Search PubMed⌕ Search

Biomedical subjects

V M Miller

Publications and source records attributed to V M Miller.

At least 91 records · Page 5Linked to original sources
PubMed1996

Mechanism of relaxations to C-type natriuretic peptide in veins.

C-type natriuretic peptide (CNP) is an endothelium-derived peptide that shares structural homology with atrial natriuretic peptide (ANP). CNP causes greater endothelium-independent relaxations in veins compared with arteries. Relaxations to CNP in porcine coronary arteries are mediated by hyperpolarization of the smooth muscle membrane. Experiments were designed to investigate the mechanism(s) by which CNP causes relaxation in canine femoral veins. Rings of canine femoral veins without endothelium were suspended for measurement of isometric force in organ chambers. Concentration-response curves to CNP were obtained in veins contracted with either endothelin-1 (10(-8) M), KCl (40 mM), phenylephrine (10(-6) M) or prostaglandin F2 alpha (2 x 10(-6) M) in the absence and presence of BQ-123 (10(-6) M), NG-monomenthyl-L-arginine (L-NMMA; 10(-4) M), HS-142-1 (10(-5) M), methylene blue (10(-5) M), or potassium channel blockers, tetraethylammonium chloride (TEA; 10(-3) M), charybdotoxin (10(-7) M), glibenclamide (10(-7) M), or apamin (10(-7) M). Relaxations to CNP were significantly attenuated when the tissue was contracted with KCl and endothelin-1. During contraction to either phenylephrine or prostaglandin F2 alpha, relaxations to CNP were inhibited by HS-142-1, methylene blue, TEA, and charybdotoxin, but not by L-NMMA, glibenclamide, or apamin. In separate experiments, guanosine 3',5'-cyclic monophosphate increased twofold within 10-60 s after the addition of CNP (10(-8) M). These data suggest that CNP mediates relaxation of canine femoral veins through activation of large-conduction, calcium-activated potassium channels and activation of particulate and soluble guanylate cyclase.

Animals↗
PubMed1996

Endothelin receptors are modulated in association with endogenous fluctuations in estrogen.

Experiments were designed to determine whether endogenous physiological fluctuations in sex steroid hormones affect expression or functional responses of endothelin receptors. Coronary arteries from sexually mature male, female, and ovariectomized pigs were prepared either for receptor binding or measurement of isometric force in organ chambers. Competitive binding of 125I-labeled endothelin-1 was significant for a one-site model with unlabeled endothelin-1 and a two-site model with unlabeled endothelin-3 and sarafotoxin S6c in all pigs. The total number of binding sites for all endothelin ligands was not different between male and female pigs. Binding affinities for the high-affinity binding site for both endothelin-3 and sarafotoxin S6c were significantly greater (lower inhibition constant) in membranes prepared from female pigs with high endogenous estrogen. In organ chamber experiments, contractions to endothelin-1 but not endothelin-3 or sarafotoxin S6c were significantly greater in coronary arterial rings from female compared with male pigs and were not affected significantly by removal of the endothelium or by treatment of the rings with either indomethacin (10(-5) mol/l) or the combination of indomethacin and NG-monomethyl-L-arginine (10(-4) mol/l). These results suggest endogenous fluctuations in estrogen are associated with an increase in affinity of a high-affinity endothelin receptor in coronary arterial smooth muscle of female pigs. In addition, independent of endogenous estrogen status, coronary arteries from female pigs generate significantly greater contractions to endothelin-1 compared with male pigs. This phenomenon occurs at the level of smooth muscle and is not dependent on the endothelium or synthesis of nitric oxide or prostaglandins.

Animals↗
PubMed1996

Differential response in cell proliferation to beta estradiol in coronary arterial vascular smooth muscle cells obtained from mature female versus male animals.

