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Biomedical subjects

R E Garfield

Publications and source records attributed to R E Garfield.

At least 55 records · Page 3Linked to original sources
PubMed1999

The effect of indomethacin and prostacyclin agonists on blood pressure in a rat model of preeclampsia.

OBJECTIVE: This study was designed to determine the effects of cyclooxygenase inhibition and prostacyclin agonists on the hypertension induced by nitric oxide synthase blockade in a previously characterized rat model of preeclampsia. STUDY DESIGN: A condition similar to preeclampsia was induced by infusing pregnant rats with the nitric oxide synthase inhibitor N G -nitro- L -arginine methyl ester through subcutaneously implanted osmotic minipumps. Blood pressure was measured with the tail cuff method. In the first experiment the rats received either vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), indomethacin (0.1 mg/d), or N G -nitro- L -arginine methyl ester plus indomethacin beginning on day 17 of pregnancy. In the second experiment the rats received vehicle alone (control group), N G -nitro- L -arginine methyl ester (50 mg/d), or N G -nitro- L -arginine methyl ester plus iloprost (31 microgram/d). In a third experiment cicaprost (15 microgram/d) was substituted for iloprost. RESULTS: Except for an increase on the day after insertion of the pump indomethacin had no significant effect on the hypertension induced by N G -nitro- L -arginine methyl ester. Both prostacyclin agonists (iloprost and cicaprost), however, attenuated the rise in blood pressure usually seen after N G -nitro- L -arginine methyl ester administration. CONCLUSIONS: Nonselective inhibition of the cyclooxygenase enzymatic system does not influence the hypertension seen in the rat preeclampsia model induced by chronic nitric oxide deficiency. The hypertension in this model can be partially reversed with prostacyclin analogs.

Animals↗
PubMed1999

Vascular reactivity in preeclampsia.

It has long been known that vascular reactivity is altered in preeclamptic patients compared with normal pregnant women. This change even occurs weeks earlier than any clinical manifestation of the disease. Many investigators believe that the conditions for the development of preeclampsia are set as early as the first trimester. These changes in vascular reactivity appear to be independent of the blood pressure because they also occur in chronic hypertensive women destined to have preeclampsia. This review focuses on these changes in vascular reactivity reported in preeclampsia. Increased reactivity of the blood vessels in preeclampsia has been described in most, but not all, studies. The cause for the differences in reactivity between vessels from preeclamptic and normal pregnant women is not known. However, it cannot be attributed solely and with certainty to abnormalities in endothelium-dependent relaxation or the nitric oxide system because the study results published to date remain contradictory. In addition to functional differences, vessels from normal pregnant and preeclamptic women show distinct mechanical properties.

Biomechanical Phenomena↗
PubMed1999

Synergistic role of nitric oxide and progesterone during the establishment of pregnancy in the rat.

Successful pregnancy is strictly dependent on the trophoblast-decidual interaction and on an adequate blood supply to the implantation sites. Nitric oxide (NO) has been shown to play an important role during advanced gestation, although its role during early pregnancy is unclear. The aim of the present study in rats was to evaluate whether NO plays a role during the preimplantation [days 1-4 post coitum (p.c.)] and peri-implantation (days 6-8 p.c.) phases of pregnancy. The rats were treated with the non-specific nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME), and the iNOS inhibitor aminoguanidine in the presence and absence of low-dose antiprogestin, onapristone, and evaluated on days 9 p.c. and 19 p.c., respectively. Before implantation, the treatments alone (L-NAME, aminoguanidine, onapristone) had little effect on pregnancy outcome. Conversely, aminoguanidine plus onapristone treatment completely prevented pregnancy, whereas L-NAME plus onapristone reduced the pregnancy rate to approximately 50%. In addition, both treatments drastically reduced decidualization. Oviductal flushing experiments revealed arrest of embryo development at around the 8-cell stage after aminoguanidine plus onapristone treatment on days 1-4 p.c. Similarly, treatment during the peri-implantation period with L-NAME, aminoguanidine, and onapristone each had only marginal effects on pregnancy. However, a combination of L-NAME and onapristone, and aminoguanidine plus onapristone prevented pregnancy in 71% and 42% of dams, respectively, as determined on day 19 p.c. These treatments also markedly inhibited the decidualization process. This study demonstrates synergistic effects of NOS inhibitors and an antiprogestin in preventing pregnancy. NOS, particularly the cytokine- and progesterone-inducible iNOS, may represent a new target for novel therapeutic agents capable of promoting or inhibiting pregnancy.

