Genotypic variability in radial resistance to water flow in olive roots and its response to temperature variations.

As radial root resistance (Rp) represents one of the key components of the soil-plant-atmosphere continuum resistance catena modulating water transport, understanding its control is essential for physiologists, modelers and breeders. Reports of Rp, however, are still scarce and scattered in the scientific literature. In this study, we assessed genetic variability in Rp and its dependence on temperature in five widely used olive cultivars. In a first experiment, cultivar differences in Rp at 25 °C were evaluated from flow-pressure measurements in excised roots and subsequent analysis of root traits. In a second experiment, similar determinations were performed continually over a 5-h period in which temperature was gradually increased from 12 to 32 °C, enabling the assessment of Rp response to changing temperature. Despite some variability, our results did not show statistical differences in Rp among cultivars in the first experiment. In the second, cultivar differences in Rp were not significant at 12 °C, but they became so as temperature increased. Furthermore, the changes in Rp between 12 and 32 °C were higher than those expected by the temperature-driven decrease in water viscosity, with the degree of that change differing among cultivars. Also, Rp at 25 °C reached momentarily in the second experiment was consistently higher than in the first at that same, but fixed, temperature. Overall, our results suggest that there is limited variability in Rp among the studied cultivars when plants have been exposed to a given temperature for sufficient time. Temperature-induced variation in Rp might thus be partly explained by changes in membrane permeability that occur slowly, which explains why our values at 25 °C differed between experiments. The observed cultivar differences in Rp with warming also indicate faster acclimation of Rp to temperature changes in some cultivars than others.

The impact of HPV cervical screening on negative large loop excision of the transformation zone (LLETZ): A comparative cohort study.

OBJECTIVE: To determine the incidence and predictors of negative large loop excision of the transformation zone (LLETZ) following the introduction of Human Papillomavirus (HPV) cervical screening. METHOD: A retrospective cohort study. Two independent cohorts, who attended for a LLETZ procedure, before and after the introduction of HPV cervical screening were compared. For each cohort, 401 individuals were randomly selected from a colposcopy database. Clinical and colposcopic variables were extracted. The incidence of negative LLETZ was estimated in each cohort. Regression analysis was used to adjust for potential confounders and explore predictors of negative LLETZ. RESULTS: Eighty women (19.9%) from the pre-HPV testing cohort and 54 women (13.4%) from the post-HPV cohort were negative for cervical intraepithelial neoplasia (RR 0.75, CI: 0.55 to 0.93). In the post-HPV testing cohort, independent predictors of negative LLETZ were low grade cytology (RR 3.60, CI: 2.18-5.97) and a type 3 transformation zone (TZ) (RR 2.88, CI: 1.76-4.72). Women with both low grade cytology and a TZ type 3 were 10.4 times more likely to have a negative LLETZ (absolute risk 40%, 95% CI: 27-54%). CONCLUSIONS: Despite a 25% reduction in negative LLETZ following the introduction of HPV cervical screening, the incidence is still high. These results highlight the importance of continuing to improve the specificity of cervical intraepithelial neoplasia screening; this should include the use of biomarkers that detect HPV-transforming infections and techniques that sample an entirely endocervical transformation zone.

Genes for prostaglandin synthesis, transport and inactivation are differentially expressed in human uterine tissues, and the prostaglandin F synthase AKR1B1 is induced in myometrial cells by inflammatory cytokines.

Prostaglandins (PGs) are important factors in the physiology of human parturition and the control of uterine contractility. We have characterized the expression of 15 genes from all stages of the PG pathway in human pregnant and non-pregnant (NP) myometrium and in other uterine tissues at delivery, and the results show patterns indicative of different capacities for PG synthesis and catabolism in each tissue. In placenta, the PG synthase expression profile favours production of PGD2, PGE2 and PGF2, with high levels of PG transporters and catabolic PG dehydrogenase suggesting rapid PG turnover. Choriodecidua is primed for PGE2, PGF2 and PGD2 production and high PG turnover, whereas amnion expresses genes for PGE2 synthesis with low levels of PG transporters and dehydrogenase. In umbilical cord, PGI2 synthase is highly expressed. In pregnant myometrium, PGI2, PGD2 and PGF2 synthases are highly expressed, whereas PG dehydrogenase is underexpressed. Myometrium from women with spontaneous or induced labour had higher expression of the PGH2 synthase PTGS2 than tissue from women not-in-labour. Myometrium from NP women had lower levels of PG synthases and higher levels of PG dehydrogenase than pregnant myometrium. Discriminant function analysis showed that expression of selected genes in myometrium could distinguish groups of women with different modes of labour from each other and from NP women. In cultured myometrial cells, there was a dose-dependent stimulatory effect of interleukin 1ß and tumour necrosis factor α on PTGS2, PTGES and AKR1B1 (PGF synthase) expression.

