Oocyte glutathione and fertilisation outcome of Macaca nemestrina and Macaca fascicularis in in vivo- and in vitro-matured oocytes

Fertilisation and development of IVM non-human primate oocytes is limited compared with that of in vivo-matured (IVO) oocytes. The present study describes the IVM of macaque oocytes with reference to oocyte glutathione (GSH). Timing of maturation, comparison of IVM media and cysteamine (CYS) supplementation as a modulator of GSH were investigated. A significantly greater proportion of oocytes reached MII after 30 h compared with 24 h of IVM. Following insemination, IVM oocytes had a significantly lower incidence of normal fertilisation (i.e. 2PN = two pronuclei and at least one polar body) and a higher rate of abnormal fertilisation (1PN = one pronucleus and at least one polar body) compared with IVO oocytes. Immunofluorescence of 1PN zygotes identified incomplete sperm head decondensation and failure of male pronucleus formation as the principal cause of abnormal fertilisation in IVM oocytes. The IVO oocytes had significantly higher GSH content than IVM oocytes. Cumulus-denuded oocytes had significantly lower GSH following IVM compared with immature oocytes at collection. Cysteamine supplementation of the IVM medium significantly increased the GSH level of cumulus-intact oocytes and reduced the incidence of 1PN formation, but did not improve GSH levels of the denuded oocyte. Suboptimal GSH levels in macaque IVM oocytes may be related to reduced fertilisation outcomes.

In vitro developmental potential of macaque oocytes, derived from unstimulated ovaries, following maturation in the presence of glutathione ethyl ester

BACKGROUND

The inadequacies of oocyte in vitro maturation (IVM) systems for both non-human primates and humans are evidenced by reduced fertilization and poor embryonic development, and may be partly explained by significantly lower glutathione (GSH) contents compared with in vivo matured (IVO) oocytes. As this influence has not been fully explored, this study investigated the effect of the GSH donor, glutathione ethyl ester (GSH-OEt), on the IVM and development of macaque oocytes as a model of human oocyte IVM.

METHODS

Macaque oocytes derived from unstimulated ovaries were cultured in mCMRL-1066 alone or supplemented with 3 or 5 mM GSH-OEt. In vitro matured oocytes were subjected to the GSH assay, fixed for the assessment of spindle morphology or prepared ICSI. Embryo development of zygotes cultured in mHECM-9 was assessed up to Day 9 post-ICSI. RESULTS Supplementation of the maturation medium with GSH-OEt significantly increased oocyte maturation and normal fertilization rates compared with control oocytes, but only 5 mM GSH-OEt significantly increased the oocyte and cumulus cell GSH content. Confocal microscopy revealed significant differences in the spindle morphology between IVO and control in vitro matured metaphase II oocytes. Oocytes matured with 5 mM GSH-OEt exhibited spindle area and spindle pole width similar to that seen in the IVO oocyte. While no significant differences were observed in blastocyst rates, addition of 3 mM GSH-OEt during IVM significantly increased the proportion of embryos developing to the 5-8 cell stage while 5 mM GSH-OEt significantly increased the proportion of morula-stage embryos compared with controls.

CONCLUSIONS

Supplementation of the IVM medium with GSH-OEt promotes better maturation and normal fertilization of macaque oocytes compared with non-supplemented medium. However, further improvement of the primate oocyte IVM culture system is required to support better blastocyst development of oocytes derived from unstimulated ovaries.

Primate model of metaphase I oocyte in vitro maturation and the effects of a novel glutathione donor on maturation, fertilization, and blastocyst development

OBJECTIVE

To assess the effect of glutathione ethyl ester (GSH-OEt) on the development of macaque metaphase (MI) oocytes as a model for human MI oocyte in vitro maturation (IVM).

DESIGN

Prospective cohort study.

SETTING

Nonhuman primate assisted reproductive technology program.

ANIMAL(S)

Twenty-three Macaca fascicularis females aged 6.5-12.5 years.

INTERVENTION(S)

Ovarian stimulation and maturation of MI oocytes in [1] human tubal fluid (HTF), [2] mCMRL-1066, [3] mCMRL-1066+GSH-OEt 3 mM, or [4] mCMRL-1066+GSH-OEt 5 mM. Oocytes were assessed for maturation after 4-6 hours (early) and 18-20 hours (late) of culture. Mature oocytes were inseminated or subjected to glutathione (GSH) assay. Zygotes were cultured to the blastocyst stage for total differential cell counts.

MAIN OUTCOME MEASURE(S)

Oocyte maturation rate, GSH content, pronuclear formation and blastocyst development, and cell number were compared between IVM treatment groups and sibling in vivo matured (IVO) MII oocytes.

RESULT(S)

Compared with HTF, mCMRL-1066 supported higher rates of normal fertilization and blastocyst development in early but not late maturing MI-MII oocytes. Five micromoles of GSH-OEt significantly increased blastocyst total cell and inner cell mass cell number in early MI-MII oocytes compared with IVO and IVM controls. GSH-OEt significantly increased oocyte GSH content and fertilization in late maturing oocytes but not blastocyst development.

CONCLUSION(S)

GSH-OEt positively affects the development of early and late maturing IVM oocytes.

An update on best practice guidelines for specialized facilities and resources necessary for weight loss surgical programs

The objective of this study is to update evidence-based best practice guidelines for specialized facilities and resources for weight loss surgery (WLS). We performed systematic search of English-language literature on WLS and facilities, equipment, and resources published between April 2004 and May 2007 in PubMed, MEDLINE, and the Cochrane Library. Keywords were used to narrow the search for a selective review of abstracts, retrieval of full articles, and grading of evidence according to systems used in established evidence-based models. Evidence-based best practice recommendations from the most recent literature on specialized facilities and resources for WLS were developed. We identified 1,647 papers in our literature search; the 46 most relevant were reviewed in detail. Regular updates of evidence-based recommendations for best practices in facilities and resources for WLS are required to address technology advances and growing recognition of the need for adequate equipment and specially built nursing units. Key factors in patient safety include availability of trained personnel and specialized equipment for the care of extremely obese WLS patients.

