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V M Miller

Publications and source records attributed to V M Miller.

At least 37 records · Page 2Linked to original sources
PubMed2000

Adventitial versus intimal liposome-mediated ex vivo transfection of canine saphenous vein grafts with endothelial nitric oxide synthase gene.

PURPOSE: Experiments were designed (1) to evaluate liposome-mediated endothelial constitutive nitric oxide synthase (ecNOS) transfection in vein grafts and (2) to compare intimal and adventitial routes of transfection. METHODS: Male mongrel dogs (N = 36) underwent bilateral femoral artery bypass grafting with the lateral saphenous vein. In each animal one vein was transfected with plasmid (pVR1012) containing the ecNOS gene, and another vein was transfected with plasmid alone (control). Gene transfer was performed from either the intimal surface (Group I, n = 18) or the adventitial surface (Group II, n = 18). In each group there were three transfection subgroups (n = 6 each): (a ) 10 microg/mL naked plasmid DNA, (b ) 10 microg/mL plasmid DNA + liposome (LipofectAMINE PLUS), and (c ) 100 microg/mL plasmid DNA + LipofectAMINE PLUS. Grafts were harvested on the third postoperative day, and the transfection was assessed with molecular techniques and enzyme assay for activity of NOS by conversion of tritiated l-arginine to tritiated l-citrulline. Proliferating cells were quantified with a digital analysis of histologic sections after nuclear antigen Ki-67 (MIB1) immunohistochemistry. RESULTS: Transgene was identified with polymerase chain reaction in all ecNOS-transfected grafts, regardless of transfection modality. However, significant transcription of the ecNOS transgene was observed only in Group IIc (mean ecNOS messenger RNA, 8.7+/-1.7 vs. 3.1+/-0.7 x 10(-2) attomole/microL, in transfected compared with control grafts, respectively, P =.01). NOS activity increased approximately twofold in this group (11.58+/-2.1 and 6.3+/-1.0 pmol tritiated l-citrulline per milligram protein per hour in transfected and control grafts, respectively, P = .05). Numbers of proliferating cells did not differ among ecNOS-transfected and control grafts in any transfection group. CONCLUSION: These results suggest that ecNOS transfection of vein grafts is feasible through intimal and adventitial routes with naked DNA or a liposomal vector. However, efficient transcription of the transgene is evident at postoperative day 3 only after adventitial transfection of 100 microg/mL of the gene.

Animals↗
PubMed2000

Mechanism of relaxations to dendroaspis natriuretic peptide in canine coronary arteries.

Experiments were designed to determine mechanisms by which Dendroaspis natriuretic peptide (DNP) causes relaxations in coronary arteries. Rings of canine left circumflex artery with and without endothelium were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution (37 degrees C, bubbled with 95% O2/5% CO2). Concentration-response curves to DNP (10(-10) to 3 x 10(-7) M) were obtained in arteries contracted with prostaglandin (PGF(2alpha), 2 x 10(-6) M), either in the absence or the presence of C-ANP (10(-6) M) to inhibit natriuretic clearance receptors; indomethacin to inhibit cyclooxygenase (INDO, 10(-5) M), N(G)-monomethyl-L-arginine to inhibit production of nitric oxide (L-NMMA; 10(-4) M), HS-142-1 to inhibit particulate guanylate cyclase (10(-5) M); 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one to inhibit soluble guanylate cyclase (ODQ; 10(-5) M), or tetraethylammonium to inhibit potassium channels (TEA; 10(-3) or 10(-2) M). Relaxations to DNP were greater in rings with than in those without endothelium. C-ANP significantly attenuated relaxations to DNP only in rings with endothelium. HS-146-1 but not INDO, L-NMMA, ODQ, and TEA significantly reduced relaxations to DNP in rings with and without endothelium contracted with PGF(2alpha). These results suggest that the endothelium augments inhibitory effects of DNP and that natriuretic clearance receptors mediate this component of the response to DNP in canine coronary arteries. In addition, relaxations to DNP in canine arterial smooth muscle involve activation of particulate guanylate cyclase but not hyperpolarization.

