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Biomedical subjects

L Zhang

Publications and source records attributed to L Zhang.

At least 451 records · Page 25Linked to original sources
PubMed2001

False-positive reduction in CAD mass detection using a competitive classification strategy.

High false-positive (FP) rate remains to be one of the major problems to be solved in CAD study because too many false-positively cued signals will potentially degrade the performance of detecting true-positive regions and increase the call-back rate in CAD environment. In this paper, we proposed a novel classification method for FP reduction, where the conventional "hard" decision classifier is cascaded with a "soft" decision classification with the objective to reduce false-positives in the cases with multiple FPs retained after the "hard" decision classification. The "soft" classification takes a competitive classification strategy in which only the "best" ones are selected from the pre-classified suspicious regions as the true mass in each case. A neural network structure is designed to implement the proposed competitive classification. Comparative studies of FP reduction on a database of 79 images by a "hard" decision classification and a combined "hard"-"soft" classification method demonstrated the efficiency of the proposed classification strategy. For example, for the high FP sub-database which has only 31.7% of total images but accounts for 63.5% of whole FPs generated in single "hard" classification, the FPs can be reduced for 56% (from 8.36 to 3.72 per image) by using the proposed method at the cost of 1% TP loss (from 69% to 68%) in whole database, while it can only be reduced for 27% (from 8.36 to 6.08 per image) by simply increasing the threshold of "hard" classifier with a cost of TP loss as high as 14% (from 69% to 55%). On the average in whole database, the FP reduction by hybrid "hard"-"soft" classification is 1.58 per image as compared to 1.11 by "hard" classification at the TP costs described above. Because the cases with high dense tissue are of higher risk of cancer incidence and false-negative detection in mammogram screening, and usually generate more FPs in CAD detection, the method proposed in this paper will be very helpful in improving the performance of early detection of breast cancer with CAD.

Biophysical Phenomena↗
PubMed2001

Expression of multiple subtypes of muscarinic receptors and cellular distribution in the human heart.

Five isoforms of the muscarinic acetylcholine receptor (mAChR) have been identified by molecular cloning and designated m(1)-m(5), of which four correspond to the functional subtypes M(1), M(2), M(3), and M(4) in primary tissues. The presence of M(5) receptors in tissues remains uncertain. The present study was designed to explore the diversity and cellular distribution of various mAChR subtypes in human hearts. Competition binding of [N-methyl-(3)H]-scopolamine methyl chloride with various mAChR antagonists yielded data consistent with the presence of multiple subtypes (M(1)/M(2)/M(3)/M(5)) of mAChRs in both human atrial (HA) and ventricular (HV) tissues. Expression of mRNAs encoding all five subtypes was readily detected by reverse transcription-polymerase chain reaction in both HA and HV samples. Immunoblotting with subtype-specific antibodies confirmed the presence of M(1), M(2), M(3), and M(5), but not M(4), proteins in membrane preparations from both HA and HV. The protein levels of M(1) and M(2) were comparable between HA and HV. Although the density of M(3) appeared approximately 10-fold higher in HV than HA, that of M(5) was approximately 5 times lower in HV than in HA. Positive immunostaining of single ventricular myocytes by M(1), M(2), M(3), and M(5) antibodies, respectively, was consistently detected. Under confocal microscopy, M(5) showed characteristic localization to the intercalated discs, whereas other subtypes were more evenly distributed throughout the surface membrane. Our results provide the first molecular evidence for the presence of multiple subtypes of mAChR, including endogenous M(5) receptors, in human hearts and suggest that different subtypes have different tissue distributions and cellular localization.

Binding, Competitive↗
PubMed2001

SmeDEF multidrug efflux pump contributes to intrinsic multidrug resistance in Stenotrophomonas maltophilia.