Derivation of a new human embryonic stem cell line, endeavour-1, and its clonal propagation

Here we describe the derivation of a novel human embryonic stem (hES) cell line, Endeavour-1 (E1), its four new clonal lines (E1C1, E1C2, E1C3, E1C4), and their characterization. E1 and its clonal lines are propagated on human fetal fibroblasts (HFFs) derived and grown in a largely serum-free medium. Seven inner cell masses were isolated from 34 donated human embryos (27 survived), and one new hES cell line was obtained. E1 has been in culture for over 1 year and possesses all the typical features of stem cells, i.e., expression of stem cell surface markers (stage-specific embryonic antigens SSEA-3 and SSEA-4, and tumor recognition antigens TRA-1-60 and TRA-1-81), staining for alkaline phosphatase, and the presence of the pluripotent gene marker (nanog). This line shows pluripotency both under in vitro and in vivo conditions. E1 has a normal karyotype (46XX). Using our optimized procedure for cloning, four new clonal lines were derived from E1: E1C1, E1C2, E1C3, and E1C4. These clonal lines show normal characteristics: karyotype of that of the parent line (46XX) except for E1C3, which showed reciprocal translocation involving chromosomes 15 and 17; stem cell surface markers SSEA-4, TRA-1-60, and TRA-1-81; and gene expression for pluripotency (Nanog). All of these clonal lines formed embryoid bodies (EBs) in suspension cultures. After seeding, the EBs differentiated, forming cell lineages derived from all three germ layers as indicated by immunolocalization for the ectodermal marker beta-III tubulin, the mesodermal marker CD34, and the endodermal marker alpha-fetoprotein (AFP). There were subtle differences in the expression of these markers between clones. These clonal lines showed pluripotency in vivo. E1 and its clonal lines can differentiate to definitive endoderm after treatment with activin A, and, as indicated by expression of SOX17, FOXa2, and GATA-4 by RT-PCR, there are some subtle differences between these clonal lines. This may help in selecting clonal lines for specific lineage specification and for developing future cell therapy for various diseases.

Effects of the selective serotonin reuptake inhibitor, fluoxetine, on regional gastric contractility

Selective serotonin reuptake inhibitors (SSRIs) are increasingly used to treat a variety of disorders but have gastrointestinal side-effects.

AIM

To determine the effects of the SSRI, fluoxetine, on gastric smooth muscle contractility.

METHODS

Fundic, antral, and pyloric circular muscle contractility of guinea pig muscle strips were measured in vitro. Fluoxetine was added in concentrations from 0.1 nmol L(-1) to 100 mumol L(-1). Receptor antagonists were used to determine the neural pathways involved.

RESULTS

Fluoxetine caused concentration dependent contractions, which were greatest in fundus compared with the antrum or pylorus. The contractile effects of fluoxetine in the antrum were reduced by tetrodotoxin, atropine, phentolamine, and the 5-HT(4) receptor antagonist GR 113808. The contractile effects of fluoxetine in the fundus were reduced by atropine, phentolamine, and GR 113808.

CONCLUSIONS

Fluoxetine affects gastric contractility with regional variability - contracting the fundus more than the antrum or pylorus. The fluoxetine contractile effect is reduced by tetrodotoxin, atropine, phentolamine, and a 5-HT(4) receptor antagonist. These results suggest fluoxetine interacts with muscarinic, alpha-adrenergic, and serotoninergic receptors and/or ongoing reuptake/release of serotonin in the stomach.

Glycosidase activity in the excretory-secretory products of the liver fluke, Fasciola hepatica

Fasciola hepatica secretes proteolytic enzymes and other molecules that are essential for host penetration and migration. This mixture may include enzymes required for the degradation of supramucosal gels, which defend epithelial surfaces against pathogen entry. These contain hydrated mucins that are heavily glycosylated. Excretory-secretory products (ES) from F. hepatica were examined for a range of glycosidase activities, using synthetic 4-methylumbelliferyl glycosides as substrates. The ES product contained at least 8 different glycosidase activities, the most abundant of which were beta-N-acetylhexosaminidase, beta-galactosidase and beta-glucosidase. Alpha-fucosidase, beta-glucuronidase, alpha-galactosidase, alpha-mannosidase and neuraminidase were also present. Beta-N-acetylhexosaminidase and beta-galactosidase were present in multiple isoforms (at least 4), whereas beta-glucosidase appeared to exist as one isoenzyme with a pI < 3.8. All three enzymes had acidic pH optima (4.5-5.0). Ovine small intestinal mucin was degraded by ES at pH 4.5 or 7.0, with or without active cathepsin L, the major protease found in F. hepatica ES. The ability of F. hepatica ES to degrade mucin in the presence or absence of active cathepsin L suggests that cathepsin L is not essential for mucin degradation. The abundance of beta-galactosidase and beta-hexosaminidase in ES supports a role for these enzymes in mucin degradation.

Effects of clonidine and tricyclic antidepressants on gastric smooth muscle contractility

To determine if and how clonidine and tricyclic antidepressants affect gastric contractility. Guinea pig fundic and antral circular muscle strips were studied in vitro. The effects of clonidine or amitriptyline added in graded concentrations on contractions to electric field stimulation (EFS), acetylcholine (ACh), and SP in the presence of N(epsilon)-nitro-l-arginine methyl ester (l-NAME) were studied. EFS produced frequency dependent contractions of fundic and antral muscle that were abolished by atropine or tetrodotoxin (TTX). ACh contractions were abolished by atropine but not TTX. Clonidine reduced contractile response to EFS but had no effect on ACh contractions. The threshold concentration of clonidine to inhibit EFS contractions was lower in the fundus than in the antrum. Amitriptyline reduced contractions to both EFS and ACh but not to SP. The threshold concentration of amitriptyline to inhibit EFS contractions was lower in the antrum than in the fundus. Both clonidine and amitriptyline affect gastric contractility. At threshold concentrations, clonidine affects fundic contractility whereas amitriptyline affects antral contractility. Clonidine affects gastric contractility in response to EFS but not to ACh, suggesting alpha-2 receptors on cholinergic nerves that reduce ACh release. Amitriptyline inhibits gastric contractility to EFS and ACh suggesting an inhibitory muscle effect.

