Natriuretic peptides: physiology, therapeutic potential, and risk stratification in ischemic heart disease

BACKGROUND

The natriuretic peptide family consists of four molecules that share significant amino acid sequence homologic characteristics and a looped motif. Atrial natriuretic peptide and brain natriuretic peptide are similar in their ability to promote natriuresis and diuresis, inhibit the renin-angiotensin-aldosterone axis, and act as vasodilators. Understanding of the actions of C-type natriuretic peptide and dendroaspis natriuretic peptide is incomplete, but these two new family members also act as vasodilators. Because of the rapid evolution of information about this peptide family, we reviewed the state of the art with respect to risk stratification and therapeutic ability.

METHODS

English-language papers were identified by a MEDLINE database search covering 1966 through 1997 and supplemented with bibliographic references and texts.

CONCLUSIONS

The natriuretic peptides are counterregulatory hormones with prognostically important levels. They are similarly upregulated in heart failure and counteract neurohormones that induce vasoconstriction and fluid retention. BNP may be the superior prognosticator for risk stratification after myocardial infarction and is independent of left ventricular ejection fraction. Lastly, experimental trials suggest that administration of exogenous natriuretic peptides or inhibitors of their catabolism to patients with ischemic heart disease may be clinically beneficial.

Wound healing is accelerated by agonists of adenosine A2 (G alpha s-linked) receptors

The complete healing of wounds is the final step in a highly regulated response to injury. Although many of the molecular mediators and cellular events of healing are known, their manipulation for the enhancement and acceleration of wound closure has not proven practical as yet. We and others have established that adenosine is a potent regulator of the inflammatory response, which is a component of wound healing. We now report that ligation of the G alpha s-linked adenosine receptors on the cells of an artificial wound dramatically alters the kinetics of wound closure. Excisional wound closure in normal, healthy mice was significantly accelerated by topical application of the specific A2A receptor agonist CGS-21680 (50% closure by day 2 in A2 receptor antagonists. In rats rendered diabetic (streptozotocin-induced diabetes mellitus) wound healing was impaired as compared to nondiabetic rats; CGS-21680 significantly increased the rate of wound healing in both nondiabetic and diabetic rats. Indeed, the rate of wound healing in the CGS-21680-treated diabetic rats was greater than or equal to that observed in untreated normal rats. These results appear to constitute the first evidence that a small molecule, such as an adenosine receptor agonist, accelerates wound healing in both normal animals and in animals with impaired wound healing.

The introduction of ambulatory electrocardiographic monitoring for the diagnosis and management of myocardial ischemia

We report on the introduction of a new technology and a new method for the management of chronic coronary artery disease into a managed care environment. The introduction incurred substantial resistance from subspecialty consultants, primary care physicians, and top management. Strategies were developed to overcome these resistances. Modification of the program as well as the development of incentives occurred. These measures continue to evolve. The program, to date, has achieved approximately 50% penetration. The demonstration of better health outcomes and financial savings will almost certainly temper the resistance encountered from all three groups identified.

The anti-inflammatory mechanism of sulfasalazine is related to adenosine release at inflamed sites

The anti-inflammatory mechanism of sulfasalazine is not well understood. It has recently been shown that sulfasalazine inhibits 5-aminoimidazole-4-carboxamidoribonucleotide (AICAR) transformylase, an enzyme involved in de novo purine biosynthesis. We recently demonstrated that methotrexate promotes intracellular AICAR accumulation, thereby increasing adenosine release and diminishing inflammation, so we tested the hypothesis that sulfasalazine similarly promotes intracellular AICAR accumulation. We studied adenosine release and the state of inflammation in in vitro and in vivo models of the inflammatory process. The adhesion of stimulated neutrophils (FMLP) to endothelial cells preincubated with sulfasalazine was inhibited in a dose-dependent manner. Elimination of extracellular adenosine by addition of adenosine deaminase or inhibition of adenosine by the adenosine A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) completely reversed the anti-inflammatory effect of sulfasalazine (at concentrations <1 microM in this in vitro model. To determine whether this phenomenon was relevant to inhibition of inflammation in vivo, we studied the effect of sulfasalazine (100 mg/kg/day by gastric gavage for 3 days) on leukocyte accumulation in the murine air pouch model of inflammation. Treatment with sulfasalazine markedly decreased the number of leukocytes that accumulated in the inflamed (carrageenan, 2 mg/ml) air pouch. Injection of either adenosine deaminase or DMPX, but not the A1 receptor antagonist 8-cyclopentyl-dipropylxanthine, significantly reversed the anti-inflammatory effects of sulfasalazine treatment. Sulfasalazine increased the exudate adenosine concentration from 127 +/- 64 nM to 869 +/- 47 nM. Moreover, sulfasalazine treatment promoted a marked increase in splenocyte AICAR concentration from 35 +/- 6 to 96 +/- 3 pmols/10(6) splenocytes, which is consistent with the in vitro observation that sulfasalazine inhibits AICAR transformylase. These results indicate that sulfasalazine, like methotrexate, enhances adenosine release at an inflamed site and that adenosine diminishes inflammation via occupancy of A2 receptors on inflammatory cells. Our studies provide evidence that sulfasalazine and methotrexate may be described as a newly recognized family of anti-inflammatory agents that share the property of using adenosine as an antagonist of inflammation.