Stenotrophomonas maltophilia is an emerging nosocomial pathogen that displays high-level intrinsic resistance to a variety of structurally unrelated antimicrobial agents. Efflux mechanisms are known to contribute to acquired multidrug resistance in this organism, and indeed, one such multidrug efflux system, SmeDEF, was recently identified. Still, the importance of SmeDEF to intrinsic antibiotic resistance in S. maltophilia had not yet been determined. Reverse transcription-PCR confirmed expression of the smeDEF genes in wild-type S. maltophilia, and deletion of smeE or smeF in wild-type strains rendered the mutants hypersusceptible to several antimicrobials, suggesting that SmeDEF contributes to intrinsic antimicrobial resistance in this organism. Expression of smeDEF was also enhanced in an in vitro-selected multidrug-resistant mutant, although deletion of smeF but not of smeE in these mutants compromised antimicrobial resistance. Apparently, hyperexpressed SmeF is capable of functioning with additional multidrug efflux components to promote multidrug resistance in S. maltophilia.

Bacterial Outer Membrane Proteins↗
PubMed2001

Synergy of histone-derived peptides of coho salmon with lysozyme and flounder pleurocidin.

Recent research has identified endogenous cationic antimicrobial peptides as important factors in the innate immunity of many organisms, including fish. It is known that antimicrobial activity, as well as lysozyme activity, can be induced in coho salmon (Oncorhynchus kisutch) mucus after exposure of the fish to infectious agents. Since lysozyme alone does not have antimicrobial activity against Vibrio anguillarum and Aeromonas salmonicida, a four-step protein purification protocol was used to isolate and identify antibacterial fractions from bacterially challenged coho salmon mucus and blood. The purification consisted of extraction with hot acetic acid, extraction and concentration on a C(18) cartridge, gel filtration, and reverse-phase chromatography on a C(18) column. N-terminal amino acid sequence analyses revealed that both the blood and the mucus antimicrobial fractions demonstrated identity with the N terminus of trout H1 histone. Mass spectroscopic analysis indicated the presence of the entire histone, as well as fragments thereof, including a 26-amino-acid N-terminal segment. These fractions inhibited the growth of antibiotic-supersuscptible Salmonella enterica serovar Typhimurium, as well as A. salmonicida and V. anguillarum. Synthetic peptides identical to the N-terminally acetylated or C-terminally amidated 26-amino-acid fragment were inactive in antimicrobial assays, but they potentiated the antimicrobial activities of the flounder peptide pleurocidin, lysozyme, and crude lysozyme-containing extracts from coho salmon. The peptides bound specifically to anionic lipid monolayers. However, synergy with pleurocidin did not appear to occur at the cell membrane level. The synergistic activities of inducible histone peptides indicate that they play an important role in the first line of salmon defenses against infectious pathogens and that while some histone fragments may have direct antimicrobial effects, others improve existing defenses.

Aeromonas↗
PubMed2001

Interferon regulatory factor 7 mediates activation of Tap-2 by Epstein-Barr virus latent membrane protein 1.

Transporter associated with antigen processing 2 (Tap-2) is responsible for ATP-dependent transport of peptides from the cytosol to the endoplasmic reticulum, where peptides bind to newly synthesized human leukocyte antigen (HLA) class I molecules, which are essential for cellular immune responses. Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) has been shown to induce the expression of Tap-2. In this study, the induction of endogenous Tap-2 by LMP-1 is shown to be associated with and requires the expression of interferon regulatory factor 7 (IRF-7). In DG75 Burkitt's lymphoma (BL) cells, in which LMP-1 induces the expression of IRF-7, LMP-1 induced endogenous Tap-2, and ectopic expression of IRF-7 could enhance the induction. In Akata BL cells, in which LMP-1 could not induce IRF-7, LMP-1 could not induce Tap-2. Addition of IRF-7, which complements the defect in Akata cells, could stimulate the expression of Tap-2. Furthermore, LMP-1 and IRF-7A but not other IRF-7 splicing variants could activate endogenous Tap-2. A Tap-2 promoter reporter construct could be activated by the overexpression of IRF-7A. The activation could be specifically enhanced by LMP-1 and was dependent on an intact interferon-stimulated response element (ISRE) present in the Tap-2 promoter. Also, IRF-7 can bind to the Tap-2 promoter under physiological conditions in vivo, as shown by formaldehyde cross-linking, as well as to the Tap-2 ISRE in vitro, as shown by gel mobility shift assays. Furthermore, LMP-1 facilitates the phosphorylation and nuclear translocation of IRF-7. These data point to the role of IRF-7 as a secondary mediator of LMP-1-activated signal transduction for Tap-2 as follows: LMP-1 stimulates the expression of IRF-7 and facilitates its phosphorylation and nuclear translocation, and then the activated IRF-7 mediates the activation of the cellular Tap-2 gene. The induction of Tap-2 by IRF-7 and LMP-1 may have an important implication for the immune response to EBV and its persistence in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Intracellular signaling molecules activated by Epstein-Barr virus for induction of interferon regulatory factor 7.