Although the cardioprotective effect of estrogen is well recognized, the mechanisms by which this sex steroid provides a reduction in coronary artery disease are not fully understood. Vascular smooth muscle cells (VSMC) are present in early atherosclerosis and become the dominant cell type. VSMC contain estrogen receptors and may have specific responses to estrogen. We studied the effect of beta-estradiol on the proliferation of coronary VSMC obtained from sexually mature male, female, and oophorectomized pigs. Alpha-estradiol, an inactive isomer of estradiol, had no effect on cells obtained from male or female animals. In vascular smooth muscle cells obtained from sexually mature female animals, significant inhibition of proliferation of coronary vascular smooth muscle cells was noted at physiologic concentrations of beta-estradiol. Progesterone inhibited VSMC proliferation at concentrations of 10(-9)M. In contrast, beta-estradiol did not alter proliferation in porcine coronary vascular smooth muscle cells obtained from sexually mature male or from oophorectomized female animals. This study is the first to indicate, in an animal model, specific gender-related differences in cell proliferation in response to sex steroid hormones.

Analysis of Variance↗
PubMed1996

Impaired endothelium-mediated vasodilatation in the peripheral vasculature of patients with acute pulmonary allograft rejection.

BACKGROUND: Experimental studies have provided evidence that, during acute pulmonary allograft rejection, endothelial dysfunction occurs not only in the transplanted lung but also in arteries of organs native to the transplant recipient. We therefore tested the hypothesis that allograft rejection leads to the release of factors into the circulation that could affect the endothelial function in lung transplant recipients. METHODS: Acetylcholine (10, 30, and 60 micrograms/min) and sodium nitroprusside (1, 3, and 6 micrograms/min) were infused into the brachial artery in nine transplant recipients (five single lung, one double lung, three heart-lung) 2 to 37 weeks after transplantation, during both acute rejection and rejection-free episodes. Changes in forearm blood flow were assessed with venous occlusion plethysmography. Plasma levels of interleukin-2, -6, and -8, endothelin-1, L-arginine, and asymmetric dimethylarginine were measured and correlated to rejection episodes. RESULTS: The vasodilatory response to acetylcholine was significantly reduced during acute rejection compared with rejection-free episodes (percentage increase from basal flow: 156% +/- 21%, 395% +/- 65%, and 585% +/- 87% during rejection versus 272% +/- 75%, 633% +/- 113%, and 933% +/- 158% during absence of rejection, p < 0.05). No statistically significant difference was found between vasodilatory responses to nitroprusside during acute rejection and rejection-free episodes. Plasma levels of L-arginine, asymmetric dimethylarginine, interleukin-6, and endothelin-1 were not significantly altered during lung rejection. CONCLUSIONS: These data indicate that a reversible peripheral decrease in endothelium-dependent vasodilatation occurs during acute rejection in lung transplant recipients. This result may be due to interactions among circulating cytokines and leukocytes activated by the rejection process and the endothelium.

Acetylcholine↗
PubMed1996

Effects of gonadal steroids on vascular function.

Estrogen and other sex steroid hormones can affect multiple functions of the vascular wall including production and activity of endothelium-derived factors, expression of adhesion molecules, contraction of the smooth muscle to adrenergic nerve stimulation and smooth muscle proliferation and migration. Effects on response of the smooth muscle may be associated with regulation of surface receptors, second messenger systems and contractile protein isoforms. Sex steroid hormones may act synergistically with other hormones to modulate vascular reactivity across the normal ovarian cycle and during pregnancy. Estrogen may also affect remodeling of the vascular wall through inhibition of smooth muscle cell proliferation, stimulation of cell migration and secretion of matrix proteins. It is becoming apparent that modulation of vascular function by sex steroid hormones involves complex interactions. Not all actions of estrogen can be explained by genomic regulation of protein synthesis. Continued progress in understanding how hormones modulate vascular function will depend, in part, on clearer interpretation of data relative to the particular conditions of each experiment. Important aspects to be considered include the effect of gender and vessel type on the distribution and function of hormone receptors present in the vessel wall; use of hormones within physiological concentration ranges; and more precise determination of the influence of hormone treatment duration whether acute, subacute or chronic.

Animals↗
PubMed1995

Protective effects of an indenoindole antioxidant on coronary endothelial function after long-term storage.

