Effects of Heliotropium indicum L. on Uterine Involution and Its Underlying Mechanisms: an in vivo and in vitro Study.

OBJECTIVE: To investigate the effect of Heliotropium indicum L. (H. indicum L.) on uterine involution and its underlying mechanisms in both in vivo and in vitro study. METHODS: For in vivo studies, postpartum rats were randomly divided into 2 groups (n=24 for each): control group and treated group which were orally and daily administered with ethanolic extract of H. indicum L. (250 mg/kg body weight) until day 5 of postpartum. Uteri were collected for analysis of weight, cross-sectional area, collagen cross-sectional area, and collagen content on postpartum day 1, 3, and 5 (n=8 for each) from both groups. Blood samples were collected for hepatotoxicity and 17ß-estradiol (E2) measurement. For in vitro studies, the extract effects on uterine contraction at half maximum effective concentration of 2.50 mg/mL were studied in organ bath system for at least 20 min. RESULTS: Uterine parameters were significantly decreased after treated with extract of H. indicum L. (P<0.05). H. indicum L. extract significantly accelerated the reduction of those parameters and significantly decreased E2 (P<0.05). The extract facilitated uterine involution with no hepatotoxicity. H. indicum L. extract significantly stimulated uterine contraction (P<0.05) and synergized with oxytocin, prostaglandin and its precursor, linoleic acid. By investigating the different sequencing of the extract with the additional stimulants (added before or after), the two showed antagonistic effects, but still showed potentiated force when compared with control (without the stimulants). CONCLUSIONS: The underlying mechanisms by which H. indicum L. facilitated uterine involution might be due to reducing E2 which induces collagenase activity, leading to decreases in uterine weight and size and stimulating uterine contraction. Our study provides new findings for future drug development for facilitating uterine involution with H. indicum L.

The Effect of Pluchea indica (L.) Less. Tea on Blood Glucose and Lipid Profile in People with Prediabetes: A Randomized Clinical Trial.

Objective: Diabetes mellitus and dyslipidemia are currently increasing dramatically, and conventional medicine in the treatment of them has limited efficacies and serious adverse effects. Pluchea indica (L.) Less. tea (PIT) is widely consumed as a health-promoting drink in Southeast Asia. This study aimed to investigate whether P. indica tea has antidyslipidemic and antihyperglycemic effects and toxicity in humans. Design: A randomized clinical trial. Setting/Location: Nakhonratchasima, Thailand. Participants: Forty-five participants with prediabetes. Interventions: Participants were randomized to receive placebo tea, 1.5 g of PIT, and 1.5 g Camellia sinensis tea (green tea, CST) once daily for 12 weeks. Outcome Measurements: The oral glucose tolerance test (OGTT), total cholesterol, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), blood urea nitrogen (BUN), creatinine, alanine transaminase (ALT), alkaline phosphatase (ALP), and complete blood count (CBC) before and after treatment were investigated. Results: The results showed that PIT significantly ameliorated hyperglycemia and significantly lower serum TG (109.22 ± 5.21 mg/dL) and LDL-C (122.20 ± 3.67 mg/dL) than placebo (145.56 ± 8.18 and 142.07 ± 8.58 mg/dL, respectively) (p < 0.05). Moreover, PIT exhibited serum TG (109.22 ± 5.21 mg/dL) significantly lower than CST (124.38 ± 4.70 mg/dL) (p < 0.05). In addition, the serum HDL-C of PIT (57.56 ± 3.05 mg/dL) was significantly higher than the placebo (46.44 ± 2.47 mg/dL) (p < 0.05). Furthermore, the toxicity testing showed that no significant difference in BUN, creatinine, ALT, ALP, and CBC of PIT-treated group compared with the placebo (p > 0.05). Conclusions: These results suggest that PIT may ameliorate hyperglycemia and dyslipidemia in prediabetes people. It may not be toxic to the kidney, liver, and blood. So, PIT has the potential to develop to be a health-promoting tea or herbal medicine for hyperglycemia and dyslipidemia prevention.