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP-1) is the principal oncogenic protein in the EBV transformation process. LMP-1 induces the expression of interferon regulatory factor 7 (IRF-7) and activates IRF-7 protein by phosphorylation and nuclear translocation. LMP-1 is an integral membrane protein with two regions in its C terminus that initiate signaling processes, the C-terminal activator regions 1 (CTAR-1) and CTAR-2. Here, genetic analysis of LMP-1 has determined that the PXQXT motif that governs the interaction between LMP-1 CTAR-1 and tumor necrosis factor receptor-associated factors (TRAFs) is needed to induce the expression of IRF-7. Mutations in the PXQXT motif in CTAR-1 that disrupt the interaction between LMP-1 and TRAFs abolished the induction of IRF-7. Also, dominant-negative mutants of TRAFs inhibited the induction of IRF-7 by CTAR-1. The last three amino acids (YYD) of CTAR-2 are also important for the induction of IRF-7. When both PXQXT and YYD were mutated (LMP-DM), the LMP-1 mutant failed to induce IRF-7. Also, LMP-DM blocked the induction of IRF-7 by wild-type LMP-1. These data strongly suggest that both CTAR-1 and CTAR-2 of LMP-1 independently induce the expression of IRF-7. In addition, NF-kappaB is involved in the induction of IRF-7. A superrepressor of IkappaB (sr-IkappaB) could block the induction of IRF-7 by LMP-1, and overexpression of NF-kappaB (p65 plus p50) could induce the expression of IRF-7. In addition, we have found that human IRF-7 is a stable protein, and sodium butyrate, a modifier of chromatin structure, induces IRF-7.

Adaptor Proteins, Signal Transducing↗
PubMed2001

The Hsp70-Ydj1 molecular chaperone represses the activity of the heme activator protein Hap1 in the absence of heme.

In Saccharomyces cerevisiae, heme directly mediates the effects of oxygen on transcription through the heme activator protein Hap1. In the absence of heme, Hap1 is bound by at least four cellular proteins, including Hsp90 and Ydj1, forming a higher-order complex, termed HMC, and its activity is repressed. Here we purified the HMC and showed by mass spectrometry that two previously unidentified major components of the HMC are the Ssa-type Hsp70 molecular chaperone and Sro9 proteins. In vivo functional analysis, combined with biochemical analysis, strongly suggests that Ssa proteins are critical for Hap1 repression in the absence of heme. Ssa may repress the activities of both Hap1 DNA-binding and activation domains. The Ssa cochaperones Ydj1 and Sro9 appear to assist Ssa in Hap1 repression, and only Ydj1 residues 1 to 172 containing the J domain are required for Hap1 repression. Our results suggest that Ssa-Ydj1 and Sro9 act together to mediate Hap1 repression in the absence of heme and that molecular chaperones promote heme regulation of Hap1 by a mechanism distinct from the mechanism of steroid signaling.

Blotting, Western↗
PubMed2001

Deficiency of reproductive tract alpha(1,2)fucosylated glycans and normal fertility in mice with targeted deletions of the FUT1 or FUT2 alpha(1,2)fucosyltransferase locus.