Experiments were designed to evaluate function of the endothelium and smooth muscle of coronary arteries following storage of hearts in cardioplegia containing an inhibitor of lipid peroxidation (H 290/51, cis-7-methyl-9-methoxy-5,5a, 6,10b tetrahydroindeno [2,1-b] indole). Canine hearts were perfused with crystalloid cardioplegia (Plegisol, 15 ml/kg, 4 degrees C) and left circumflex arteries were isolated and studied either immediately (group I, n = 6), or after storage of the hearts at 4 degrees C for 10 (group II, n = 6) or 24 hr with (group III, n = 6) or without (group IV, n = 6) addition of H 290/51. The final concentration of H 290/51 was 1 mumol/L. Arteries were removed, cut into rings, and suspended in organ chambers for measurements of isometric force. In selected rings, the endothelium was removed in order to study the function of the smooth muscle. In order to discriminate effects of ischemia/reperfusion and protective properties on coronary endothelium or smooth muscle, drugs with different mechanisms were used. The function of the endothelium were studied with the alpha 2-adrenergic agonist UK 14,304, bradykinin and A 23187. The smooth muscle function were studied with isoproterenol and nitric oxide. Endothelium-dependent relaxations to the alpha 2-adrenergic agonist UK 14,304 and bradykinin, but not to A 23187, were reduced significantly in arteries from hearts stored for 24 hr in cardioplegic solution alone. Relaxations of arteries from hearts stored for 24 hr with H 290/51 were comparable to those arteries from hearts that were not stored. Endothelium-independent relaxations to isoproterenol and nitric oxide among the different groups were comparable. These results suggest that storage of canine hearts with crystalloid cardioplegia selectively inhibits endothelium-dependent relaxations mediated by receptor activation. Inhibition of lipid peroxidation with H 290/51 preserves these relaxations and may therefore represent a therapeutic alternative to preserve hearts used for transplantation.

Adrenergic alpha-Agonists↗
PubMed1995

Impact of acute pulmonary rejection on cardiac function.

BACKGROUND: Experiments were designed to define cardiac function in dogs with single lung allografts during acute rejection of the allografted lung. METHODS AND RESULTS: Left lungs were either autotransplanted (n = 4) or allotransplanted (n = 8) in adult male mongrel dogs. All allotransplanted animals were maintained on triple-drug immunosuppression (cyclosporine, azathioprine, and steroids) for 5 days after the operation. In 4 allotransplanted animals, treatment was discontinued, allowing the animals to reject (usually after a further 3 days; rejecting group); 4 other allotransplanted animals were maintained on immunosuppression for an additional 3 days (immunosuppressed group). Another group of dogs were not operated on but were maintained on the same immunosuppression as the rejecting group (controls). All experimental animals underwent fast computed tomographic scanning with measurement of left ventricular pressure and calculation of ventricular chamber volumes, cross-sectional areas of coronary arteries, myocardial perfusion, and intramyocardial blood volume. Neither cardiac output, left ventricular mass, left ventricular pressure, nor myocardial oxygen consumption was altered during acute rejection of lung allografts. However, left ventricular contractility (systolic elastance, Emax) and ejection fraction were depressed to approximately one half (P < .05) in acutely rejecting animals compared with other groups. The cross-sectional area of the coronary arteries was less in autotransplanted and allotransplanted treated animals than in animals that were not operated on. Cross-sectional area of the coronary arteries was decreased by an additional 30% in the rejecting group (P < .05). CONCLUSIONS: The results of this study indicate that acute rejection of a single lung allograft decreases cardiac performance and reduces diameter of coronary arteries in the recipient. Alterations of circulating humoral factors and activated leukocytes may contribute to these changes.

Animals↗
PubMed1995

Inferior mesenteric venous sampling to detect colonic ischemia: a comparison with laser Doppler flowmetry and photoplethysmography.