Animals↗
PubMed1999

Nitric oxide synthase distribution during implantation in the mouse.

The peri-implantation period is a critical time during murine development. Although the importance of nitric oxide has been demonstrated during gestation, its role in implantation has not been fully defined. The aim of this study was to quantify (by Western blotting) two prominent nitric oxide synthase (NOS) isoforms, inducible (iNOS) and endothelial (eNOS) and localize all three forms [iNOS, eNOS, and neuronal (nNOS)] by immunohistochemistry in uterine tissue from days 4 through 8 of pregnancy. By day 6, iNOS values were significantly elevated in implantation sites compared with interimplantation regions and continued to rise through day 8. Analysis of eNOS was similar, but implantation site values peaked by days 6 and 7. Labelled iNOS cells were within the decidua, around myometrial vessels, and within the ectoplacental cone. At implantation, eNOS was conspicuous, displaying label adjacent to the embryo in vessels of the primary decidual zone. nNOS was localized mainly in the mesometrium and myometrium and did not appear to change throughout the peri-implantation period. The increased iNOS and eNOS values following implantation in the embryonic site may imply roles in tissue remodelling, immunosuppression and vasoregulation. Nitric oxide may play an important role in the mechanisms of implantation where these factors are keys to successful pregnancy.

Animals↗
PubMed1999

Localization of regulatory protein binding sites in the proximal region of human myometrial connexin 43 gene.

Parturition is preceded by a large increase in gap junctions between myometrial smooth muscle cells. Connexin 43 is the major structural protein of myometrial gap junctions. To explore transcriptional regulation of the myometrial Cx43 gene, we used DNase I footprinting, electrophoretic mobility shift and transient transfection assays to examine a 312 bp promoter region (-164 to +148) of the gene, utilizing human myometrial cell cultures and nuclear extracts. The DNase I studies showed four regions of nucleoprotein interactions. Protection of region 1 (-80 to -31) encompassed an Activator Protein 1 (AP1) (-44 to -36) and two Specificity Protein 1 (Sp1) (-77 to -69 and -59 to -48) consensus sequences. Regions 2 to 4 included the transcription initiation site (-10 to +25), an Ets/NF-kB consensus sequence (+47 to +74) and a TA-rich region (+81 to +101) respectively. Gel mobility shift and supershift assays demonstrated c-Jun and Sp1 binding at the AP1 and Sp1 sites respectively. Promoter mutagenesis and transient transfection analyses combined with Sp1 and c-Jun/c-Fos over-expression studies indicate that both Sp1 and c-Jun are required for maximal promoter activity and, therefore, may positively regulate transcription of myometrial Cx43 during the initiation of labour.

Base Sequence↗
PubMed1999

Changes in cervical resistance and collagen fluorescence during gestation in rats.

During pregnancy the role of the cervix shifts between two opposing functions. Throughout most of gestation, the cervix is rigid and resists tension in order to maintain the products of conception inside the uterus. At term, however, cervical function changes drastically in order to accommodate stretch and delivery. The events that control cervical function are not known. The aim of this study was to characterize changes in cervical resistance and collagen content during pregnancy in the rat. To determine the change in cervical resistance, non-pregnant and timed pregnant Sprague Dawley rats were sacrificed at various times. Their cervices were isolated and suspended in organ baths connected to a cervimeter for measurement of the stretch-tension relationship. In a different group of animals, cervical collagen content was measured using light-induced fluorescence in non-pregnant and, longitudinally, in pregnant rats. Cervical resistance and collagen content decreased progressively during pregnancy. The changes in cervical resistance mirrored those in cervical collagen content and the nadir in both occurred about two days prior to the onset of labor. Our study suggests that cervical preparation for delivery does not occur acutely at the time of labor and that cervical collagen content determines cervical resistance.