The fucose alpha(1-->2) galactose beta structure is expressed by uterine epithelial cells in the mouse and has been implicated in blastocyst adhesion events thought to be required for murine implantation. Fucalpha(1-->2)Galbeta moieties and cognate fucosyltransferases are also expressed by epithelial cells of the male reproductive tract and have been implicated in sperm maturation events that may contribute to fertilization. To determine directly if Fucalpha(1-->2)Galbeta moieties are required for fertility, we have generated strains of mice that are deficient in genes encoding FUT1 and FUT2, a pair of GDP-L-fucose:beta(1-->4)-D-galactosyl-R 2-alpha-L-fucosyltransferase enzymes (EC 2.4.1.69) responsible for Fucalpha(1-->2)Galbeta synthesis and expression. FUT1 null mice and FUT2 null mice develop normally and exhibit no gross phenotypic abnormalities. The Fucalpha(1-->2)Galbeta epitope is absent from the uterine epithelia of FUT2 null mice and from the epithelia of the epididymis of FUT1 null mice. Fully normal fertility is observed in FUT1 null intercrosses and in FUT2 null intercrosses. These observations indicate that Fucalpha(1-->2)Galbeta moieties are not essential to blastocyst-uterine epithelial cell interactions required for implantation and are not required for sperm maturation events that permit fertilization and that neither the FUT loci nor their cognate fucosylated glycans are essential to normal development.

Alleles↗
PubMed2001

Anti-HIV activity of medicinal herbs: usage and potential development.

The acquired immunodeficiency syndrome (AIDS) is a result of human immunodeficiency virus (HIV) infection which subsequently leads to significant suppression of immune functions. AIDS is a significant threat to the health of mankind, and the search for effective therapies to treat AIDS is of paramount importance. Several chemical anti-HIV agents have been developed. However, besides the high cost, there are adverse effects and limitations associated with using chemotherapy for the treatment of HIV infection. Thus, herbal medicines have frequently been used as an alternative medical therapy by HIV positive individuals and AIDS patients. The aim of this review is to summarize research findings for herbal medicines, which are endowed with the ability to inhibit HIV. In this article, we will emphasize a Chinese herbal medicine, Scutellaria baicalensis Georgi and its identified components (i.e., baicalein and baicalin), which have been shown to inhibit infectivity and replication of HIV. Potential development of anti-AIDS compounds using molecular modeling methods will also be discussed.

Anti-HIV Agents↗
PubMed2001

Smad4 mediates activation of mitogen-activated protein kinases by TGF-beta in pancreatic acinar cells.

Transforming growth factor-beta (TGF-beta) inhibits pancreatic acinar cell growth. In many cell types, TGF-beta mediates its growth inhibitory effects by activation of Smad proteins. Recently, it has been reported that Smad proteins may interact with the mitogen-activated protein (MAP) kinase signaling pathways. In this study, we report on the interactions between the TGF-beta and MAP kinase signaling pathways in isolated rat pancreatic acinar cells. TGF-beta activated the MAP kinases extracellular signal-related kinases (ERKs) and p38 in pancreatic acinar cells, but had no effect on c-jun NH2-terminal kinase activity. Activation of MAP kinase by TGF-beta was maximal 4 h after treatment. The ability of TGF-beta to activate ERKs was concentration dependent and dependent on protein synthesis. TGF-beta's stimulation of ERK activation was blocked by PD-98059, an inhibitor of MAP kinase kinase 1, and by adenoviral transfer of dominant negative RasN17. Furthermore, adenoviral-mediated expression of dominant negative Smad4 blocked the ability of TGF-beta to activate acinar cell MAP kinase, demonstrating that this activation is downstream of Smads. The biological relevance of ERK activation by TGF-beta was indicated by demonstrating that inhibition of ERK signaling by PD-98059 blocked the ability of TGF-beta to activate the transcription factor activator protein-1. These studies provide new insight into the signaling mechanisms by which TGF-beta mediates biological actions in pancreatic acinar cells.

Adenoviridae↗
PubMed2001

Bcl-2 protects lymphoma cells from apoptosis but not growth arrest promoted by cAMP and dexamethasone.

