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S T Davidge

Publications and source records attributed to S T Davidge.

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

Differential regulation of platelet aggregation by matrix metalloproteinases-9 and -2.

We have recently found matrix metalloproteinase-2 (MMP-2) in human platelets and reported that the release of this enzyme during platelet activation stimulates aggregation. We have now identified matrix metalloproteinase-9 (MMP-9) in human platelets and resistance-sized (approximately 200 microm) arteries. Resting platelets released small quantities of pro-MMP-9. Maximal release of MMP-9 was detected during partial (appr. 30% maximum) aggregation with thrombin. However, maximal release of MMP-2 was associated with maximal aggregation. MMP-9 antibodies induced aggregation of resting platelets and potentiated aggregation of platelets induced by thrombin and collagen. Moreover, MMP-9 microisolated from arteries as well as recombinant human MMP-9 (0.1-30 ng/ml) inhibited thrombin and collagen-induced aggregation. We conclude that MMP-9 is an inhibitor of aggregation and in this action opposes the effects of MMP-2. The MMP-2/MMP-9 system may play an important role in the regulation of platelet-platelet and platelet-vessel wall interactions.

Arteries↗
PubMed1998

Estrogen replacement suppresses a prostaglandin H synthase-dependent vasoconstrictor in rat mesenteric arteries.

There is evidence that estrogen can upregulate nitric oxide (NO) synthase expression. There is also evidence that NO increases the activity of prostaglandin H synthase (PGHS). Our initial hypothesis was that removal of ovarian steroids would decrease endothelium/NO-dependent relaxation responses but that estrogen replacement would increase NO and PGHS activity, leading to increased vasodilation. Resistance-sized (<250 microm) mesenteric arteries from ovariectomized Sprague-Dawley rats without and with 17beta-estradiol replacement (0.15 or 0.5 mg/pellet, 60-day release) for 4 weeks were studied in a myograph system. The vasodilator response to methacholine, an endothelium-dependent muscarinic agonist, was reduced in the arteries of the ovariectomized rats compared with estradiol-replaced rats. In the presence of PGHS inhibitors (meclofenamate, valeryl salicylate, and NS-398) or a thromboxane A2 (TxA2)/prostaglandin H2 (PGH2) receptor blocker (SQ-29548), there was no longer a significant difference among the groups. Contrary to our initial hypothesis, inhibition of the PGHS pathway significantly enhanced the relaxation response in the arteries from the ovariectomized rats, which was similar to the response in the arteries from estradiol-replaced rats, indicating that a PGHS-dependent vasoconstrictor had modified the response to methacholine. Confirming these data, in response to exogenous arachidonic acid, arteries from ovariectomized rats exhibited constriction, whereas the arteries from the estradiol-replaced rats exhibited vasodilation. In the ovariectomized rats, pretreatment with inhibitors of the PGHS pathway reversed the vasoconstriction to a vasodilation. In addition, the vasoconstrictor response to the thromboxane mimetic U-46619 as well as PGH2 was enhanced in endothelium-denuded arteries from the ovariectomized rats compared with the estradiol-replaced rats. These data demonstrate that removal of ovarian steroids increased endothelium-mediated PGHS-dependent vasoconstriction that was associated with augmented sensitivity of the TxA2/PGH2 receptor. Chronic estrogen replacement in the ovariectomized rat suppressed this PGHS-dependent vasoconstrictor response.

Animals↗
PubMed1998

Altered active but not passive properties of mesenteric resistance arteries from the vitamin E-deprived rat.