RHO protein regulation of contraction in the human uterus.

The state of contraction in smooth muscle cells of the human uterus is dependent on the interaction of activated forms of actin and myosin. Ras homology (RHO) proteins are small monomeric GTP-binding proteins that regulate actin polymerisation and myosin phosphorylation in smooth muscle cells. Their action is determined by their level of expression, GTP-bound state, intracellular localisation and phosphorylated status. Agonist activated RHO proteins bind to effector kinases such as RHO kinase (ROCK) and diaphanous proteins (DIAPH) to regulate smooth muscle contraction by two mechanisms: ROCK activates smooth muscle myosin either by direct phosphorylation at Ser19/Thr18 or through inhibition of myosin phosphatase which is a trimeric protein regulated by ROCK and by other protein kinases. Actin-polymerising proteins such as DIAPH homolog 1 increase filamentous actin assembly to enhance acto-myosin cross bridge formation and contraction. This review explores recent advances in RHO protein signalling in human myometrium and proposes areas of further research to investigate the involvement of these proteins in the regulation of uterine contractility in pregnancy and labour.

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.

Up-regulation of myometrial RHO effector proteins (PKN1 and DIAPH1) and CPI-17 (PPP1R14A) phosphorylation in human pregnancy is associated with increased GTP-RHOA in spontaneous preterm labor.

RHO GTP-binding proteins are important regulators of actin-myosin interactions in uterine smooth muscle cells. Active (GTP-bound) RHOA binds to RHO-associated protein kinase (ROCK1), which inhibits the myosin-binding subunit (PPP1R12A) of myosin light chain phosphatase, leading to calcium-independent increases in myosin light chain phosphorylation and tension, which are termed "calcium sensitization." The RHO effector protein kinase N (PKN1) also increases calcium sensitization by phosphorylating the protein kinase C (PRKCB)-dependent protein CPI-17 (PPP1R14A) to inhibit the PPP1c subunit of myosin phosphatase. Moreover, other RHO proteins, such as RHOB, RHOD, and their effectors (DIAPH1 and DIAPH2), may modulate PKN1/ ROCK1 signaling to effect changes in myosin phosphatase activity and myosin light chain phosphorylation. The increases in contractile activity observed in term and preterm labor may be due to an increase in RHO activity and/or changes in RHO-related proteins. We found that the RHOA and RHOB mRNA levels in the myometrium were increased in pregnancy, although the expression levels of the RHOA and RHOB proteins did not change with pregnancy or labor. GTP-bound RHOA was increased in pregnancy, and this increase was significant in spontaneous preterm labor myometrium. PKN1 expression and PPP1R14A phosphorylation were dramatically increased in the pregnant myometrium. We also observed increases in DIAPH1 expression in spontaneous term and preterm labor myometrial tissues. The present study shows that human pregnancy is characterized by increases in PKN1 expression and PPP1R14A phosphorylation in the myometrium. Moreover, increases in GTP-bound RHOA and DIAPH1 expression may contribute to the increase in uterine activity in idiopathic preterm labor.

Internalization and desensitization of the oxytocin receptor is inhibited by Dynamin and clathrin mutants in human embryonic kidney 293 cells.

