PubMed Health⌕ Search

Biomedical subjects

R F O'Brien

Publications and source records attributed to R F O'Brien.

At least 37 records · Page 2Linked to original sources
PubMed1990

Effects of hypoxia on endothelium-dependent relaxation of rat pulmonary artery.

We have previously reported that the isolated rat branch pulmonary artery (PA) contracts when made hypoxic and that the contraction is dependent in large part on the presence of a functioning endothelium. This study tested if the hypoxic contraction was caused by reduced endothelium-derived relaxing factor (EDRF) activity. To do so we tested if chemical inhibitors of EDRF mimicked the effect of hypoxia, if PA guanosine 3',5'-cyclic monophosphate (cGMP) fell during hypoxic contraction, and if stimulation of smooth muscle cGMP attenuated hypoxic contraction. We found that the EDRF inhibitors hemoglobin and methylene blue caused a concentration-dependent increase in PA force that equaled that produced by hypoxia. PA cGMP decreased in endothelium-intact rings from 105 +/- 14 pM/g (wet wt) during normoxia to 41 +/- 9 pM/g during hypoxia. In endothelium-denuded rings normoxic cGMP was reduced to 32 +/- 10 pM/g with no further decrease during hypoxia. The endothelium-independent stimulators of cGMP, nitric oxide, and 8-bromo-cGMP, reduced maximum hypoxic contraction by 80 +/- 11 and 93 +/- 3%, respectively, whereas the endothelium-dependent stimulator acetylcholine did not. PA adenosine 3',5'-cyclic monophosphate (cAMP) fell only slightly during hypoxia and cAMP inhibitors failed to mimic the hypoxic contraction. We conclude that the hypoxic contraction of isolated rat PA is caused largely by decreased EDRF activity.

Acetylcholine↗
PubMed1989

Comparative pharmacology of rat and porcine endothelin in rat aorta and pulmonary artery.

Endothelins are potent vasoactive polypeptides produced by endothelial cells. This study compared the potency and efficacy of porcine and rat endothelin in rat aortic and pulmonary artery rings. We found that porcine endothelin was 25 to 55 times more potent than rat endothelin in both endothelium-intact and -denuded rings. Removal of the endothelium augmented and acetylcholine reduced contraction by either endothelin. We conclude that porcine endothelin is intrinsically more potent than rat endothelin and that the endothelium modulates the contraction of both endothelins.

Animals↗
PubMed1989

Role of cyclic adenosine monophosphate in the induction of endothelial barrier properties.

Cyclic adenosine monophosphate (AMP) has numerous important effects on cell structure and function, but its role in endothelial cells is unclear. Since cyclic AMP has been shown to affect transmembrane transport, cell growth and morphology, cellular adhesion, and cytoskeletal organization, it may be an important determinant of endothelial barrier properties. To test this we exposed bovine pulmonary artery endothelial cell monolayers to substances known to increase cyclic AMP and measured their effect on endothelial permeability to albumin and endothelial cell cyclic AMP concentrations. Cholera toxin (CT), a stimulant of the guanine nucleotide binding subunit of adenylate cyclase, led to a concentration-dependent 2-6-fold increase in cyclic AMP which was associated with a 3-10-fold reduction in albumin transfer across endothelial monolayers. The effect was not specific to albumin as similar barrier-enhancing effects were also noted with an unrelated macromolecule, fluorescein isothiocyanate (FITC)-dextran (MW 70,000). Barrier enhancement with cyclic AMP elevation was also observed with forskolin, a stimulant of the catalytic subunit of adenylate cyclase. The temporal pattern of barrier enhancement seen with these agents paralleled their effects on increasing cyclic AMP, and the barrier enhancement could be reproduced by incubation with either dibutyryl cyclic AMP or Sp-cAMPS, cyclic AMP-dependent protein kinase agonists. Furthermore, the forskolin effect on barrier enhancement was partially reversed with Rp-cAMPS, an antagonist of cyclic AMP-dependent protein kinase. Since endothelial actin polymerization may be an important determinant of endothelial barrier function, we sought to determine whether the cyclic AMP-induced effects were associated with increases in the polymerized actin pool (F-actin). Both cholera toxin and forskolin led to apparent endothelial cell spreading and quantitative increases in endothelial cell F-actin fluorescence. In conclusion, increased endothelial cell cyclic adenine nucleotide activity was an important determinant of endothelial barrier function in vitro. The barrier enhancement was associated with increased endothelial apposition and increases in F-actin, suggesting that influences on cytoskeletal assembly may be involved in this process.