1 We tested the hypothesis that lowering antioxidant protection through dietary vitamin E deprivation would alter active and passive mechanical properties in resistance arteries of the rat. Specifically, we hypothesized that vascular tone in isolated mesenteric arteries of the vitamin E-deprived rats would be altered due to impaired endothelial influences of nitric oxide and/or prostaglandins. 2 Lumen diameter and wall thickness were measured in pressurized arteries (approximately 250 microm diameter) from control (n=9) and vitamin E deprived (n=9) Sprague-Dawley female rats by use of a dimension analysing system. 3 Treatment with a cyclo-oxygenase inhibitor (meclofenamate) did not affect the basal vascular tone in either group. Treatment with a nitric oxide synthase inhibitor (NG-methyl-L-arginine) caused a significant increase in basal tone only in the vitamin E-deprived rats (% tone: 6.2+/-1.1 vs 1.2+/-0.3%; P<0.05). When tone was induced to 25% of the initial diameter with phenylephrine, treatment with the nitric oxide synthase inhibitor resulted in a greater potentiated tone in the vitamin E-deprived rats compared to the controls (26.5+/-2.7 vs 16.4+/-3.4%; P<0.05); suggesting a greater nitric oxide affect in the vessels from the vitamin E-deprived rats. Meclofenamate treatment in the induced tone arteries significantly relaxed (-17.4+/-4.0%; P<0.05) only the arteries from the vitamin E-deprived rats, indicating that a vasoconstrictor was modifying tone. The passive characteristics of distensibility and stress-strain relationship were not different between the two groups of rats. 4 In summary, vitamin E deprivation in the rat enhanced the modulation of vascular tone by both the nitric oxide and cyclo-oxygenase pathways but did not alter passive characteristics of mesenteric arteries.

Animals↗
PubMed1998

Oxidative stress and altered endothelial cell function in preeclampsia.

Evidence continues to accumulate that oxidative stress is a mediator of endothelial cell dysfunction and thus contributes to the cardiovascular complications of preeclampsia. The mechanisms for the interaction of oxidative stress and endothelial cell function have not been well defined. This review explores potential vasoactive pathways that may be affected by oxidative stress and have been reported to be altered in women with preeclampsia. In pathologic conditions of oxidative stress, increased production of superoxide peroxide anions and nitric oxide has been recognized to inactivate the nitric oxide as a vasorelaxant as well as produce peroxynitrite, a potent oxidant. Increase prostaglandin H (PGH) synthase activity resulting in vasoconstriction predominates in models of oxidative stress. Peroxynitrite increases PGH synthase activity in vitro, providing a potential, but as yet untested, link between oxidative stress, nitric oxide, and PGH synthase pathway, leading to reduced relaxation and increased constriction in the vasculature of women with preeclampsia. Other vasoconstrictors (such as isoprostanes and endothelin) that may be interrelated with oxidative stress and altered endothelial cell function in preeclampsia are also discussed.

Endothelium, Vascular↗
PubMed1998

Vascular function in the vitamin E-deprived rat: an interaction between nitric oxide and superoxide anions.

We tested the hypothesis that oxidative stress, mediated by dietary vitamin E deprivation, would alter vascular function through the interaction of oxygen-derived free radicals and nitric oxide (NO). This interaction may play an important role in the vascular pathophysiology of many diseases associated with oxidative stress. Mesenteric arteries from control (n = 12) and vitamin E-deprived (n = 12) Sprague-Dawley rats were studied with a myograph. Superoxide dismutase, which scavenges superoxide anions, produced a significantly greater relaxation in the arteries from the vitamin E-deprived rats compared with the controls (P<.05). Superoxide dismutase and catalase produced results similar to superoxide dismutase alone. Pretreatment with an NO synthase inhibitor eliminated the superoxide dismutase-induced relaxation in arteries from both control and vitamin E-deprived rats. L-Arginine induced a greater relaxation in arteries of the vitamin E-deprived group (P<.05). Agonist-induced relaxation with methacholine was not altered by superoxide dismutase for either group of animals, indicating that stimulated release of NO was not influenced by superoxide anions. With the use of Western immunoblot analysis, nitrotyrosine residues were shown to be present in arteries from both the vitamin E-deprived and control rats, but the amount of nitrotyrosine observed was not different between the two groups. In summary, our data indicate that there is a greater inhibition of NO caused by superoxide anions in the vitamin E-deprived group. We speculate that in conditions of oxidative stress (reduced vitamin E levels), altered vascular function may be due to increased destruction of NO by oxygen-derived free radicals.