Pluchea indica (L.) Less. Tea Ameliorates Hyperglycemia, Dyslipidemia, and Obesity in High Fat Diet-Fed Mice.

Pluchea indica (L.) Less. (P. indica) tea has been used for a health-promoting drink, especially in Southeast Asia. The effect of P. indica tea (PIT) on amelioration of hyperglycemia; dyslipidemia that was total cholesterol (TC), LDL-cholesterol (LDL-C), HDL-cholesterol (HDL-C), and triglyceride (TG); and obesity in high fat diet-induced (HFD) mice was investigated. Oral glucose tolerance test (OGTT) displayed that PIT at 400 and 600 mg/kg orally ameliorated hyperglycemia with a dose-dependent manner compared to the untreated group. Moreover, PIT at these dosages exhibited significantly lower TC, LDL-C, TG, and perigonadal fat weight in HFD treated mice compared to HFD mice (P < 0.05) with a dose-dependent manner. In contrast, HDL-C was higher than in the HFD group, but not a significant difference (P > 0.05). The PIT chemical analysis results demonstrated that PIT contained total phenolic content (TPC), total flavonoid content (TFC), 4-O-caffeoylquinic acid (4-CQ), 5-O-caffeoylquinic acid (5-CQ), 3,4-O-dicaffeoylquinic acid (3,4-CQ), 3,5-O-dicaffeoylquinic acid (3,5-CQ), 4,5-O-dicaffeoylquinic acid (4,5-CQ), beta-caryophyllene, and gamma-gurjunene that may play an important role in inhibiting hyperlipidemia and hyperglycemia. Also, histological analysis expressed that the mean area and amount of perigonadal fat adipocytes of PIT treated groups were significantly lower and higher than the HFD group (P < 0.05), respectively. The toxicity test of PIT at 600 mg/kg/day in mice showed that serum creatinine, alanine transaminase (ALT), alkaline phosphatase (ALP), and complete blood count (CBC) levels of HFD and PIT treated groups were not significantly different compared to the normal control diet group (NCD) (P > 0.05). These results suggest that PIT does not become toxic to the kidney, liver, and blood. In conclusion, PIT has the potential to develop into healthy food supplement or medicine for the prevention and treatment of hyperglycemic, hyperlipidemic, and obese patients.

The Effects of Cordyceps sinensis (Berk.) Sacc. and Gymnema inodorum (Lour.) Decne. Extracts on Adipogenesis and Lipase Activity In Vitro.

This study aimed to investigate the effects of Cordyceps sinensis extract (CSE) and Gymnema inodorum extract (GIE), used alone and combined, on antiadipogenesis in 3T3-L1 cells. Oil Red O staining was used to examine the effects of these extracts on inhibition of intracellular lipid accumulation in 3T3-L1 adipocytes and on lipid droplet morphology. Fourier transform-infrared (FTIR) microspectroscopy was used to examine biomolecular changes in 3T3-L1 adipocytes. The pancreatic lipase assay was used to evaluate the inhibitory effects of CSE and GIE on pancreatic lipase activity. Taken together, the results indicated that CSE, GIE, and their combination suppressed lipid accumulation. The FTIR microspectroscopy results indicated that CSE, GIE, and their combination had inhibitory effects on lipid accumulation in the adipocytes. Compared with the untreated adipocytes, the signal intensity and integrated areas of glycogen and other carbohydrates, the acyl chain of phospholipids, and the lipid/protein ratios of the CSE, GIE, alone, and combined treated adipocytes were significantly lower (p < 0.05). Combination treatment resulted in a synergistic effect on lipid accumulation reduction in the adipocytes. Principal component analysis of the biomolecular changes revealed six distinct clusters in the FTIR spectra of the sample cells. The pancreatic lipase assay results indicated that CSE and GIE inhibited the pancreatic lipase activity in a dose-dependent manner (mean ± standard error of the mean IC50 values, 2312.44 ± 176.55 µg mL-1 and 982.24 ± 44.40 µg mL-1, resp.). Our findings indicated that FTIR microspectroscopy has potential application for evaluation of the effectiveness of medicinal plants and for the development of infrared biochemical obesity markers useful for treating patients with obesity. These results suggested that use of CSE and GIE alone and in combination may be efficacious as a complementary therapy for hyperlipidemia and obesity management. However, clinical trials in animals and humans must first be completed.