Actins↗
PubMed1989

Prostacyclin contributes to inhibition of hypoxic pulmonary vasoconstriction by alkalosis.

The mechanism by which extracellular alkalosis inhibits hypoxic pulmonary vasoconstriction is unknown. We investigated whether the inhibition was due to intrapulmonary production of a vasodilator prostaglandin such as prostacyclin (PGI2). Hypoxic vasoconstriction in isolated salt-solution-perfused rat lungs was blunted by both hypocapnic and NaHCO3-induced alkalosis (perfusate pH increased from 7.3 to 7.7). The NaHCO3-induced alkalosis was accompanied by a significant increase in the perfusate level of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), an hydrolysis product of PGI2. Meclofenamate, an inhibitor of cyclooxygenase, counteracted both the blunting of hypoxic vasoconstriction and the increased level of 6-keto-PGF1 alpha. In intact anesthetized dogs, hypocapnic alkalosis (blood pH increased from 7.4 to 7.5) blunted hypoxic pulmonary vasoconstriction before but not after administration of meclofenamate. In separate cultures of bovine pulmonary artery endothelial and smooth muscle cells stimulated by bradykinin, the incubation medium levels of 6-keto-PGF1 alpha were increased by both hypocapnic and NaHCO3-induced alkalosis (medium pH increased from 7.4 to 7.7). These results suggest that inhibition of hypoxic pulmonary vasoconstriction by alkalosis is mediated at least partly by PGI2.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

Diagnosis of Pneumocystis carinii pneumonia by induced sputum in a city with moderate incidence of AIDS.

Examination of induced sputum from AIDS patients has been reported to provide the noninvasive diagnosis of PCP in 10 to 76 percent of cases. Since previous studies were done in centers with a high incidence of AIDS, we asked whether this test could be implemented successfully in a center with a lower incidence of AIDS. Over a 13-month period 25 of 38 (66 percent) AIDS patients with PCP had positive Giemsa (Diff-Quik) stains of induced sputum. We were unable to predict before sputum induction which patients would be positive based on clinical severity (increased A-a gradient or serum LDH levels). We confirmed prior observations that a normal serum LDH level was found in only 5 percent of documented PCP cases. This noninvasive technique significantly decreased the number of bronchoscopies performed and led to a considerable cost savings.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Serosanguineous pleural effusions in AIDS-associated Kaposi's sarcoma.

We describe the clinical course and pleural fluid findings in patients with AIDS-associated pleural KS and survival analysis of cases from the Colorado registry with and without pleuropulmonary KS. Twenty-one of 105 (20 percent) of AIDS cases with KS had pleuropulmonary involvement with KS and 13 (62 percent) had pleural effusions. All cases were homosexual males with cutaneous lesions of KS that antedated pleural involvement by several months. Clinical presentation and physical examination findings were nonspecific. Chest roentgenograms generally showed nonloculated bilateral pleural effusions; concurrent parenchymal infiltrates were present in 90 percent. Pleural fluid analysis showed that most effusions were serosanguineous, mononuclear cell-predominant exudates. Pleural fluid was visibly blood-tinged in nine of ten cases, with median RBC counts of 52,000/microliters (range 16,000 to 803,000/microliters). Cytologic examination of pleural fluid or needle biopsy of the parietal pleura failed to establish the diagnosis. In two cases the effusions were chylous. Postmortem examination of the lungs typically showed multiple cherry red to purple lesions on the visceral but not parietal pleural surface. In half the cases progressive pleural effusions led to significant morbidity or mortality. Systemic chemotherapy for disseminated KS was minimally effective; chest tube thoracostomy with attempted tetracycline sclerosis was unsuccessful in controlling pleural effusions in three cases. Median survival from diagnosis of KS to death was 205 and 338 days, respectively, for patients with and without pleuropulmonary KS (p less than 0.01). Pleural effusions are common in AIDS-associated pleuropulmonary KS, and finding a serosanguineous exudative effusion in an AIDS patient with cutaneous KS is highly suggestive of the diagnosis of pleural KS.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Pulmonary non-Hodgkin's lymphoma in AIDS.