Frontal brain activity predicts individual performance in an associative memory exclusion test

Event-related brain potentials (ERPs) were recorded from 24 young adults during a recognition test including Old, New, and Recombined pairs composed of two words studied in different pairs. Recombined pairs called for a response of 'new'. Task difficulty was increased by repetition of some words during the study phase; a subject might study tower/pie, puppet/pie, drill/wreath and bee/wreath (pairs with a Common word), and at test, encounter the Common Recombined pair of puppet/wreath (in addition to Unique Recombined pairs composed of two words studied once). Individual accuracy in the Recombined conditions varied widely, but was unrelated to general memory ability as indexed by accuracy on the Old and New pairs. Posterior brain potentials showed graded amplitudes dependent on the oldness of both the individual words and their combinations (Old > Recombined > New, and Common > Unique), but were also unrelated to accuracy in the Recombined conditions. Amplitudes of ERPs recorded over prefrontal scalp accounted for a large proportion of the individual variability in differentiating studied combinations of words from recombinations of studied elements. The experimental design differentiates three possible roles of prefrontal cortex in source or associative memory tests: resolving a conflict between familiarity and a response of 'new', extended memory search, and evaluation of ambiguous memory signals.

The cytoplasmic linker protein CLIP-170 is a human autoantigen

The purpose of this study was to identify autoantigens that are recognized by human sera and are associated with a speckled cytoplasmic fluorescent staining pattern on tissue culture cells, and to determine clinical features associated with specific autoantibodies. A serum from a patient with systemic lupus erythematosus was used to identify a 3.7-kb cDNA insert from a HeLa cell expression library. The purified cDNA (VLK2.1) encoded a peptide of 1051 amino acids that shared 98.4% similarity with the carboxyl terminal portion of a previously reported 170 kD protein named cytoplasmic linker protein-170 (CLIP-170). Antibodies affinity purified with the recombinant CLIP-170 protein, the prototype human serum and a monoclonal antibody raised against CLIP-170 exhibited identical speckled staining of the cytoplasm in HEp-2 cells. The human autoantibodies reacted with the purified recombinant protein in a Western immunoblot and immunoprecipitated the in vitro translated recombinant protein. Three additional human sera also immunoprecipitated the recombinant CLIP-170 protein. The clinical diagnoses in these patients were limited scleroderma, glioblastoma and idiopathic pleural effusion. This is the first report that identifies CLIP-170 as a human autoantigen.

An unusual subcellular localization of GLUT1 and link with metabolism in oocytes and preimplantation mouse embryos

Although mouse oocytes and cleavage-stage embryos prefer pyruvate and lactate for metabolic fuels, they do take up and metabolize glucose. Indeed, presentation of glucose during the cleavage stages is required for subsequent blastocyst formation, which normally relies on uptake and metabolism of large amounts of glucose. Expression of the facilitative glucose transporter GLUT1 was examined using immunohistochemistry and Western blotting, and in polyspermic oocytes, metabolism of glucose was measured and compared with that of pyruvate and glutamine. GLUT1 was observed in all oocytes and embryos, and membrane and vesicular staining was present. Additionally, however, in polyspermic oocytes, the most intense staining was in the pronuclei, and this nuclear staining persisted in cleaving normal embryos. Furthermore, GLUT1 expression appeared to be up-regulated both in nuclei and plasma membranes following culture of oocytes in the absence of glucose. In polyspermic oocytes, the metabolism of glucose, but not of pyruvate or glutamine, was directly proportional to the number of pronuclei formed. After compaction, nuclear staining diminished, and GLUT1 localized to basolateral membranes of the outer cells and trophectoderm. In blastocysts, a weak but uniform staining of inner-cell-mass plasma membranes was apparent. The results are discussed in terms of potential roles for GLUT1 in pronuclei of oocytes and zygotes, nuclei of cleavage-stage embryos, and a transepithelial transport function for GLUT1, probably coupled with GLUT3, in compacted embryos and blastocysts.

Effect of indomethacin on gallbladder inflammation and contractility during acute cholecystitis

OBJECTIVE

The aim of this study was to determine whether the prostaglandin synthase inhibitor indomethacin reverses the inflammation and abnormal gallbladder contractility that occur after common bile duct ligation (CBDL), a model of acute cholecystitis.

METHODS

Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Animals were treated with saline or indomethacin in vivo. Acetylcholine (ACh) was used to directly contract the muscle and electric field stimulation (EFS) to activate intrinsic nerves. Hematoxylin and eosin-stained slides of muscle strips were scored for inflammation.

RESULTS

CBDL in saline-treated animals increased the inflammation score and decreased gallbladder muscle contractility to ACh and EFS. Indomethacin decreased the inflammation score and partly reversed the smooth muscle contractile response to ACh 6 and 24 h after CBDL, but not at 48 h. Indomethacin did not reverse the CBDL-induced decrease in nerve-evoked contractions.

CONCLUSION

Gallbladder inflammation and contractile dysfunction after CBDL are partly reversed with indomethacin at 6 and 24 h, but not at 48 h. This suggests that, early in the course of CBDL, the inflammation and contractile dysfunction are, in part, prostaglandin-mediated.

Myosin light chain phosphorylation correlates with contractile force in guinea pig gallbladder muscle

Acetylcholine (ACh)-induced gallbladder smooth muscle contraction involves myosin light chain phosphorylation (MLCP). ACh-induced contraction is dose dependent. Whether MLCP by ACh is also dose dependent and how it correlates with contractile force have not been carefully evaluated. This study investigated the correlation between gallbladder muscle contraction and MLCP. Guinea pig gallbladder muscle strips were studied isometrically and frozen after different doses of ACh (0, 0.1, 5, 100 microM) for different periods of incubation (0.5, 1, 2, 3, 4 min). MLCP was determined using gel electrophoresis. Both contraction and MLCP in response to ACh were concentration dependent. Peak MLCP to ACh 100 microM occurred at 30 sec. There was a high correlation between active force and MLCP (r = 0.991; P = 0.009 at 30 sec stimulation). Nifedipine 1 microM reduced ACh-induced contraction and MLCP by a similar degree (31% and 33%, respectively). In conclusion, gallbladder contractile force significantly correlates with MLCP. This is consistent with the hypothesis that initiation of gallbladder cholinergic contraction is dependent on phosphorylation of myosin light chains.

The contractile action of platelet-activating factor on gallbladder smooth muscle

Platelet-activating factor (PAF) may be a mediator of some sequelae of cholecystitis, a disorder with gallbladder motor dysfunction. The aims of this study were to determine the effect and mechanism of PAF on gallbladder muscle. Exogenous administration of PAF-16 or PAF-18 caused dose-dependent contractions of gallbladder muscle strips in vitro with threshold doses of 1 ng/ml and 10 ng/ml, respectively. The PAF-induced contractions were not significantly reduced by TTX, atropine, or hexamethonium but were significantly inhibited with the PAF receptor antagonists ginkolide B and CV-3988. The PAF-induced contraction was reduced by indomethacin. Preventing influx of extracellular calcium with a calcium-free solution nearly abolished the PAF contractile response. Nifedipine inhibited the PAF contractile response, whereas ryanodine had no effect. Pertussis toxin reduced the PAF contractile response. In conclusion, PAF causes gallbladder contraction through specific PAF receptors on gallbladder muscle. These PAF receptors appear to be linked to a prostaglandin-mediated mechanism and to pertussis toxin-sensitive G proteins. The contractile response is largely mediated through the utilization of extracellular calcium influx through voltage-dependent calcium channels.

