Down-regulation of protein kinase C potentiates atrial natriuretic peptide-stimulated cGMP accumulation in vascular smooth-muscle cells.

It has been reported that atrial natriuretic peptide (ANP) produces inositol phosphates and diacylglycerol in vascular smooth muscle cells (VSMC). The purpose of this study is to investigate whether diacylglycerol produced by ANP affects ANP-induced cyclic GMP (cGMP) accumulation through the activation of protein kinase C. Short-term (15 min) treatment of rat aortic VSMC with protein kinase C activating phorbol 12-myristate 13-acetate (PMA, 100 nM) decreased ANP (100 nM)-induced cGMP accumulation by 34.7% in the presence of IBMX (0.5 mM). However, the long-term (24 h) treatment to decrease the activity of protein kinase C led to an enhancement of the cGMP accumulation by 69.6% compared with that of control VSMC. There were no significant differences in Bmax and Kd for ANP and ANP-dependent particular guanylyl cyclase activity between long-term PMA-treated and control VSMC. In the present study, we show that the activation of protein kinase C attenuates the cGMP accumulation induced by ANP and that down-regulation of protein kinase C results in an enhancement of the cGMP accumulation. These data are consistent with the role of protein kinase C as a negative regulator in ANP-receptor/guanylyl cyclase pathway.

High glucose attenuates insulin-induced mitogen-activated protein kinase phosphatase-1 (MKP-1) expression in vascular smooth muscle cells.

The mechanisms for the effect of hyperglycemia on insulin-induced mitogenesis were investigated using rat vascular smooth muscle cells (VSMC). VSMC were preincubated in serum-free medium with low (5 mM) glucose (LG condition) or high (25 mM) glucose (HG condition), and examined for DNA synthesis using bromodeoxyuridine (BrdUrd) incorporation. Mitogen-activated protein kinase (MAPK) activity and MAPK phosphatase (MKP-1) protein expression were detected by Western blot analysis. Phosphatidylinositol 3-kinase (PI-3K) activity was detected by thin layer chromatography. Insulin induced a dose-dependent increase in BrdUrd incorporation (123.3+/-2.6% over basal level with 1 microM insulin) in the LG group and this effect was significantly enhanced (161.6+/-10.4% over basal level) in the HG group. In the LG group, MAPK activity was transient with a peak activation (137.4+/-11.2% over basal level) after 10 min exposure to 100 nM insulin. In the HG group, the MAPK activity was significantly potentiated (two-fold compared to the LG group) and was sustained even after 60 min. Insulin also induced PI-3K activity and MKP-1 expression, both of which were blocked by the PI-3K inhibitor wortmannin. In the HG group, insulin-induced PI-3K and MKP-1 expression was almost abolished. In conclusion, high glucose enhances insulin-induced mitogenesis associated with the potentiation of insulin-stimulated MAPK activity in VSMC. These effects of glucose might in part be due to the attenuation of MKP-1 expression through the blockage of the insulin-PI-3K signal pathway.

Enhanced expression of heparin-binding EGF-like growth factor and its receptor in hypertrophied left ventricle of spontaneously hypertensive rats.

OBJECTIVES: Although heparin-binding epidermal growth factor-like growth factor (HB-EGF) is thought to produce hypertrophy in isolated cardiomyocytes via an autocrine mechanism, the pathophysiological role of HB-EGF, in myocardial hypertrophy in vivo, is not yet known. To investigate the involvement of HB-EGF in cardiac remodeling associated with hypertension in vivo, we assayed the expression of HB-EGF mRNA and protein in the left ventricle (LV) during the development of left ventricular hypertrophy in spontaneously hypertensive rats (SHR). METHODS: Prior to sacrifice and assay of HB-EGF and EGF-receptor (EGF-R) mRNA, morphologic and hemodynamic variables were measured in SHR and in age-matched Wistar Kyoto rats (WKY). At 5, 9 and 12 weeks of age, rats were killed, their hearts were removed, and the expression of HB-EGF and EGF-R mRNA and protein were measured. In addition, SHR and WKY were treated with enalapril, atenolol, or both for 4 weeks. RESULTS: In untreated SHR, double products (i.e. systolic blood pressure (sBP) multiplied by heart rate (HR), an index of mechanical load, peaked at 9 weeks. Expression of HB-EGF mRNA was also observed to peak in these animals at 9 weeks, while expression of EGF-R mRNA increased from 5 to 9 weeks, but remained constant thereafter. In untreated WKY, double products and EGF-R mRNA expression did not change over time, whereas the level of HB-EGF message increased gradually. Antibody to HB-EGF reacted primarily with myocyte membranes in SHR, whereas antibody to EGF-R reacted mainly with interstitial cells in these animals. The angiotensin-converting enzyme inhibitor, enalapril, markedly decreased sBP in SHR, whereas the beta 1-adrenoreceptor antagonist, atenolol, significantly decreased HR. While neither alone affected the expression of HB-EGF mRNA, their combination significantly reduced the expression of HB-EGF mRNA, as well as double products, in these rats, but had no effect on expression of EGF-R mRNA. CONCLUSIONS: The enhanced expression of HB-EGF mRNA and protein in LV of SHR suggest that this growth factor may play an important role during the early development of LV hypertrophy and cardiac fibrosis in SHR. The association between double products and HB-EGF expression suggest that the latter may be induced by increased mechanical load and may contribute, in turn, to cardiac remodeling.

