a more appropriate indicator for luteal function during the bovine estrous cycle than luteal size.

The objective of this study was to assess the reliability of luteal blood flow (LBF) as recorded by color Doppler sonography to monitor luteal function during the estrous cycle of dairy cows and to compare the results with that for the established criterion luteal size (LS) as determined by B-mode sonography. In total, 14 consecutive sonographic examinations were carried out in 10 synchronized lactating Holstein-Friesian cows (Bos taurus) on Days 4, 5, 6, 7, 8, 10, 12, 14, 16, -5, -4, -3, -2, -1 of the estrous cycle (Day 1=ovulation). Plasma progesterone concentrations in venous blood (P(4)) were quantified by enzyme immunoassay. Luteal size was determined by sonographic measurement of the maximal cross-sectional area of the corpus luteum (CL). Luteal blood supply was estimated by calculating the maximum colored area of the CL from power Doppler sonographic images. Luteal size doubled during the luteal growth phase (until Day 7) and remained at this level during the luteal static phase (Day 8 to 16) before decreasing rather slowly during luteal regression (Days -5 to -1). Luteal blood flow doubled during the growth phase, doubled furthermore during the static phase, and decreased rapidly during luteal regression. Thus, LBF values represented highly reliable predictors of luteal status. Luteal blood flow predicted reliably a P(4)>1.0 ng/mL by reaching only 35% of the maximal values, whereas LS had to exceed 60% of the maximal values to indicate reliably a functional CL. It is concluded that LBF reflected luteal function better than LS specifically during luteal regression.