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Biomedical subjects

M Phillippe

Publications and source records attributed to M Phillippe.

At least 37 records · Page 2Linked to original sources
PubMed1995

Ionomycin-stimulated phasic myometrial contractions.

Ionomycin, a calcium ionophore, facilitates the sustained entry of extracellular calcium; however, in myometrial tissue it stimulates phasic contractions. This study sought to define further this unanticipated effect of ionomycin and to begin to explore the possible mechanism(s) involved. Utilizing rat uterine strips, in vitro isometric contraction studies were performed to determine the effects of ionomycin with and without membrane-permeant inhibitors of cytosolic calcium oscillations. To determine the effects of ionomycin on phospholipase C, qualitative inositol phosphate production studies were performed. The in vitro contraction studies confirmed that ionomycin-stimulated phasic myometrial contractions were potentially dependent on stimulation of phospholipase C, calcium-induced calcium release, and additional calcium influx through dihydropyridine-sensitive membrane calcium channels. The inositol phosphate production studies confirmed that ionomycin stimulated phospholipase C in a dose-related fashion to levels comparable to oxytocin. In summary, these observations have confirmed the ability of ionomycin to generate dose-related phasic myometrial contractions through mechanisms potentially involving the phosphatidylinositol-signaling pathway.

Animals↗
PubMed1995

Potassium chloride effects on the hormonal signal transduction mechanisms underlying phasic myometrial contractions.

These studies sought to test the hypothesis that potassium-stimulated phasic myometrial contractions utilize cytosolic calcium oscillation-like mechanisms comparable to those activated in response to oxytocin. Uterine tissue was obtained from pro-oestrus/oestrus Sprague-Dawley rats. In vitro isometric contraction studies were performed using longitudinal myometrial strips; computer digitalized contraction data were analyzed for contraction area, and normalized for tissue cross-section area. Dose-response studies were performed using potassium chloride with and without inhibitors of cytosolic calcium oscillation mechanisms. Qualitative inositol-phosphate production studies were performed after preloading uterine tissue with [3H]inositol; subsequently, the individual inositol-phosphates produced in response to stimulation were isolated by anion exchange chromatography. Potassium chloride over a concentration of 10 to 30 mM produced a dose-related increase in phasic contractile activity. The potassium-stimulated phasic contractions were significantly suppressed in response to inhibition of phospholipase C, stimulation of protein kinase C, inhibition of calcium-induced calcium release, and prevention of extracellular calcium influx. The qualitative inositol-phosphate production studies confirmed activation of phospholipase C in response to 20 mM potassium. These studies have provided support for the hypothesis that potassium-stimulated phasic myometrial contractions activate intracellular signal transduction mechanisms comparable to those activated in response to hormonal uterotonic agonists.

Analysis of Variance↗
PubMed1994

Neomycin inhibition of hormone-stimulated smooth muscle contractions in myometrial tissue.

These studies sought to determine the effects of neomycin, a phospholipase C inhibitor, on hormone-stimulated myometrial contractions. For these studies, computer digitalized in vitro isometric contraction data were analyzed for changes in contractile activity in response to oxytocin and aluminum fluoride with and without neomycin. Neomycin (1-5 mM) produced dose-related inhibition of oxytocin and aluminum fluoride-stimulated myometrial contractions. This neomycin effect was apparent within 2-3 minutes of addition and was completely reversible, with resolution of its inhibitory effects within 6-8 minutes of washout. This study is the first to demonstrate the functional effect of neomycin inhibition of the phosphatidylinositol signaling pathway in myometrial smooth muscle tissue.

Aluminum Compounds↗
PubMed1994

Mechanisms underlying phasic contractions of pregnant rat myometrium stimulated with aluminum fluoride.