Animals↗
PubMed1999

Endothelium-dependent and -independent mechanisms of vasorelaxation by corticotropin-releasing factor in pregnant rat uterine artery.

Corticotropin-releasing factor (CRF), a potent vasorelaxant, is increased tremendously during human pregnancy. Placenta is the main source for this increase. CRF is thought to be important in modulating vascular resistance and uteroplacental blood flow during pregnancy. Here we investigated pathways mediating a vasorelaxant effect of CRF in the uterine artery. Two-millimeter segments of uterine artery (o.d. 300-400 microm) from day 18 pregnant rats were mounted in a small vessel myograph and precontracted with norepinephrine, and relaxation responses to CRF were studied. CRF relaxed the uterine artery in a concentration-dependent manner. Relaxation of uterine artery by CRF was abolished completely by alpha-helical CRF 9-41 (CRF antagonist, 1 micromol) and partially by removal of endothelium, Nomega-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor, 0.1 mmol), 6-anilino-5,8-quinolinedione (guanylate cyclase inhibitor, 10 micromol), or thiopental/miconazole (cytochrome P-450 inhibitors, 0.3 mmol/30 micromol), but remained unaffected by indomethacin (cyclo-oxygenase inhibitor, 10 micromol). Relaxation was also inhibited when depolarizing solution (K+, 120 mmol) was used for precontraction. In deendothelized preparations, relaxation was not inhibited by 9-tetrahydro-2-furanyl-9H-purin-6-amine (adenylate cyclase inhibitor, 0.2 mmol), glibenclamide (adenosine triphosphate-dependent K+ channel blocker, 10 micromol), tetrabutyl ammonium (nonspecific K+ channel blocker, 1 mmol), nitrendipine (voltage-gated Ca++ channel blocker, 1 micromol), or when vessels were precontracted with depolarizing solution. CRF causes vasorelaxation by receptor-operated, endothelium-dependent and -independent pathways. The endothelium-dependent relaxation is mediated by nitric oxide-cyclic guanosine monophosphate pathway and endothelium-derived hyperpolarizing factor but not prostacyclin. However, cyclic adenosine monophosphate, K+ channels, or Ca++ channels are not involved in endothelium-independent vasorelaxation by CRF.

Animals↗
PubMed1998

The effects of nitric oxide on the contractility of isolated uterine and aortic rings from pregnant rats.

OBJECTIVE: The object was to compare the effects of nitric oxide on isolated uterus and aorta of pregnant rats. STUDY DESIGN: Rings of uterus and thoracic aorta without endothelium from Sprague-Dawley rats at mid and late gestation were used for isometric tension recording. The concentration-response curve for diethylamine/nitric oxide was studied in the presence or absence of oxyhemoglobin (10(-5) mol/L), or oxyhemoglobin was added after the response to diethylamine/nitric oxide. RESULTS: Diethylamine/nitric oxide concentration dependently inhibited uterine contractions, and the effect was attenuated by previous treatment with oxyhemoglobin at mid gestation (n = 8). The effects were negligible at late gestation (n = 8). The relaxation of aortic rings by diethylamine/nitric oxide and its attenuation by previous treatment with oxyhemoglobin were similar at mid (n = 6) and late (n = 6) gestation. The sensitivity of aortic rings to diethylamine/nitric oxide is significantly higher than that of uterine rings. Oxyhemoglobin partly restored inhibited diethylamine/nitric oxide phenylephrine tension in aortic rings and had no effect on diethylamine/nitric oxide-inhibited uterine rings. CONCLUSIONS: Uterine smooth muscle is less sensitive to nitric oxide than is aortic smooth muscle. Nitric oxide sensitivity of rat uterus but not aorta decreases toward term.

Animals↗
PubMed1998

Effect of glycosylated hemoglobin on endothelium-dependent relaxation of omental arteries from pregnant women.

