[Image quality parameters characterizing radiologic imaging systems]

The image quality of imaging systems can be characterized by a number of parameters, such as the easy to appreciate concepts of resolution or contrast or such precisely defined and measurable characteristics as the modulation transfer function or the noise spectrum. The meaning of these qualities and their interrelation are discussed. From these parameters, we can derive one of the most important characteristics for the description of the physical image quality = the signal-to-noise ratio.

Isoproterenol impairs the rat coronary vasculature: effects of angiotensin-converting enzyme inhibition

The purpose of the present study was to evaluate whether in addition to its myocardial effects, chronic beta-adrenergic stimulation with isoproterenol could modify the coronary vasculature. For this purpose, rats were treated for 2 weeks with isoproterenol, and the hearts were isolated for determination of the minimal coronary vascular resistance under maximal vasodilation and then perfused-fixed for morphometry of the coronary arteries. In addition, because isoproterenol stimulates the renin-angiotensin system (RAS), the effects of angiotensin-converting enzyme (ACE) inhibition on the coronary vasculature were assessed. Isoproterenol increased heart weight by 65% and minimal coronary resistance by 55%. This effect was associated with medial thickening in intermediate (32%) and large coronary arterioles (26%). Cilazapril, a long-acting ACE inhibitor, completely prevented the medial thickening induced by isoproterenol and normalized the minimal coronary resistance. We conclude that impairment of the rat coronary vasculature induced by chronic beta-adrenergic stimulation might be in part mediated by activation of the RAS.

Left ventricular outflow tract obstruction in patients with hypertrophic cardiomyopathy: increase in gradient after exercise

To define alterations in the magnitude of the left ventricular outflow tract gradient during supine exercise, 10 patients with hypertrophic obstructive cardiomyopathy were studied under basal conditions and during exercise and recovery with simultaneous invasive hemodynamic measurements, particularly of the peak to peak systolic pressure gradient across the left ventricular outflow tract. Basal outflow pressure gradient ranged from 0 to 89 mm Hg (average 37.4 +/- 9.6). No increase was observed during 5 min of exercise (average 29.6 +/- 10 mm Hg, range 0 to 91; p = NS), even though arterial blood pressure, heart rate and cardiac index increased significantly in association with a decrease in peripheral vascular resistance. However, a rapid and highly significant increase in left ventricular outflow gradient occurred after exercise was completed (average 83.5 +/- 11.4 mm Hg, range 10 to 130; p less than 0.001), while arterial blood pressure, heart rate and cardiac index closely approached basal levels and total peripheral vascular resistance increased. In contrast to previous assumptions regarding the behavior of the outflow gradient in hypertrophic cardiomyopathy, obstruction to left ventricular outflow increases after rather than during supine exercise. Rapid changes in preload during recovery represent the most likely explanation for the postexercise development of outflow obstruction. New considerations regarding the mechanisms of sudden cardiac death and the therapeutic approach in patients with hypertrophic cardiomyopathy may result from this pathophysiologic observation.

Imaging characteristics of different mammographic screens

A study of mammography systems with green-emitting screens was conducted to determine how the image quality parameters (apart from dose requirement), such as modulation transfer function (MTF) and Wiener spectrum (WS), depend on the dye content of the compound and coating weight of the screen. In addition, the contribution to total noise of the individual components, i.e., film, screen, and quantum noise, was studied. The quantities derived from MTF and WS, namely detective quantum efficiency (DQE) and noise equivalent quanta (NEQ), were also investigated in regard to their dose dependency. It can be demonstrated that the MTF of the screens becomes more favorable when the dye content is increased, while noise is not significantly affected. This suggests the use of a mammography screen capable of greater detail recognition, requiring at least double the dose of today's conventional systems with approximately 80 microGy system dose. On the other hand, the manufacture of a screen with about 60% of the dose of the conventional system is possible with very little loss in image quality. For the systems in common use today (80 microGy), quantum noise represents a considerable share of the total noise at low spatial frequencies, whereas in high spatial frequencies, the graininess of the film dominates quantum noise and screen structure.