Effects of egg yolk and soybean lecithin on sperm quality determined by computer-assisted sperm analysis and confocal laser scanning microscope in chilled canine sperm.

The reduction of spermatozoa survival time is a major problem of canine chilled sperm for artificial insemination. The aim of the study was to improve the quality of canine chilled sperm during storage time. We therefore, evaluated the effects of eight treatments with different levels of soybean lecithin concentration (1, 3 and 5%) and egg yolk (20%) in Tris-citric-fructose or Tris-citric-fructose-mineral salts extender on chilled canine sperm quality during 10 days of storage. The sperm motility was analysed by computer-assisted sperm analysis (CASA), whereas plasma membrane integrity, acrosome membrane integrity and mitochondrial membrane potential parameters were determined using a fluorescent staining combination of propidium iodide (PI), Hoechst 33342 (H342), fluorescein isothiocyanate-conjugated Pisum sativum agglutinin (FITC-PSA) and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyanine iodide (JC-1) by confocal laser scanning microscope. The results showed that egg yolk was found to be better than soybean lecithin in Tris-citric-fructose or Tris-citric-fructose-mineral salts extender for maintaining the quality of chilled canine sperm within 10 days of storage (P < 0.05). Although egg yolk in Tris-citric-fructose extender could maintain the motility better than other extenders, egg yolk in Tris-citric-fructose-mineral salts extender was the highest in intact plasma membrane, intact acrosome membrane and high mitochondrial membrane potential (P < 0.05). In contrast, the sperm quality of soybean lecithin in Tris-citric-fructose-mineral salts extender was lower than that of soybean lecithin in Tris-citric-fructose extender, and soybean lecithin 1% was greater than soybean lecithin 3% and 5% in plasma membrane integrity, acrosome membrane integrity and mitochondrial membrane potential (P < 0.05). In conclusion, soybean lecithin cannot replace egg yolk in Tris-citric-fructose or Tris-citric-fructose-mineral salts extenders, and egg yolk in Tris-citric-fructose-mineral salts extender is superior to other extenders in chilling canine sperm.

The effects of Ginseng Java root extract on uterine contractility in nonpregnant rats.

Ginseng Java or Talinum paniculatum (Jacq.) Geartn has long been used in herbal recipes because of its various therapeutic properties. Ginseng Java is believed to be beneficial to the female reproductive system by inducing lactation and restoring uterine functions after the postpartum period. There are, however, no scientific data on verifying the effects on the uterus to support its therapeutic relevance. Therefore, the purpose of this study was to investigate the effects of Ginseng Java root extract and its possible mechanism(s) of action on uterine contractility. Female virgin rats were humanely killed by CO2 asphyxia and uteri removed. Isometric force was measured in strips of longitudinal myometrium. The effects of Ginseng Java root extract at its IC50 concentration (0.23 mg/mL) on spontaneous, oxytocin-induced (10 nmol/L), and depolarized (KCl 40 mmol/L) contraction were investigated. After establishing regular phasic contractions, the application of Java root extract significantly inhibited spontaneous uterine contractility (n = 5). The extract also significantly inhibited the contraction induced by high KCl solution (n = 5) and oxytocin (n = 5). The extract also inhibited oxytocin-induced contraction in the absence of external Ca entry (n = 7) and the tonic force induced by oxytocin in the presence of high KCl solution. Taken together, the data demonstrate a potent and consistent ability of extract from Ginseng Java root to reduce myometrial contractility. The tocolytic effects were demonstrated on both spontaneous and agonist-induced contractions. The fact that force was inhibited in depolarized conditions suggests that the possible mechanisms may be blockade of Ca influx via L-type Ca channels. The data in Ca-free solutions suggest that the extract also reduces IP3-induced Ca release from the internal store. These tocolytic effects do not support the use of ginseng to help with postpartum contractility, but instead suggest it may be helpful in reducing inappropriate uterine contractions, such as in threatened preterm delivery.