Oxytocin (OT) has long been used as an uterotonic during labor management in women, and yet responses to OT infusion remain variable and unpredictable among patients. The investigation of oxytocin receptor (OTR) regulation will benefit labor management, because the clinical practice of continuous iv infusion of OT is not optimal. As with other G protein-coupled receptors, it is likely that the OTR internalizes and/or desensitizes upon continuous agonist exposure. The mechanisms by which this might occur, however, are unclear. Here we explore OTR internalization and desensitization in human embryonic kidney cells by utilizing inhibitors of heterologous second messenger systems and recently available mutant cDNA constructs. We report rapid and extensive internalization and desensitization of the OTR upon agonist exposure. Internalization was unaffected by inhibitors of protein kinase C or Ca(2+) calmodulin-dependant kinase II but was significantly reduced after transfection with dominant-negative mutant cDNAs of G protein-coupled receptor kinase 2, beta-Arrestin2, Dynamin, and Eps15 (a component of clathrin-coated pits). Moreover, desensitization of the OTR, measured by a calcium mobilization assay, was also inhibited by the aforementioned cDNA constructs. Thus, our data demonstrate, for the first time, the importance of the classical clathrin-mediated pathway during agonist-induced OTR internalization and desensitization.

Loss of myometrial oxytocin receptors during oxytocin-induced and oxytocin-augmented labour.

Oxytocin is used widely for the induction and augmentation of labour, but there is little information about the dynamics of oxytocin receptors in human myometrium during parturition, and the possible effect of oxytocin infusion. This information is important because G protein-coupled receptors, such as the oxytocin receptor, undergo desensitization after prolonged or repeated stimulation. The concentration of myometrial oxytocin receptors and the steady state of its mRNA were measured in patients undergoing Caesarean sections before or during spontaneous or induced labour. The concentration of receptors before labour was 477 (175-641) fmol mg(-1) protein (median, quartile range), and decreased to 140 (72-206; P < 0.05) and 118 (69-75; P < 0.01) fmol mg(-1) protein during prolonged oxytocin-augmented and oxytocin-induced labour, respectively. The corresponding oxytocin receptor mRNA concentrations decreased by 60- and 300-fold, respectively. The decrease in receptor binding and mRNA in women receiving oxytocin infusion indicates that homologous receptor desensitization occurs in vivo.

Preterm labour.

Spontaneous preterm labour remains a major obstetric problem because of the high incidence of neonatal mortality or long-term handicap associated with it. The drugs available for the management of preterm labour are poorly effective and have potentially serious side-effects for the mother or fetus. In recent years, there has been a remarkable increase in the knowledge of the biochemical mechanism underlying uterine quiescence and contractility. Many of the G protein-coupled receptors that participate in the regulation of myometrial activity have been cloned and characterized, and their intracellular signalling pathways have been elucidated. The role of G protein receptor kinases in uterine tachyphylaxis is better understood. New developments in our understanding of the cellular mechanisms involved in uterine contractions in idiopathic and infection-associated preterm labour are expected, which will lead to better, more selective therapy for this problem. However, much research remains to be done before the mechanism of human parturition is fully understood.

Up-regulation of p21- and RhoA-activated protein kinases in human pregnant myometrium.

The role of small ras homologous GTP-binding proteins in the regulation of smooth muscle contractility has become increasingly apparent but there is still little information about the presence of these proteins in human uterine smooth muscle. Messenger RNAs for p21-activated protein kinase isoforms (PAK1, PAK2, and PAK3) were detectable in both nonpregnant and pregnant human myometrial tissue. However, PAK3 protein was not detectable and the proteins for PAK1 and PAK2 were only detectable in pregnant tissue. Moreover there was a large increase in the constitutively active p34 protein fragment of PAK2 in pregnant tissue. Protein expression of RhoA-activated protein kinases isoforms (ROK1 and ROK2) also increased during pregnancy. Stimulation of RhoA signaling in pregnant myometrial tissue with lysophosphatic acid (LPA) increased the level of myosin light chain (MLC20) phosphorylation. Preincubation of the tissue with C3 toxin inhibited LPA-stimulated MLC20 phosphorylation and lowered the basal phosphorylation level of MLC20. Thus ROKS and PAKS have the potential to regulate uterine contractility and/or load-bearing during human pregnancy.

Adenylyl cyclase isoforms in pregnant and non-pregnant human myometrium.