PURPOSE: No single method has been identified that accurately and reliably detects patients with impending bowel infarction during aortic reconstruction. Serial sampling of blood gas from the inferior mesenteric vein (IMV) for detecting colonic ischemia was compared with two previously described techniques: laser Doppler flowmetry (LDF) and photoplethysmography. METHODS: Nine dogs underwent induced partial colonic ischemia followed by complete ischemia. Serial IMV blood gas measurements were obtained at four intervals: baseline, partial ischemia, complete ischemia, and reperfusion. Simultaneous direct colon wall LDF and PPG measurements also were obtained. RESULTS: Changes in pH, Po2, O2 saturation, and Pco2 demonstrated progressive acidosis, hypoxemia, and hypercapnia in association with progressive arterial occlusion and a reversal of these trends toward baseline after restoration of flow. The absence of a pulsatile photoplethysmography tracing and oxygen saturation less than 90% were predictive of altered perfusion but could not differentiate partial from complete ischemia. Although the differences in mean LDF values were statistically different during ischemia and reperfusion, there was considerable variability between each measurement. CONCLUSIONS: Analysis of blood gas from the IMV and pulse oximetry are useful techniques for detecting colonic ischemia, but only the former can distinguish partial from complete ischemia. The variability in colonic measurements with LDF limits its usefulness for detecting levels of colonic perfusion.

Animals↗
PubMed1995

Modulation of contractions to and receptors for endothelins in canine veins.

Experiments were designed to characterize endothelin receptors in canine femoral veins and to determine whether their distribution or sensitivity could be altered by chronic changes in blood flow and oxygen tension in veins proximal to an arteriovenous fistula. Endothelium was removed from unoperated or fistula-operated femoral veins of anesthetized dogs. Veins were cut into rings and suspended in organ chambers for the measurement of isometric force or frozen for isolation of membrane proteins. Endothelin-1, endothelin-3, and sarafotoxin S6c caused concentration-dependent increases in tension in all rings. In rings of unoperated veins, maximal tensions were significantly less to endothelin-3 and sarafotoxin S6c than to endothelin-1. In rings of fistula-operated veins, maximal tensions to endothelin-1 and endothelin-3 were the same. Contractions to endothelin-1 or endothelin-3 in unoperated veins were not inhibited by an antagonist of endothelin-A receptors, BQ-123. Binding of 125I-labeled endothelin-1 (125I-endothelin-1) to membranes from veins without endothelium increased as a function of membrane protein. Affinity of receptors, as determined by competitive inhibition of 125I-endothelin-1 was as follows: endothelin-1 > endothelin-3 > sarafotoxin S6c. Competitive inhibition of 125I-endothelin-1 by endothelin-3 and sarafotoxin S6c was significant for a two-site binding model in all veins. The total number of binding sites was reduced significantly in fistula-operated veins; the relative proportions of high- and low-affinity binding sites did not change. Affinity of high- and low-affinity receptors increased in fistula-operated veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1994

Vascular actions of C-type natriuretic peptide in isolated porcine coronary arteries and coronary vascular smooth muscle cells.

C-type natriuretic (CNP) caused concentration-dependent relaxations in porcine coronary arteries with a maximal relaxation (10(-6)M) of 46%. Relaxations to CNP in isolated coronary arteries were significantly attenuated with potassium channel antagonists charybdotoxin (10(-7)M) and glibenclamide (10(-7)M). Membrane potential and K+ currents were measured in enzymatically dissociated smooth muscle cells from porcine coronary arteries with patch-clamp techniques in a whole-cell mode (n = 5). CNP caused K+ channel activation and membrane hyperpolarization in a dose-dependent manner. This hyperpolarization was markedly suppressed by the potassium channel inhibitor tetraethylammonium (TEA, 5 mM). These results demonstrate that CNP relaxes porcine coronary arterial smooth muscle by hyperpolarization of vascular smooth muscle through potassium channel stimulation.

Animals↗
PubMed1994

Chronic changes in blood flow alter endothelium-dependent responses in autogenous vein grafts in dogs.

PURPOSE: Experiments were designed to determine the effects of blood flow on endothelium-dependent relaxations in canine vein grafts. METHODS: Blood flow through reversed femoral vein grafts was either increased by a distal arteriovenous fistula (increased flow), unmanipulated (normal flow), or reduced by a proximal adjustable clamp (reduced flow). Six weeks after implantation, blood flow through the graft was measured. Rings cut from grafts were suspended for the measurement of isometric force in organ chambers to determine endothelial function. RESULTS: Blood flow was significantly greater in grafts with a distal fistula compared to grafts with normal or decreased flow. Endothelium-dependent relaxations to acetylcholine were absent in all grafts. Endothelium-dependent relaxations to adenosine diphosphate, thrombin, and the calcium ionophore A23187 were less in grafts with reduced flow compared with grafts with increased flow. Relaxations to these agents in grafts with increased flow were reduced by an analog of L-arginine. Neointimal hyperplasia was increased in grafts with reduced flow. CONCLUSIONS: These data demonstrate that chronic diminution of blood flow decreases receptor-mediated release of endothelium-derived relaxing factors and increases neointimal hyperplasia in canine vein grafts. The production of endothelium-derived relaxing factors, one of which is nitric oxide, may influence the development of myointimal hyperplasia in vein grafts.