Effects of chronic aortic coarctation on atherosclerosis and arterial lipid accumulation in the Watanabe hereditary hyperlipidemic (WHHL) rabbit

The effects of high blood pressure on atherosclerosis were examined in the Watanabe heritable hyperlipidemic (WHHL) rabbit. For this purpose, the subdiaphragmatic aorta of rabbits was partially ligated (coarctation) to increase blood pressure. Atherosclerosis was assessed 4 months later by morphometric analyses and quantitation of arterial lipids. Results were compared to control WHHL rabbits with matched plasma triglycerides and cholesterol levels. A marked increase in atherosclerotic lesions was observed in the thoracic aorta of the hypertensive rabbits without qualitative changes in its morphometric features. The cross sectional area of the atherosclerotic plaques of the ascending and descending aorta in the hypertensive rabbits was two- and six-times larger than in normotensive rabbits, respectively. Lesions represented 12.0% +/- 3.5% of the total medial cross sectional area of the descending aorta of normotensive rabbits, versus 45.0% +/- 5.7% in hypertensive rabbits. No lesions were observed downstream of the coarctation in hypertensive rabbits, nor in the normotensive rabbits. Accumulation of cholesterol and choline-containing phospholipids in the descending aorta of hypertensive rabbits was increased 3.2- and 1.5-fold, respectively, when compared to normotensive rabbits. Hypertension did not change the unesterified cholesterol/total cholesterol and sphingomyelin/lecithin + lysolecithin molar ratios. In conclusion, chronic coarctation enhances the atherosclerotic response in WHHL rabbits in the high blood pressure compartment, and reduces the variability of this response.

Physiological asymmetry in etiolated pea epicotyls: relation to patterns of auxin distribution and phototropic behavior

Etiolated pea seedlings require transformation of Pr phytochrome to Pfr before they display optimal phototropic response to unilateral blue light. This study investigates the possible role of auxin transport in explaining these phenomena. Labeled [2-14C]IAA applied to the intact terminal buds of dark-grown and red light-treated pea seedlings was measured 210 min later on the shaded and illuminated sides of the epicotyl as a function of direction and duration of irradiation with blue light. Totally darkened epicotyls show an asymmetry in distribution of radioactivity in the upper growth zone of the epicotyl, in favor of the side under the concave part of the apical hook. Red light, which greatly potentiates curvature toward subsequent unilateral blue light, lowers this asymmetry. Blue light directed to the epicotyl of red-pretreated plants in a plane parallel to the hook and from the side bearing the convex portion of the hook induces positive phototropic curvature as well as a surplus of radioactivity on the illuminated side of the upper epicotyl and on the shaded side of the lower growth zone of the epicotyl. Light directed to the side bearing the concave part of the hook also causes an accumulation of counts in the upper part of the lighted side but produces neither curvature of the epicotyl nor accumulation of counts in the lower shaded side. Because of this built-in physiological asymmetry in the growth zone just below the apical hook, it is difficult to explain the effects of red and blue light on curvature in terms of patterns of auxin distribution alone.

Specific inflammatory cytokines regulate the expression of human monocyte 15-lipoxygenase

Arachidonate 15-lipoxygenase (arachidonate:oxygen 15-oxidoreductase, EC 1.13.11.33) is a lipid-peroxidating enzyme that is implicated in oxidizing low density lipoprotein to its atherogenic form. Monocyte/macrophage 15-lipoxygenase is present in human atherosclerotic lesions. To pursue a basis for induction of the enzyme, which is not present in blood monocytes, the ability of relevant cytokines to regulate its expression was investigated. Interleukin 4 (IL-4), among 16 factors tested, specifically induced 15-lipoxygenase mRNA and protein in cultured human monocytes. Interferon gamma and hydrocortisone inhibited this induction. High-performance liquid chromatography analysis of lipid extracts from IL-4-treated monocytes detected 15-lipoxygenase products esterified to the cellular membrane lipids, indicating enzymatic action on endogenous substrates. Stimulation of IL-4-treated monocytes with calcium ionophore or opsonized zymosan A enhanced the formation of 15-lipoxygenase products. These data identify IL-4 and interferon gamma as physiological regulators of lipoxygenase expression and suggest an important link between 15-lipoxygenase function and the immune/inflammatory response in atherosclerosis as well as other diseases.

Protective effect of cilazapril on the cerebral circulation

The goal of an antihypertensive treatment is to prevent "end-organ" damage. Cerebral vascular complications are among the most important because they are life threatening and can occur even at an early stage of the disease. Recently, it has been shown that cilazapril can decrease the mortality of stroke-prone rats, suggesting a decrease in the incidence of strokes, which occur spontaneously in these animals. The present article reviews the different functional and morphological changes that may explain the cerebral protective effects of cilazapril, such as the normalization of cerebral vascular reserve, decrease in the media, increase in the external diameter, and normalization of the mechanics and endothelial function of cerebral arterioles. In addition, the inhibition by cilazapril of injury-induced proliferation of smooth muscle cells and the infiltration of the endothelium by macrophages could prevent the development of atherosclerosis.