The precise factors involved in the transition of the relaxed pregnant uterus to the contractile state at the onset of parturition remain unclear, but it is accepted that cAMP-generating pathways contribute to uterine relaxation. We have previously reported an increased expression of the adenylyl cyclase (AC)-stimulating protein Galphas in human myometrium during gestation, with a corresponding increase in GTP-stimulated AC activity. However, little is known about the predominating AC isoforms expressed during pregnancy. This information is important, because although all AC isoforms are stimulated by Galphas, their regulation by other signalling molecules is very different. In the present study we have identified the isoforms of AC expressed in both pregnant and non-pregnant myometrium by mRNA analysis and immunoblotting. mRNA encoding for AC I, II, III, VIII and IX was present in non-pregnant and pregnant myometrium, and in cultured myometrial cells. Differing levels of AC protein could be detected in myometrial plasma membranes, with decreased levels of Group 1 (isoforms I, III and VIII) and Group 4 (IX) ACs allied with increased levels of Group 2 (II, IV and VII) and 3 (V and VI) ACs during pregnancy. These findings imply a role for Group 2-activating pathways, e.g. G-protein betagamma-subunits and protein kinase C, in the maintenance of uterine quiescence, whilst suggesting a lesser involvement of calcium-calmodulin complex, an activator of Group 1 AC isoforms, in uterine relaxation during gestation. These data may provide an alternative pharmacological approach for the attenuation of preterm labour.

Expression of G-protein-coupled receptor kinases in pregnant term and non-pregnant human myometrium.

There is evidence for hormonal receptor desensitisation in human myometrium, but little is known about the mechanisms involved in the loss of myometrial response to agonists such as beta(2)-adrenergic agonists, prostaglandin gamma and oxytocin. It is well known that the receptors for these hormones are coupled to G-proteins. The first step of receptor desensitisation is the phosphorylation of activated receptors by a G-protein-coupled receptor kinase (GRK). GRKs are members of a multigene family and the various subtypes differ in their localisation, regulation and mode of action. We have used Western blotting and reverse transcription PCR to identify the GRKs present in human myometrium from pregnant and non-pregnant women as well as in cultured human myometrial cells. We have found that human myometrium expresses the GRK subtypes 2, 4gamma, 5 and 6. On the other hand, GRK3 and the isoforms GRK4alpha, beta and delta were not found in myometrial tissue. Our data indicate that GRK2 is only expressed in pregnant term myometrium and is not found in non-pregnant tissue. Moreover, GRK6 appears to be expressed at a much higher level in pregnant term tissue than in non-pregnant myometrium. Our observations suggest that GRK2 and GRK6 may contribute to the regulation of uterine contractility at term. Further work is necessary to determine whether GRKs and receptor desensitisation play a role in disorders of uterine contractility.

Poor responders to ovulation induction: is proceeding to in-vitro fertilization worthwhile?

A 'poor response' in the context of in-vitro fertilization (IVF) can be defined as failure to produce an adequate number of mature follicles, and/or a peak oestradiol concentration less than a defined minimum. The cut-off points implied in this definition vary between different centres. Many opt to cancel the IVF cycle when their defined minimum concentrations are not reached despite the lack of evidence of improved outcome in subsequent cycles. Patients attending the Oxford Fertility Unit who are 'poor responders' have always been given the option of continuing with treatment. The first cycles of IVF in 124 patients, with normal day 3 follicle stimulating hormone (FSH), who produced less than five follicles within a 2 year period were studied. The patients were divided into three groups according to the number of follicles produced: A (one or two follicles; n = 33), B (three follicles; n = 33) and C (four follicles; n = 58). The three groups were similar in age, day 3 FSH, total gonadotrophin dose, duration of stimulation, peak oestradiol concentration, oocyte yield, fertilization rate and the clinical pregnancy rate. However, group A had a significantly higher oestradiol concentration per follicle (P < 0.001). The clinical pregnancy rate/cycle in the three groups was comparable to our overall rate in the study period (25.5%). This paper suggests that poor responders with a normal day 3 FSH may still achieve a pregnancy rate similar to that of normal responders.

A novel method of purifying lung surfactant proteins A and D from the lung lavage of alveolar proteinosis patients and from pooled amniotic fluid.

A simple procedure has been developed for the purification of the surfactant proteins SP-A and SP-D from lung lavage of patients with alveolar proteinosis. The SP-D is purified by fractionation of the supernatant obtained after spinning the lavage at 10000 X g for 40 min, while the bulk of the SP-A is purified by fractionation of the pellet. The supernatant is applied to a maltosyl-agarose column and the bound SP-D is specifically eluted using MnCl2. The pellet is solubilised in 6 M urea and, following renaturation, the solubilised proteins are applied to maltosyl-agarose and SP-A eluted using a gradient of EDTA. Both SP-A and SP-D are further purified by gel-filtration on Superose-6. This procedure has also been used to prepare successfully human SP-A and SP-D from amniotic fluid and may be generally applicable to the isolation of these surfactant proteins from lung washings obtained from other species.