Synergistic activity and mechanism of action of Stephania suberosa Forman extract and ampicillin combination against ampicillin-resistant Staphylococcus aureus.

BACKGROUND: Ampicillin-resistant S. aureus (ARSA) now poses a serious problem for hospitalized patients, and their care providers. Plant-derived antibacterial that can reverse the resistance to well-tried agents which have lost their original effectiveness are the research objectives of far reaching importance. To this aim, the present study investigated antibacterial and synergistic activities of Stephania suberosa extracts (SSE) against ARSA when used singly and in combination with ampicillin. RESULTS: The majority chemical compounds of SSE were alkaloid (526.27 ± 47.27 mg/1 g of dried extract). The Minimum inhibitory concentration (MICs) for ampicillin and SSE against all ARSA strains were >512 µg/ml and 4 mg/ml, respectively. Checkerboard assay revealed synergistic activity in the combination of ampicillin (0.15 µg/ml) and SSE (2 mg/ml) at fractional inhibitory concentration index (FICI) <0.5. The killing curve assay had confirmed that the viability of ARSA was dramatically reduced from 5 x 10(5) cfu/ml to 10(3) cfu/ml within 6 h after exposure to SSE (2 mg/ml) plus ampicillin (0.15 µg/ml) combination. Electron microscopic study clearly revealed that these ARSA cells treated with this combination caused marked morphological damage, peptidoglycan and cytoplasmic membrane damage, and average cell areas significant smaller than control. Obviously, Immunofluorescence staining and confocal microscopic images confirmed that the peptidoglycan of these cells were undoubtedly disrupted by this combination. Furthermore, the CM permeability of ARSA was also increased by this combination. Enzyme assay demonstrated that SSE had an inhibitory activity against ß-lactamase in concentrations manner. CONCLUSIONS: So, these findings provide evidence that SSE has the high potential to reverse bacterial resistance to originate traditional drug susceptibility of it and may relate to three modes of actions of SSE: (1) inhibits peptidoglycan synthesis, resulting in morphological damage, (2) inhibits ß-lactamases activity, and (3) increases CM permeability. It is widely recognized that many types of drugs are derived from alkaloids. So, this SSE offers the prominent potential to develop a novel adjunct phytopharmaceutical to ampicillin for the treatment of ARSA. Further active ingredients study, toxicity of it, and the synergistic effect on blood and tissue should be performed and confirmed in an animal test or in humans.

Finding new agents in medicinal plants to act on the myometrium.

This report summarizes work investigating the effects of some medicinal plants on uterine contraction. As there is a clinical need to find better drugs to help control uterine activity, and novel compounds are sought, the mechanisms whereby the medicinal plants exert their effects, as well as their major compounds, are discussed. By identifying the plants, major constituents and mechanisms, this review also illustrates the potential for development of new drugs, so that better ways to treat uterine disorders will be available to women worldwide.

Antibacterial activity of Aquilaria crassna leaf extract against Staphylococcus epidermidis by disruption of cell wall.