OBJECTIVE: The mechanisms underlying phasic myometrial contractions are unknown at this time. Phasic contractions, however, are characterized by repetitive cycles of elevated intracellular calcium (i.e., calcium oscillations). These studies were performed to test the hypothesis that mechanisms underlying phasic myometrial contractions are similar to those producing classic cytosolic calcium oscillations. STUDY DESIGN: Uterine tissue was obtained from pregnant Sprague-Dawley rats (i.e., day 18 to 22 of gestation). In vitro isometric contraction studies were performed with longitudinal strips of myometrial tissue; computer-digitized data were analyzed for contraction area and normalized for tissue cross-section area. Dose-response studies were performed with aluminum fluoride and various inhibitors of cytosolic calcium oscillations. RESULTS: Aluminum fluoride stimulated a significant increase in phasic contractions. In contrast, the addition of 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (an inhibitor of phosphoinositide-specific phospholipase C), adenine (an inhibitor of calcium-induced calcium release), and phorbol 12,13-dibutyrate (an activator of protein kinase C) resulted in significant suppression of aluminum fluoride-stimulated contractions. Similarly, nifedipine (an L-type calcium channel blocker) and removal of extracellular calcium significantly inhibited phasic myometrial contractions. CONCLUSIONS: These studies have confirmed that phosphoinositide-specific phospholipase C, calcium-induced calcium release, protein kinase C, and transmembrane calcium influx are important components of the intracellular calcium oscillator that generates agonist-stimulated phasic contractions of pregnant myometrial tissue.

Aluminum Compounds↗
PubMed1994

Protein kinase C, an inhibitor of oxytocin-stimulated phasic myometrial contractions.

One of the roles previously reported for protein kinase C (PKC) is modulation of the activity of the phosphatidylinositol signaling pathway. Studies were performed to test the hypothesis that activation of PKC results in inhibition of agonist-stimulated phasic myometrial contractions: contractions that appear to be mediated by phosphatidylinositol signaling mechanisms comparable to those producing cytosolic calcium oscillations. In vitro isometric contraction studies were performed using myometrium from adult Sprague-Dawley rats. Oxytocin and aluminium fluoride (a G-protein activator) produced comparable increases in phasic contractile activity. Phorbol 12,13-dibutyrate (PDB) significantly suppressed agonist-stimulated phasic myometrial contractions; in contrast, phorbol 13,20-diacetate (PDA), an inactive phorbol ester, had no significant effect on myometrial contractions. Prolonged exposure of myometrial tissue to PDB failed to down-regulate myometrial PKC and had no consistent effect on spontaneous and oxytocin-stimulated phasic contractions. These studies have provided support for a role for PKC as an intracellular regulator of the phosphatidylinositol signaling pathway, which itself appears to be part of the myometrial calcium oscillator that results in agonist-stimulated phasic myometrial contractions.

Aluminum Compounds↗
PubMed1993

Adrenergic stimulation of diacylglycerol production in genital tract smooth muscle myocytes.

Diacylglycerol (DAG) production has not been reported in previous studies that have characterized inositol phosphate production during alpha-1 adrenergic receptor signal transduction in the DDT1 MF-2 genital tract myocytes. The current study sought to measure norepinephrine (NE)-stimulated DAG production in these transformed myocytes utilizing thin layer chromatography. DAG production was characterized as an alpha-1 adrenergic mediated event utilizing subtype specific adrenergic agonist and antagonists. DAG production occurred in response to physiologic concentration of NE, was apparent by 30 s and was significantly increased by 2 min. Maximal DAG production was unaffected by pretreatment of the myocytes for 96 h with testosterone, which has previously been shown to induce a doubling of alpha-1 adrenergic receptors in these cells. In contrast, testosterone pretreatment did result in a shift of the dose-response curve resulting in a significantly lower EC50 for NE in the treated cells compared to control myocytes. In conclusion, these studies have confirmed that DAG production occurs as a component of alpha-1 adrenergic signal transduction in the DDT1 MF-2 myocytes; transduction events that were modulated by testosterone resulting in increased agonist sensitivity.

Animals↗
PubMed1992

Gestational modulation of myometrial proteins in the timed-pregnant Sprague-Dawley rat.