Effect of acalculous cholecystitis on gallbladder neuromuscular transmission and contractility

BACKGROUND

Impaired smooth muscle contractility is important in the pathophysiology of acalculous cholecystitis. Common bile duct ligation (CBDL) is a model of acalculous cholecystitis, producing acute inflammatory changes and decrease in gallbladder smooth muscle contractility. The aim of this study was to determine whether there is coexistent dysfunction of neural efferent motor pathways of the gallbladder after CBDL.

MATERIALS AND METHODS

Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Electric field stimulation (EFS; 2-16 Hz) was used to activate intrinsic nerves and exogenous acetylcholine (ACh) was used to directly stimulate the muscle. H&E-stained slides of muscle strips were scored for inflammatory changes.

RESULTS

After CBDL, there was a progressive increase in the inflammation score and decrease in gallbladder muscle contractility to ACh. There was also a progressive decline in EFS-induced contractility when expressed as absolute force or normalized to the maximal muscle contractile response to ACh. The nitric oxide synthase inhibitor l-NNA (10 microM) increased EFS-induced contractions by 50 +/- 25% (P = 0.05) in CBDL animals but had no effect in sham surgical controls.

CONCLUSIONS

CBDL with its acute gallbladder inflammation affects gallbladder contractility by two mechanisms: (1) decreased smooth muscle contractility, and (2) decreased neurally mediated contractions. The neurally mediated alterations result from dysfunction of cholinergic excitatory nerves and upregulation of nitric-oxide-mediated inhibition of smooth muscle contractility.

Subtypes of muscarinic receptors regulating gallbladder cholinergic contractions

The aim of this study was to determine the functional role of muscarinic receptor subtypes regulating gallbladder cholinergic contractions. Electrical field stimulation (EFS; 16 Hz) produced contractile responses of guinea pig gallbladder muscle strips in vitro that were inhibited by 1 microM tetrodotoxin (2 +/- 2% of control) and 1 microM atropine (1 +/- 1% of control), indicating activation of intrinsic cholinergic nerves. Exogenous ACh (5 microM)-induced contractions were inhibited by atropine (1 +/- 1% of control) but not tetrodotoxin (102 +/- 1% of control), indicating a direct effect on smooth muscle. The M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh-induced contractions but inhibited EFS-induced contractions by 11 +/- 3%. The M2 antagonist methoctramine (10 nM) had no effect on ACh-induced contractions but augmented EFS-induced contractions by 5 +/- 2%. The M3 antagonist 4-DAMP (10 nM) inhibited ACh-induced contractions by 14 +/- 4% and EFS-induced contractions by 22 +/- 5%. In conclusion, specific M1, M2, and M3 receptors modulate gallbladder muscle contractions by regulating ACh release from cholinergic nerves and mediating the contraction. Cholinergic contractions are mediated by M3 receptors directly on the smooth muscle. M2 receptors are on cholinergic nerves and function as prejunctional inhibitory autoreceptors. M1 receptors are on cholinergic nerves and function as prejunctional facilitatory autoreceptors.

Investigation of endogenous neurotransmitters of guinea pig gallbladder using nicotinic agonist stimulation

Gallbladder motility is modulated by intrinsic nerves, the identities of which are not well established. The aim of this study was to determine the effect of nicotinic receptor stimulation of intrinsic nerves on gallbladder muscle contractility. Guinea pig gallbladder muscle strips were studied in vitro. Histamine 1 microM was used to increase baseline tone. The nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP), produced a biphasic response characterized by an initial transient contraction followed by a sustained relaxation. The initial contraction was inhibited by the neural blocker tetrodotoxin, the nicotinic antagonist hexamethonium, and the muscarinic antagonist atropine, but not by a substance P receptor antagonist or a bombesin receptor antagonist. The relaxation response to DMPP was not affected by tetrodotoxin, but was reduced by hexamethonium and omega-conotoxin GVIA, an inhibitor of neurotransmitter release. The relaxation response was reduced by the nitric oxide synthase inhibitor L-NAME, but not by a vasoactive intestinal peptide antagonist or propranolol. DMPP produces a biphasic response in the guinea pig gallbladder. The initial contractile response is mediated by nicotinic receptors on the cell body or axon of cholinergic nerves. The relaxation response appears to result, in part, from activation of nicotinic receptors on nerve terminals of nitric oxide-releasing nerves. These results suggest nicotinic receptors have heterogeneity in location depending on excitatory or inhibitory neuronal function.

Ranitidine and nizatidine stimulate antral smooth muscle contractility via excitatory cholinergic mechanisms

Histamine type 2 receptor antagonists (H2RAs) have been found to alter gastric motility. The aims of this study were to determine if H2RAs affect antral contractility in vitro and the mechanism of this effect. Guinea pig antral muscle strips were pinned in an organ bath after removing the mucosa, and circular muscle tension was measured using an isometric force transducer. Gastric myocytes were isolated from guinea pig stomach using collagenase digestion, and cell lengths were measured using an image analysis system. In muscle strips, ranitidine and nizatidine increased the amplitude of spontaneous phasic antral contractions in a concentration-dependent fashion with threshold concentrations of 5 microM. The order of potency for the H2RAs was ranitidine = nizatidine >> cimetidine > famotidine. The contractile effects of ranitidine and nizatidine were reduced, but not abolished, by tetrodotoxin and omega-conotoxin GVIA and nearly abolished by atropine. In isolated cells, ranitidine and nizatidine, but not famotidine or cimetidine, induced concentration-dependent cell shortening, with maximal shortening at 10 microM. These contractile effects of ranitidine and nizatidine in isolated cells were inhibited by atropine. Ranitidine and nizatidine increase antral contractility; this effect appears to be mediated by an interaction between ranitidine and nizatidine on cholinergic pathways with both direct effects on smooth muscle cholinergic receptors and indirect effects by increasing cholinergic neurotransmission.