Levels of corticotrophin-releasing hormone receptor subtype 1 mRNA in pregnancy and during labour in human myometrium measured by quantitative competitive PCR.

It is suggested that corticotrophin-releasing hormone (CRH) is involved in parturition. We have previously reported the presence of the CRH receptor subtype 1 (CRH R1) in human uterine myocytes. The aim of the present study was to investigate whether expression of the CRH R1 in myometrial tissue changes in pregnancy and labour. We used a quantitative competitive PCR method to measure the mRNA levels of this receptor in non-pregnant and in term pregnant myometrium before and at different stages of labour. The levels of mRNA for the housekeeping gene for glucocerebrosidase (GCB) were also determined. The results were expressed as a ratio of CRH R1 and GCB mRNA levels. We have found that in pregnancy the CRH R1 is down-regulated from a ratio of 0.093+/-0.011 in non-pregnant myometrium to 0.012+/-0.005 (P<0.001) in term non-labouring myometrium. No significant changes were observed in the CRH R1:GCB ratio in tissues sampled within 13 h (0.013+/-0.004) from the start of labour. In summary, normalised levels of CRH R1 are down-regulated in pregnancy and do not change during labour. We speculate that our results do not support a direct role for the CRH R1 receptor in myometrial stimulation.

Superovulation with a high gonadotropin dose for in vitro fertilization: is it effective?

PURPOSE: Our purpose was to investigate the effect on the ovarian response of increasing the gonadotropin dose. METHODS: We analyzed retrospectively the in vitro fertilization data for patients who had two cycles of treatment, with a higher dose in cycle 2. The patients were stratified according to age, ovarian response, and gonadotropin dose in the first cycle. The main outcome measure was the number of follicles, eggs, and embryos and the peak estradiol (E2) level. RESULTS: The study included 244 patients. Patients in both age groups (n = 118, < or = 33 years; n = 126, > 33 years), low (n = 66) and intermediate (n = 145) responders, and patients who received < 225 IU follicle-stimulating hormone (n = 175) in cycle 1 had a better response in cycle 2. However, the high responders (n = 33) and those who received 225 or 300 IU follicle-stimulating hormone (n = 69) in cycle 1 showed a similar response in both cycles, except for a significantly higher E2 level in cycle 2. CONCLUSIONS: Our results indicate that exceeding a daily dose of 300 IU is unrewarding.

The cytoskeleton of human myometrial cells.

Eukaryotic cells have an internal cytoskeletal scaffolding, giving them their distinctive shapes. The cytoskeleton enables cells to transport vesicles, undergo changes in shape, migrate and contract. This dynamic structure is formed by three classes of filamentous assembly: actin microfilaments, intermediate filaments and microtubules. In this investigation the cytoskeleton of cultured human myometrial cells was studied by immunohistochemistry using specific antibodies against vinculin, cytokeratin, vimentin, tubulin and RhoA, covalently labelled with a fluorescent tag. Polymerized actin was visualized with fluorescein-conjugated phalloidin. Myometrial cells were very rich in actin fibres, which generally appeared as parallel bundles along the longest axis of the cells. There was a strong expression of vinculin which concentrated at actin--vinculin focal adhesion sites. By contrast, intermediate filaments (vimentin and cytokeratin) were organized in a dense cytoplasmic meshwork which excluded the nuclear space. A similar pattern was observed for tubulin. RhoA had a diffuse distribution and was associated with actin fibres. Exposure of the cells to oxytocin provoked a 10% shortening of actin stress fibres. These results demonstrate that myometrial smooth muscle cells have a rich cytoskeletal structure and that agonists that stimulate myometrial activation provoke measurable changes in actin fibres which may be important for efficient contractility.

Comparison of highly purified FSH (metrodin-high purity) with pergonal for IVF superovulation.