These studies sought to test the hypothesis that the expression of myometrial proteins is modulated as the onset of parturition approaches. Myometrial proteins from timed-pregnant rats were analyzed utilizing sodium dodecylsulfate polyacrylamide gel and 2-dimensional electrophoresis, and Western blot techniques. SDS-PAGE gels demonstrated increased expression of at least 10 protein bands from 17 to 200+ KD. 2-dimensional gels confirmed the presence of at least five groups of gestationally modulated proteins. Western blots for phosphoinositide-specific phospholipase C demonstrated significant modulation of the expression of three isozymes. These studies have confirmed differential expression of myometrial proteins near term in the timed-pregnant rat; some of which play an important role in intracellular signal transduction in response to hormones and pharmacologic agents.

Animals↗
PubMed1991

A mechanism for testosterone modulation of alpha-1 adrenergic receptor expression in the DDT1 MF-2 smooth muscle myocyte.

Previous reports have confirmed that steroid hormones modulate the expression of adrenergic receptors on the surface of smooth muscle myocytes. The present study was undertaken to evaluate the mechanism by which testosterone modulates alpha-1 adrenergic receptor expression in the DDT1 MF-2 transformed smooth muscle cell. Utilizing 3H-prazosin radioligand binding studies, alpha-1 adrenergic receptors were noted to increase more than 2 fold in response to incubation with 10(-8)M testosterone for 96 hours. Dihydrotestosterone similarly stimulated a significant increase in alpha-1 receptors; whereas, estradiol and hydrocortisone appeared to suppress the expression of this receptor in DDT myocytes. The testosterone effect was dose related with a maximal response observed in response to 10(-7)M testosterone at both 48 and 96 hours. Kinetic experiments utilizing 10(-8)M testosterone demonstrated a peak effect on alpha-1 receptor expression at 96 hours, and maintenance of the effect for at least 168 hours (7 days). The testosterone effect was completely prevented at both 48 and 96 hours by inhibition of transcription with actinomycin-D, or inhibition of translation with cycloheximide. Consistent with the receptor binding studies, RNA blotting studies have demonstrated maximal alpha-1 receptor mRNA levels at 48-96 hours of testosterone stimulation. In conclusion, these in vitro experiments have confirmed the physiologic concentrations of testosterone stimulate the increased expression of alpha-1 receptors in the DDT1 MF-2 myocyte after a delay of 48-96 hours; and that this effect appears to be mediated by transcription, translation, and synthesis of new proteins in these genital tract myocytes.

Animals↗
PubMed1991

Degradation of a developmentally regulated mRNA in Xenopus embryos is controlled by the 3' region and requires the translation of another maternal mRNA.

By injecting the appropriately constructed plasmids into one-cell Xenopus embryos, we determined that the 3' region of the maternal Xenopus Eg2 mRNA confers instability on the chimeric mRNA transcribed from these plasmids. This instability, like that of the maternal Eg2 transcript, was abolished by treatment of the embryos with cycloheximide. Analysis of the polysome distribution of the maternal Eg2 mRNA in cycloheximide-treated and untreated embryos showed that Eg2 mRNA was released from polysomes after fertilization and that the stabilization caused by cycloheximide treatment was not due to a reloading of ribosomes onto the mRNA. Insertion of a stable hairpin loop (delta G = -50 kcal/mol) 5' to the reporter gene in the injected plasmid caused a 10- to 20-fold decrease in translation from the transcribed mRNAs. This decrease in translation did not abolish the instability conferred by the 3' Eg2 region. Therefore, the degradation of these chimeric mRNAs in Xenopus embryos requires the translation of another maternal mRNA coding for a trans-acting factor involved in mRNA degradation. Further restriction of the 3' Eg2 region, placed 3' to the reporter gene, showed that a cis-acting instability-conferring sequence is contained in a 497-nucleotide fragment.

Animals↗
PubMed1990

Alpha-1, alpha-2, and beta adrenergic signal transduction in cultured uterine myocytes.