The anti-inflammatory mechanism of sulfasalazine is related to adenosine release at inflamed sites

The anti-inflammatory mechanism of sulfasalazine is not well understood. It has recently been shown that sulfasalazine inhibits 5-aminoimidazole-4-carboxamidoribonucleotide (AICAR) transformylase, an enzyme involved in de novo purine biosynthesis. We recently demonstrated that methotrexate promotes intracellular AICAR accumulation, thereby increasing adenosine release and diminishing inflammation, so we tested the hypothesis that sulfasalazine similarly promotes intracellular AICAR accumulation. We studied adenosine release and the state of inflammation in in vitro and in vivo models of the inflammatory process. The adhesion of stimulated neutrophils (FMLP) to endothelial cells preincubated with sulfasalazine was inhibited in a dose-dependent manner. Elimination of extracellular adenosine by addition of adenosine deaminase or inhibition of adenosine by the adenosine A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) completely reversed the anti-inflammatory effect of sulfasalazine (at concentrations <1 microM in this in vitro model. To determine whether this phenomenon was relevant to inhibition of inflammation in vivo, we studied the effect of sulfasalazine (100 mg/kg/day by gastric gavage for 3 days) on leukocyte accumulation in the murine air pouch model of inflammation. Treatment with sulfasalazine markedly decreased the number of leukocytes that accumulated in the inflamed (carrageenan, 2 mg/ml) air pouch. Injection of either adenosine deaminase or DMPX, but not the A1 receptor antagonist 8-cyclopentyl-dipropylxanthine, significantly reversed the anti-inflammatory effects of sulfasalazine treatment. Sulfasalazine increased the exudate adenosine concentration from 127 +/- 64 nM to 869 +/- 47 nM. Moreover, sulfasalazine treatment promoted a marked increase in splenocyte AICAR concentration from 35 +/- 6 to 96 +/- 3 pmols/10(6) splenocytes, which is consistent with the in vitro observation that sulfasalazine inhibits AICAR transformylase. These results indicate that sulfasalazine, like methotrexate, enhances adenosine release at an inflamed site and that adenosine diminishes inflammation via occupancy of A2 receptors on inflammatory cells. Our studies provide evidence that sulfasalazine and methotrexate may be described as a newly recognized family of anti-inflammatory agents that share the property of using adenosine as an antagonist of inflammation.

Effects of amlodipine on glomerular filtration, growth, and injury in experimental hypertension

The objective of this study was to determine whether the calcium antagonist amlodipine could slow the progression of chronic renal disease. We examined the effects of amlodipine on kidney structure and function in two experimental models of hypertension. In the first study, adult, male Munich Wistar rats underwent uninephrectomy and were given weekly injections of desoxycorticosterone and 1% saline for drinking. Rats ingested normal chow or chow containing amlodipine for 8 weeks. The drug reduced systemic blood pressure, but glomerular filtration rate, kidney weight, proteinuria, and morphological evidence of glomerular injury were not affected. In the second study, male spontaneously hypertensive rats underwent uninephrectomy at 5 weeks of age and were followed for 6 months, during which they received no therapy or amlodipine. The drug dose was determined in preliminary studies to be the highest dose not associated with marked growth retardation. Again, although systemic blood pressure was significantly reduced by amlodipine, proteinuria and the prevalence of glomerulosclerosis were similar in amlodipine-treated and control spontaneously hypertensive rats. Micropuncture studies revealed that glomerular pressure remained elevated in amlodipine-treated spontaneously hypertensive rats. Kidney weight and glomerular volume were also similar in amlodipine-treated and control rats. Amlodipine also failed to inhibit platelet aggregation. Therefore, antihypertensive therapy with amlodipine fails to reduce glomerular pressure in spontaneously hypertensive rats as well as glomerular size and injury in spontaneously hypertension rats and desoxycorticosterone-salt hypertension. Although other dihydropyridine calcium antagonists have been found to reduce experimental glomerular injury, these data suggest that amlodipine may not prevent hypertensive nephrosclerosis.

Identification of C1q as the heat-labile serum cofactor required for immune complexes to stimulate endothelial expression of the adhesion molecules E-selectin and intercellular and vascular cell adhesion molecules 1

To examine the role of complement components as regulators of the expression of endothelial adhesive molecules in response to immune complexes (ICs), we determined whether ICs stimulate both endothelial adhesiveness for leukocytes and expression of E-selectin and intercellular and vascular cell adhesion molecules 1 (ICAM-1 and VCAM-1). We found that ICs [bovine serum albumin (BSA)-anti-BSA] stimulated endothelial cell adhesiveness for added leukocytes in the presence of complement-sufficient normal human serum (NHS) but not in the presence of heat-inactivated serum (HIS) or in tissue culture medium alone. Depletion of complement component C3 or C8 from serum did not prevent enhanced endothelial adhesiveness stimulated by ICs. In contrast, depletion of complement component C1q markedly inhibited IC-stimulated endothelial adhesiveness for leukocytes. When the heat-labile complement component C1q was added to HIS, the capacity of ICs to stimulate endothelial adhesiveness for leukocytes was completely restored. Further evidence for the possible role of C1q in mediating the effect of ICs on endothelial cells was the discovery of the presence of the 100- to 126-kDa C1q-binding protein on the surface of endothelial cells (by cytofluorography) and of message for the 33-kDa C1q receptor in resting endothelial cells (by reverse transcription-PCR). Inhibition of protein synthesis by cycloheximide blocked endothelial adhesiveness for leukocytes stimulated by either interleukin 1 or ICs in the presence of NHS. After stimulation with ICs in the presence of NHS, endothelial cells expressed increased numbers of adhesion molecules (E-selectin, ICAM-1, and VCAM-1). Endothelial expression of adhesion molecules mediated, at least in part, endothelial adhesiveness for leukocytes, since leukocyte adhesion was blocked by monoclonal antibodies directed against E-selectin. These studies show that ICs stimulate endothelial cells to express adhesive proteins for leukocytes in the presence of a heat-labile serum factor. That factor appears to be C1q.