Animals↗
PubMed2000

Increased coronary effects of stimulation of endothelin-B receptor in experimental hypercholesterolemia.

BACKGROUND: Vasoconstriction in response to endothelin-1 has been shown to be primarily related to its effects on the endothelin-A receptor. Experimental hypercholesterolemia is associated with an increase in coronary vasoconstrictor response to endothelin-1 in vivo, although the relative contributions of subtypes of endothelin receptor in this model remain unknown. OBJECTIVE: To test the hypothesis that there is an increase in coronary vasoconstriction in response to stimulation of endothelin-B receptor in hypercholesterolemia, which might be related to attenuation of activity of endothelin-derived relaxing factor. METHODS: We infused 5 ng/kg/min sarafotoxin, a specific endothelin-B receptor agonist, or 50 micrograms/kg/min NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of nitric oxide synthase, into the left anterior descending coronary arteries of pigs before and after feeding them a cholesterol-rich diet for 10 weeks. RESULTS: There was a significant increase in serum level of cholesterol. After 10 weeks, infusion of sarafotoxin resulted in an accentuated decrease in coronary blood flow (CBF) compared with baseline (decreases by 60 +/- 7 versus 34 +/- 6%, P < 0.05). There was no significant difference between the effects on diameter of coronary arteries for the two time periods. The effect of L-NMMA on CBF was attenuated after 10 weeks (by 5 +/- 10.1 versus 45.6 +/- 4.7%, P < 0.05). Endothelin-receptor status of epicardial coronary arteries remained unchanged. Sarafotoxin and L-NMMA were co-infused at the above-mentioned doses into normolipidemic animals; the decrease in CBF in response to this co-infusion was comparable to the decrease observed with sarafotoxin alone in hypercholesterolemic animals (decreases of 67 +/- 5 versus 60 +/- 7, NS). CONCLUSIONS: The present results demonstrate that selective stimulation of the endothelin-B receptor increases coronary vasoconstriction in experimental hypercholesterolemia, primarily at the level of the microvasculature. These findings may be related to the attenuation of activity of endothelin-derived relaxing factor in this model, and support the hypothesis that endothelin-B receptor plays a role in the regulation of coronary vascular tone in pathophysiologic states.

Animals↗
PubMed2000

Time and dose effect of transdermal nicotine on endothelial function.

Nicotine patches are available as an over-the-counter medication for aid in smoking cessation. This study was designed to determine how nicotine patch therapy over time and dose ranges used in smoking cessation programs in humans affects endothelium-dependent relaxations. Dogs were treated with nicotine patches (11, 22, or 44 mg/day) for 2 and 5 wk. Circulating nicotine and oxidized products of nitric oxide (NOx) were measured. Coronary arteries were prepared for measurement of isometric force and aortic endothelial cells were prepared for measurement of mRNA or NO synthase (NOS) activity. Circulating nicotine increased with increasing concentrations of nicotine patches. After 5 wk of treatment with 22 mg/day patches, circulating NOx was reduced but NOS activity was increased. NOS mRNA was similar among groups. Only after 5 wk of treatment with 22 mg/day patches were endothelium-dependent relaxations reduced to alpha(2)-adrenergic agonists, ADP, and the calcium ionophore A-23187. These results suggest a time and biphasic dose effect of nicotine treatment on endothelium-dependent responses that may be related to bioavailability of NO. This complex relationship of duration and dose of nicotine treatment may explain, in part, discrepancies in effects of nicotine on endothelium-dependent responses.

Adenosine Diphosphate↗
PubMed2000

Effects of transdermal nicotine treatment on structure and function of coronary artery bypass grafts.