Animals↗
PubMed1998

Vascular wall reactivity in conductance and resistance arteries: differential effects of insulin resistance.

Insulin resistance is associated with an increased risk of cardiovascular disease that is probably related to abnormalities of vascular wall function. The JCR:LA-cp rat is a unique animal model of human vascular disease that exhibits a profound insulin resistance, vasculopathy, and cardiovascular disease, and allows study of the relationships between insulin resistance and vascular function. Conductance and resistance arteries serve different functions, thus vascular disease may affect these types of artery differently. Concentration-response curves to norepinephrine, phenylephrine, and acetylcholine were studied in conductance vessels (aortic rings) and resistance vessels (mesenteric arteries) from 12-week-old male obese and lean JCR:LA-cp rats. The aortic rings and mesenteric arteries from obese rats showed increased maximal response to phenylephrine compared with those from lean rats, whereas only the mesenteric arteries from obese rats showed increased maximal response to norepinephrine. In aortic rings, relaxation to acetylcholine was similar for both genotypes, but the mesenteric arteries of obese rats showed impaired relaxation to acetylcholine. We conclude that the sensitivity to vasoconstriction is enhanced in aortic rings and mesenteric arteries of obese male JCR:LA-cp rats, but endothelial function is impaired only in the mesenteric resistance arteries of these animals. Hence functional aberrations in the obese, insulin-resistant state are more pronounced in mesenteric resistance arteries than in a major conductance artery.

Acetylcholine↗
PubMed1996

Evidence of endothelial activation and endothelial activators in cord blood of infants of preeclamptic women.

OBJECTIVE: In preeclampsia markers of endothelial activation (e.g., increased cellular fibronectin and activities that alter in vitro endothelial function (e.g., stimulation of nitric oxide and prostacyclin generation) are increased in the maternal circulation. We tested preeclamptic infant blood for these markers and activities and correlated these findings with fetal growth. STUDY DESIGN: Plasma was obtained from 17 term nulliparcus preeclamptic and normal pregnant women and their infants and from 8 additional preeclamptic mother-baby pairs from earlier gestations. Plasma cellular fibronectin and production of nitric oxide and prostacyclin by cultured endothelial cells exposed to 2% plasma were measured. RESULTS: Cellular fibronectin was higher in maternal plasma of preeclamptic than nonpregnant women (6.1 +/- 0.29 vs 4.2 +/- 0.27 microgram/ml, p < 0.01), as were stimulated endothelial nitric oxide and prostacyclin production (nitric oxide 42.5 +/- 3.9 vs 26.9 +/- 2.3 nmol nitrite/microgram protein/24 hours, p < 0.05; prostacyclin 261.7 +/- 31.2 vs 151.9 +/- 18.7 pg prostaglandin F1 alpha/microgram protein/24 hours, p < 0.05). In the preeclamptic infants cellular fibronectin was also greater (3.3 +/- 0.15 vs 2.6 +/- 0.14 microgram/ml, p < 0.01), as was endothelial nitric oxide production in response to the plasma (24.4 +/- 1.1 vs 21.4 +/- 0.09 mumol/L nmol nitrite/microgram protein/24 hours, p < 0.05). Prostacyclin production was not significantly different. In preeclamptic infants across a wide gestational age there was no correlation of endothelial activation and fetal growth. CONCLUSIONS: Infants of women with preeclampsia may be affected by endothelial dysfunction, as well as reduced uteroplacental perfusion.

Adult↗
PubMed1996

Urine but not plasma nitric oxide metabolites are decreased in women with preeclampsia.