Colchicine alters the quantitative and qualitative display of selectins on endothelial cells and neutrophils

Since colchicine-sensitive microtubules regulate the expression and topography of surface glycoproteins on a variety of cells, we sought evidence that colchicine interferes with neutrophil-endothelial interactions by altering the number and/or distribution of selectins on endothelial cells and neutrophils. Extremely low, prophylactic, concentrations of colchicine (IC50 = 3 nM) eliminated the E-selectin-mediated increment in endothelial adhesiveness for neutrophils in response to IL-1 (P < 0.001) or TNF alpha (P < 0.001) by changing the distribution, but not the number, of E-selectin molecules on the surface of the endothelial cells. Colchicine inhibited stimulated endothelial adhesiveness via its effects on microtubules since vinblastine, an agent which perturbs microtubule function by other mechanisms, diminished adhesiveness whereas the photoinactivated colchicine derivative gamma-lumicolchicine was inactive. Colchicine had no effect on cell viability. At higher, therapeutic, concentrations colchicine (IC50 = 300 nM, P < 0.001) also diminished the expression of L-selectin on the surface of neutrophils (but not lymphocytes) without affecting expression of the beta 2-integrin CD11b/CD18. In confirmation, L-selectin expression was strikingly reduced (relative to CD11b/CD18 expression) on neutrophils from two individuals who had ingested therapeutic doses of colchicine. These results suggest that colchicine may exert its prophylactic effects on cytokine-provoked inflammation by diminishing the qualitative expression of E-selectin on endothelium, and its therapeutic effects by diminishing the quantitative expression of L-selectin on neutrophils.

Nonsteroidal antiinflammatory agents inhibit stimulated neutrophil adhesion to endothelium: adenosine dependent and independent mechanisms

All nonsteroidal antiinflammatory drugs (NSAIDs) inhibit neutrophil aggregation (homotypic cell-cell adhesion) and do so without affecting expression of CD11b/CD18. Since the first step in acute inflammation is a critical interaction between neutrophils and the vascular endothelium (heterotypic cell-cell adhesion), we determined whether NSAIDs diminish the adherence of neutrophils to the endothelium. At antiinflammatory concentrations (0.5-5 mM) sodium salicylate, an NSAID that does not inhibit prostaglandin synthesis, inhibited stimulated but not unstimulated neutrophil adherence to endothelial cells (IC50 < 1 mM, P < 0.00001). Salicylates have previously been shown to inhibit oxidative phosphorylation and, predictably, sodium salicylate inhibited oxidative phosphorylation, as evidenced by depletion of ATP stores (875 +/- 75 pmol/10(6) PMN, [2.92 +/- 0.25 mM]) in stimulated (FMLP, 0.1 microM) but not resting neutrophils treated with antiinflammatory doses of sodium salicylate (EC50 = 1 mM, P < 0.00001). Indomethacin and piroxicam (10 and 30 microM) only minimally decreased ATP concentrations in stimulated and resting neutrophils. ATP is metabolized to adenosine, and we have previously demonstrated that both endogenously released (180-200 nM) and exogenous adenosine (IC50 = 250 nM) inhibit stimulated neutrophil adherence to endothelial cells. To determine whether the increased metabolism of ATP and the resultant increase in adenosine release were responsible for inhibition of neutrophil adhesion to endothelium, we determined whether addition of adenosine deaminase (ADA, 0.125 IU/ml), an enzyme that converts extracellular adenosine to its inactive metabolite, inosine, affected inhibition of neutrophil adhesion to endothelium by stimulated neutrophils. ADA significantly reversed inhibition of neutrophil adherence to endothelium by sodium salicylate (0.5-5 mM, P < 0.00001). This suggests that sodium salicylate inhibits neutrophil adherence by increasing adenosine release. Whereas indomethacin and piroxicam (10-50 microM) also inhibited stimulated neutrophil adherence to endothelial cells, ADA did not affect their inhibition of adherence. These studies demonstrate a heretofore unexpected antiinflammatory mechanism for salicylates: salicylates increase ATP hydrolysis and thereby enhance release of adenosine. Moreover, these data are consistent with the hypothesis that NSAIDs differ from one another with respect to their mechanisms of action.

The cardiomyopathy of Duchenne's muscular dystrophy and the function of dystrophin

Duchenne's muscular dystrophy (DMD) is a common X-linked neuromuscular disease which predominantly affects skeletal and cardiac muscle. The absence of dystrophin, the metabolic defect that causes DMD, leads to a peculiar cardiomyopathy which initially affects the posterior wall of the left ventricle. We review evidence that dystrophin deficient myocytes become dystrophic in order of increasing axial stress upon the myocyte. Thus, dystrophin's function may be that of physically reinforcing the sarcolemma against the axial forces exerted upon the myocyte.

A mechanism for the antiinflammatory effects of corticosteroids: the glucocorticoid receptor regulates leukocyte adhesion to endothelial cells and expression of endothelial-leukocyte adhesion molecule 1 and intercellular adhesion molecule 1