The following studies were undertaken to develop a cultured uterine myocyte model which would allow further clarification of the adrenergic signal transduction mechanisms utilized by these myocytes. After mechanical removal of the endometrium, rabbit uterine myocytes were isolated by an overnight enzymatic disaggregation using collagenase and DNase I. The isolated myocytes were maintained in culture in 75-cm2 flasks containing Waymouth's MB 751/1 medium-10% fetal bovine serum along with 10(-8) M estradiol, penicillin, streptomycin, and Fungizone. The phase contrast and electron micrographic appearance of these cells was consistent with that previously reported for smooth muscle myocytes in culture. Immunocytochemical studies utilizing monoclonal anti-alpha-smooth muscle actin antibodies confirmed the presence of smooth muscle actin in these cultured myocytes. Western blot studies similarly confirmed the presence of alpha-smooth muscle actin in rabbit myometrial tissue and the cultured myocytes, both the primary and F1 generation. After prelabeling the myocytes with [3H]inositol, adrenergic stimulation experiments demonstrated alpha-1 receptor mediated stimulation of inositol phosphates. Beta receptor stimulation experiments confirmed cAMP production in these cultured myocytes, and the ability of clonidine, an alpha-2 agonist, to inhibit forskolin stimulated cAMP production confirmed the presence of functional alpha-2 adrenergic receptors in these myocytes. In conclusion, these cultured rabbit uterine myocytes have provided an in vitro model which can be utilized to further clarify the adrenergic receptor signal transduction mechanisms in genital tract smooth muscle.

Actins↗
PubMed1990

A model for the prospective analysis of perinatal deaths in a perinatal network.

This prospective study assesses factors that contribute to perinatal mortality. The study population includes the 1362 perinatal deaths that occurred among 85,402 live births between 1983 and 1987 at hospitals of the University of Chicago Perinatal Network. After peer review of demographic, clinical, and pathologic data, each perinatal death was classified in one of the following categories: (1) the result of congenital malformation incompatible with life, (2) unavoidable, (3) potentially avoidable by patient, by health provider, or by both, or (4) of undetermined responsibility. Of 1362 deaths, 12.3% involved congenital malformations incompatible with life, 56.9% were classified as unavoidable, 28.1% were judged potentially avoidable, and 2.7% due to undetermined causes. Of potentially avoidable deaths, 36% were due to patient factors (primarily noncompliance), 59% to health provider factors, and 15% to combined patient and provider factors. There was a significant reduction in the potentially avoidable cases during the study period. The maximum attainable reduction in perinatal mortality under optimal conditions is calculated. Intervention plans to achieve this goal are discussed.

Chicago↗
PubMed1989

Prematurity among insulin-requiring diabetic gravid women.

From Jan. 1, 1983, through Dec. 31, 1987, 420 gravidas with insulin-requiring diabetes antedating pregnancy delivered on the Joslin Clinic service. Among them, 110 pregnancies (26.2% of the total) delivered before 37 completed weeks of gestation compared with a 9.7% incidence (906/9368) for the general population at the Brigham and Women's Hospital during calendar year 1985. Thirty-three percent of all premature deliveries were the result of the development of preeclampsia. The relative risk of prematurity for diabetic patients with any hypertensive complication was 2.0 (95% confidence interval, 1.40 to 2.87) compared with normotensive diabetic subjects. Compared with the general population, most of the excess risk of prematurity was confined to hypertensive diabetics and normotensive patients of more advanced White class. A history of having had a previous premature delivery, increasing duration of diabetes antedating pregnancy, and carrying a male fetus in the index pregnancy were significantly associated with premature delivery. Future efforts to reduce the incidence of prematurity among diabetic gravidas should be directed toward reducing the incidence of preeclampsia.

Diabetes Mellitus, Type 1↗
PubMed1989

The impact of the acquired immunodeficiency syndrome epidemic on the philosophy of childbirth.