Smoking is a major risk factor for failure of coronary artery bypass grafts (CABG). Experiments were designed to determine effects of transdermal nicotine, independent of smoking, on structure and function of CABG. Saphenous veins were placed as CABG in untreated dogs (control) or in dogs treated with transdermal nicotine (one 11-mg or two 22-mg patches/day) for 5 wk. Serum nicotine and plasma nitric oxide were measured. Grafts were removed and prepared for organ chamber studies and histology. Serum nicotine averaged 12.1 and 118.7 ng/ml in the 11 mg/day and 44 mg/day groups, respectively. Plasma nitric oxide was higher in dogs treated with 11 mg/day doses compared with controls. In organ chamber studies, endothelium-dependent relaxations to thrombin and A-23187 and endothelium-independent relaxations to nitric oxide were greatest in grafts from dogs treated with 11 mg/day doses. Intimal thickness of the grafts were similar among groups. However, staining for bone sialoprotein was increased in the media of grafts from the 11 mg/day treatment group. These data suggest that transdermal nicotine in doses comparable and double to those used for conventional smoking cessation treatment in humans does not adversely affect early patency of canine CABG up to 4 wk postoperatively. Transdermal nicotine, however, may increase production of and response to nitric oxide in bypass grafts.

Actins↗
PubMed2000

Neuroprotective effects of female gonadal steroids in reproductively senescent female rats.

BACKGROUND AND PURPOSE: Young adult female rats sustain smaller infarcts after experimental stroke than age-matched males. This sex difference in ischemic brain injury in young animals disappears after surgical ovariectomy and can be restored by estrogen replacement. We sought to determine whether ischemic brain injury continues to be smaller in middle-aged, reproductively senescent female rats compared with age-matched males and to test the effect of ovarian steroids on brain injury after experimental stroke in females. METHODS: Four groups of 16-month old Wistar rats (males [n=9], untreated females [n=9], and females pretreated with 17beta-estradiol [25-microgram pellets administered subcutaneously for 7 days; n=9] or progesterone [10-mg pellets administered subcutaneously for 7 days; n=9] were subjected to 2 hours of middle cerebral artery occlusion with the intraluminal filament technique, followed by 22 hours of reperfusion. Physiological variables and laser-Doppler cerebral cortical perfusion were monitored throughout ischemia and early reperfusion. In a separate cohort of males (n=3), untreated females (n=3), females pretreated with 17beta-estradiol (n=3), and females pretreated with progesterone (n=3), end-ischemic regional cerebral blood flow was measured by [(14)C]iodoantipyrine autoradiography. RESULTS: As predicted, infarct size was not different between middle-aged male and female rats. Cortical infarcts were 21+/-5% and 31+/-6% of ipsilateral cerebral cortex, and striatal infarcts were 44+/-7% and 43+/-5% of ipsilateral striatum in males and females, respectively. Both estrogen and progesterone reduced cortical infarct in reproductively senescent females (5+/-2% and 16+/-4% in estrogen- and progesterone-treated groups, respectively, compared with 31+/-6% in untreated group). Striatal infarct was smaller in the estrogen- but not in the progesterone-treated group. Relative change in laser-Doppler cerebral cortical perfusion from preischemic baseline and absolute end-ischemic regional cerebral blood flow were not affected by hormonal treatments. CONCLUSIONS: We conclude that the protection against ischemic brain injury found in young adult female rats disappears after reproductive senescence in middle-aged females and that ovarian hormones alleviate stroke injury in reproductively senescent female rats by a blood flow-independent mechanism. These findings support a role for hormone replacement therapy in stroke injury prevention in postmenopausal women.

Administration, Cutaneous↗
PubMed2000

Short-term treatment with transdermal nicotine affects the function of canine saphenous veins.

Experiments were designed to determine the effects of nicotine treatment on the functions of saphenous veins used for coronary artery bypass grafts in dogs. Dogs received either no treatment or transdermal nicotine for 5 weeks at doses of 11 mg, 22 mg or 44 mg/day. Saphenous veins were removed and suspended for the measurement of isometric force in organ chambers. Endothelium was removed mechanically from some rings. N(G)-mono-methyl-L-arginine (L-NMMA; 10(-4) M) was used to inhibit the production of nitric oxide. Contractions to alpha2-adrenergic stimulation were decreased in veins from dogs treated with a 22-mg/day dose of transdermal nicotine. In addition, endothelium-dependent relaxations to adenosine-diphosphate (10(-8)-10(-4) M) and the calcium ionophore A23,187 (10(-8)-10(-6) M) were decreased in veins from dogs with a 22-mg/day dose and increased in veins from dogs treated with a 44-mg/day dose. These relaxations were inhibited by L-NMMA. Plasma concentrations of oxidized products of nitric oxide were decreased only in dogs treated with 22 mg/day of nicotine. The relaxation of rings without endothelium (direct response on the smooth muscle) to nitric oxide were not altered by nicotine treatment. These results suggest that the short-term treatment of dogs with intermediate (22 mg/day) but not low (11 mg/day) or high (44 mg/day) doses of transdermal nicotine decreases the endothelial function of veins used for coronary artery bypass grafts. Therefore, changes in plasma products of nitric oxide and endothelium-dependent relaxations mediated by nitric oxide are related to the dose of nicotine treatment.