Corticosteroids are the preeminent antiinflammatory agents although the molecular mechanisms that impart their efficacy have not been defined. The endothelium plays a critical role in inflammation by directing circulating leukocytes into extravascular tissues by expressing adhesive molecules for leukocytes [e.g., endothelial-leukocyte adhesion molecule 1 (ELAM-1) and intercellular adhesion molecule 1 (ICAM-1)]. We therefore determined whether corticosteroids suppress inflammation by inhibiting endothelial expression of adhesion molecules for neutrophils (polymorphonuclear leukocytes). Preincubation of endothelial cells with endotoxin [lipopolysaccharide (LPS), 1 microgram/ml] led to a 4-fold increase in subsequent adherence of polymorphonuclear leukocytes (P < 0.0001, n = 10) to endothelial cells, an increase that was markedly attenuated when endothelial cells were treated with dexamethasone (IC50 < 1 nM, P < 0.0001, n = 6 or 7) during preincubation with LPS. Moreover, the steroid receptor agonist cortisol (10 microM), but not its inactive metabolite tetrahydrocortisol (10 microM), diminished LPS-induced endothelial cell adhesiveness. Further evidence that the action of dexamethasone was mediated through ligation of corticosteroid receptors [human glucocorticoid receptors (hGRs)] was provided by experiments utilizing the steroid antagonist RU-486. RU-486 (10 microM), which prevents translocation of ligated hGR to the nucleus by inhibiting dissociation of hGR from heat shock protein 90, completely aborted the effect of dexamethasone on adhesiveness of endothelial cells (P < 0.0005, n = 3). Treatment of endothelial cells with LPS (1 microgram/ml) stimulated transcription of ELAM-1, as shown by Northern blot analysis, and expression of membrane-associated ELAM-1 and ICAM-1, as shown by quantitative immunofluorescence (both P < 0.001, n = 9). Dexamethasone markedly inhibited LPS-stimulated accumulation of mRNA for ELAM-1 and expression of ELAM-1 and ICAM-1 (IC50 < 10 nM, both P < 0.001, n = 4-9); inhibition of expression by dexamethasone was reversed by RU-486 (both P < 0.005, n = 4-6). As in the adhesion studies, cortisol but not tetrahydrocortisol inhibited expression of ELAM-1 and ICAM-1 (both P < 0.005, n = 3 or 4). In contrast, sodium salicylate (1 mM) inhibited neither adhesion nor expression of these adhesion molecules. These studies suggest that antagonism by dexamethasone of endotoxin-induced inflammation is a specific instance of the general biological principle that the glucocorticoid receptor is a hormone-dependent regulator of transcription.

Neutrophil adherence to endothelium is enhanced via adenosine A1 receptors and inhibited via adenosine A2 receptors

We have recently demonstrated that human neutrophils (PMN) possess two different classes of adenosine receptors (A1 and A2) that, when occupied, promote chemotaxis and inhibit the generation of reactive oxygen species (e.g., O2- and H2O2), respectively. We have previously demonstrated that adenosine protects endothelial cells (EC) from injury by stimulated neutrophils (PMN) both by diminishing generation of H2O2 and inhibiting adherence of PMN to EC. We therefore determined whether occupancy of A1 or A2 adenosine receptors regulated adherence of PMN to EC. At concentrations similar to those required to inhibit release of O2- by ligation of A2 receptors, both adenosine (IC50 = 56 nM) and 5'N-ethylcarboxamidoadenosine (NECA, IC50 = 8 nM), the most potent A2 agonist, inhibited adherence to EC by stimulated PMN (FMLP, 0.1 microM). In direct contrast, the specific A1 agonists N6-phenylisopropyladenosine and N6-cyclopentyladenosine (CPA) promoted PMN adherence to EC at concentrations of 1-100 nM. To further investigate the mechanisms by which adenosine receptor agonists affected the adherence of stimulated PMN we examined the effect of NECA (A2) and CPA (A1) on the adherence of PMN to fibrinogen (a ligand for the beta 2 integrin CD11b/CD18) and to gelatin. In a dose-dependent manner (IC50 = 2 nM), NECA inhibited the adherence of FMLP-treated PMN to fibrinogen- but not gelatin-coated plates. In contrast, CPA (A1) promoted adherence of stimulated PMN to gelatin-(EC50 = 13 pM) but not fibrinogen-coated plates. Theophylline (10 microM), an adenosine receptor antagonist, reversed the inhibition by NECA (0.3 microM) of stimulated neutrophil adherence to fibrinogen. These observations not only confirm the presence of A1 and A2 receptors on PMN but also suggest two opposing roles for adenosine in inflammation. Occupancy of A1 receptors promotes neutrophil adherence to endothelium and chemotaxis (a proinflammatory role) whereas occupancy of A2 receptors inhibits adherence and generation of toxic oxygen metabolites (an antiinflammatory role).

Neutrophil adherence to endothelium is enhanced via adenosine A1 receptors and inhibited via adenosine A2 receptors

We have recently demonstrated that human neutrophils (PMN) possess two different classes of adenosine receptors (A1 and A2) that, when occupied, promote chemotaxis and inhibit the generation of reactive oxygen species (e.g., O2- and H2O2), respectively. We have previously demonstrated that adenosine protects endothelial cells (EC) from injury by stimulated neutrophils (PMN) both by diminishing generation of H2O2 and inhibiting adherence of PMN to EC. We therefore determined whether occupancy of A1 or A2 adenosine receptors regulated adherence of PMN to EC. At concentrations similar to those required to inhibit release of O2- by ligation of A2 receptors, both adenosine (IC50 = 56 nM) and 5'N-ethylcarboxamidoadenosine (NECA, IC50 = 8 nM), the most potent A2 agonist, inhibited adherence to EC by stimulated PMN (FMLP, 0.1 microM). In direct contrast, the specific A1 agonists N6-phenylisopropyladenosine and N6-cyclopentyladenosine (CPA) promoted PMN adherence to EC at concentrations of 1-100 nM. To further investigate the mechanisms by which adenosine receptor agonists affected the adherence of stimulated PMN we examined the effect of NECA (A2) and CPA (A1) on the adherence of PMN to fibrinogen (a ligand for the beta 2 integrin CD11b/CD18) and to gelatin. In a dose-dependent manner (IC50 = 2 nM), NECA inhibited the adherence of FMLP-treated PMN to fibrinogen- but not gelatin-coated plates. In contrast, CPA (A1) promoted adherence of stimulated PMN to gelatin-(EC50 = 13 pM) but not fibrinogen-coated plates. Theophylline (10 microM), an adenosine receptor antagonist, reversed the inhibition by NECA (0.3 microM) of stimulated neutrophil adherence to fibrinogen. These observations not only confirm the presence of A1 and A2 receptors on PMN but also suggest two opposing roles for adenosine in inflammation. Occupancy of A1 receptors promotes neutrophil adherence to endothelium and chemotaxis (a proinflammatory role) whereas occupancy of A2 receptors inhibits adherence and generation of toxic oxygen metabolites (an antiinflammatory role).