Whereas extralymphatic involvement is common in lymphomas associated with HIV infection, there have been few reports of pulmonary lymphoma. In 648 cases of AIDS reported in Colorado, 40 have had non-Hodgkin's lymphoma. Of these, four have had documented pulmonary involvement and are reported in detail. Clinical manifestations were nonspecific and included fever, weight loss, generalized lymphadenopathy, dyspnea, chest pain and cough. Chest roentgenograms revealed multiple nodules or interstitial infiltrates. Transbronchial biopsy failed to establish the diagnosis in all cases. Three of four patients died four to five months after appearance of pulmonary nodules; one patient with stage IE disease showed slow radiographic progression over 16 months following radiation and chemotherapy and died 18 months after appearance of pulmonary nodules. Pulmonary involvement with lymphoma should be considered in patients with HIV infection, especially if multiple nodules are seen on chest roentgenograms.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Hypoxic contraction of isolated rat pulmonary artery.

This study was undertaken to test if isolated rat pulmonary artery (PA) rings contract in response to hypoxia, if the response behaves similarly to previously described physiologic and pharmacologic features of hypoxic pulmonary vasoconstriction (HPV) in the isolated perfused rat lung and if the endothelium is necessary for the response. Rings (2-3 mm wide) cut from the main extrapulmonary PA branches were studied. Hypoxic contractions of up to 80 mg (mean +/- S.E. 34 +/- 5 mg, n = 20) were seen in resting rings. The contraction was more reproducible and was potentiated in rings prestimulated with either phenylephrine, norepinephrine, KCl, angiotensin II or the thromboxane mimetic U46619. The magnitude of the hypoxic contraction was proportional to the level of prestimulation and the severity of the hypoxia, with maximum hypoxic contraction seen during exposure to 0% oxygen. The hypoxic dose response showed a threshold bath pO2 of between 30 and 60 Torr, was potentiated by BAY K8644 (10(-7) M), was inhibited by both nifedipine (10(-7) M) and cooling to 29 degrees C and was not inhibited by meclofenamate (1.6 x 10(-6) M). All these characteristics are comparable to previously described features of HPV in the isolated perfused rat lung. Removal of the endothelium resulted in a 48-80% reduction in maximum PA hypoxic contraction. Similar hypoxic contraction was seen in precontracted aortic rings. We conclude that the hypoxic contraction of isolated rat PA may be a useful in vitro model of HPV, that both the endothelium and smooth muscle may be involved in the sensing of PO2 and that the direct hypoxic response is not unique to pulmonary arteries.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1988

Mechanism of the antihypertensive effect of K depletion in the spontaneously hypertensive rat.

K depletion reverses hypertension in the SHR (systolic blood pressure: K deplete 122 +/- 5 vs. K replete 164 +/- 4 mm Hg, P less than 0.001). To determine the role of the renin angiotensin system in the protective effect of K depletion, we performed studies of vascular reactivity in intact SHR and of angiotensin II (Ang II) binding to mesenteric artery particles and vascular smooth muscle cells (VSMC) in culture from SHR. Pressor sensitivity to Ang II (+/- converting enzyme inhibition) but not norepinephrine was reduced in K depleted SHR. Thus, the decreased vascular reactivity in K depletion was specific for Ang II rather than a generalized defect. Ang II binding and receptor number (Bmax) (156 +/- 20 vs. 81 +/- 5 fmol/mg of protein, P less than 0.01) were increased in K depleted mesenteric artery particles. Since K depletion and increases in Ang II have both been associated with increased Ang II binding, Ang II binding was measured after bilateral nephrectomy. Despite reduction of plasma renin activity, total binding and Bmax were still increased in nephrectomized K depleted SHR. To determine the specific effect of K depletion independent of Ang II on Ang II binding, studies were performed in mesenteric artery VSMC from SHR grown in culture. VSMC from K replete SHR were grown to confluency in K replete medium and then were incubated in K depleted medium for 24 hours. Binding was saturable, time and temperature-dependent in K replete and K depleted cells. Total binding and Bmax (139 +/- 13 vs. 93 +/- 7 fmol/mg protein, P less than 0.01) were increased in K depleted cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1988

Hypoxia-induced increases in pulmonary transvascular protein escape in rats. Modulation by glucocorticoids.