BACKGROUND: Aquilaria crassna Pierre ex Lecomte has been traditionally used in Thailand for treatment of infectious diseases such as diarrhoea and skin diseases for a long time. The main objectives of this study were to examine antibacterial activity of the Aquilaria crassna leaf extract against Staphylococcus epidermidis and its underlying mechanism. The antioxidant activity and acute toxicity were studied as well. METHODS: Antioxidant activities were examined by FRAP, ABTS and DPPH scavenging methods. Antibacterial activity was conducted using disc diffusion assay and the minimum inhibitory concentration (MIC) was determined by dilution method. The minimum bactericidal concentration (MBC) was reported as the lowest concentration producing no growth of microbes in the subcultures. Morphological changes of the microbe were observed by scanning electron microscopy, while an inhibitory effect on biofilm formation was evaluated by phase contrast microscopic analysis. Bacterial cell wall integrity was assessed by transmission electron microscopy. Acute toxicity was conducted in accordance with the OECD for Testing of Chemicals (2001) guidelines. RESULTS: The extract exhibited considerable antioxidant activity. Staphylococcus epidermidis was susceptible to the extract with the MIC and MBC of 6 and 12 mg/ml, respectively. The extract caused swelling and distortion of bacterial cells and inhibited bacterial biofilm formation. Rupture of bacterial cell wall occurred after treated with the extract for 24 h. Acute toxicity test in mice showed no sign of toxicity or death at the doses of 2,000 and 15,000 mg/kg body weight. CONCLUSION: The aqueous extract of Aquilaria crassna leaves possesses an in vitro antibacterial activity against Staphylococcus epidermidis, with no sign of acute oral toxicity in mice, probably by interfering with bacterial cell wall synthesis and inhibiting biofilm formation.

Participation of citral in the bronchodilatory effect of ginger oil and possible mechanism of action.

The extract of ginger, the rhizomes of Zingiber officinale Roscoe (Zingiberaceae), has been reported to possess anti-hyperactivity and anti-inflammation on airway. The present study described brochodilatory activity of ginger oil and identified its active compound. Ginger oil was extracted by hydro-distillation. The compositions of ginger oil were analyzed by gas chromatography and mass spectrometer. Citral, eucalyptol and camphene were found to be the major components. Ginger oil and citral, but not camphene, suppressed rat tracheal contraction induced by carbachol (CCh). Consistent with previous report, eucalyptol showed a relaxing effect on rat airway. Since the content of eucalyptol in ginger oil was relatively low, the contribution of eucalyptol to the bronchodilatory effect of ginger oil was small. To elucidate the mechanisms responsible for the myorelaxing effect, propranolol (a ß-adrenergic receptor antagonist), indomethacin (a COX inhibitor) and L-NAME (a NOS inhibitor) were used to block the inhibitory effects of ginger oil and citral. It was found that propranolol, but not indomethacin and L-NAME, reversed bronchodilatory effects of both ginger oil and citral, suggesting that a possible mechanism involved ß-adrenergic receptor. This study provides the pharmacological basis supporting the therapeutic potential of Z. officinale rhizomes as a bronchodilator.

The effects of watermelon (Citrullus lanatus) extracts and L-citrulline on rat uterine contractility.

In uterine smooth muscle, the effects of watermelon and its citrulline content are unknown. The aims of this study were therefore, to determine the effects of watermelon extract and citrulline on the myometrium and to investigate their mechanisms of action. The effects of extracts of watermelon flesh and rind and L-citrulline (64 µmol/L) were evaluated on 3 types of contractile activity; spontaneous, those elicited by potassium chloride (KCl) depolarization, or oxytocin (10 nmol/L) application in isolated rat uterus. Inhibitors of nitric oxide (NO) and its mechanisms of action, N ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 100 µmol/L), LY83583 (1 µmol/L), and tetraethylamonium chloride (5 mmol/L), as well as Ca signaling pathways, were determined. Both flesh and rind extracts significantly decreased the force produced by all 3 mechanisms, in a dose-dependent manner. The extracts could also significantly decrease the force under conditions of sustained high Ca levels (depolarization and agonist) and when the force was produced only by sarcoplasmic reticulum (SR) Ca release. L-citrulline produced the same effects on force as watermelon extracts. With submaximal doses of extract, the additive effects of L-citrulline were found. The inhibitory effects of extracts and L-citrulline were reversed upon the addition of NO inhibitors, and pretreatment of tissues with these inhibitors prevented the actions of both extracts and L-citrulline. Thus, these data show that watermelon and citrulline are potent tocolytics, decreasing the force produced by calcium entry and SR release and arising by different pathways, including oxytocin stimulation. Their major mechanism is to stimulate the NO-cyclic guanosine monophosphate (cGMP) relaxant pathway.