Deep bite treatment in relation to mandibular growth rotation

This paper illustrates some of the changes which occur during the treatment of Class II division 1 malocclusions complicated by a deep bite, and reviews the significance of these changes in relation to concepts of deep bite treatment. Particular reference is made to mandibular growth rotation and consequent differential tooth eruption in assessing factors involved in initial bite opening and consolidation of the opened bite. The cases shown illustrate that although an initial bite opening may occur by incisor intrusion and molar eruption, when viewed over a longer period of time rotational mandibular growth and associated differential eruption of teeth in which molars erupt more than incisors may be a more significant factor. Differential eruption which takes place in response to vertical condylar growth under guidance of the appliance would appear to be a significant factor in treatment of deep bite.

Methotrexate inhibits neutrophil function by stimulating adenosine release from connective tissue cells

Although commonly used to control a variety of inflammatory diseases, the mechanism of action of a low dose of methotrexate remains a mystery. Methotrexate accumulates intracellularly where it may interfere with purine metabolism. Therefore, we determined whether a 48-hr pretreatment with methotrexate affected adenosine release from [14C]adenine-labeled human fibroblasts and umbilical vein endothelial cells. Methotrexate significantly increased adenosine release by fibroblasts from 4 +/- 1% to 31 +/- 6% of total purine released (EC50, 1 nM) and by endothelial cells from 24 +/- 4% to 42 +/- 7%. Methotrexate-enhanced adenosine release from fibroblasts was further increased to 51 +/- 4% (EC50, 6 nM) and from endothelial cells was increased to 58 +/- 5% of total purine released by exposure to stimulated (fMet-Leu-Phe at 0.1 microM) neutrophils. The effect of methotrexate on adenosine release was not due to cytotoxicity since cells treated with maximal concentrations of methotrexate took up [14C]adenine and released 14C-labeled purine (a measure of cell injury) in a manner identical to control cells. Methotrexate treatment of fibroblasts dramatically inhibited adherence to fibroblasts by both unstimulated neutrophils (IC50, 9 nM) and stimulated neutrophils (IC50, 13 nM). Methotrexate treatment inhibited neutrophil adherence by enhancing adenosine release from fibroblasts since digestion of extracellular adenosine by added adenosine deaminase completely abrogated the effect of methotrexate on neutrophil adherence without, itself, affecting adherence. One hypothesis that explains the effect of methotrexate on adenosine release is that, by inhibition of 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) transformylase, methotrexate induces the accumulation of AICAR, the nucleoside precursor of which (5-aminoimidazole-4-carboxamide ribonucleoside referred to hereafter as acadesine) has previously been shown to cause adenosine release from ischemic cardiac tissue. We found that acadesine also promotes adenosine release from and inhibits neutrophil adherence to connective tissue cells. The observation that the antiinflammatory actions of methotrexate are due to the capacity of methotrexate to induce adenosine release may form the basis for the development of an additional class of antiinflammatory drugs.

Effects of nifedipine and enalapril on glomerular injury in rats with deoxycorticosterone-salt hypertension

Male Munich-Wistar rats underwent right nephrectomy and were given weekly injections of deoxycorticosterone acetate (DOCA) and 1% saline (salt) to drink. Two studies were performed. In the first, rats given enalapril (ENP) were compared with controls. In the second, rats ingested either standard chow or chow to which the calcium-entry blocker nifedipine (NIF) had been added. Six to eight weeks after nephrectomy, both control DOCA-salt rats and those given ENP had severe hypertension and significant proteinuria. Rats given NIF excreted less protein, and glomerular lesions were not observed in this group. The effects of NIF on several parameters that have been associated with glomerular injury were examined. Micropuncture studies revealed that glomerular capillary pressure was increased in DOCA-salt rats and was not reduced by NIF. Platelet aggregation was also similar in NIF-treated and control rats. Morphometric studies revealed a tendency toward lower glomerular volume of NIF-treated rats; however, kidney weight and glomerular capillary radius were unaffected by therapy. Thus NIF, but not ENP, prevents DOCA-salt rats from developing hypertension and glomerular injury. This effect does not depend on reduction in glomerular pressure or inhibition of platelet aggregation.

Uremic levels of oxalic acid suppress replication and migration of human endothelial cells

Patients with chronic renal failure who undergo hemodialysis experience accelerated atherosclerosis and premature death. Since the end-metabolite, oxalic acid, accumulates in plasma in proportion to the severity of renal failure, we studied whether sodium oxalate (0 to 300 microM) is an endothelial toxin and, therefore, might enhance atherogenesis. Exposure to uremic levels of oxalate (greater than 30 microM) for 9 to 28 days depressed endothelial cell replication by 33% to 84% (mean +/- SD, 54% +/- 15.7%, n = 17 experiments, p = 0.002). In contrast, replication of fibroblasts exposed to 200 microM oxalate for 45 days was not inhibited. The inhibitory effect of oxalate on endothelial cell replication was both dose- and time-dependent (both p less than 0.0001) and was first detected 3 to 7 days after the initial exposure to oxalate. Further, the inhibitory effect was fully reversible upon removal of oxalate, but only if exposure was limited to 5 days or less. Sodium salts of other carboxylic acids (citric, succinic, glyoxylic, and malonic; 200 microM) as well as HCl (200 microM) did not suppress endothelial cell replication. Oxalate also inhibited endothelial cell migration but had no effect on basal, thrombin-induced, or arachidonate-induced prostacyclin production by endothelial cells. Exposure of endothelial cells to sodium oxalate (200 microM) for as little as 24 hours-a time period sufficient to induce delayed, transient inhibition of replication not detectable until approximately 1 week after exposure-inhibited incorporation of 3H-leucine into protein by 40% (p = 0.009). We conclude that sodium oxalate acts as a uremic toxin, inhibiting endothelial cell replication and migration, functions which may be important for constitutive inhibition of atherosclerosis.