Acute experimental colitis decreases colonic circular smooth muscle contractility in rats

Distal colitis decreases the contractility of the underlying circular smooth muscle. We examined how time after injury and lesion severity contribute to the decreased contractility and how colitis alters the calcium-handling properties of the affected muscle. Distal colitis was induced in rats by intrarectal administration of 4% acetic acid. Contractile responses to acetylcholine, increased extracellular potassium, and the G protein activator NaF were determined for circular muscle strips from sham control and colitic rats at days 1, 2, 3, 7, and 14 postenemas. Acetylcholine stimulation of tissues from day 3 colitic rats was performed in a zero calcium buffer, in the presence of nifedipine, and after depletion of intracellular stores of calcium. The colitis was graded macroscopically as mild, moderate, or severe. Regardless of agonist, maximal decrease in force developed 2 to 3 days posttreatment, followed by a gradual return to control by day 14. The inhibitory effect of colitis on contractility increased with increasing severity of inflammation. Limiting extracellular calcium influx had a greater inhibitory effect on tissues from colitic rats; intracellular calcium depletion had a greater inhibitory effect on tissues from control animals. The data suggest that both lesion severity and time after injury affect the contractile response of circular smooth muscle from the inflamed distal colon. Impaired utilization of intracellular calcium may contribute to the decreased contractility.

Electric field stimulation-induced guinea pig gallbladder contractions: role of calcium channels in acetylcholine release

Gallbladder motility is modulated by intrinsic cholinergic neurons. The aims of this study were to determine: (1) the effect of electric field stimulation (EFS) on guinea pig gallbladder smooth muscle, and (2) the role of calcium channels in mediating neurotransmitter release. Gallbladder muscle strips were studied isometrically in vitro. EFS (1-16 Hz, 100 V, 0.5-msec pulse width, 30-sec train duration) was used to activate the intrinsic nerves. Exogenous acetylcholine was also used to directly stimulate the smooth muscle. EFS produced a frequency-dependent contractile response that was completely abolished by tetrodotoxin. EFS-induced contractions at 16 Hz were suppressed by 84 +/- 4% with atropine, whereas hexamethonium had no effect. The L-type calcium channel blocker, nifedipine, reduced EFS contractions by 51 +/- 4%, whereas it reduced contractions to acetylcholine by only 11 +/- 5%. The N-type calcium channel blocker, omega-conotoxin GVIA, reduced EFS-induced contractions by 22 +/- 9%, but did not affect acetylcholine-induced contractions. EFS-induced contractions of the guinea pig gallbladder are primarily mediated by activation of postganglionic cholinergic neurons. The acetylcholine release from these cholinergic neurons is regulated by L- and N-type calcium channels. The inhibitory effect of calcium channel blockers on the gallbladder seen in vivo may be in part related to inhibition of acetylcholine release from the intrinsic cholinergic nerves of the gallbladder.

PACAP and VIP inhibit pyloric muscle through VIP/PACAP-preferring receptors

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with structural homology to vasoactive intestinal polypeptide (VIP). Two receptor types for PACAP have been described: PACAP preferring receptors are selective for PACAP; whereas VIP/PACAP preferring receptors have similar affinity for both PACAP and VIP. Both VIP and PACAP are present in enteric nerves at the pylorus. VIP is known to exert inhibitory effects on pyloric muscle; the effect of PACAP is unknown. The aims of this study were to determine the effect of PACAP on pyloric muscle and to characterize the PACAP receptor.

METHODS

Rabbit pyloric muscle strips were cut parallel to circular muscle fibres and placed in muscle baths. The effect of PACAP and VIP were quantitated as percent of basal motility index (MI).

RESULTS

PACAP-27, PACAP-38, and VIP had dose dependent inhibitory effects on the spontaneous phasic contractions of the pylorus. The PACAP-27- induced relaxation was inhibited by the PACAP receptor antagonist PACAP6-27, but was not affected by tetrodotoxin. VIP also had dose dependent inhibitory effects on pyloric muscle. The VIP relaxation was inhibited by PACAP6-27, but not affected by tetrodotoxin.

CONCLUSIONS

These studies indicate that, similar to VIP, PACAP inhibits pyloric muscle. The inhibitory effect of the PACAP receptor antagonist on both PACAP and VIP-induced relaxation suggest that PACAP and VIP act at the same receptor, a VIP/PACAP preferring receptor.

Dual effects of PACAP on guinea pig gallbladder muscle via PACAP-preferring and VIP/PACAP-preferring receptors

The aims of this study were to determine the effect and mechanism of action of pituitary adenylate cyclase-activating peptide (PACAP) on gallbladder muscle. Guinea pig gallbladder muscle strips were studied isometrically. In noncontracted muscle strips, PACAP-27 and PACAP-38 caused dose-dependent contractions, whereas vasoactive intestinal peptide (VIP) caused dose-dependent relaxation. PACAP-27 contractions were resistant to tetrodotoxin, atropine, and the substance P receptor antagonist [D-Arg1,D-Trp7,9,Leu11]substance P (Spantide) but were inhibited by the selective PACAP receptor antagonist PACAP-(6-38) and slightly increased with the VIP receptor antagonist [4-chloro-D-Phe6,Leu17]VIP. In cholecystokinin-precontracted muscle strips, both VIP and PACAP caused relaxations. This relaxant effect of PACAP-27 was inhibited by PACAP-(6-38) and [4-chloro-D-Phe6,Leu17]VIP, but not by tetrodotoxin. These studies suggest that PACAP has dual excitatory and inhibitory effects on guinea pig gallbladder muscle. The contractile effect of PACAP is a direct action on muscle through PACAP-preferring receptors. The relaxant effect of PACAP is seen in precontracted muscle strips and mediated through VIP/ PACAP-preferring receptors.

Acute experimental distal colitis alters colonic transit in rats

Data from humans with active distal colitis suggest that the proximal colon exhibits increased contractile activity and delayed transit, whereas the distal colon shows decreased contractile activity and rapid transit. The present study used the acetic acid rat model of experimental colitis to determine the effect of distal colitis on total and regional colonic transit in vivo and on the in vitro contractility of circular smooth muscle from the proximal and distal colon. Distal colitis was induced in rats by intracolonic administration of 4% acetic acid; sham control rats received saline enemas. Control and colitic rats were studied 2 days postenemas. Total colon transit was determined by calculating the geometric center of distribution of a radiolabeled marker (51Cr) instilled into the proximal colon. Regional transit was assessed by expressing the radioactivity in the cecum, proximal and distal colon, and excreted stool as a percent of total radioactivity. Muscle strips from the proximal and distal colon were stimulated with 100 microM acetylcholine (ACh) and 60 mM KCl and the tension was expressed as kilograms per square centimeter. Distal colitis was characterized by decreased total colon transit, increased retention of marker in the cecum and proximal colon, and decreased retention of marker in the distal colon. In vitro contractility studies revealed that distal colitis increased proximal colon circular smooth muscle contractility and decreased distal colon circular smooth muscle contractility to both ACh and potassium. Distal colitis is associated with regional differences in colonic circular smooth muscle contractility, which may contribute to delayed transit in the proximal colon and rapid transit in the distal colon.