Acetylcholine↗
PubMed1994

Mononuclear cells from dogs with acute lung allograft rejection cause contraction of pulmonary arteries.

PURPOSE: Experiments were designed to determine whether or not leukocytes activated by acute pulmonary rejection cause contractions of isolated pulmonary arteries. METHODS AND RESULTS: Separate suspensions of (a) polymorphonuclear cells (> 95%) and (b) mononuclear cells (85% lymphocytes/10% monocytes/5% polymorphonuclear cells), respectively, were obtained from the arterial blood of four groups of adult male mongrel dogs: unoperated dogs (controls), dogs with single-lung autotransplants, dogs with rejecting single-lung allotransplants, and unoperated dogs treated with the same immunosuppressants as allotransplanted dogs. These suspensions were added to rings of control intralobar pulmonary arteries suspended in organ chambers for measurement of isometric force. The endothelium was removed mechanically from selected rings. No significant change in basal tension of pulmonary arterial rings occurred by adding suspensions of polymorphonuclear cells from any of the four groups of dogs. Significant cell-number-dependent increases in tension occurred with suspensions of mononuclear cells from unoperated dogs, autotransplanted dogs, and unoperated, medicated dogs. These increases in tension were less in rings with compared to those without endothelium. Addition of a synthetic analogue of L-arginine abolished this difference. Suspensions of mononuclear cells from rejecting allotransplanted dogs caused significantly greater contractions in rings with endothelium than those observed with suspended cells from either unoperated, autotransplanted dogs or unoperated, medicated dogs. Addition of superoxide dismutase plus catalase or an antagonist of endothelin-A receptors (BQ-123) reduced contractions in rings with endothelium but not in those without endothelium to suspensions of mononuclear cells from rejecting allotransplanted dogs. CONCLUSIONS: The results of this study suggest that mononuclear cells cause contraction of pulmonary arteries, which can be partially inhibited by endothelium-derived nitric oxide. However, if the mononuclear cells are activated by acute pulmonary rejection, contractions are no longer inhibited by the endothelium. Under conditions of rejection, contractions are mediated in part by oxygen radicals and endothelin(s).

Animals↗
PubMed1994

Atrial natriuretic peptide and C-type natriuretic peptide in spontaneously hypertensive rats and their vasorelaxing actions in vitro.

The present study determined circulating concentrations of atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) in Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) and also investigated the vasorelaxing action of ANP and CNP on isolated contracted aorta. We also defined the vasorelaxing action of a novel and newly synthesized 27-amino acid chimera of ANP and CNP termed vasonatrin peptide (VNP), which we compared with ANP and CNP in WKY rats and SHR. Plasma and urinary cyclic GMP and sodium excretion were also investigated. Plasma ANP was increased in SHR in contrast to no change in circulating CNP. Plasma and urinary cyclic GMP and sodium excretion were no different between WKY rats and SHR. In WKY rats maximal relaxations to VNP in aortic rings without endothelium were greater than those to ANP and CNP. In SHR aortic rings the potency of VNP relaxation was preserved, the actions of ANP were enhanced, and the actions of CNP were markedly impaired. In association with these vasorelaxing actions, these data suggest that (1) circulating CNP is not different in SHR and WKY rats, but the aortic relaxing action of CNP is markedly impaired in SHR; (2) endogenous plasma ANP is significantly increased in SHR without associated increases in plasma or urinary cyclic GMP; (3) there is an increase in aortic relaxation to exogenous ANP in SHR; and (4) VNP has a potent endothelium-independent aortic relaxing action in both WKY rats and SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Increased production of nitric oxide in coronary arteries during congestive heart failure.