Inhibition of tissue plasminogen activator activity by aspirin in vivo and its relationship to levels of tissue plasminogen activator inhibitor antigen, plasminogen activator and their complexes

The observation that aspirin inhibits the increment in tissue plasminogen activator (t-PA) activity induced by venous occlusion of the forearm became controversial with the publication of several nonconfirmatory studies. The current study was performed to confirm the original observation and determine the mechanism by which aspirin suppresses the incremental t-PA activity induced by venous occlusion. Aspirin (650 mg/d X 2) caused no change in resting levels of t-PA antigen (t-PA:Ag) or activity, plasminogen activator inhibitor 1 antigen (PAI-1:Ag), or activity or t-PA-PAI-1 complexes. In contrast, aspirin reduced the increments induced by venous occlusion as follows: t-PA:Ag by 45% (P = .001); t-PA activity (euglobulin lysis time, ELT) by 43% (P = .006); and t-PA activity (alpha 2-plasmin inhibitor-plasmin complexes, PIPC) by 41% (P = .003). The inhibition of incremental t-PA activity measured as ELT or PIPC was linearly correlated with the inhibition of incremental t-PA:Ag (respectively, r = .75, P less than .02; r = .67, P less than .05). Aspirin had no effect on the increment in PAI-1:Ag induced by venous occlusion, but similar to the effect on t-PA:Ag, aspirin induced a 51% inhibition of the increment in t-PA-PAI-1 complex formation. Aspirin did not alter the ability of alpha 2-plasmin inhibitor to bind plasmin, nor the ability of plasma to support the fibrin-catalyzed generation of plasmin by t-PA, nor the subsequent formation of PIPC. Aspirin inhibits the t-PA activity induced by venous occlusion primarily by inhibiting the release of t-PA antigen.

The effect of aspirin on the hemodynamic response to nitroglycerin

The role of prostaglandins in mediating the hemodynamic response to nitroglycerin in vivo is controversial. To determine the effect of inhibiting prostaglandin production on the response to nitroglycerin, either placebo or aspirin (650 mg) was administered 1 hour prior to the administration of nitroglycerin (432 micrograms) sublingually to 40 healthy volunteers in a double-blind, randomized, cross-over study. Prior to nitroglycerin administration, blood pressure and pulse rate were determined noninvasively every 2 minutes until stable conditions were reached, and then after nitroglycerin administration determinations were made every 1 minute for the first 10 minutes, every 2 minutes for the next 10 minutes, and every 5 minutes until 30 minutes had elapsed. At peak response in the placebo study, nitroglycerin lowered systolic pressure from 117 +/- 10 to 111 +/- 10 mm Hg (p less than 0.0001). Unexpectedly, nitroglycerin increased diastolic pressure from 75 +/- 8 to 80 +/- 7 mm Hg (p less than 0.005), thus reducing pulse pressure significantly. Pulse rate after nitroglycerin increased from 72 +/- 11 to 85 +/- 14 (p less than 0.001). Aspirin slightly modified the pattern of response at 1 minute but altered neither the peak hemodynamic responses nor the areas under the time-pressure and time-pulse curves. Thus nitroglycerin-induced prostaglandin production does not play a major role in the systemic hemodynamic response to nitroglycerin in vivo.

Quantitation of transient myocardial ischemia by digital, ambulatory electrocardiography

Transient myocardial ischemia is more frequently silent than accompanied by angina. The frequency of ischemia varies markedly from day to day, so that in order to accurately define the total ischemic burden, it may be necessary to quantitate ischemic episodes for periods longer than 24 hours. Therefore, a programmable, digital device was developed for long-term, interactive, ambulatory monitoring of the electrocardiogram, which uses variations in a time-averaged ST level as an indicator of myocardial ischemia. The electrocardiographic signal is digitized at 256 Hz and analyzed by an algorithm. If ST depression is planar or downsloping and persists for more than 40 seconds, and if the ST depression is equal to or more than a user-programmed threshold, the device marks the onset of an ischemic event and times it. The algorithm has been validated by comparison of its analysis of the ST segment to human and computerized analyses of frequency-modulated Holter recordings and stress tests. To assess the feasibility and utility of long-term monitoring, patients with documented coronary artery disease were monitored continuously for 14-day periods. Of 26 patients enrolled, 8 completed a protocol for individualization of anti-ischemic therapy using transdermal nitroglycerin. Over 90% of ischemic episodes in this group of patients, all of whom had had a previous myocardial infarction, were silent. Treatment with 10 mg of transdermal nitroglycerin reduced the number of ischemic episodes by 59% and the duration of ischemia by 60% (p less than 0.001); there was no diminution in the effectiveness of treatment from week 1 to week 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential for real-time processing of the continuously monitored electrocardiogram in the detection, quantitation, and intervention of silent myocardial ischemia

Current technology for monitoring and analyzing the ST segment allows for accurate description of ST-segment deviation, which in most cases is a valid measure of myocardial ischemia. In this article, the authors describe a new method that utilizes microprocessor analysis of the electrocardiogram to detect ST-segment deviation in ambulatory subjects. This technique results in the ability to characterize the total ischemic burden over long periods of time and to intervene acutely in order to treat myocardial ischemia and possibly to prevent complications of coronary artery disease.