OBJECTIVE: This study was intended to test the hypothesis that glycosylated hemoglobin adversely affects endothelium-dependent vascular relaxation during pregnancy. STUDY DESIGN: Omental artery rings (3 mm) obtained from patients undergoing cesarean delivery at term were suspended in organ chambers for isometric tension recording in Krebs bicarbonate solution. They were bubbled with 5% carbon dioxide in air (37 degrees C, pH 7.4). After equilibration at 1-g passive tension and contraction with endothelin 1, concentration-relaxation curves in response to bradykinin were determined in the presence or absence of oxyhemoglobin, glycosylated hemoglobin, or nitric oxide synthase inhibitors (N(omega)-nitro-L-arginine methyl ester or N(omega)-nitro-L-arginine). RESULTS: Oxyhemoglobin and glycosylated hemoglobin attenuated the endothelium-dependent relaxation induced by bradykinin. The inhibition did not differ significantly between the 2 nitric oxide scavengers and was of the same magnitude as that noted with the nitric oxide synthase inhibitors. CONCLUSION: Glycosylation of hemoglobin does not change its effect on endothelium-dependent relaxation in human omental vessels during pregnancy. These data do not support the hypothesis that glycosylated hemoglobin may be the reason for abnormal endothelial function in diabetes.

Adult↗
PubMed1998

Both soluble guanylate cyclase and particulate guanylate cyclase regulate myometrial contractility.

OBJECTIVE: Our purpose was to compare the effects of agents stimulating particulate and soluble guanylate cyclase with spontaneous rat uterine contractions at midgestation and term. STUDY DESIGN: Uterine rings from midgestation (day 13) and term nonlaboring (day 22) rats were positioned in organ chambers for isometric force recording. Rings were treated with increasing concentrations of atrial natriuretic peptide, permeable analogs of cyclic guanosine monophosphate, and diethylamine/nitric oxide. RESULTS: Atrial natriuretic peptide was more effective in inhibition of uterine contractions than diethylamine/nitric oxide. The 50% inhibitory concentrations were -7.4 +/- 0.12 and -7.38 +/- 0.11 for atrial natriuretic peptide and -5.68 +/- 0.09 and -4.23 +/- 0.12 for diethylamine/nitric oxide at midgestation and term, respectively. Pretreatment of uterine rings with atrial natriuretic peptide significantly attenuated inhibition of spontaneous contractions by diethylamine/nitric oxide at midgestation. CONCLUSIONS: Uterine spontaneous contractions are influenced by both soluble and particulate guanylate cyclase; the former, but not latter, is gestational age dependent.

Animals↗
PubMed1998

Gap junction currents in cultured muscle cells from human myometrium.

OBJECTIVE: The electrophysiologic properties of gap junctions between human myometrial smooth muscle cells were studied. STUDY DESIGN: Double whole-cell patch clamp recordings were made on pairs of cells from primary cultures of myometrial cells from women undergoing cesarean section. Macroscopic gap junction currents were measured as the change in current in a cell held at a constant voltage while the other member of a pair was subjected to a test pulse of voltage. The blockade by halothane was examined. RESULTS: Mean junctional conductance between pairs of cells was 23 +/- 14 nanosiemens (n = 57). Instantaneous gap junction conductance was constant as a function of transjunctional voltage. For transjunctional voltages of < or = 50 mV, currents were constant during a 5-second test pulse. For larger voltages, however, the currents showed a time-dependent decay. The currents were blocked completely and reversibly with 3.5 mmol/L halothane. Single-channel conductances of 60 picosiemens and 15 picosiemens were observed. CONCLUSION: This first study of gap junction currents in human myometrial cells confirms that connexin43 is the major functional constituent. Functional studies of myometrial gap junction channels may suggest new strategies for controlling uterine contractility.

Anesthetics, Inhalation↗
PubMed1998

Uterine activity during pregnancy and labor assessed by simultaneous recordings from the myometrium and abdominal surface in the rat.