Erythromycin inhibits rabbit pyloric smooth muscle through neuronal motilin receptors

BACKGROUND & AIMS

Erythromycin's effect in accelerating gastric emptying is attributed primarily to increased antral contractility. The aim of this study was to characterize erythromycin's effect on pyloric muscle.

METHODS

Rabbit pyloric muscle strips were studied in vitro.

RESULTS

Pyloric muscle strips developed spontaneous phasic contractions with a frequency of 1.9 +/- 0.1 contractions per minute. Erythromycin and motilin had dose-dependent inhibitory effects on pyloric muscle. At the maximal effective dose (50 mumol/L), erythromycin caused cessation of spontaneous contractions for 1.8 +/- 0.2 minutes, decreasing the initial 2-minute motility index to 35% +/- 9% (P < 0.01) of basal. In the presence of tetrodotoxin, both erythromycin and motilin increased pyloric contractility. Motilin tachyphylaxis both in the presence or absence of tetrodotoxin abolished the effects of erythromycin. The inhibitory effect of erythromycin was decreased by NG-nitro-L-arginine methyl ester and the vasoactive intestinal peptide antagonist [4-Chloro-D-Phe6, Leu17]vasoactive intestinal peptide.

CONCLUSIONS

These studies suggest that motilin receptors are present on both pyloric muscle and inhibitory neurons to pyloric muscle, that the primary effect of erythromycin on the pylorus is mediated by activating motilin receptors on inhibitory motor neurons, and that both nitric oxide and vasoactive intestinal peptide may mediate the inhibitory effect of erythromycin.

Effect of modulating voltage-dependent calcium channels on cholecystokinin and acetylcholine-induced contractions of the guinea pig gallbladder

The aim of this study was to investigate the role of extracellular Ca2+ utilization in cholecystokinin (CCK) and acetylcholine-induced guinea pig gallbladder contractions by using agents that modulate influx of extracellular Ca2+ through voltage-dependent calcium channels.

METHODS

Guinea pig gallbladder muscle strips were studied isometrically at Lmax in vitro.

RESULTS

(1) Acetylcholine and CCK caused dose-dependent contractions, with EDmax of 10(-4) and 10(-6) M, respectively. (2) Preventing influx of extracellular Ca2+ by incubation in Ca(2+)-free/0.1 mM EGTA solution inhibited the acetylcholine (10(-4) M)-induced contraction by 60 +/- 3% compared to only 46 +/- 5% (P < 0.05) for CCK (10(-6) M)-induced contraction. (3) Nifedipine (3 microM) inhibited the response to acetylcholine (10(-4) M) by 54 +/- 3%, compared to only 34 +/- 3% (P < 0.01) for CCK (10(-6) M). (4) Bay K 8644 (10(-7) M) significantly increased (P < 0.05) the contractile responses to low doses of each agonist: acetylcholine (10(-6) M) by 121 +/- 44% and CCK (10(-9) M) by 94 +/- 31%, but had no effect on the contraction to the EDmax of each agonist.

CONCLUSIONS

These studies demonstrate: (1) acetylcholine and CCK cause guinea pig gallbladder contraction by both intracellular Ca2+ release and influx of extracellular Ca2+ through voltage-dependent calcium channels; (2) the CCK-induced contraction is more dependent on intracellular Ca2+ than is acetylcholine; and (3) acetylcholine and CCK-induced contractions can by modulated by manipulating influx of extracellular Ca2+ through voltage-dependent calcium channels.

Myosin light chain phosphorylation in contraction of gastric antral smooth muscle from neonate and adult rabbits

The decreased contractility of gastric antral smooth muscle in the neonate has been attributed to reduced levels of activator calcium. It is generally accepted that calcium-dependent myosin light chain phosphorylation (MLCP) is the key step in the initiation of force development in smooth muscle. In this study, we investigated the relationship between MLCP and force development in gastric antral smooth muscle from neonatal (4-6 d old) and adult rabbits. We tested the hypothesis that the reduced force development of circular smooth muscle from the neonate would be accompanied by decreased levels of MLCP, as compared with data from adult animals. Full thickness muscle strips oriented parallel to the circular muscle layer were examined for their contractile response to acetylcholine (ACh) (10(-8) M to 10(-3) M) or 10(-4) M ACh only. In the latter study, tissues were rapidly frozen in a dry ice-acetone slurry for subsequent MLCP determination. MLCP was determined at times corresponding to 5, 10, 15, 30, and 60 s of stimulation. For each age group, maximal active force developed at an ACh concentration of 10(-4) M and was significantly greater in tissues from adults (1.86 +/- 0.24 N/m2, adult; 0.95 +/- 0.05 N/m2, neonate; p < 0.05). In contrast, no significant differences were observed with respect to basal or agonist-stimulated levels of MLCP. The data suggest that factors other than levels of MLCP contribute to the reduced force-generating capacity of antral smooth muscle from the neonate.

Developmental capacity, energy metabolism and ultrastructure of mature oocytes from prepubertal and adult sheep

Development to the blastocyst stage was assessed for oocytes obtained from prepubertal and adult sheep matured and fertilized in vitro. The proportion of cleaved oocytes reaching the blastocyst stage was significantly lower for oocytes derived from prepubertal sheep than for those from adult sheep (7.4% and 24.6% respectively). There were no differences in the metabolism of glucose, glutamine or pyruvate between oocytes matured in vivo and in vitro, or of glucose or pyruvate between oocytes from prepubertal and adult sheep. Glutamine metabolism by mature oocytes from prepubertal sheep was significantly lower than that by oocytes from adult sheep. Ultrastructural studies revealed no differences in the morphology of cytoplasmic organelles of oocytes matured in vitro from prepubertal and adult sheep, but differences in the volume fraction and size of mitochondria and cortical granules were observed. These data suggest that mature oocytes from prepubertal sheep do not possess the developmental potential of their adult-derived counterparts, and this phenomenon may be associated with metabolic and ultrastructural anomalies.