Administration, Cutaneous↗
PubMed2000

Pharmacological assessment of adrenergic receptors in human varicose veins.

BACKGROUND: Experiments were to characterize pharmacologically adrenergic receptors in human varicose veins to the natural transmitter norepinephrine and to an extract of Ruscus. METHODS: Greater saphenous veins and varicose tributaries from patients undergoing elective surgery for primary varicose disease and portions of greater saphenous veins from patients undergoing peripheral arterial reconstruction (control) were suspended for the measurement of isometric force in organ chambers. Concentration response curves were obtained to norepinephrine or the extract of Ruscus aculeatus in the absence and presence of selective antagonists of alpha, and alpha2 adrenergic receptors. RESULTS: Norepinephrine and Ruscus extract caused concentration-dependent contractions in all veins. Contractions to norepinephrine were greater in control veins than in varicose tributaries. Contractions to the extract were greater in varicose tributaries than in greater saphenous veins from varicose patients. Contractions to norepinephrine were reduced similarly by alpha and alpha2-adrenergic agonists in control and varicose veins but to a greater extent by alpha2-blockade in greater saphenous veins from varicose patients. Contractions to Ruscus extract were not reduced by alpha-adrenergic blockade in control veins but were reduced by alpha2-adrenergic blockade in varicose veins. CONCLUSIONS: These results suggest a differential distribution of alpha adrenergic receptors on greater saphenous veins from non-varicose patients compared to those with primary varicose disease. Venotropic agents from plant extract probably exert effects by way of multiple receptor and non-receptor mediated events.

Adrenergic alpha-Agonists↗
PubMed2000

Modulation of nitric-oxide synthase by nicotine.

Effects of nicotine on arterial endothelium-dependent relaxations mediated by nitric oxide are controversial. Experiments were designed to test the hypothesis that nicotine can directly alter activity of endothelial nitric-oxide synthase (eNOS). NOS from aortic endothelial cells of untreated dogs and recombinant eNOS, neuronal NOS, and inducible NOS were used for these experiments. NOS activity was determined as conversion of L-[(3)H]arginine to L-[(3)H]citrulline in the absence or presence of nicotine (10(-7)-10(-3) M) in vitro. In separate assays, concentrations of cofactors NADPH, FAD, and tetrahydrobioprotein were reduced by half to assess for possible interaction with nicotine. With enzyme from aortic endothelial cells, total and calcium-dependent accumulation of citrulline increased by 30% in the presence of 10(-5) M nicotine. Nicotine dose dependently also increased citrulline accumulation by recombinant eNOS and neuronal NOS but not inducible NOS. Effects of nicotine on accumulation of citrulline by isolated eNOS and recombinant eNOS were further modulated by changes in the concentration of NADPH in the incubation solution. Our data demonstrate a significant effect of nicotine on eNOS-mediated citrulline accumulation. These results suggest that effects of nicotine on production of nitric oxide may depend on NADPH or oxygen radical interactions with NOS and thus may explain, in part, inconsistent findings of changes in production of endothelium-derived nitric oxide with nicotine administration.

Animals↗
PubMed2000

Prostaglandins but not nitric oxide are endothelium-derived relaxing factors in the trout aorta.