Cilazapril inhibits wall thickening of vein bypass graft in the rat

Venous grafts implanted in the systemic circulation progressively undergo wall thickening, a phenomenon thought to be responsible for late saphenous graft disease after bypass surgery. Angiotensin converting enzyme (ACE) inhibitors recently have been shown to prevent myointimal thickening after arterial injury. Thus, the goal of the present study was to test the effects of ACE inhibition in a rat model of venous graft. For this purpose, a segment of jugular vein was interposed in the right carotid artery of normotensive rats that received either placebo or 10 mg/kg/day cilazapril, a long-acting ACE inhibitor. Three weeks later, the venous grafts and the implanted carotid arteries were fixed under perfusion and embedded for morphometric analysis. In the control group, the wall of the venous graft thickened dramatically compared with the nonimplanted contralateral jugular vein (up to 20 times increase in total cross-sectional area). On the arterial side, thickening of the wall and a neointima also were observed, most likely because of the surgical arterial injury. Cilazapril decreased by 33% (p less than 0.05) and 26% (p less than 0.01) the total cross-sectional area of the wall of the venous grafts and of the carotid arteries, respectively. Thus, these results suggest a role of the renin-angiotensin system in the early process of venous graft thickening. This study also suggests that ACE inhibitors could be a new therapeutic means to prevent late saphenous graft disease.

Endothelial dysfunction and subendothelial monocyte macrophages in hypertension. Effect of angiotensin converting enzyme inhibition

Hypertension is associated with an impairment of endothelium-dependent relaxation. The angiotensin converting enzyme inhibitors captopril and cilazapril can prevent this endothelial dysfunction. We recently observed that long-term treatment with cilazapril could also prevent subendothelial infiltration by mononuclear cells in spontaneously hypertensive rats. This prompted us to examine whether, in spontaneously hypertensive rats, endothelial dysfunction and subendothelial infiltration by mononuclear cells are associated. These cells were characterized as monocyte macrophages. Infiltration by monocyte macrophages was quantified by morphometry. Endothelial function was estimated by calculating serotonin ratio (maximal contraction to serotonin on isolated arterial rings with endothelium over maximal contraction on paired rings without endothelium). The regional distribution of endothelial dysfunction and subendothelial monocyte macrophages was similar. Both were maximal in the carotid artery, less in the aorta, and nonexistent in the renal artery. A 2-week treatment with cilazapril decreased both endothelial dysfunction (serotonin ratio decreased by 32%) and the number of subendothelial monocyte macrophages in the aorta, which decreased by 38%. We conclude that in spontaneously hypertensive rats, endothelial dysfunction and subendothelial monocyte macrophage infiltration are associated and that cilazapril can decrease both. The observation that angiotensin converting enzyme inhibitors affect subendothelial accumulation of monocyte macrophage may lead to a better understanding of the mechanism of action of this class of drugs.

Vascular protection with cilazapril

The hypertrophy of the media of coronary arteries associated with hypertension reduces cross-sectional area and limits vascular reserve. Cilazapril 10 mg/kg daily decreased cardiac hypertrophy, and decreased minimal coronary vascular resistance by 40% when administered to spontaneously hypertensive rats (SHR) at the onset of hypertension. After hypertension had developed, cilazapril restored arterial pressure to normal and increased the maximal coronary blood flow in isolated perfused hearts by 96%, which was probably a result of a marked decrease in medial hypertrophy of the coronary arteries. Similarly, cilazapril improved cerebral vascular reserve in the mesenteric and renal arteries of SHR. In the rat model of vascular injury produced by ballooning, cilazapril 10 mg/kg daily demonstrated a marked preventive effect on the myointimal proliferation that resulted in untreated controls, a phenomenon responsible for restenosis in humans after arterial angioplasty. Although this effect occurred with usual antihypertensive dosages in rats, it appeared to be independent of the decrease in arterial pressure since effective antihypertensive dosages of verapamil did not prevent neointima formation. In view of the clinical potential for preventing restenosis after coronary angioplasty, 2 multicentre trials of cilazapril are ongoing to test this hypothesis.