OBJECTIVES: The aim of this study was to analyze records of uterine electrical activity made from the abdominal surface of pregnant and laboring rats to examine whether similar quantitative information can be extracted as from direct recording from the uterine muscle. STUDY DESIGN: Electrical activity during pregnancy (nonlabor, days 18 to 22), term labor (day 22), and preterm labor (onapristone injected on day 18, delivery on day 19) was measured with use of electrodes attached to the uterine wall and to the abdominal surface. The fast Fourier transform and wavelet transforms were obtained for representative electromyographic bursts. Power spectra were generated. Intrauterine pressure was also measured. RESULTS: (1) Several parameters have been identified for use in following up the progressive increase in uterine activity that occurs in preparation for and during labor. Analyses of amplitude, frequency, and percent time active represent a convenient method for objectively determining the efficiency of uterine contraction. (2) Most of the changes in these parameters appear in the last 24 hours before delivery. (3) Although the uterine electromyographic signals on the abdominal surface are attenuated, the abdominal surface signals are generally similar to the signals obtained from the uterine muscle during pregnancy and during preterm and term labor. (4) The characteristics of onapristone-induced preterm labor are generally similar to those of spontaneous term labor. CONCLUSIONS: Recording of uterine electromyographic activity from the abdominal surface may be useful in following the progression of pregnancy and in predicting and diagnosing labor.

Abdomen↗
PubMed1998

In vivo effects of corticotropin-releasing factor in pregnant rats.

OBJECTIVES: Our purpose was to study the effects of corticotropin-releasing factor on (1) maternal blood pressure, (2) uterine vasculature, and (3) parturition in pregnant rats. STUDY DESIGN: Infusion minipumps containing vehicle, corticotropin-releasing factor, or alpha-helical corticotropin-releasing factor 9-41 (corticotropin-releasing factor receptor antagonist) were inserted subcutaneously in timed pregnant rats on day 16 of gestation. Systolic blood pressure was measured daily by the tail-cuff method. The time of onset of labor was determined and the newborn pups were weighed. Circulating levels of corticotropin-releasing factor were measured in untreated controls by radioimmunoassay. Relaxant responses to corticotropin-releasing factor were studied in isolated segments of uterine artery from late (day 18) and term (day 22) pregnant rats mounted in a wire myograph. RESULTS: The blood pressure was decreased by corticotropin-releasing factor and increased by alpha-helical corticotropin-releasing factor 9-41 (p < 0.05). The time of onset of labor was not affected by either treatment. Pup weight was decreased by corticotropin-releasing factor (p < 0.05). Circulating levels of corticotropin-releasing factor (immunoreactive) were not changed in pregnancy. In vitro, corticotropin-releasing factor caused relaxation of the uterine artery in a concentration-dependent manner and the relaxation was decreased at term compared with late pregnancy (p < 0.05). CONCLUSIONS: Endogenously produced corticotropin-releasing factor lowers blood pressure during pregnancy in rats. It is a relaxant of uterine vasculature and this effect is decreased at term. It does not play an essential role in the initiation of labor in rats.

Animals↗
PubMed1998

Effect of red blood cells and hemoglobin on spontaneously hypertensive and normotensive rat aortas.

Experiments were designed to compare the contractile effect of red blood cells (RBC) on aortic rings with and without endothelium from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Red blood cells of 4 week old WKY and SHR rats induced a negligible increase in tension of aortic rings, either with or without endothelium, being slightly more effective in SHR rats. However, red blood cells of 16 week old rats increased tension of WKY and SHR aortic rings, with endothelium at this age being more pronounced then red blood cells in 4 week old animals. The contractions induced by WKY and SHR red blood cells both in WKY and SHR aortic rings without endothelium at this age are significantly greater compared to the effect on aortic rings with endothelium. Red blood cell ghosts of rats of both strains increased the tension of the rings without endothelium of SHR aorta to near 50% of those induced by red blood cells, whereas they were ineffective in aortic rings without endothelium of WKY rats. Oxyhemoglobin increased the tension of 16 week SHR aortic rings both with and without endothelium, whereas the effect on the rings of WKY rats was negligible. This increase in tension was inhibited by BM 13505, nordihydroguaiaretic acid, and indomethacin in SHR rings both with and without endothelium, demonstrating an eicosanoid involvement in oxyhemoglobin-induced contractions. Hemoglobin or its metabolites may be involved in development or in maintenance of spontaneous hypertension.