AIM: To identify the type of prostanoids produced by endothelial cells of trout aorta and to determine whether or not the smooth muscle responds to nitric oxide. METHODS: Ventral aortas, with and without endothelium from rainbow trout (S gairdneri), were incubated in a buffered salt solution. RESULTS: Addition of the calcium ionophore A23187 caused a significant increase in prostaglandin E's and a consistent increase in the stable metabolite of prostacyclin (6-keto-prostaglandin F1 alpha) in the incubation media only when the endothelium was present. This production was inhibited by methylene blue (10 mumol/L). In rings of trout aorta without endothelium suspended for the measurement of isometric force in organ chambers, prostacyclin and prostaglandin E1 but not prostaglandin E2 caused concentration-dependent decreases in tension when the rings were contracted with acetylcholine. The smooth muscle did not relax to nitric oxide but did so to sodium nitroprusside. Relaxations to the latter nitrovasodilator were not inhibited by methylene blue. Descending aorta without endothelium from frogs relaxed in a concentration-dependent manner to nitric oxide. CONCLUSION: Predominant endothelium-derived relaxing factors in trout aorta are prostaglandins, the synthesis of which can be inhibited by methylene blue. A phylogenetic appearance of nitric-oxide sensitive mechanism for vasodilatation, perhaps is associated with the transition from water to air respiration.

6-Ketoprostaglandin F1 alpha↗
PubMed1999

Endothelin-1 modulates intrahepatic resistance in a rat model of noncirrhotic portal hypertension.

Factors that increase resistance to blood flow through the hepatic sinusoids when portal hypertension occurs in the absence of significant hepatic fibrosis are not completely understood. Experiments were designed to test the hypothesis that endothelin-1 (ET-1) is one of the humoral factors that increases sinusoidal vascular resistance in a bile duct- ligated noncirrhotic portal hypertensive (BDL) rat. The effect of ET-1 and nitric oxide (NO) on contractility of rings of portal vein taken from BDL rats was tested. The effect of ET-1 and NO on intrahepatic resistance in an isolated perfused liver was studied, and localization of ET-1 in the liver was identified by immunohistochemistry. Portal vein rings in BDL rats showed increased maximal tension in response to ET-1, as well as a shift of the dose-response curve to the left as compared with sham-operated animals. Removal of the endothelium further increased contractility. In isolated perfused liver studies, ET-1 increased portal resistance in both sham operated and BDL rats. The endothelin Type A receptor antagonist BQ 123 lowered the high portal resistance in BDL rats to levels comparable with sham operated animals. Infusion of L-arginine lowered resistance to a much smaller extent. In livers from BDL rats, ET-1 was localized in periportal and pericentral hepatocytes and hepatic sinusoidal cells. We conclude that in a BDL model of portal hypertension where distortion of hepatic architecture by fibrosis is minimal, increased resistance to portal blood flow may be mediated by ET-1.

Animals↗
PubMed1999

Distribution and function of recombinant endothelial nitric oxide synthase in transplanted hearts.

Introducing recombinant genes into donor hearts may offer a therapeutic intervention that could potentially attenuate the complications of heart transplantation, including rejection, infection and accelerated atherosclerosis. In the cardiovascular system, reduced bioactivity of endothelial nitric oxide is a feature of atherosclerosis and vascular injury. Nitric oxide is an arterial vasodilator that also inhibits proliferation of vascular smooth muscle cells and platelet aggregation. Experiments were designed to determine the distribution of adenoviral-mediated transfer of recombinant endothelial nitric oxide synthase gene (eNOS) and the effect of recombinant gene expression on the function of transplanted hearts. Adenoviral vectors for (a) bovine eNOS (AdeNOS) or (b) beta-galactosidase (AdLacZ; control) were infused into two groups (n = 12, per group) of explanted rat hearts. The transduced hearts were then implanted heterotopically into the abdomen of syngeneic recipient rats. After four days, the hearts were excised and examined for distribution and function of the recombinant genes. Polymerase chain reaction (PCR) verified the presence of the recombinant eNOS gene in eNOS-transduced but not in beta-galactosidase-transduced hearts; reverse transcriptase-PCR identified mRNA for eNOS in AdeNOS-transduced hearts. NOS activity (conversion of tritiated L-arginine to citrulline) was greater in homogenates of AdeNOS-compared to AdLacZ-transduced hearts. Positive immunoreactivity for eNOS was present in cardiomyocytes predominantly in eNOS-transduced hearts. Myocardial contractility and coronary blood flow, as determined using a Langendorff preparation, were not different between hearts transduced with AdeNOS or AdLacZ. These results suggest that, up to four days post transplantation, adenoviral-mediated transfer of eNOS into transplanted hearts is possible. However, expression of the recombinant protein did not result in measurable changes in myocardial contractility or coronary perfusion.