Serotonin organelles of rabbit platelets contain synaptophysin

Synaptophysin, an integral membrane protein of synaptic vesicles in nerve terminals and a class of small translucent vesicles in neuroendocrine cells, was detected in intact rabbit platelets by immunoblotting, immunofluorescence staining and immuno-electron microscopy. In a highly purified preparation of serotonin organelles isolated from rabbit platelets, synaptophysin was enriched approximately 10-15-fold over platelet homogenate. About 80% of total platelet synaptophysin was present in this purified fraction. The apparent molecular mass (approximately 38 kDa) and the extent of glycosylation of platelet-derived synaptophysin was more similar to the neuronal than to the neuroendocrine form of the protein. Immunofluorescence microscopy revealed that synaptophysin was compartmentalized in intact rabbit platelets and immuno-electron microscopy of subcellular fractions showed that it was localized exclusively to the membrane surface of serotonin organelles. No synaptophysin-like immunoreactivity was detected in platelets from other species such as human, guinea pig and rat. Another integral membrane protein of synaptic vesicles, p65, and a family of synaptic vesicle-associated phosphoproteins, the synapsins, were not detected in platelets of any species tested. These results provide evidence that serotonin organelles from rabbit platelets share a subset of protein components with synaptic vesicles from neurons. Synaptophysin in serotonin organelles from rabbit platelets, as suggested for small synaptic vesicles in neurons, might play a role in the formation of protein channels for the exocytotic release of serotonin.

Effects of angiotensin converting enzyme inhibitors and of hydralazine on endothelial function in hypertensive rats

The function of the endothelium is impaired in hypertension. In spontaneously hypertensive rats (SHR), acetylcholine-induced relaxation is decreased and serotonin-induced constriction is increased. The goal of our study was to evaluate the effect of a long-term treatment with cilazapril, a new angiotensin converting enzyme inhibitor, or hydralazine, a vasodilator, on the endothelium-dependent responses in aorta of SHR. Wistar-Kyoto rats were used as normotensive reference. Isolated aortic rings with or without endothelium were suspended in organ chambers. The rings with intact endothelium were contracted with norepinephrine. Acetylcholine-induced relaxation was markedly enhanced by cilazapril treatment. The tension achieved at maximal relaxation was 8 +/- 4% of norepinephrine contraction in the cilazapril-treated SHR versus 55 +/- 5% in the untreated SHR (p less than 0.001). Hydralazine had no significant effect. The effect of serotonin was also markedly modified by cilazapril. In untreated SHR, serotonin induced the release of a vasoconstrictor substance by the endothelium as assessed by the ratio of maximal tension induced by serotonin in rings with endothelium over maximal tension in rings without endothelium, which was greater than 1. This ratio was reversed in cilazapril-treated SHR but not in hydralazine-treated SHR. Captopril had effects similar to cilazapril. Finally, evaluation of carotid arteries showed that cilazapril also prevented morphological changes of the intima in SHR (i.e., infiltration by mononuclear cells). We conclude that angiotensin converting enzyme inhibitors prevent the functional and morphological alterations in endothelium that are found in hypertension and speculate that this action might participate in their antihypertensive effect.

Oxygenation of biological membranes by the pure reticulocyte lipoxygenase

We find that the reticulocyte lipoxygenase can oxygenate rat liver mitochondrial membranes, beef heart submitochondrial particles, rat liver endoplasmic membranes, and erythrocyte plasma membranes (inside-out and right side-out ghosts) without prior action of a phospholipase. After alkaline hydrolysis of the ester lipids, the main products were identified as 15S-hydro(pero)xy-5Z,8Z,11Z,13E-eicosatetr aenoic acid, 17S-hydro(pero)xy-4Z,7Z,10Z,13Z,15E, 19Z,-docosahexaenoic acid, 13S-hydro(pero)xy-9Z,11E-octadecadienoic acid, 9(S/R)-hydro(pero)xy-10E,12Z-octadecadienoic acid as well as the two all-E hydro(pero)xy octadecadienoic acid isomers. At low membrane concentrations (1 mg of protein/ml), the enzyme maintains a high stereospecificity for the S-configuration, but at higher concentrations (20 mg/ml), the products were virtually racemic. Addition of the antioxidant 2,6-ditert-butyl-p-cresol counteracted this tendency to lose stereospecificity. During these enzyme-catalyzed reactions, substantially more oxygen is consumed than can be accounted for as the hydro(pero)xy products. This discrepancy is due to secondary reactions which lead to the decomposition of the primary oxygenation products, the hydroperoxy lipids, and to oxidative modifications of membrane proteins. These data indicate that the reticulocyte lipoxygenase can oxygenate polyenoic fatty acids in various types of biological membrane and that the oxidative modifications are not restricted to the membrane lipids. The results are discussed in terms of the proposed role of the enzyme in the breakdown of mitochondria and other intracellular organelles during the maturation of red blood cells.