Graphomotor perseveration and wandering in Alzheimer's disease

Perseveration, spatial orientation, and attention/concentration were assessed in 15 patients with a probable diagnosis of senile dementia of the Alzheimer's type. Subjects were divided into two groups, wanderers and nonwanderers, based on caregiver ratings using a modified version of the Caregiver Checklist. Graphic productions of wanderers on the Bender Visual Motor Gestalt Test and Clock Drawing Test displayed greater total perseveration and more recurrent and continuous perseverations than those of nonwanderers. Spatial orientation and attention/concentration were similar between groups. These preliminary results suggest that graphomotor perseverations exhibited during the mild to moderate stages may serve as a marker for wandering in Alzheimer's disease.

Gastrokinetic effects of erythromycin: myogenic and neurogenic mechanisms of action in rabbit stomach

The aims of this study were to determine regional differences and the mechanism of gastric contractile effects of erythromycin. Rabbit gastric circular muscle strips were studied in vitro. The threshold dose for erythromycin was significantly less and the maximum contraction greater in the antrum (1 microM and 0.9 +/- 0.3 kg/cm2) than in the fundus (10 microM and 0.3 +/- 0.1 kg/cm2). Erythromycin-induced antral contractions were decreased by motilin tachyphylaxis but unaffected by tetrodotoxin, atropine, hexamethonium, or ondansetron. At a subthreshold dose (0.1 microM), erythromycin increased the frequency, but not the amplitude, of bethanechol (10 +/- 3%)-and substance P-induced (13 +/- 5%) phasic antral contractions. This chronotropic effect was inhibited with tetrodotoxin, atropine, or motilin tachyphylaxis. Erythromycin (10 microM) and motilin (1 microM) enhanced the amplitude of substance P-induced tonic fundic contractions by 38 and 32%, respectively, without effect on bethanechol-induced contractions. In summary, erythromycin contracts antral muscle more potently and forcefully than fundic muscle. Erythromycin increases antral contractility by two mechanisms: an inotropic effect acting on smooth muscle motilin receptors, and, at lower doses, a cholinergic chronotropic effect mediated through neuronal motilin receptors.

The influence of bladder management on fertility in spinal cord injured males

Male infertility is a well recognised problem following spinal cord injury. The techniques of vibration induced ejaculation and transrectal electroejaculation have significantly increased the likelihood of sperm retrieval in spinal cord injured males; however, the reproductive capacity remains markedly reduced due to poor semen quality. The Spinal Injuries Unit at Royal North Shore Hospital has developed a programme to achieve seminal emission and enhance fertility. This study analysed the results of the first sample obtained at stimulation in 70 spinal cord injured males with respect to procedure performed, neurological level, completeness of lesion, bladder management, infection, age and duration since injury. Our study demonstrated that bladder management and neurological level were significant factors affecting the presence of motile sperm. Individuals managing their neuropathic bladder by catheter (intermittent self-catheterisation, indwelling urethral or suprapubic catheter) had significantly enhanced semen quality compared to those voiding by reflex or straining. Differences were also noted within the catheter group itself with intermittent self-catheterisation achieving a higher percentage of motile sperm present.

Clinical intracytoplasmic sperm injection (ICSI) results from Royal North Shore Hospital

The technique of intracytoplasmic sperm injection (ICSI) was first introduced to the Royal North Shore Hospital in April 1993 as part of a controlled study of 100 patient cycles in which sibling oocytes were inseminated by either subzonal insemination (SUZI) or ICSI. This trial showed direct sperm injection to be superior in terms of fertilization. In that study, 58 embryo transfers of 101 ICSI-derived embryos resulted in 10 pregnancies. No miscarriages have occurred and a total of 10 fetal hearts (9.8% per embryo transferred) were detected on ultrasound. There have been 10 deliveries of 10 babies. Since the beginning of 1994, intracytoplasmic injection has been used exclusively for patients requiring micromanipulation to achieve fertilization. There have been 200 patient cycles with 1650 oocytes collected (8.8 oocytes per cycle). Of these oocytes, 1548 were mature (94%) and were subjected to ICSI, and normal fertilization occurred in 874 (56%) of the injected oocytes. The number of oocytes which cleaved and were suitable for fresh transfer or cryopreservation was 818 (94%). There have been 153 fresh embryo transfers of 326 embryos. Twenty-six pregnancies (17% per embryo transfer) have resulted, 22 of which proceeded to ultrasound examination in which 23 fetal hearts were detected (7% per embryo transferred). Three miscarriages have occurred, leaving 19 ongoing pregnancies. There have been 127 cryopreservation procedures involving 492 embryos. To date, there have been 47 embryo thaw cycles, and 93 of the 115 (81%) thawed embryos survived and were transferred. These 47 embryo transfers resulted in 10 pregnancies (21% per embryo transfer), one of which one has miscarried.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in gastric fundus smooth muscle contractility and involvement of extracellular calcium in fetal and adult guinea pigs

Delayed gastric emptying is a common problem in preterm infants. The factors underlying this gastroparesis remain unsettled but may involve immaturity of smooth muscle contraction. The present study was designed to test this hypothesis. Muscle strips from the gastric fundus of fetal and adult guinea pigs were studied in vitro for their contractile response to receptor activation (acetylcholine and bethanechol) and membrane depolarization (potassium chloride). The dose-response curves were analyzed for differences in active force development (kg/cm2). The role of extracellular calcium (Ca2+) in the contractile responses was determined by contracting the tissues in a zero-Ca2+ physiologic saline solution and in the presence of nifedipine, a voltage-dependent Ca2+ channel blocker. The results demonstrate the following: 1) tissues from adult animals developed significantly more active force when tested with acetylcholine, bethanechol, and potassium chloride; 2) tissues from the fetal animals were relatively unresponsive to contraction with potassium chloride compared with the adult; and 3) both nifedipine and incubation in a zero-Ca2+ physiologic saline solution had a significantly greater inhibitory effect on the contractions of adult than fetal muscle strips. Our data indicate that smooth muscle in the gastric fundus develops increasing force with maturation. The increased contractility in the adult fundus appears to be due to an increased involvement of extracellular calcium influx, in part through voltage-dependent Ca2+ channels.