Adenosine: an endogenous inhibitor of neutrophil-mediated injury to endothelial cells

Since adenosine and its analogue 2-chloroadenosine prevent neutrophils from generating superoxide anion in response to chemoattractants, we sought to determine whether these agents could inhibit neutrophil-mediated injury of endothelial cells. The chemoattractant N-formyl-methionyl-leucyl-phenylalanine (FMLP, 0.1 microM) enhanced the adherence of neutrophils to endothelial cells twofold (18 +/- 2% vs. 39 +/- 3% adherence, P less than 0.001) and caused substantial neutrophil-mediated injury to endothelial cells (2 +/- 2% vs. 39 +/- 4% cytotoxicity, P less than 0.001). 2-Chloroadenosine (10 microM) not only inhibited the adherence of stimulated neutrophils by 60% (24 +/- 2% adherence, P less than 0.001) but also diminished the cytotoxicity by 51% (20 +/- 4% cytotoxicity, P less than 0.002). Furthermore, depletion of endogenously released adenosine from the medium by adenosine deaminase-enhanced injury to endothelial cells by stimulated neutrophils (from 39 +/- 4% to 69 +/- 3% cytotoxicity, P less than 0.001). Indeed, in the presence of adenosine deaminase, even unstimulated neutrophils injured endothelial cells (19 +/- 4% vs. 2 +/- 2% cytotoxicity, P less than 0.001). These data indicate that engagement of adenosine receptors prevents both the adhesion of neutrophils and the injury they cause to endothelial cells. Adenosine inhibits injury provoked not only by cells that have been stimulated by chemoattractants but also by unstimulated cells. Based on this model of acute vascular damage we suggest that adenosine is not only a potent vasodilator, but plays the additional role of protecting vascular endothelium from damage by neutrophils.

Modes of action of aspirin-like drugs

Current dogma holds that nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibition of the synthesis and release of prostaglandins. However, NSAIDs also inhibit the activation of neutrophils, which provoke inflammation by releasing products other than prostaglandins. We now report that NSAIDs (e.g., indomethacin, piroxicam) inhibit activation of neutrophils by inflammatory stimuli, such as C5-derived peptides and leukotriene B4, even when cyclooxygenase products generated in suspensions of stimulated neutrophils (prostaglandin E and thromboxanes) are present. Sodium salicylate (3 mM) greatly inhibited aggregation of neutrophils but had no effect on aggregation of platelets or production of thromboxane induced by arachidonate. Sodium salicylate and other NSAIDs also inhibit calcium movements (45Ca uptake, changes in fluorescence of chlortetracycline and quin-2). Aspirin, sodium salicylate, indomethacin, and piroxicam also enhanced the poststimulation increase in intracellular cyclic AMP. NSAIDs therefore inhibit early steps in neutrophil activation as reflected by their capacity to inhibit movements of Ca and to enhance intracellular levels of cyclic AMP.

Physician choices in the treatment of angina pectoris

Uncertainty about optimal treatment for many diseases results in heterogeneous management by definition. It was hypothesized that identifiable characteristics in a physician's background would influence the management of any such condition and thereby explain some of this heterogeneity. A vignette describing a patient with new-onset angina and a questionnaire ascertaining individual physician characteristics and management preferences were sent to attending physicians and house staff in the Department of Medicine at New York University School of Medicine. Although physicians believed very strongly that the patient had angina on the basis of the history, there was no consensus about managing the hypothetic patient. The age of the physician was the single most important predictor of management, with the younger half of the sample more likely to hospitalize (p less than 0.001), less likely to prescribe nitroglycerin as a sole therapy (p less than 0.005), and more likely to prescribe beta blockers (p less than 0.005). The era in which a physician trains may determine practices that persist for a lifetime. These findings may have important implications for medical education and the quality and cost of medical care.

Activator headgear therapy

A method of treatment is described using an activator and cervical headgear simultaneously to correct malocclusions of the Class II, Division 1 type. The case reports of ten treated patients are used to demonstrate the effects of the application of this technique. Changes in the dentition and facial skeleton were analyzed and the significance of the different responses to the application of the same appliances assessed. The hypothesis proposing that a simultaneous application of both appliances may result in a number of desirable effects greater than that induced by each individual appliance is examined. The hypothetical basis for the application of this technique is partially substantiated by the clinical observations. Within a period of about 1 year, correction of the Class II molar occlusion to a Class I molar occlusion is obtained, with a simultaneous reduction of overbite and overjet. Skeletal changes were found to be variable and related to facial type and the rate of facial growth. Brachyfacial and mesofacial types responded most favorably to treatment. The most favorable effects were observed when there was a large quantitative mandibular growth and brachyfacial or mesofacial growth pattern. In dolichofacial types with a slow mandibular growth rate, mandibular rotation was found to be clockwise; cervical traction appears contraindicated, and a combination of activator with occipital medium to high pull is considered more appropriate.

Human neutrophil elastase modulates platelet function by limited proteolysis of membrane glycoproteins

During blood coagulation human polymorphonuclear leukocytes release elastase in amounts that can exceed 100 nmol/liter. We therefore studied the effect of elastase on platelet structure and function. Physiologic concentrations of elastase specifically inhibited thrombin-induced platelet aggregation and ristocetin-induced agglutination of washed platelets in a time- and dose-dependent manner. This was associated with a decrease in the number of high affinity thrombin binding sites on the platelet surface (analysis by "Ligand" program) from 31 per platelet to 12 per platelet (P less than 0.05). As analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, treatment of 3H-labeled platelets with elastase resulted in a decrease in the percent glycoprotein at 130,000-150,000 Mr = and an increase in the percent protein at Mr = 102,000. The supernatant from elastase-treated platelets contained a Mr = 88,000 glycoprotein not found in the supernatant from untreated platelets. Immunoprecipitation studies with monoclonal antiglycoprotein Ib demonstrated that treatment of whole platelets with physiologic concentrations of elastase resulted in proteolytic cleavage of glycoprotein Ib. Elastase treatment of glycoprotein immunoisolated with monoclonal antiglycoprotein Ib antibody resulted in formation of a glycopeptide with the same electrophoretic mobility as the Mr = 102,000 membrane-related glycopeptide. In contrast, analysis by Western blot technique using antiglycoprotein IIb and IIIa antibodies demonstrated that elastase did not degrade glycoproteins IIb or IIIa. We conclude that elastase inhibition of thrombin-induced platelet stimulation is accompanied by (a) a reduction in the number of thrombin binding sites per platelet and (b) proteolysis of glycoprotein Ib.