OBJECTIVE: Nitric oxide is a potent vasorelaxant produced by endothelial cells. We tested the hypothesis that urinary and perhaps plasma nitric oxide metabolites would be reduced in women with preeclampsia. STUDY DESIGN: Plasma and urine from 14 women meeting strict clinical criteria for the diagnosis of preeclampsia and 20 normal nulliparous women were assayed for the stable metabolites of nitric oxide, nitrate and nitrite. RESULT: There was no significant difference of plasma concentrations of nitrate and nitrite between women with preeclampsia and women with normal pregnancies (32.7 +/- 3.1 vs 25.8 +/- 2.4 micromol/L). Plasma creatinine levels were elevated in women with preeclampsia (0.85 +/- 0.09 vs 0.66 +/- 0.02 mg/dl, p<0.01), indicating a reduced glomerular filtration rate. Urine concentrations of nitrate and nitrite normalized by creatinine excretion were significantly lower in women with preeclampsia compared with normal pregnant women (0.37 +/- 0.06 vs 0.69 +/- 0.11 micromol of nitrite per milligram creatinine, p. <0.05). CONCLUSIONS: Our study using concomitant measurement of plasma and urine nitrate and nitrite suggests a reduced production of nitric oxide in women with preeclampsia compared with normal pregnant women.

Adult↗
PubMed1996

Mechanical stress eliminates the effects of plasma from patients with preeclampsia on endothelial cells.

OBJECTIVE: Our purpose was to determine whether mechanical deformation alters in vitro effects of plasma from patients with preeclampsia on endothelial cell function to produce a paradigm similar to the in vivo disease state. STUDY DESIGN: The effects of 2% plasma from 12 patients with preeclampsia and 12 normal pregnant women on prostacyclin, nitric oxide, and endothelin production by cultured endothelial cells were measured in the presence or absence of cyclic stretch and laminar shear stress. RESULTS: In the absence of mechanical stress plasma from patients with preeclampsia resulted in greater prostacyclin and nitric oxide production (but no change in endothelin production) compared with plasma from normal pregnant women. Cyclic stretch did not affect prostacyclin or endothelin production but produced similar increases in nitric oxide production in cells exposed to plasma from the two groups. Shear stress markedly increased prostacyclin and nitric oxide production (but did not alter endothelin production). In the presence of shear stress there were no differences in production rates of nitric oxide or prostacyclin between cells exposed to plasma from the two groups. CONCLUSION: Shear stress alters the effects of plasma on endothelial cells. This is an important caveat in the interpretation of previous static in vitro culture studies and may partially explain the dichotomy between in vitro studies and in vivo findings in preeclampsia.

Adult↗
PubMed1996

Decreased transferrin and increased transferrin saturation in sera of women with preeclampsia: implications for oxidative stress.

OBJECTIVE: The concerted iron-binding antioxidant activity of transferrin and ceruloplasmin decreases with increasing transferrin saturation by iron. We examined interactions between serum iron and iron-binding capacity and concentrations of the lipid peroxidation metabolite malondialdehyde in normal and preeclamptic pregnancies. We also asked if the release of iron from free hemoglobin by lipid hydroperoxides is a potential mechanism to increase transferrin saturation in preeclampsia. STUDY DESIGN: Predelivery and 24 to 48 hour postpartum venous blood was collected from 19 women with uncomplicated pregnancies and 17 with preeclampsia. Serum iron, iron binding capacity, and malondialdehyde were measured. In a subset of predelivery samples electron paramagnetic resonance spectroscopy was used to determine diferric transferrin, total transferrin, and ceruloplasmin concentrations and to examine interactions of an organic hydroperoxide with hemoglobin and transferrin. RESULTS: Antepartum serum iron concentrations were 46% greater, percent saturation of iron binding capacity was 98% greater, and malondialdehyde 50% greater, whereas total iron-binding capacity was 14% lower, in women with preeclampsia. By 48 hours post partum group differences between these variables other than total iron-binding capacity were not observed. Electron paramagnetic resonance spectroscopy confirmed antepartum differences and that total iron-binding capacity and percent saturation were equivalent to total transferrin and the ratio diferric transferrin/total transferrin, respectively. Antepartum concentrations of ceruloplasmin were not different. Antepartum malondialdehyde concentrations correlated positively with percent transferrin saturation and negatively with unsaturated iron-binding capacity (apotransferrin). Electron paramagnetic resonance spectroscopy demonstrated that the release of iron from free hemoglobin by lipid hydroperoxides in serum is a potential mechanism to increase transferrin saturation. CONCLUSION: Increased transferrin saturation and decreased unsaturated iron-binding capacity in preeclampsia may occur consequent to oxidative stress and then further promote oxidative stress by decreasing serum antioxidant buffering against redox-active iron.