Animals↗
PubMed1998

Effect of gestational age on in-vitro responses of pregnant rat aorta.

The hypothesis that the changes in vascular reactivity seen during pregnancy are determined by the gestational age was examined. Experiments were designed to investigate changes in vascular responses with progression of pregnancy. The contractile responses to potassium and phenylephrine (in the presence and absence of N(omega)-nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor) and the relaxant responses to acetylcholine and sodium nitroprusside were measured in isolated aortic rings from pregnant rats at various stages of gestation and from non-pregnant female rats. Potassium-evoked contractile response was higher early in pregnancy and was decreased at term (P < 0.05). The contractile response to phenyllephrine was decreased and the relaxant response to acetylcholine was increased in early pregnancy (P < 0.05). Inhibition of nitric oxide synthase caused an increase in the contractile response to phenylephrine in all the groups, but the attenuation of the response in early pregnancy was maintained (P < 0.05). There was a small decrease in the maximal relaxant response to sodium nitroprusside at term (P < 0.05). It was concluded that the effects of pregnancy on the responses of rat aorta in vitro vary at different stages of gestation. Vascular resistance may be lowered by changes in vascular reactivity in early gestation and by a decrease in the contractile potential of the vasculature during the later stages.

Analysis of Variance↗
PubMed1998

Instrumentation for the diagnosis of term and preterm labour.

The problems associated with labor during pregnancy are among the most important health issues facing physicians. Understanding the role of the uterus and cervix in labor and developing methods to control their function is essential to solving problems relating to labor. At the moment, only crude, inaccurate and subjective methods are used to assess changes in the uterus and cervix that occur in preparation for or during labor. In the past several years, we have developed noninvasive methods to quantitatively evaluate the uterus and cervix based respectively on recording of uterine electrical signals from the abdominal surface (uterine EMG) and measurement of light-induced cervical collagen fluorescence (LIF) with an optical device (Collascope). The methods are rapid and allow assessment of uterine contractility and cervical ripening. Studies in rats and humans indicate that uterine and cervical function can be successfully monitored during pregnancy using these approaches and that these techniques might be used in a variety of conditions associated with labor to better define management. The potential benefits of the proposed instrumentation and methods include a reducing the rate of preterm delivery, improving maternal and perinatal outcome, monitoring treatment, decreasing cesarean section rate and improving research methods to understand uterine and cervical function.

Animals↗
PubMed1998

Role of nitric oxide in the uterus and cervix: implications for the management of labor.

The results of our experimental studies indicate that that parturition is composed principally of two major phases, a relatively long conditioning (preparatory) phase followed by a short and probably irreversible active labor phase. The major events of conditioning phase are: (i) the progression of uterine contractility from an inactive to a vigorously active state, (ii) cervical ripening, and (iii) activation of fetal membranes. Our experimental and molecular studies indicate that nitric oxide (NO) is an important element in controlling uterine and cervical functions during the transition from pregnancy to the conditioning phase of labor. These studies show that NO acts in concert with progesterone to regulate uterine quiescence and cervical rigidity. In the rat uterus and cervix NO is produced mainly by the cytokine-inducible NO synthase (iNOS) which expression is gestationally-regulated and progesterone-dependent. During pregnancy iNOS expression is up-regulated in the uterus and down-regulated in the cervix. Opposite changes occur during term and antiprogestin-induced preterm labor. Our studies with NOS-inhibitors and NO donors suggest that in the uterus a decrease in NO production contributes to the initiation of labor, whereas in the cervix NO acts as a final metabolic mediator of cervical ripening. The evidence also indicates that NO donors have therapeutic potential as tocolytic agents. On the other hand, locally applied NO donors can be used to induce cervical ripening. In addition iNOS, may represent a new target for novel therapeutic agents capable of promoting or inhibiting uterine of both contractility and cervical ripening. There is an urgent need for controlled studies demonstrating clinical efficacy and safety of NO donors in obstetrics.

Animals↗