Adenoviridae↗
PubMed1999

Cyclic nucleotides and production of prostanoids in human varicose veins.

OBJECTIVE: Experiments were designed to determine the production of prostacyclin and thromboxane and the activation of cyclic nucleotides in human varicose and nonvaricose veins and to determine whether these second messenger pathways were differentially activated by the venotropic extract of Ruscus aculeatus. METHODS: The experiments were designed to characterize the activity of cyclic nucleotides and the production of prostaglandins in human varicose and nonvaricose veins. Segments of the greater saphenous veins and the adjacent tributaries were obtained from patients who underwent vein stripping and excision of primary varicose veins. The saphenous veins from the patients who underwent peripheral arterial bypass grafting were used as controls. The segments of veins were incubated in Krebs-Ringer bicarbonate solution in the presence of venotropic extract of Ruscus aculeatus (10(-3) g/mL) or in water-miscible organic solvent (dimethyl sulfoxide, 10(-3) g/mL), for 1, 5, and 10 minutes at 37 degrees C. The nonspecific phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine, 10(-4) g/mL) was used to block cyclic nucleotide degradation in some samples. Tissue and media samples were collected. Tissue concentrations of both cyclic adenosine monophosphate and cyclic guanosine monophosphate (cAMP and cGMP, respectively) and media concentrations of 6-ketoprostaglandin-F(1)(alpha) (the stable metabolite of prostacyclin) and thromboxane B(2) (the stable metabolite of thromboxane A(2)) were measured by means of radioimmunoassay. Cyclooxygenase 2 was measured with Western blot analysis. RESULTS: The varicose veins showed greater levels of cAMP but not of cGMP at all time points as compared with the control veins. Prostanoid production was not significantly altered in the varicose veins. Stimulation with Ruscus aculeatus increased the cAMP concentration in the varicose veins but did not affect the cGMP levels. The ratio between 6-ketoprostaglandin-F(1)(alpha) and thromboxane B(2) was two-fold greater in the varicose veins as compared with the control veins. In the presence of the extract, the ratio of 6-ketoprostaglandin-F(1)(alpha) and thromboxane B(2) was identical in both types of veins. Cyclooxygenase 2 was not present in either the control or the varicose veins. CONCLUSION: These results suggest that cAMP levels are elevated in varicose veins and that they can be altered with drug treatment in varicose veins. This chemical pathway may be considered as a modulatory target to affect contraction with venotropic drugs.

6-Ketoprostaglandin F1 alpha↗
PubMed1999

Gender differences and endothelium- and platelet-derived factors in the coronary circulation.

1. Experiments were designed to determine whether or not interactions of platelets with coronary arteries are affected by gender or oestrogen-status. 2. Platelets and right coronary arteries were isolated from sexually mature male, female and ovariectomized pigs. Arteries were suspended in organ chambers for the measurement of isometric force. Responses of rings, with and without endothelium, were evaluated to aggregating platelets and the platelet products 5-hydroxytryptamine (5-HT) and adenosine diphosphate (ADP). 3. Release of 5-HT, thromboxane A2 (TXA2) and prostacyclin were measured from platelets. 4. Platelets caused relaxations of rings with endothelium from all pigs. However, in rings without endothelium, consistent contractions were observed only in rings from male pigs. 5. The release of 5-HT and prostacyclin was greatest from platelets of ovariectomized pigs compared with male and female pigs. Release of TXA2 was greatest from platelets of male pigs. 6. Endothelium-dependent relaxations to ADP and contractions to 5-HT were similar among the three groups. 7. These results suggest that there may be gender-specific differences in vasomotor responses to autogenous platelets but not to the platelet-derived products 5-HT and ADP. Furthermore, there are gender differences in platelets in the release of cyclo-oxygenase metabolites of arachidonic acid and 5-HT. These products could contribute to gender differences in response to injury in the coronary circulation.