Pulmonary edema after ascent to altitude is well recognized but its pathogenesis is poorly understood. To determine whether altitude exposure increases lung vascular permeability, we exposed rats to a simulated altitude of approximately 14,500 feet (barometric pressure [Pb] 450 Torr) and measured the pulmonary transvascular escape of radiolabeled 125I-albumin corrected for lung blood content with 51Cr-tagged red blood cells (protein leak index = PLI). Exposures of 24 and 48 h caused significant increases in PLI (2.30 +/- 0.08 and 2.40 +/- 0.06) compared with normoxic controls (1.76 +/- 0.06), but brief hypoxic exposures of 1-13 h produced no increase in PLI, despite comparable increases in pulmonary artery pressure. There were associated increases in gravimetric estimates of lung water in the altitude-exposed groups and perivascular edema cuffs on histologic examination. Normobaric hypoxia (48 h; fractional inspired oxygen concentration [FIO2] = 15%) also increased lung transvascular protein escape and lung water. Dexamethasone has been used to prevent and treat altitude-induced illnesses, but its mechanism of action is unclear. Dexamethasone (0.5 or 0.05 mg/kg per 12 h) started 12 h before and continued during 48 h of altitude exposure prevented the hypoxia-induced increases in transvascular protein escape and lung water. Hemodynamic measurements (mean pulmonary artery pressure and cardiac output) were unaffected by dexamethasone, suggesting that its effect was not due to a reduction in pulmonary artery pressure or flow. The role of endogenous glucocorticoid activity was assessed in adrenalectomized rats that showed augmented hypoxia-induced increases in transvascular protein escape, which were prevented by exogenous glucocorticoid replacement. In summary, subacute hypoxic exposures increased pulmonary transvascular protein escape and lung water in rats. Dexamethasone prevented these changes independent of reductions of mean pulmonary artery pressure or flow, whereas adrenalectomy increased pulmonary vascular permeability and edema at altitude. Increases in vascular permeability in hypoxia could contribute to the development of high-altitude pulmonary edema and endogenous glucocorticoids may have an important influence on pulmonary vascular permeability in hypoxia.

Adrenalectomy↗
PubMed1988

Pulmonary vascular reactivity.

The pulmonary vasculature responds to a multitude of constrictor and dilator mediators, but the exact physiologic and pathologic significance of such responsiveness is unknown. Further careful studies with specific mediator receptor blockers and synthesis inhibitors are required to determine if dilators play a role in maintaining the low vascular tone of the normal pulmonary circulation and if constrictors contribute to either the onset or the maintenance of the pulmonary hypertension associated with chronic airway hypoxia, lung injury, and pulmonary microembolism. It would be a mistake to summarily dismiss the possible involvement of vasoconstrictors in chronic pulmonary hypertension, but the apparent difficulty in establishing their importance emphasizes that mediators of vascular cell migration, proliferation, synthesis, and secretion may be at least as important in the etiology of the increased vascular resistance as the mediators of vascular tone.

Animals↗
PubMed1987

Endothelial cells in culture produce a vasoconstrictor substance.