PURPOSE: The use of highly purified follicle-stimulating hormone (Metrodin-HP) was compared with that of a preparation containing follicle-stimulating hormone and luteinizing hormone (Pergonal) for production of superovulation in an IVF program. METHODS: We used the Oxford Fertility Unit database to identify patients undergoing their first cycle of IVF, using either Metrodin-HP or Pergonal. Patients were treated with a standardized drug protocol and were stratified by age and cause of infertility. Ovarian stimulation with either Metrodin-HP (Serono Laboratories) or human menopausal gonadotropin (hMG; Pergonal; Serono Laboratories) after pituitary desensitization commenced in the midluteal phase of the preceding cycle. Monitoring was performed by ultrasound and serum estradiol measurement prior to transvaginal oocyte recovery, followed by IVF and transfer of no more than three embryos. RESULTS: For Metrodin-HP versus Pergonal, the rates of egg retrieval (98 vs 94%), fertilization (89 vs 92%), clinical pregnancy (32.9 vs 23.4%), miscarriage (4.1 vs 4.5%), live birth (26 vs 18.5%), and ovarian hyperstimulation syndrome (5.5% vs 5.9%) were similar in both groups. The apparent increase in clinical pregnancy and live birth with Metrodin-HP did not reach statistical significance. The dosages of gonadotropins used were comparable. Estradiol levels measured on day 8 of stimulation were significantly lower in the Metrodin-HP group than in the Pergonal group, but the difference did not reach statistical significance on the day of hCG administration. Significantly more follicles (greater than 12 mm) were obtained in the Metrodin-HP group, but the numbers of eggs recovered and fertilized were similar in the two groups. CONCLUSIONS: These findings demonstrate that highly purified FSH (Metrodin-HP) is as effective and successful as hMG (Pergonal) for ovarian stimulation in a standard IVF regimen. Exogenous luteinizing hormone (LH) is not required for satisfactory ovarian stimulation in IVF. Measurement of estradiol may be less helpful in the monitoring of Metrodin-HP cycles, but the level reached on the day of hCG administration can still be used to predict, and hence avoid, ovarian hyperstimulation syndrome.

The desensitization of oxytocin receptors in human myometrial cells is accompanied by down-regulation of oxytocin receptor messenger RNA.

We have recently provided evidence for the desensitization of oxytocin receptors in human myometrial cells. In the present study, we have investigated the possible mechanisms by which oxytocin (OT) might regulate OT receptor density. The steady state level of OT binding in cultured myometrial cells was 220 x 10(3) binding sites/ cell, but this was time-dependently reduced to 27 x 10(3) sites/cell by exposure to OT for up to 20 h. Similarly, OT exposure decreased the binding of OT to cell membranes. In contrast, Western blotting data showed that the total amount of OT receptor protein was not affected by OT treatment for up to 48 h. Flow cytometry experiments demonstrated that OT receptors are not internalized during prolonged exposure of the cells to OT. However, RNase protection assays and Northern analysis showed that OT receptor mRNA was reduced by OT treatment to reach a new low steady state level with a time course similar to that of the disappearance of cell surface OT binding sites. Possible mechanisms involved in mRNA down-regulation include transcriptional suppression and destabilization of mRNA by RNA binding proteins.

Expression of human myometrial G alpha s messenger ribonucleic acid transcript during pregnancy and labour: involvement of alternative splicing pathways.

We have shown previously that expression of 46 and 54 kDa human myometrial G alpha s protein isoforms is increased during gestation and then subsequently decreased during labour. These proteins appear to be coded for by G alpha s-Small (with a serine residue at position 72) and G alpha s-Large (with a serine residue at position 87) mRNA splice variants respectively. In the study presented here we have used a G alpha s cDNA template to generate [32P]cytidine cRNA riboprobes for use in RNase protection assays, so as to measure total myometrial G alpha s mRNA levels in relation to the pattern of expression of G alpha s mRNA splice variants during pregnancy and labour. We report that total levels of human myometrial G alpha s mRNA remain similar in non-pregnant and pregnant women but are substantially reduced during parturition. Our data also provide strong evidence that alternative splicing of G alpha s precursor mRNA has a primary role in regulating expression of G alpha s protein isoforms during pregnancy and labour. The inclusion of an additional serine codon in G alpha s mRNAs during pregnancy involves a switch in alternative splicing pathways. We speculate that this switch may be due to a change in specificity of splicing factors that are modulated during pregnancy and labour.