The effects of wild ginger (Costus speciosus (Koen) Smith) rhizome extract and diosgenin on rat uterine contractions.

The aim of this study was to investigate the effects of wild ginger (Costus speciosus (Koen) Smith, Costaceae) rhizome extract on uterine contractility. We particularly examined the effects on spontaneous phasic contractions and the mechanisms whereby it exerts its effects. Wild ginger rhizomes were ethanolic extracted and their constituents analyzed. Isometric force was measured in strips of longitudinal myometrium and the effects of the extract studied. The extract (10 mg/100 mL) increased spontaneous contractions. The amplitude and frequency of the phasic contraction were significantly increased along with basal tension. Force produced in the presence of the extract was abolished by inhibition of l-type calcium channels or myosin light chain kinase (MLCK). The actions of the extract were not blocked by the estrogen receptor blocker, fulvestrant. Although significant amounts of diosgenin were present in the extract, we found that, depending upon its concentration, diosgenin had either no effect or was inhibitory on force. Interestingly, the extract induced significant amounts of force in the absence of extracellular calcium, which could be blocked by inhibition of the sarcoplasmic reticulum calcium-ATPase (SERCA), but not fulvestrant. We conclude that wild ginger rhizome extract stimulates phasic activity in rat uterus. Our data suggest that the uterotonic effect is due to nonestrogenic effects and not those of diosgenin. Wild ginger was able to increase contraction via calcium entry on l-type calcium channels and sarcoplasmic reticulum (SR) calcium release. We suggest that wild ginger rhizome extract may be a useful uterine stimulant.

The effects of pomegranate seed extract and beta-sitosterol on rat uterine contractions.

The aim of this study was to investigate the effects of pomegranate (Punica granatum L., Punicaceae) seed extract on uterine contractility. Pomegranate seeds were methanolic extracted and their constituents analyzed using gas chromatography and mass spectrometry. Isometric force was measured in strips of longitudinal rat myometrium and the effects of pomegranate seed extract studied. We found beta-sitosterol to be the main constituent of the extract (16%) and its effects were also investigated. Pomegranate seed extract and beta-sitosterol increased spontaneous contractions in a concentration-dependent manner with a maximum effect at 250 mg/100 mL and 1 mg/100 mL, respectively. The amplitude and frequency of the phasic contraction were significantly increased along with basal tension. The effects of pomegranate seed extract were very similar to those of beta-sitosterol. Force produced in the presence of pomegranate seed extract was abolished by the inhibition of L-type calcium channels or myosin light chain kinase (MLCK). Contractions were not potentiated by pomegranate extract following the inhibition of K channels or inhibition of the sarcoplasmic reticulum calcium ATPase (SERCA). The actions of beta-sitosterol and the extract were not blocked by the estrogen receptor blocker, fulvestrant. We conclude that pomegranate seed extract is a potent stimulator of phasic activity in rat uterus. Our data suggest that the uterotonic effect is due to nonestrogenic effects of beta-sitosterol acting to inhibit K channels and SERCA and thereby increasing contraction via calcium entry on L-type calcium channels and MLCK. We suggest that pomegranate extract and beta-sitosterol may be a useful uterine stimulant.

Inhibitory effects of ginger oil on spontaneous and PGF2alpha-induced contraction of rat myometrium.