Few other specialists in medicine are as exposed to body fluids as obstetricians. Anxiety among these health care providers is therefore considerable. Guidelines for universal infection precautions are aimed at minimizing the risk of human immunodeficiency virus transmission by the creation of adequate physical barriers between the patient and the health care provider. Some of these guidelines are mutually exclusive to currently popular childbirth techniques in the very practical sense. However, the more important impact of universal infection precautions is likely to be psychological. Anxiety and the necessity for physical isolation are probably the worst basis for an empathic human relationship with the patient. It is the current challenge of obstetrics to maintain a sensitive and client-centered approach while judiciously dealing with the acquired immunodeficiency syndrome epidemic.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Absence of alpha-2 adrenergic effects on cAMP production in a genital tract smooth muscle cell line.

This study sought to evaluate alpha-2 and beta adrenergic modulation of cAMP production in the DDT1 MF-2 transformed smooth muscle myocyte. After stimulation with forskolin or adrenergic agonists with or without subtype specific antagonists, cAMP production was determined. These experiments confirmed an increase of cAMP in response to forskolin, isoproterenol, epinephrine, and norepinephrine; the adrenergic stimulation was inhibited by propranolol. On the other hand, the alpha-2 agonist clonidine did not inhibit cAMP production. Likewise, alpha-2 receptor blockade did not increase cAMP production in response to epinephrine. These studies, therefore, suggest that the DDT1 MF-2 myocyte does not contain a significant population of functional alpha-2 adrenergic receptors.

Animals↗
PubMed1989

Adrenergic stimulation of inositol-phosphate production in a genital tract smooth muscle cell line.

Catecholamines are important in the modulation of smooth muscle contractile activity; this study was undertaken to evaluate adrenoceptor stimulation of intracellular inositol-phosphate production in a genital tract smooth muscle myocyte. DDT1 MF-2 smooth muscle myocytes, derived from a hamster ductus deferens leiomyosarcoma, were loaded with 3H-inositol, incubated in 10 mM LiCl, then stimulated with adrenergic agonists with and without antagonists. Subsequently, the inositol phosphates were isolated by anion-exchange chromatography. In the presence of norepinephrine (NE), inositol trisphosphate (IP3) was produced by 30 s and peaked at 2 min; inositol 1-phosphate was also apparent by 30 s, and continued to increase over 15 min. Clonidine (an alpha-2 agonist), isoproterenol, and NE in the presence of phentolamine or prazosin (an alpha-1 antagonist) failed to increase IP3. In contrast, NE in the presence of yohimbine (an alpha-2 antagonist) or propranolol stimulated IP3 production to levels comparable to that stimulated by NE alone. These studies provide evidence that inositol phosphate production is involved in alpha-1 adrenergic signal transduction in DDT1 MF-2 myocyte.

Adrenergic Agonists↗
PubMed1988

Effects of prazosin and indomethacin on the alpha-adrenergic stimulation of rabbit myometrium.

The effect of norepinephrine (NE) stimulation of near-term pregnant rabbit myometrium was studied by comparing cumulative dose-response curves for NE and NE with prazosin or indomethacin. Prazosin blocked the stimulatory effects of NE. Indomethacin pretreatment resulted in attenuation, but not suppression of contractile activity. Myometrial activity was associated with a progressive increase in the synthesis of prostaglandin (PG) F2 alpha. Our observations suggest that alpha-adrenergic agonists have some myometrial stimulating effect independent of PG production.

Animals↗
PubMed1987

Dopamine binding to the alpha receptor in pregnant rabbit myometrium.

This study evaluated in vitro binding of dopamine ligands to myometrial alpha adrenoceptors. With cell membranes from pregnant rabbits, receptor radioligand binding studies utilizing [3H] dihydroergocryptine +/- dopamine demonstrated receptor affinity (KD) = 0.75 +/- 0.10 nM (+/- SEM) and density (Bmax) = 533.2 +/- 45.2 fM/mg protein. Similar studies utilizing phentolamine or apomorphine gave essentially identical results. Competition binding studies demonstrated steriospecific butaclamol binding, along with significant binding of haloperidol, spiperone, apomorphine, and bromoergocryptine. These observations provide a mechanism for the observed uterotonic effects of dopamine.

Animals↗