Adult↗
PubMed1996

Impairment of vascular function is associated with an age-related increase of lipid peroxidation in rats.

We tested the hypothesis that an increase in endogenous lipid peroxidation over time is associated with an impairment of endothelium-dependent vascular function in resistance-sized mesenteric arteries that is due in part to alterations of arachidonate metabolism. Susceptibility to red blood cell hemolysis and sera levels of malondialdehyde were increased (P < 0.05) from 20 wk (n = 12) to 40 wk (n = 12) in female Sprague-Dawley rats. Arteries were studied in a myograph by examining the endothelial modification of phenylephrine vasoconstriction and the relaxation responses of the mesenteric arteries to methacholine. We observed the following. 1) An increase in sensitivity to alpha 1-adrenergic stimulation occurred between 20 and 40 wk of age. Cyclooxygenase inhibition decreased the sensitivity to phenylephrine only in the arteries from the 40-wk-old rats, indicating that a cyclooxygenase-dependent vasoconstrictor was modifying the phenylephrine response. 2) Nitric oxide synthase inhibition caused a greater increase in phenylephrine sensitivity in the arteries from the 20-wk-old rats than those from the 40-wk-old rats, indicating that nitric oxide modification of phenylephrine sensitivity decreased with age. 3) Endothelium-independent relaxations were not affected between 20 and 40 wk of age. 4) At 40 wk, the sensitivity to the methacholine-mediated relaxation response decreased without impairing the maximal relaxation response. This reduced sensitivity was removed with cyclooxygenase inhibition or thromboxane A2/prostaglandin H2 (PGH2) receptor blockade. 5) Aortas from the 40-wk-old rats had an increased expression of PGH synthase. Collectively, these observations indicate that, in the female rat, an increase in lipid peroxidation over time is associated with changes in endothelium-dependent vascular function that were due in part to a cyclooxygenase-dependent vasoconstrictor.

Aging↗
PubMed1996

Plasma of preeclamptic women stimulates and then inhibits endothelial prostacyclin.

We propose that the dichotomy between the in vivo reduction in intravascular prostacyclin production that occurs in preeclampsia and the in vitro stimulatory effect of plasma from preeclamptic patients on endothelial cell prostacyclin production is due to differential effects of chronic versus acute exposure to the plasma. We studied the acute versus chronic effects of 2% plasma from healthy pregnant and preeclamptic subjects by measuring endothelial prostacyclin production at different time periods after exposure to plasma. To determine whether such effects were specific to prostacyclin, we also measured prostaglandin E2 production. To determine whether chronic changes in prostacyclin production resulted from altered cellular responsiveness, we stimulated cells that had been exposed to plasma for 72 hours with arachidonic acid and measured prostaglandin production. Preliminary characterization of the plasma factor or factors responsible for alterations in prostaglandin production was performed. After 24 hours cells exposed to plasma from preeclamptic women produced more prostacyclin and prostaglandin E2 than cells exposed to plasma from healthy pregnant women. In contrast, after 72 hours exposure to plasma from preeclamptic women resulted in less endothelial cell prostacyclin production than exposure to plasma from healthy pregnant women, but there were no such differences in prostaglandin E2 production. Cells that had been exposed to plasma from preeclamptic women for 72 hours produced less prostacyclin but the same quantity of prostaglandin E2 after stimulation with arachidonic acid than cells exposed to plasma from healthy pregnant women. The plasma factor or factors responsible for altered prostacyclin production were sensitive to heat, acid, and proteases. In contrast to acute exposure, chronic exposure to plasma from preeclamptic women alters endothelial cells to result in decreased prostacyclin production, an observation consistent with in vivo findings.