Aspirin inhibits vascular plasminogen activator activity in vivo. Studies utilizing a new assay to quantify plasminogen activator activity

Vascular or tissue-type plasminogen activator (TPA) is a key enzyme in physiologic fibrinolysis. To study the role of prostaglandins in modulating the synthesis and release of TPA in vivo, we prospectively studied the effect of aspirin (650 mg/d X 2) on TPA activity in 13 human subjects before and after 10 min of forearm venous occlusion. TPA activity was quantified by a newly developed enzyme-linked immunosorbent assay that both measures and differentiates between TPA and urokinase (UK)-like plasminogen activator activity. This assay is based on the observation that the concentration of alpha 2-plasmin inhibitor-plasmin complexes in Reptilase-clotted plasma increases linearly in proportion to the amount of activator added. Resting TPA activity was higher in women than in men (0.56 +/- 0.59 vs. 0.15 +/- 0.11 U/ml, P = 0.049). Venous occlusion induced an eightfold rise in TPA activity in women (to 4.5 U/ml, P = 0.006) and a 15-fold rise in men (to 2.28 U/ml, P = 0.004), whereas UK activity was not detected. Aspirin inhibited the rise in TPA activity after venous occlusion by 69% in men (P = 0.004) and 70% in women (P = 0.014). In contrast, aspirin had no effect on pre- or post-occlusion hematocrits or Factor VIII-related antigen levels. There was no correlation between plasma salicylate level and percentage inhibition of TPA. Neither exogenous aspirin (0-1 microgram/ml) nor salicylate (0-70 micrograms/ml) inhibited the generation of alpha 2-plasmin inhibitor-plasmin complexes by exogenous TPA or interfered with the assay system. We conclude that aspirin may have an antifibrinolytic effect in man that has not been previously described.

The interaction of sodium nitroprusside with human endothelial cells and platelets: nitroprusside and prostacyclin synergistically inhibit platelet function

Sodium nitroprusside (NP) is a potent vasodilator that also inhibits platelet aggregation. To test the hypothesis that NP causes both of these effects by altering the balance between prostacyclin (PGI2) produced by endothelial cells and thromboxane A2 (TXA2) produced by platelets, we incubated each of these cell types with NP for 5 minutes and assayed the PGI2 and TXA2 produced. NP at pharmacologically achieved doses (0.01--30 micrograms/ml) inhibited platelet aggregation and resultant TXA2 synthesis in a dose- and time-dependent manner (p less than 0.001). The inhibition was not dependent on cAMP production, external calcium concentration, or suppression of TXA2 synthesis. NP did not alter the production of PGI2 by cultured human endothelial cells as measured by radioimmunoassay for 6-Keto-PGF1 alpha, the stable hydrolysis product of PGI2. However, supernates of NP-treated endothelial cells containing low, noninhibitory concentrations of NP unexpectedly inhibited platelet aggregation. This inhibition of platelet aggregation was due to synergy between PGI2 (0.1--3 nM) and NP (p interaction less than 0.03). The synergistic inhibition by NP and PGI2 of platelet aggregation and TXA2 synthesis in vivo may explain some of the beneficial actions of NP in the treatment of hypertension and congestive heart failure.

The urban emergency department: the issue of professional responsibility

The urban emergency department is routinely asked to manage not only medical emergencies, but also a great variety of social emergencies. This situation is caused in part by budgetary constraints which prevent other agencies from providing 24-hour coverage. In an age of instant access to computerized information, these conditions often result in ethical and legal problems of extreme complexity. A case is presented which raises the issues of confidentiality and liberty in the fiduciary relationship between doctor and patient. The concept of personal care is found to be paramount.

Nitroglycerin stimulates synthesis of prostacyclin by cultured human endothelial cells

Nitroglycerin (NTG), the agent most commonly used to treat acute angina pectoris, is a vasodilator whose mechanism of action remains unknown. We hypothesized that NTG might induce endothelial cells to synthesize prostacyclin (PGI(2)), a known vasodilator and inhibitor of platelet aggregation. Therefore, cultured human endothelial cells were incubated with NTG at various concentrations for 1-3 min. PGI(2) biologic activity in the endothelial cell supernates was assayed by inhibition of platelet aggregation in vitro. The concentration of 6-keto-PGF(1alpha), the stable hydrolysis product of PGI(2), was measured by specific radioimmunoassay.NTG alone significantly inhibited platelet aggregation and thromboxane A(2) synthesis only at suprapharmacologic concentrations (>/=1 mug/ml). However, when NTG at clinically attainable concentrations (0.1-10 ng/ml) was incubated with endothelial cells, the endothelial cell supernates inhibited platelet aggregation in a dose-dependent manner. The inhibitor was heat labile. Radioimmunoassay of the endothelial cell supernates for 6-keto-PGF(1alpha) demonstrated that NTG elicited dose-dependent increments in the synthesis of PGI(2) by endothelial cells, ranging from 13% at NTG 10 pg/ml to 63% at NTG 10 ng/ml (P < 0.01, n = 10). Pretreatment of endothelial cells with either aspirin (50 muM for 120 min) or the prostacyclin synthetase inhibitor 15-hydroperoxyarachidonic acid (20 mug/ml for 15 min) abolished production of the platelet inhibitory substance. Synergy between NTG and PGI(2) in the inhibition of platelet aggregation was not present at clinically attainable concentrations of NTG.Thus, NTG at clinically attainable concentrations causes a dose-dependent increase in PGI(2) synthesis by endothelial cells. If this phenomenon occurs in vivo, the PGI(2) produced could ameliorate myocardial ischemia by causing peripheral vasodilation and decreasing cardiac work, inhibiting platelet aggregation and thromboxane A(2) synthesis, and possibly reversing coronary artery vasospasm.