Response of colonic smooth muscle from newborn and adult rabbits to electrical field stimulation

Electrical field stimulation (EFS) of circular smooth muscle from the proximal and distal colon of adult rabbits elicits region-specific patterns of contraction and relaxation referred to as on and off responses. The present study examined EFS-mediated on and off responses in neonatal (3- to 5-d-old), juvenile (2-wk-old), and adult rabbits to determine whether colonic motility undergoes a period of postnatal maturation with respect to the pattern of contraction/relaxation that develops in response to stimulation of the enteric nervous system. Muscle strips from the proximal and distal colon were oriented parallel to the circular muscle layer and stimulated electrically (80 V;0.5-ms pulse width) for 10 s using platinum wire electrodes. Stimulus frequency varied between 1 and 64 Hz. EFS stimulation of circular smooth muscle from the proximal colon of neonatal, juvenile, and adult rabbits was characterized by the development of atropine-sensitive on-contractions. The frequency-response curves were similar for each age group. In the distal colon, EFS of circular smooth muscle from neonatal, juvenile, and adult rabbits produced on-relaxations and atropine-insensitive off-contractions. The frequency-response data for the off-contractions were similar for each age group. Although no age-related differences were observed with respect to the pattern of contractile response to EFS, the force of the proximal colon on contractions and the distal colon off-contractions increased as the animals matured. The results suggest that the pattern of colonic enteric neurotransmission is established early in the neonatal period and does not undergo any significant change during the postnatal period.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of myosin light-chain phosphorylation in guinea pig gallbladder smooth muscle contraction

In acetylcholine (ACh)-stimulated gallbladder smooth muscle, we have previously shown that phosphorylation of the 20,000-Da myosin light chains is necessary for the initiation of contraction, that myosin is stably phosphorylated at steady state, and that dephosphorylation of cross bridges is not necessary for the slowing of cross-bridge cycling rates during the period of steady-state isometric stress. The present studies were undertaken to determine whether 1) K+ (60 or 80 mM) or cholecystokinin (CCK, 10(-8) M) stimulation is accompanied by changes in myosin light-chain phosphorylation in gallbladder smooth muscle and 2) dephosphorylated noncycling cross bridges exist in K(+)- or CCK-stimulated gallbladder smooth muscle. Isometric stress, isotonic shortening velocity, and myosin light-chain phosphorylation were determined during contraction with K+ or CCK. Steady-state isometric stress was reached within 2.5 min of stimulation with K+ or CCK and was maintained for the duration of the stimulation. Stimulation with K+ or CCK was associated with rapid increases in myosin light-chain phosphorylation and maintenance of myosin light-chain phosphorylation during the stimulation. In contrast, isotonic shortening velocity was maximal at 1 min of stimulation with either K+ or CCK and then declined significantly to values that were only 26-32% of the peak velocity. These data, along with data from previous experiments with ACh, suggest that myosin light-chain phosphorylation is essential in the initiation of contraction in gallbladder smooth muscle, regardless of the source of Ca2+ or of the contractile agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term corticosteroid treatment does not improve implantation for embryos derived from subzonal insertion of sperm

A total of 111 patients undergoing treatment for male factor infertility using SUZI participated in the trial for one treatment cycle only. They were allocated to have either corticosteroid treatment to induce immunosuppression or placebo. An elevated beta-hCG was found in 25% (9 of 36) of patients having an ET and receiving treatment. The corresponding figure for the control group was 33% (10 of 30). On ultrasound examination, fetal hearts were found in 22% (8 of 36) and 20% (6 of 30), respectively, of patients having an ET. chi 2 analysis showed no difference in the results. When the results were analyzed on a per oocyte basis there was no significant difference in the implantation rate.

Injection of multiple sperm into the perivitelline space as a treatment of male infertility

This paper reports the outcome of 274 treatment cycles using multiple injection of sperm into the perivitelline space as a treatment of male factor infertility. A total of 170 couples underwent this form of treatment; 59.1% of cycles had at least one oocyte normally fertilized with an overall normal fertilization rate of 17.2%. The development rate of normally fertilized embryos was high (98.5%) and resulted in a pregnancy rate (positive human chorionic gonadotrophin 18 days after embryo transfer) of 21.4% per embryo transfer procedure (a maximum of 3 embryos were transferred per procedure). The relationship between the number of sperm injected and the fertilization rate and other factors affecting the outcome are discussed.

Removal of the zona pellucida and parthenogenetic activation affect rates of survival of ultrarapidly frozen mouse oocytes

Survival rates on thawing were assessed for ultrarapidly frozen mouse oocytes following the removal of zonae pellucidae using an acid Tyrode's solution, pronase or a mechanical dissection technique. Significantly higher rates of survival were observed for zona-free oocytes than for zona-intact control oocytes (303/684, 44% v. 130/498, 26%; P < 0.001). The rates of survival observed for pronuclear stage embryos (72-76%) were much greater than those observed for oocytes and were not influenced by zona removal techniques. Parthenogenetic activation of oocytes by exposure to a 7% (v/v) ethanol solution was also shown to increase survival rates of ultrarapidly frozen oocytes (155/185, 84% v. 19/102, 19%) indicating that fusion of sperm to the plasma membrane or formation of a male pronucleus are not directly responsible for the increased survival rates of pronuclear stage embryos compared with oocytes. These data support the hypothesis that increased survival of ultrarapidly frozen pronuclear stage embryos is the result of changes to the plasma membrane and/or to the zona pellucida that occur following fertilization.

Decreased electromechanical activity of guinea pig circular muscle during pregnancy

BACKGROUND

Delayed gastric emptying has been reported during pregnancy; however, its underlying mechanism is poorly understood. The purpose of this study was to determine if electromechanical activity of antral circular muscle is decreased during pregnancy.

METHODS

Antral muscle strips from third-trimester pregnant and age-matched control virgin female guinea pigs were studied in vitro.

RESULTS

Spontaneous and bethanechol-induced phasic antral contractions from pregnant guinea pigs were reduced significantly in force compared with control virgin animals. Although the resting membrane potentials were similar, the electric slow waves of pregnant animals displayed significant decreases in upstroke amplitude, plateau amplitude, and number of spikes during the plateau potential compared with control animals. The voltage-tension relationship was similar in pregnant and control animals.

CONCLUSIONS

This study indicates that (1) the force of antral circular muscle contractions is decreased during pregnancy and (2) this decreased force is secondary to a diminished slow wave depolarization. The results suggest that a change in electromechanical activity of gastric muscle is a cause of altered gastric motility in pregnancy.