Up-regulation of rat myometrial phospholipases C{beta}1 and C{beta}3 correlates with increased term sensitivity to carbachol and oxytocin

Calcium signaling cascades differentially regulate PGF2α-induced myometrial contractions in water buffaloes (Bubalus bubalis)

This study unravels the differential involvement of calcium signaling pathway(s) in PGF_2α-induced contractions in myometrium of nonpregnant (NP) and pregnant buffaloes. Compared to the myometrium of pregnant animals, myometrium of NP buffaloes was more sensitive to PGF_2α as manifested by changes in mean integral tension (MIT) and tonicity. In the presence of nifedipine, myometrial contraction to PGF_2α was significantly attenuated in both NP and pregnant uteri; however, mibefradil and NNC 55-0396 produced inhibitory effects only in uterus of pregnant animals, thus suggesting the role of extracellular Ca²⁺ influx through nifedipine-sensitive L-type Ca²⁺-channels both in NP and pregnant, but T-type Ca²⁺ channels seem to play a role only during pregnancy. Entry of extracellular Ca²⁺ is triggered by enhanced functional involvement of Pyr3-sensitive TRPC3 channels and Rho-kinase pathways as evidenced by a significant rightward shift of the concentration-response curve of PGF_2α in the presence of Pyr3 and Y-27632 in NP myometrium. But significant down-expressions of TRPC3 and Rho-A proteins during pregnancy apparently facilitate uterine quiescence. In the presence of Ca²⁺-free solution and cyclopiazonic acid (SERCA blocker), feeble contraction to PGF_2α was observed in both NP and pregnant myometrium which suggests minor role of intracellular source of Ca²⁺ in mediating PGF_2α-induced contractions in these tissues.

Contractions in the Isolated Uterus of a Rat Model of Polycystic Ovary Syndrome Compared to Controls in Adulthood

BACKGROUND

Polycystic ovary syndrome (PCOS) is one of the most common endocrine disorders in women during the reproductive age. Considering disorders reported in women with PCOS, e.g. infertility, pregnancy complications (premature delivery, caesarean section and spontaneous miscarriages), and hormonal disorders, we hypothesized that uterine contractions in PCOS rats may be different from controls. We aimed to compare uterine contractions in PCOS rats with controls.

METHODS

Rats in the experimental group were subcutaneously injected with 5 mg of free testosterone on gestational day 20, while controls received solvent. The contractions of isolated uterus in offspring of both groups were recorded by the power lab system, after exposure to carbachol and oxytocin. Two-way analysis of variance was used to compare results between 2 groups.

RESULTS

PCOS rats showed more irregular uterine contractions compared to controls. After exposure to carbachol, frequency, and resting tone in the PCOS rats were significantly increased compared to controls (P = 0.004, P = 0.02, respectively). After exposure to oxytocin, the frequency, resting tone and amplitude of rhythmic contractions did not differ between the 2 groups.

CONCLUSIONS

Our study indicates irregular uterine contractions and different mechanical responses of isolated uterus in PCOS rats compared to controls.

WITHDRAWN: Differential involvement of L- and T-type Ca2+ channels, store-operated calcium channel (TRPC) and Rho-kinase signaling pathway(s) in PGF2α-induced contractions in myometrium of non-pregnant and pregnant buffaloes (Bubalus bubalis)

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Phospholipase Cβ3 mediates LH-induced granulosa cell differentiation

Previous studies showed that under certain conditions LH can stimulate not only adenylate cyclase (AC) but also phospholipase Cβ (PLCβ) signaling in target cells; however, the physiological involvement of PLCβ in LH-induced ovarian follicular cell differentiation has not been determined. To address this, ex vivo expression analyses and specific PLCβ targeting were performed in primary bovine granulosa cells. Expression analyses in cells from small (2.0-5.9 mm), medium (6.0-9.9 mm), and ovulatory-size (10.0-13.9 mm) follicles revealed an increase in mRNA and protein levels of heterotrimeric G protein subunits-αs, -αq, -α11, and -αi2 in ovulatory-size follicles, simultaneous with a substantial increase in LH receptor expression. Among the four known PLCβ isoforms, PLCβ3 (PLCB3) was specifically up-regulated in cells from ovulatory-size follicles, in association with a predominantly cytoplasmic location of PLCB3 in these cells and a significant inositol phosphate response to LH stimulation. Furthermore, RNA interference-mediated PLCB3 down-regulation reduced the ability of LH to induce hallmark differentiation responses of granulosa cells, namely transcriptional up-regulation of prostaglandin-endoperoxide synthase 2 and down-regulation of both aromatase expression and estradiol production. Responses to the AC agonist, forskolin, however, were not affected. In addition, PLCB3 down-regulation did not alter cAMP responses to LH in granulosa cells, ruling out a primary involvement of AC in mediating the effects of PLCB3. In summary, we provide evidence of a physiological involvement of PLCβ signaling in ovulatory-size follicles and specifically identify PLCB3 as a mediator of LH-induced differentiation responses of granulosa cells.

Increased potency of α1-adrenergic receptors to induce inositol phosphates production correlates with the up-regulation of α1d/Ghα/phospholipase Cδ1 signaling pathway in term rat myometrium

In the present study, we studied the potential regulation by rat myometrial α1-adrenergic receptors (α1-AR) of the newly identified Ghα protein/phospholipase Cδ1 (PLCδ1) signaling pathway and compared myometrial inositol phosphates (InsP) production and activity of the uterine circular muscle in response to α1-AR activation between mid-pregnancy and term. For this, we quantified the level of rat myometrial α1-AR coupling to Ghα protein by photoaffinity-labeling, the cytosolic amount of PLCδ1 enzyme by immunoblotting, and the expression level of α1-AR subtypes by RT-PCR. The results showed an increased level of α1-AR/Ghα protein coupling and the amount of PLCδ1 at term (+147 and +65% respectively, versus mid-pregnancy). This was correlated with an up-regulation of α1d-AR subtype (+70% versus mid-pregnancy). Incubation of myometrial strips with phenylephrine (Phe), a global α1-agonist, increased InsP production in a dose-dependent manner at both mid-pregnancy and term, but with an enhanced potency (tenfold decrease in EC50value) at term. Phe also dose-dependently induced contraction of the circular muscle at both mid-pregnancy and term. However, unlike InsP response, no amelioration of potency was observed at term. Similar results were obtained with the endogenous agonist norepinephrine. Our results show, for the first time, that rat myometrial α1d-AR/Ghα/PLCδ1 signaling pathway is up-regulated at term. This is associated with an increased potency of α1-AR to elicit InsP production but not uterine contraction at this period. It is thus hypothesized that α1-AR, through activation of Ghα/PLCδ1 system, are not primarily involved in the initiation of labor but may rather regulate responses such as myometrial cell proliferation or hypertrophy.

The regulation of uterine relaxation

The regulation of uterine relaxation is poorly understood but research in myometrial tissue and other types of smooth muscle has defined a number of receptors, ion channels and regulatory proteins that are likely to be involved. Some of these proteins are substrates for protein kinases, especially cyclic nucleotide dependent kinases. More research is necessary to identify the key molecules involved in the maintenance of uterine quiescence in pregnancy. The use of tocolytics in preterm labour remains controversial; there is a need to identify better pharmacological targets to provoke safe and selective uterine relaxation and improve neonatal outcome.