Glucocorticoids or increases in cellular cAMP promote apoptosis in many cell types, including murine S49 cells. We examined the impact of Bcl-2, an antiapoptotic protein, on S49 cell growth and death promoted by the glucocorticoid dexamethasone or agents that increase cAMP: isoproterenol (a beta-adrenergic agonist) + 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor) and forskolin (diterpene). These agents promoted apoptosis (i.e., increased expression of annexin V) of wild-type (WT) S49 cells, but Bcl-2-overexpressing S49 cells were protected from this response. Bcl-2 overexpression did not protect cells from G(1) growth arrest but did allow cells to grow longer in culture and protected cells from culture-dependent necrosis. Commitment to and reversal from apoptosis vs. G(1) growth arrest by isoproterenol + 3-isobutyl-1-methylxanthine showed different kinetics. Although both processes required several hours to develop, removal of agonists readily reversed growth arrest, but not apoptosis. Thus commitment to apoptosis is less reversible than G(1) growth arrest. The findings also indicate that glucocorticoid- and cAMP-mediated G(1) growth arrest is unaffected by Bcl-2 overexpression, even though increased Bcl-2 allows these lymphoma cells to resist necrosis and apoptosis.

1-Methyl-3-isobutylxanthine↗
PubMed2001

Developmental changes in ryanodine- and IP(3)-sensitive Ca(2+) pools in ovine basilar artery.

To explore the hypothesis that cerebrovascular maturation alters ryanodine- and inositol 1,4,5-trisphosphate (IP(3))-sensitive Ca(2+) pool sizes, we measured total intracellular Ca(2+) with (45)Ca and the fractions of intracellular Ca(2+) released by IP(3) and/or caffeine in furaptra-loaded permeabilized basilar arteries from nonpregnant adult and term fetal (139-141 days) sheep. Ca(2+) mass (nmol/mg dry weight) was similar in adult (1.60 +/- 0.18) and fetal (1.71 +/- 0.16) arteries in the pool sensitive to IP(3) alone but was significantly lower for adult (0.11 +/- 0.01) than for fetal (1.22 +/- 0.11) arteries in the pool sensitive to ryanodine alone. The pool sensitive to both ryanodine and IP(3) was also smaller in adult (0.14 +/- 0.01) than in fetal (0.85 +/- 0.08) arteries. Because the Ca(2+) fraction in the ryanodine-IP(3) pool was small in both adult (5 +/- 1%) and fetal (7 +/- 4%) arteries, the IP(3) and ryanodine pools appear to be separate in these arteries. However, the pool sensitive to neither IP(3) nor ryanodine was 10-fold smaller in adult (0.87 +/- 0.10) than in fetal (8.78 +/- 0.81) arteries, where it accounted for 72% of total intracellular membrane-bound Ca(2+). Thus, during basilar artery maturation, intracellular Ca(2+) mass plummets in noncontractile pools, decreases modestly in ryanodine-sensitive pools, and remains constant in IP(3)-sensitive pools. In addition, age-related increases in IP(3) efficacy must involve factors other than IP(3) pool size alone.

Animals↗
PubMed2001

Adenovirus-mediated gene transfer of dominant-negative Smad4 blocks TGF-beta signaling in pancreatic acinar cells.

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of pancreatic acinar cell growth. Smad4 is a central mediator in the TGF-beta signaling pathway. To study the effect of Smad4 on pancreatic growth, cell cycle protein expression, and the expression of a TGF-beta-responsive promoter in vitro, we constructed an adenovirus containing dominant-negative COOH terminal truncated Smad4 (AddnSmad4) downstream of the rat elastase promoter. Acinar cells expressed dominant-negative Smad4 within 8 h after infection, and expression persisted for 72 h. Mouse pancreatic acini were infected with either AddnSmad4 or control adenovirus expressing green fluorescent protein, and TGF-beta was added 8 h after infection. Acinar cells were then incubated for 1, 2, or 3 days, and [(3)H]thymidine incorporation was determined. AddnSmad4 significantly reduced TGF-beta inhibition of [(3)H]thymidine incorporation, with maximal effects on day 3. AddnSmad4 also completely blocked TGF-beta-mediated growth inhibition in the presence of basic fibroblast growth factor. We next examined the effects of AddnSmad4 on TGF-beta-induced expression of the cell cycle regulatory proteins p21(Cip1) and p27(Kip1). TGF-beta induced upregulation of p21(Cip1), which was completely blocked by AddnSmad4. AddnSmad4 also inhibited TGF-beta-induced expression of the TGF-beta-responsive luciferase reporter 3TP-Lux. These results show that Smad4 is essential in TGF-beta-mediated signaling in pancreatic acinar cells.