Adult↗
PubMed1996

Distinct factors in plasma of preeclamptic women increase endothelial nitric oxide or prostacyclin.

The pathogenesis of preeclampsia is proposed to be due to uncharacterized circulating factors that activate endothelial cells. Support for this hypothesis is provided by in vitro activation of endothelial cells by plasma from preeclamptic women, eg, increased nitric oxide and prostacyclin generation. We performed molecular sizing, lipid extraction, and lipoprotein fractionation of plasma from normal pregnant and preeclamptic women and determined the ability of these plasma fractions to increase nitric oxide or prostacyclin generation by endothelial cells. Fractions from plasma of preeclamptic women were consistently more active than fractions from normal pregnant women, although characterization was qualitatively similar. The factors stimulating nitric oxide and prostacyclin were different. The factor (or factors) stimulating nitric oxide generation was extractable by charcoal and present in lipid extracts and lipoprotein isolates with a molecular weight greater that 1.5 million daltons, which is characteristic of a lipoprotein or lipoprotein aggregate. By contrast, activity to stimulate prostacyclin persisted after charcoal stripping or lipoprotein removal, partitioned to the aqueous fraction, and had a molecular weight of approximately 50,000 D. Two distinct factors in the blood of preeclamptic women alter endothelial function in vitro. This information should guide the search for circulating factors contributing to the pathophysiology of preeclampsia.

6-Ketoprostaglandin F1 alpha↗
PubMed1995

Plasma from preeclamptic women increases human endothelial cell prostacyclin production without changes in cellular enzyme activity or mass.

OBJECTIVE: We investigated differences in prostacyclin production by endothelial cells exposed to plasma from either preeclamptic women or normal pregnant women. STUDY DESIGN: A case-control study of matched preeclamptic and normal pregnancies was used to compare prostacyclin synthesis by human umbilical vein endothelial cells incubated with pregnancy plasma for 24 hours. Prostacyclin concentrations in conditioned media were measured by radioimmunoassay of its stable metabolite (6-keto-prostaglandin F1 alpha). Human umbilical vein endothelial cell lysates were used to determine concentrations of the enzymes cyclooxygenase and prostacyclin synthase. RESULTS: Prostacyclin production by human umbilical vein endothelial cells incubated with plasma from preeclamptic women was significantly greater than that by cells exposed to normal pregnancy plasma. Differences in prostacyclin production under the two experimental conditions could be explained neither by differences in enzyme mass nor activities of cyclooxygenase and prostacyclin synthase. CONCLUSION: The stimulatory effect of preeclampsia plasma on prostacyclin biosynthesis in human umbilical vein endothelial cells appears to be manifested at a step(s) proximal to the activation of cyclooxygenase. Possible mechanisms are increased phospholipase A2, lipoprotein, or lipid peroxide activities in preeclampsia.

Case-Control Studies↗
PubMed1995

NOS expression is increased in endothelial cells exposed to plasma from women with preeclampsia.