Experiments were designed to determine whether a heterogeneity of endothelium-dependent relaxations in arteries from different vascular beds exists in experimental congestive heart failure (CHF) and to determine the mediators of those responses. CHF was produced in dogs by rapid ventricular pacing for 15 d. Rings of coronary, femoral, and renal arteries with and without endothelium from control and CHF dogs were suspended in organ chambers for measurement of isometric force. In arteries contracted with prostaglandin F2 alpha, endothelium-dependent relaxations to BHT 920 (an alpha 2-adrenergic agonist) were increased in coronary arteries from dogs with CHF (maximal relaxation: control -15 +/- 9% vs CHF -92 +/- 5%; n = 5-6; P < 0.05), with a modest enhancement in renal arteries. Relaxations to adenosine diphosphate and the calcium ionophore were unchanged. Relaxations to BHT 920 in CHF were reduced by NG monomethyl-L-arginine (L-NMMA) and pertussis toxin but not by indomethacin. These data suggest that endothelium-dependent relaxations are affected heterogeneously in CHF. The enhanced response to alpha 2-adrenergic agonists in the coronary artery is mediated by nitric oxide through a mechanism sensitive to inhibition by pertussis toxin. This selective increase in endothelium-dependent relaxations in the coronary artery may contribute to preserving coronary blood flow during CHF.

Acetylcholine↗
PubMed1993

Cofactors of constitutive nitric oxide synthase and endothelium-dependent relaxations in canine femoral veins.

Enzymatic production of nitric oxide (NO) in arterial endothelial cells requires the cofactors calmodulin and nicotinamide adenine dinucleotide phosphate (NADPH). Experiments were designed in investigate whether these cofactors are required for endothelium-dependent relaxations in canine femoral veins. Veins were removed from anesthetized dogs and cut into rings. Endothelium was deliberately removed from some rings. All rings were incubated with indomethacin (1 x 10(-5) M). In separate sets of experiments, rings were incubated with calmidazolium (1 x 10(-5) M), fendiline (1 x 10(-6) M), both inhibitors of calmodulin or diphenylene-iodonium (1 x 10(-5) M; DPI) an inhibitor of NADPH. Concentration-response curves were obtained for acetylcholine (ACh), ADP, thrombin, A23187, and NO in rings contracted with a submaximal concentration of prostaglandin F2 alpha (PGF2 alpha) in the presence of the inhibitors and compared with a solvent control (dimethyl sulfoxide, DMSO). Relaxations to ACh, ADP, and thrombin were reduced by the inhibitors of both cofactors. Relaxations to A23187 were reduced by inhibitors of calmodulin but not NADPH; inhibitors of both NADPH and calmodulin caused no significant reduction in relaxations to NO. These data suggest that endothelium-dependent relaxations in canine femoral veins are mediated by factor(s) that are partly dependent on calmodulin or NADPH as cofactors for their production or release.

Amino Acid Oxidoreductases↗
PubMed1993

Action of C-type natriuretic peptide in isolated canine arteries and veins.

C-type natriuretic peptide (CNP) is a hormone that shares structural homology to atrial natriuretic peptide (ANP); however, distinct receptors have been found for each in cultured aortic endothelial and smooth muscle cells. CNP in vivo reduces arterial pressure, atrial pressures, and cardiac output. These actions are consistent with a decrease in cardiac preload. Therefore, the current studies were designed to test the hypothesis that CNP is a vasodilator distinct from ANP. Rings of canine renal and saphenous arteries and renal, saphenous, and femoral veins with and without endothelium were suspended to measure isometric force in an organ chamber. CNP caused significant concentration-dependent relaxations in veins with and without endothelium contracted with phenylephrine (10(-6) log M). In marked contrast, ANP caused no significant relaxation in veins either with or without endothelium. In arterial rings, responses to the peptides were heterogeneous. ANP caused relaxation in renal but not saphenous arteries. CNP induced modest and comparable relaxation in rings of saphenous but not renal arteries with and without endothelium. These results demonstrate that: 1) CNP and not ANP is a relaxing factor of isolated peripheral canine veins, and 2) the responses of arteries to ANP and CNP are heterogeneous. These findings support a distinct biological role for CNP in the regulation of cardiovascular tone.

Animals↗