Adenoviridae↗
PubMed2001

Upregulation of eNOS in pregnant ovine uterine arteries by chronic hypoxia.

We tested the hypothesis that chronic high-altitude (3,820 m) hypoxia during pregnancy was associated with the upregulation of endothelial nitric oxide (NO) synthase (eNOS) protein and mRNA in ovine uterine artery endothelium and enhanced endothelium-dependent relaxation. In pregnant sheep, norepinephrine-induced dose-dependent contractions were increased by removal of the endothelium in both control and hypoxic uterine arteries. The increment was significantly higher in hypoxic tissues. The calcium ionophore A23187-induced relaxation of the uterine artery was significantly enhanced in hypoxic compared with control tissues. However, sodium nitroprusside- and 8-bromoguanosine 3',5'-cyclic monophosphate-induced relaxations were not changed. Accordingly, chronic hypoxia significantly increased basal and A23187-induced NO release. Chronic hypoxia increased eNOS protein and mRNA levels in the endothelium from uterine but not femoral or renal arteries. In nonpregnant animals, chronic hypoxia increased eNOS mRNA in uterine artery endothelium but had no effects on eNOS protein, NO release, or endothelium-dependent relaxation. Chronic hypoxia selectively augments pregnancy-associated upregulation of eNOS gene expression and endothelium-dependent relaxation of the uterine artery.

Altitude Sickness↗
PubMed2001

Maturation depresses cGMP-mediated decreases in [Ca2+]i and Ca2+ sensitivity in ovine cranial arteries.

Because cerebrovascular cGMP levels vary significantly during maturation, we examined the hypothesis that the ability of cGMP to relax cerebral arteries also changes during maturation. In concentration-response experiments, potassium-induced tone in basilar arteries was significantly more sensitive to a nonmetabolizable cell-permeant cGMP analogue 8-(p-chlorophenylthio)-cGMP (8-pCPT-cGMP) in term fetal [-log one-half maximal concentration (EC(50)) = 4.4 +/- 0.1 M] than in adult (-log EC(50) = 4.0 +/- 0.1 M) ovine basilar arteries. Serotonin-induced tone also revealed significantly greater sensitivity to the cGMP analogue in fetal (-log EC(50) = 4.9 +/- 0.1 M) than in adult (-log EC(50) = 4.7 +/- 0.1 M) basilars. In fura 2-loaded preparations, 8-pCPT-cGMP had no significant effect on cytosolic calcium concentrations in potassium-contracted arteries but at 6 microM significantly reduced calcium only in fetal basilars (Delta = 33 +/- 8%). Higher 8-pCPT-cGMP concentrations reduced cytosolic calcium in both fetal and adult basilars. Similarly, in both potassium- and 5-hydroxytryptamine (5-HT)-contracted preparations, low concentrations of 8-pCPT-cGMP reduced myofilament calcium sensitivity only in fetal basilars (Delta = 29 +/- 6 and Delta = 42 +/- 10%, respectively), whereas higher concentrations reduced calcium sensitivity in both fetal and adult arteries. In beta-escin-permeabilized arteries, equivalent reductions in basal and agonist-enhanced myofilament calcium sensitivity were produced by much lower 8-pCPT-cGMP concentrations in fetal (172 and 61 microM, respectively) than in adult (410 and 231 microM, respectively) basilars. The mechanisms mediating cGMP-induced vasorelaxation appear similar in fetal and adult arteries, with the exception that they are much more sensitive to cGMP in fetal than adult arteries. These age-related differences in the sensitivity of cytosolic calcium concentration, basal, and agonist-enhanced myofilament calcium sensitivity to cGMP can easily explain why both potassium- and 5-HT-induced tone are more sensitive to cGMP in fetal than adult cerebral arteries.