Solvent extracts of ginger, the rhizome of Zingiber officinale Roscoe (Zingiberaceae), have been extensively studied for their pharmacological activities in smooth muscles. However, the effects of ginger essential oil on smooth muscle contractility have not been elucidated. The aims of the study were to investigate the effects of ginger oil on rat myometrial contractility. We particularly examined the effects on phasic contractions arising either spontaneously or with PGF (2) (alpha) stimulation. Ginger oil was obtained by hydrodistillation and its constituents analyzed using gas chromatography and mass spectrometry. Rats were humanely killed by asphyxiation with CO (2), and longitudinal uterine smooth muscles were isolated. Isometric force was measured and the effects of ginger oil studied. It was found that citral was the main constituent of ginger oil (24 %). Ginger oil inhibited spontaneous contractions with an IC (50) of 50 microL/100 mL (10 - 150 microL/100 mL). The PGF (2) (alpha)-induced contractions were also significantly reduced by ginger oil. Increases in external calcium concentration completely reversed the relaxant effects of ginger oil. This was the case for both spontaneous and PGF (2) (alpha)-induced contractions. The effects of ginger oil were indistinguishable from those of pure citral. In conclusion, ginger oil is a potent inhibitor of phasic activity in rat uterus, irrespective of how it was produced. Our data suggest that the effects are largely due to citral, and could be via inhibition of L-type Ca channels.

The effects of pH change on Ca(++) signaling and force in pregnant human myometrium.

OBJECTIVE: This study was designed to determine the effects of both intracellular and extracellular pH change on contractile activity and intracellular Ca(++) during spontaneous contractions, oxytocin, and depolarization-induced stimulation of human myometrium. STUDY DESIGN: Human myometrial tissue was obtained at elective caesarean delivery at term (37-41 completed weeks of gestation). Longitudinal strips were dissected and loaded with the calcium sensitive indicator Indo-1. Statistical significance was tested with the Student t test. RESULTS: Both intracellular and extracellular acidification significantly reduces or even abolishes phasic activity, whether it arises spontaneously or in the presence of oxytocin. These contractile changes can be accounted for by the changes in intracellular Ca(++). Alkalinization produced the opposite effects. However, baseline or maintained tension changes could not be accounted for by changes in intracellular Ca(++). CONCLUSION: We suggest that the effects on phasic activity are due to the inhibition of L-type calcium entry and that, during maintained or baseline activity, pH-sensitive Ca(++) release, possibly from the sarcoplasmic reticulum occurs; but it is insufficient to overcome the inhibitory effects at the myofilaments. We conclude that alterations of pH significantly affect calcium signaling and force production in the human myometrium and may contribute to dysfunction in labor.

Role of the sarcoplasmic reticulum in uterine smooth muscle.

The sarcoplasmic reticulum (SR) is present as an extensive network in uterine cells. In this chapter we examine its functional importance, relating in particular, to the control of contractility in pregnancy. The uterine SR has both ryanodine receptors (RyR) and inositol-1 ,4,5-trisphosphate InsP3 receptors (InsP3R). The RyR and subsequent Ca24-induced Ca2+ release play little role in either human or rat contractions or Ca2+ transients. There may be subtle, spatiotemporal effects at the single cell level. Caffeine, an agonist for RyR fails to release Ca2+ and indeed produces relaxation not contraction. InsP3 dearly causes release of Ca2+ from the uterine SR and an increase in force, although these changes are only small and transient compared to those occurring due to external Ca2+ entry. Inhibition of the SR Ca-ATPase by cyclopiazonic acid, empties Ca2+ from the SR. This is associated with an augmentation of force and Ca2+ transient. Thus the SR normally functions in the uterus to limit, not increase contractions. The mechanism may involve vectoral release of Ca2+ from the SR and activation of surface membrane K+ channels. This activation would tend to decrease L-type Ca2+ entry and hence reduce contraction. Thus the SR is playing a role in controlling membrane excitability and hence contractility. The SR also plays a role in the relaxation of force. This is not primarily due to a direct sequestering of large amounts of Ca2+, but rather that the SR directs Ca2+ to the surface membrane extrusion mechanisms, i.e. Ca-ATPase and Na+/Ca2+ exchanger. This enables them to act more efficiently, and therefore aids relaxation. Recent direct measurements of SR luminal content show decreases with agonist application but not during spontaneous activity; confirming the results described above. This technique will be used to better characterize the uterine SR, its control and relevance to normal and abnormal labours.