Effect of Proteasome Pathway on Initiation of Mouse Labor Induced by Antiprogesterone

CyPPA, a positive modulator of small-conductance Ca(2+)-activated K(+) channels, inhibits phasic uterine contractions and delays preterm birth in mice

Organized uterine contractions, including those necessary for parturition, are dependent on calcium entry through voltage-gated calcium channels in myometrial smooth muscle cells. Recent evidence suggests that small-conductance Ca(2+)-activated potassium channels (K(Ca)2), specifically isoforms K(Ca)2.2 and 2.3, may control these contractions through negative feedback regulation of Ca(2+) entry. We tested whether selective pharmacologic activation of K(Ca)2.2/2.3 channels might depress uterine contractions, providing a new strategy for preterm labor intervention. Western blot analysis and immunofluorescence microscopy revealed expression of both K(Ca)2.2 and K(Ca)2.3 in the myometrium of nonpregnant (NP) and pregnant (gestation day 10 and 16; D10 and D16, respectively) mice. Spontaneous phasic contractions of isolated NP, D10, and D16 uterine strips were all suppressed by the K(Ca)2.2/2.3-selective activator CyPPA in a concentration-dependent manner. This effect was antagonized by the selective K(Ca)2 inhibitor apamin. Whereas CyPPA sensitivity was reduced in D10 and D16 versus NP strips (pIC(50) 5.33 ± 0.09, 4.64 ± 0.03, 4.72 ± 0.10, respectively), all contractions were abolished between 30 and 60 μM. Blunted contractions were associated with CyPPA depression of spontaneous Ca(2+) events in myometrial smooth muscle bundles. Augmentation of uterine contractions with oxytocin or prostaglandin F(2α) did not reduce CyPPA sensitivity or efficacy. Finally, in an RU486-induced preterm labor model, CyPPA significantly delayed time to delivery by 3.4 h and caused a 2.5-fold increase in pup retention. These data indicate that pharmacologic stimulation of myometrial K(Ca)2.2/2.3 channels effectively suppresses Ca(2+)-mediated uterine contractions and delays preterm birth in mice, supporting the potential utility of this approach in tocolytic therapies.

In vitro comparison of myometrial contractility induced by aglepristone-oxytocin and aglepristone-PGF2alpha combinations at different stages of the estrus cycle in the bitch

The aim of this in vitro study was to compare the uterokinetic activity of oxytocin and dinoprost, the natural PGF2α, with or without aglepristone, in canine myometrial fibers. Thirty-three bitches were allocated into one of four groups, depending on their estrous stage and whether or not they had received a treatment with aglepristone (metestrus aglepristone, n = 5; metestrus without treatment, n = 9; anestrus aglepristone, n = 9; anestrus without treatment, n = 10). After hysterectomy, longitudinal and circular uterine strips were mounted in organ baths. Oxytocin or PGF2α (10 nmol/l to 10 micromol/l) were applied non-cumulatively. A linear mixed effects models theory was used to compare the fiber effect, the aglepristone effect, and the treatment effect, from the area under the curves calculated from the contractile effect/concentration curves for each drug. Oxytocin and PGF2α induced concentration-dependent myometrial contractions in longitudinal (LF) and circular myometrial fibers (CF), indicating the presence of functional contractile oxytocin- and PGF2α-receptors in metestrus and anestrus. The contractile response to oxytocin was greater in LF than in CF in all of the groups; the response to PGF2α was greater in LF than in CF in non-treated bitches in anestrus and in treated bitches in metestrus. These results suggest that there is a difference in sensitivity or a heterogeneous distribution of oxytocin and PGF2α-receptors in the myometrial layers, which is independent of hormonal impregnation. The contractile response to oxytocin and PGF2α was significantly increased after aglepristone treatment in LF during metestrus, suggesting that the progesterone withdrawal induced by aglepristone has a role to play. The longitudinal myometrial layer also appeared to be the target for the two drugs at this stage. This study provides new information about canine uterine contractile activity, notably the differing behavior of myometrial CF and LF; in vivo studies are required to test the use of a combination of aglepristone and oxytocin in the treatment of canine pyometra.

Plasma amino acids in pregnancy, placental intervillous space and preterm newborn infants

Plasma amino acid levels have never been studied in the placental intervillous space of preterm gestations. Our objective was to determine the possible relationship between plasma amino acids of maternal venous blood (M), of the placental intervillous space (PIVS) and of the umbilical vein (UV) of preterm newborn infants. Plasma amino acid levels were analyzed by ion-exchange chromatography in M from 14 parturients and in the PIVS and UV of their preterm newborn infants. Mean gestational age was 34 +/- 2 weeks, weight = 1827 +/- 510 g, and all newborns were considered adequate for gestational age. The mean Apgar score was 8 and 9 at the first and fifth minutes. Plasma amino acid values were significantly lower in M than in PIVS (166%), except for aminobutyric acid. On average, plasma amino acid levels were significantly higher in UV than in M (107%) and were closer to PIVS than to M values, except for cystine and aminobutyric acid (P < 0.05). Comparison of the mean plasma amino acid concentrations in the UV of preterm to those of term newborn infants previously studied by our group showed no significant difference, except for proline (P < 0.05), preterm > term. These data suggest that the mechanisms of active amino acid transport are centralized in the syncytiotrophoblast, with their passage to the fetus being an active bidirectional process with asymmetric efflux. PIVS could be a reserve amino acid space for the protection of the fetal compartment from inadequate maternal amino acid variations.

Identification of 9 uterine genes that are regulated during mouse pregnancy and exhibit abnormal levels in the cyclooxygenase-1 knockout mouse

BACKGROUND

Preterm birth is the leading cause of all infant mortality. In 2004, 12.5% of all births were preterm. In order to understand preterm labor, we must first understand normal labor. Since many of the myometrial changes that occur during pregnancy are similar in mice and humans and mouse gestation is short, we have studied the uterine genes that change in the mouse during pregnancy. Here, we used microarray analysis to identify uterine genes in the gravid mouse that are differentially regulated in the cyclooxygenase-1 knockout mouse model of delayed parturition.

METHODS

Gestational d18.0 uteri (n = 4) were collected from pregnant wild-type and cyclooxygenase-1 knockout mice. Part of the uterus was used for frozen sections and RNA was isolated from the remainder. Microarray analysis was performed at the Indiana University School of Medicine Genomic Core and analyzed using the Microarray Data Portal. Northern analysis was performed to confirm microarray data and the genes localized in the gravid uterus by in situ hybridization.

RESULTS

We identified 277 genes that are abnormally expressed in the gravid d18.0 cyclooxygenase-1 knockout mouse. Nine of these genes are also regulated in the normal murine uterus during the last half of gestation. Many of these genes are involved in the immune response, consistent with an important role of the immune system in parturition. Expression of 4 of these genes; arginase I, IgJ, Tnfrsf9 and troponin; was confirmed by Northern analysis to be mis-regulated during pregnancy in the knockout mouse. In situ hybridization of these genes demonstrated a similar location in the gravid wild-type and Cox-1 knockout mouse uteri.

CONCLUSION

To our knowledge, this is the first work to demonstrate the uterine location of these 4 genes in the mouse during late pregnancy. There are several putative transcription factor binding sites that are shared by many of the 9 genes identified here including; estrogen and progesterone response elements and Ets binding sites. In summary, this work identifies 9 uterine murine genes that may play a role in parturition. The function of these genes is consistent with an important role of the immune system in parturition.