We report that cultured vascular endothelial cells release into the culture medium a vasoconstrictor peptide, a substance we call an endothelium-derived constricting factor (EDCF). Conditioned medium from cultured bovine aortic and pulmonary artery endothelial cells caused sustained, dose-dependent isometric constriction of vascular rings isolated from bovine coronary and pulmonary arteries and rat and guinea pig pulmonary arteries and aortas. The medium also caused vasoconstriction when infused into isolated, perfused rabbit hearts and rat kidneys. Conditioned medium from bovine aortic intimal explants also contained constrictor activity, whereas medium from denuded intimal explants, cultured microvascular endothelial cells, vascular smooth muscle cells, or lung fibroblasts did not. Constrictor activity increased progressively in the culture medium over 2-12 h of incubation. Thrombin stimulated the release of constrictor activity; hypoxia, anoxia and meclofenamate had no effect and the calcium ionophore A23187 inhibited EDCF release. The EDCF caused a characteristic slow-onset and sustained constriction of the vascular rings that relaxed slowly over 60-90 min following removal. The constriction was not affected by inhibitors of arachidonic acid metabolism or by antagonists of serotonergic, histaminergic, alpha-adrenergic, opioid, leukotriene, angiotensin II, or substance P receptors; constriction was reversed partly by verapamil and acetylcholine and completely by nitroprusside and isoproterenol. EDCF was heat stable, not extractable into organic solvents, and completely destroyed by trypsin and neutral protease. Cycloheximide blocked the production of EDCF. These properties and the results of polyacrylamide gel filtration experiments suggested that EDCF was a peptide with a molecular weight of 3,000 daltons. These findings show that endothelial cells in culture produce a vasoconstrictor substance and support the idea that endothelial cell products play a role in mediating vascular tone.

Animals↗
PubMed1986

A role for interleukin-1 in the pathogenesis of Lyme disease.

Interleukin-1 (IL-1) is the major immunoregulatory molecule produced by macrophages in response to a variety of environmental insults including chemicals, phagocytosis, bacteria, and bacterial products. Macrophages stimulated by Borrelia burgdorferi produced large quantities of IL-1 when spirochetes were added to macrophages at a ratio of 10 spirochetes per macrophage. The release of IL-1 was dose dependent: a single spirochete per macrophage was sufficient to produce significant quantities of IL-1. Spirochetal lipopolysaccharide was not required for this activity in that polymyxin B in the spirochete-macrophage culture had no effect on IL-1 production. Normal murine fibroblasts cultured with this IL-1 were shown to have an increased rate of DNA synthesis and an increase in secreted collagenase. IL-1 was found in joint fluids from Lyme disease patients. When IL-1 was injected intradermally into the backs of rabbits, the injection sites became indurated, erythematous, and warm to the touch after 4 hrs and annular lesions much like those of erythema chronicum migrans were seen in some animals after 24 hrs. B. burgdorferi is a powerful inducer for IL-1 in vitro, and it is reasonable to presume that it acts similarly in Lyme disease patients. Our results suggest that IL-1 in turn, may play a role in many of the clinical manifestations of Lyme disease.

Animals↗
PubMed1986

Sustained coronary vasoconstriction provoked by a peptidergic substance released from endothelial cells in culture.

Recent reports have shown that cultured endothelial cells release into the culture medium a substance (or substances) that contracts isolated preparations of arterial smooth muscle [endothelial-derived constrictor factor (EDCF)]. To evaluate the coronary and cardiac effects of EDCF, isolated rabbit hearts retroperfused in a nonrecirculating system with Krebs-Henseleit solution were challenged with bolus injections (100-600 microliter) of either serum-free minimum essential medium (vehicle) or aortic endothelial cell supernates concentrated in minimum essential medium (EDCF). EDCF, but not its vehicle, produced dose-dependent coronary vasoconstriction unaccompanied by changes in left ventricular contraction or heart rate. The constrictor responses were remarkably well sustained with little or no decrement in resistance occurring over a 15-min observation period. Nitroprusside inhibited the development of and reversed on-going vasoconstriction evoked by EDCF. Neither meclofenamate nor diethylcarbamazine influenced EDCF-induced pressor responses, thereby negating a role for arachidonic acid metabolites. Coronary vasoconstriction induced by EDCF also was unaffected by blockade of alpha-adrenergic, histaminergic or serotonergic receptors. Incubation of EDCF with trypsin attenuated the pressor effects markedly, suggesting that EDCF may be a peptide. Roles for angiotensin or substance P were ruled out, however, as saralasin failed to influence EDCF-induced constriction and since substance P was inactive in the perfused rabbit heart preparation. We conclude that a substance (or substances), probably a peptide, released from cultured endothelial cells provokes sustained coronary vasoconstriction by an unknown mechanism.

Animals↗