Adenosine Diphosphate↗
PubMed1999

Activation of soluble guanylate cyclase and potassium channels contribute to relaxations to nitric oxide in smooth muscle derived from canine femoral veins.

Experiments were designed to examine mechanisms of relaxations to nitric oxide (NO) in venous smooth muscle. Rings of canine femoral veins without endothelium were suspended for measurement of isometric force in organ chambers. Concentration-response curves to NO and 8-Br-cyclic guanosine monophosphate (cGMP) were obtained in veins contracted with KCl (60 mM) or prostaglandin F2alpha (PGF2alpha; 2x10(-6) M) in the absence and presence of inhibitors of soluble or particulate guanylate cyclase or K+ channel antagonists. In rings contracted with PGF2alpha, relaxations to NO were reduced significantly by inhibition of soluble but not particulate guanylate cyclase. Relaxations to NO were reduced in rings contracted with KCI. Tetraethylammonium (10(-2) M) and glibenclamide (10(-7) M) + charybdotoxin (10(-7) M) significantly reduced relaxations to NO in rings contracted with PGF2alpha. Relaxations to 8-Br-cGMP were decreased significantly only by charybdotoxin. These results suggest that relaxations to NO in canine femoral veins involve at least two intracellular processes: activation of soluble guanylate cyclase and activation of adenosine triphosphate (ATP)-sensitive and large-conductance, Ca+2-activated K+ channels. The large-conductance, Ca+2-activated K+ channels seem to be activated by cGMP-dependent mechanisms. Therefore relaxations to NO in venous smooth muscle involve intracellular processes similar to those in arterial smooth muscle.

Animals↗
PubMed1999

Estrogen increases Ca2+ efflux from female porcine coronary arterial smooth muscle.

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca2+ concentration ([Ca2+]i). In the present study, we examined the hypothesis that this reduction in [Ca2+]i is mediated in part by enhanced Ca2+ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca2+]i response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17beta-Estradiol (E2beta), but not 17alpha-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC50 = 10 nM) decrease in the [Ca2+]i response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca2+ influx and sarcoplasmic reticulum Ca2+ reuptake were blocked, E2beta still decreased [Ca2+]i. The response was blocked by extracellular lanthanum. These data indicate that E2beta decreases [Ca2+]i in coronary artery smooth muscle by affecting Ca2+ efflux via a receptor-mediated mechanism.

Animals↗
PubMed1999

Further attenuation of endothelium-dependent relaxation imparted by natriuretic peptide receptor antagonism.

Nitric oxide (NO) is an important endothelium-derived relaxing factor that functions via activation of soluble guanylyl cyclase and cGMP generation in vascular smooth muscle. Recently, studies have described the synthesis and secretion of C-type natriuretic peptide (CNP) from endothelial cells. This peptide also mediates relaxation via cGMP but through activation of particulate guanylyl cyclase. We tested the hypothesis that endothelium-dependent relaxations to acetylcholine or bradykinin in isolated canine coronary arteries involve both releases of NO and CNP. Rings of canine coronary arteries were incubated with either inhibitors of NO production (N(G)-monomethyl-L-arginine, L-NMMA) or the natriuretic peptide receptor antagonist HS-142-1. CNP caused concentration-dependent relaxations of rings with and without endothelium. These relaxations were attenuated by HS-142-1. Relaxations to acetylcholine and bradykinin were attenuated by L-NMMA alone but not attenuated by HS-142-1 alone. Coinhibition with L-NMMA and HS-142-1 significantly inhibited acetylcholine- and bradykinin-induced relaxation to a magnitude greater than either inhibitor alone. In summary, a novel interaction between the NO and the natriuretic peptide system is demonstrated by increased attenuation of endothelium-dependent relaxations to acetylcholine and bradykinin when both NO synthase and natriuretic peptide receptors are inhibited. These investigations support the concept of release of multiple endothelium-derived factors in response to acetylcholine- and bradykinin-receptor stimulation in endothelial cells, which may include CNP, as well as NO.

Acetylcholine↗