Endothelial cell function is proposed to be altered by a factor(s) in the maternal circulation of women with the pregnancy disorder preeclampsia. Our initial hypothesis was that in preeclampsia, such factor(s) would reduce synthesis of nitric oxide (NO) by endothelial cells. However, we previously observed increased NO synthase activity in endothelial cells exposed to plasma from preeclamptic women. This study tested whether exposing cells to plasma from preeclamptic women increased transcription and/or translation of endothelial NO synthase. Cultured bovine coronary microvascular endothelial cells were exposed to 2% plasma from patients with preeclampsia and patients with uncomplicated pregnancies. Nitrite production was greater in endothelial cells exposed to plasma from preeclamptic women (8.97 +/- 0.54 vs. 6.39 +/- 0.59 nmol nitrites.10(6) cells-1 x 24 h-1; P < 0.05). Similarly, endothelial NO synthase mass as measured by Western immunoblotting was significantly increased (20,980 +/- 1,406 vs. 15,047 +/- 1,003 absorbancy units; P < 0.02). There was no detectable difference in mRNA for endothelial NO synthase. However, actinomycin (3 micrograms/ml), a transcription inhibitor, significantly decreased nitrite production only in cells exposed to plasma from preeclamptic women (5.28 +/- 0.52 vs. 3.56 +/- 0.36 nmol.10(6) cells-1 x 24 h-1, P < 0.05). These findings indicate a regulation of the "constitutive" isoform of NO synthase by factor(s) in the blood of preeclamptic women, which may have significance in this pathological condition of pregnancy.

Adult↗
PubMed1995

Plasma from women with preeclampsia increases endothelial cell nitric oxide production.

In preeclampsia, a factor in the maternal circulation alters endothelial function via a reduction in nitric oxide synthesis. We measured the in vitro effects of 2% plasma from women with preeclampsia, compared with 2% plasma from normotensive pregnant women, on cultured endothelial cell nitrite production and nitric oxide synthase activity. On finding differential effects, we measured the effects on cellular viability (assessed by lactate dehydrogenase levels) and performed a time course study. Endothelial cell nitrite production was found to be higher after exposure to plasma from the preeclamptic group than the normotensive pregnant group. The effects of long-term exposure (120 hours) were similar to those of short-term exposure (24 hours). In addition, nitric oxide synthase activity was significantly greater after exposure to preeclamptic plasma than after exposure to normotensive pregnant plasma. No differential effect on cellular viability was found. Contrary to our hypothesis, exposure of endothelial cells to preeclamptic plasma resulted in increased nitric oxide production and nitric oxide synthase activity.

Adult↗
PubMed1995

Nitric oxide produced by endothelial cells increases production of eicosanoids through activation of prostaglandin H synthase.

The endothelium serves many functional roles, including the modulation of vascular smooth muscle tone through the release of vasoactive agents such as nitric oxide (NO) and the eicosanoids. We proposed that NO produced by endothelial cells would increase the production of eicosanoids through enhanced expression and/or activation of prostaglandin H synthase. NO and eicosanoid synthesis were stimulated in a bovine coronary microvessel endothelial cell line with the calcium ionophore A23187 (1 mumol/L). Our data demonstrated the following: (1) A23187 stimulated NO synthesis along with prostacyclin and thromboxane production. (2) Inhibition of NO synthesis with NG-nitro-L-arginine methyl ester (0.1 mmol/L) significantly diminished both prostacyclin and thromboxane production. (3) Cells incubated with hemoglobin (2 micrograms/mL), which inactivates NO, decreased A23187-stimulated prostacyclin production, whereas cells incubated with superoxide dismutase (20 U/mL), which protects NO from superoxide anions, enhanced prostacyclin production. (4) Exogenous NO stimulated prostacyclin production. (5) The interaction of NO with prostacyclin persisted in the presence of excess exogenous arachidonic acid (100 mumol/L). (6) Cyclooxygenase activity in cell lysates increased in the first hour of NO stimulation. (7) NO stimulation of prostacyclin occurred within 1 hour and continued for 8 hours. (8) Neither constitutive nor inducible prostaglandin H synthase enzyme expression was altered by NO. (9) Cycloheximide (10 mumol/L) had no effect on A23187 stimulation of prostacyclin production. (10) Exogenous cGMP (10 mumol/L) or a phosphodiesterase inhibitor (1 mmol/L) did not affect prostacyclin production. These data indicate that stimulating synthesis of endogenous NO in cultured endothelial cells increased eicosanoid production through activation of prostaglandin H synthase.

Animals↗