Animals↗
PubMed2001

Pregnancy enhances endothelium-dependent relaxation of ovine uterine artery: role of NO and intracellular Ca(2+).

The present study tested the hypothesis that the pregnancy-associated increase in endothelium-dependent relaxation of the uterine artery was mediated primarily by an increase in nitric oxide (NO) release, resulting in a reduction in smooth muscle intracellular Ca(2+) concentration ([Ca(2+)](i)). Uterine arteries obtained from nonpregnant and near-term (140 days gestation) pregnant sheep were used. The Ca(2+) ionophore A23187 induced endothelium-dependent relaxations in both nonpregnant and pregnant uterine arteries, with an increased relaxation in the pregnant tissue. In contrast, endothelium-independent relaxations induced by sodium nitroprusside were the same in nonpregnant and pregnant arteries. In addition, removal of the endothelium significantly increased noradrenaline-induced contractions in pregnant, but not nonpregnant, uterine arteries. In accordance, pregnancy increased both basal and A23187-stimulated NO releases in the uterine artery. Simultaneous measurement of tension and [Ca(2+)](i) in the smooth muscle demonstrated a linear correlation with the slope of unity between A23187-induced relaxation and the reduction of [Ca(2+)](i) in both nonpregnant and pregnant uterine arteries. The A23187-induced reduction of [Ca(2+)](i) was significantly enhanced in pregnant, compared with nonpregnant, uterine arteries. The results indicate that pregnancy increases NO release, which, through decreasing [Ca(2+)](i) in the smooth muscle, accounts for the increased endothelium-dependent relaxation of the uterine artery. Signal transduction pathways distal to NO production are not changed by pregnancy.

Animals↗
PubMed2001

Effects of maturation and acute hypoxia on receptor-IP(3) coupling in ovine common carotid arteries.

Whereas previous studies have established that many mechanisms mediating pharmacomechanical coupling are subject to regulation, evidence of physiological regulation of the coupling efficiency between receptor activation and second-messenger production is scarce. The present studies address the hypothesis that acute hypoxia and maturation can influence the mass of second-messenger production for each activated agonist-bound receptor ("receptor gain"). For this assessment, receptor density and agonist affinity values were used to calculate 5-hydroxytryptamine (5-HT) concentrations that would produce standardized numbers of bound receptors (8.5 fmol/mg protein) in each experimental group and thus minimize effects of age or hypoxia on receptor density or agonist affinity. After 3 min of exposure to these 5-HT concentrations, normoxic magnitudes of contraction were similar (as %potassium maxima) in fetal (50 +/- 14%) and adult (40 +/- 9%) arteries, but hypoxia (PO(2) approximately 9--12 Torr for 30 min) depressed contractile tensions with a significantly different time course and magnitude in fetal (30 +/- 10%) and adult (17 +/- 11%) arteries (P < 0.05). Basal inositol 1,4,5-trisphosphate (IP(3)) values (in pmol/mg protein) were significantly greater in fetal (94 +/- 16) than in adult (44 +/- 6) arteries, and integrated areas above baseline for the IP(3) time courses (in nmol-s/mg protein) were significantly greater in fetal than in adult arteries both in normoxic (14.3 +/- 1.8 vs. 9.1 +/- 1.6) and hypoxic (15.0 +/- 2.1 vs. 8.6 +/- 1.2) conditions (P < 0.05). Hypoxia altered the IP(3) time courses both in the fetus and the adult but had no significant effect on IP(3 )mobilization or receptor gain. These data demonstrate that for the 5-HT(2a) receptor predominant in this preparation, receptor gain can be experimentally determined, is not influenced by acute hypoxia, but is greater in fetal than in adult ovine carotid arteries.

Animals↗