Regulation of type V adenylyl cyclase by PMA-sensitive and -insensitive protein kinase C isoenzymes in intact cells.

Abstract Type V adenylyl cyclase (AC) was stably over-expressed in HEK293 cells (293AC-V). Forskolin-stimulated cAMP accumulation in 293AC-V was 5 times as great as that in control cells. PMA, a protein kinase C (PKC) activator, enhanced cAMP accumulation in 293AC-V cells dose-and time-dependently and this enhancement was abolished by staurosporine. Insulin also enhanced cAMP accumulation in 293AC-V cells. Co-transfection of PKC-zeta, but not PKC-alpha, potentiated the effects of insulin. These data suggest that type V AC activity is regulated in cells by PKC isoenzymes through different extracellular stimuli.

Isoform-dependent activation of adenylyl cyclase by proteolysis.

Recent findings have suggested that the cellular proteolytic system plays a major role in the regulation of various intra- and extra-cellular signaling. It was previously shown that proteolytic treatment of adenylyl cyclase leads to the activation of this enzyme. We demonstrate that this activation occurs in an adenylyl cyclase isoform-dependent manner. The type II isoform was strongly activated (approximately 500%), the type III isoform was modestly activated (approximately 30%),and the type V isoform was inhibited by trypsin. Activation of type II adenylyl cyclase occurred in trypsin dose- and time-dependent manners and was blocked by a trypsin inhibitor in a dose-dependent manner. Other proteases, such as thrombin and plasminogen, similarly activated the type II isoform, but not the others. Our data suggest that proteolytic activation is an isoform- and thus cell type-dependent mechanism of altering adenylyl cyclase catalytic activity.

Glucose modifies the cross-talk between insulin and the beta-adrenergic signalling system in vascular smooth muscle cells.

BACKGROUND: Abnormalities in the vascular function of insulin are observed in insulin resistance, and hyperglycaemia is one of the important factors inducing insulin resistance. OBJECTIVE: To investigate the role of glucose in the interaction of insulin and beta-adrenergic signalling systems in vascular smooth muscle cells (VSMC). METHODS: After cells were treated with D-glucose (525 mmol/l) and insulin (100 nmol/l), adenylyl cyclase activity was measured in the presence of isoproterenol, forskolin, and cholera toxin. Assays for insulin-induced activities of insulin receptor substrate (IRS)-1, phosphoinositide 3-kinase (PI3-K) and mitogen-activated protein kinase (MAPK) were performed. RESULTS: In the presence of low glucose concentrations (5 mmol/l), insulin enhanced isoproterenol-, forskolin- and cholera toxin-stimulated adenylyl cyclase activities. This stimulatory effect was abolished by PI3-K inhibitors, wortmannin, or LY294002. In contrast, in the presence of high glucose concentrations (25 mmol/l), insulin attenuated isoproterenol-stimulated activity but not cholera toxin- or forskolin-stimulated activity. Insulin-stimulated activities of IRS-1 and PI3-K, but not MAPK activity, were also attenuated in the presence of high concentrations of glucose. The MAPK kinase inhibitor, PD98059, abolished the inhibitory effect of insulin on the beta-adrenergic signalling system. Troglitazone and pioglitazone prevented this inhibitory effect of insulin by restoring IRS-1 and PI3-K activities. CONCLUSIONS: In the presence of low glucose concentrations, insulin stimulates the beta-adrenergic signalling system through the IRS-1/PI3-K pathway. However, in the presence of high glucose concentrations, the effect of insulin is switched to an inhibitory one, through the MAPK pathway. Our finding suggests that high glucose concentrations modify the cross-talk between insulin and the beta-adrenergic signalling systems in VSMC.

Clinical usefulness of scintigraphy with 99mTc-galactosyl-human serum albumin for prognosis of cirrhosis of the liver.

UNLABELLED: Scintigraphy with 99mTc-diethylenetriamine pentaacetic acid-galactosyl-human serum albumin (99mTc-GSA) is useful for evaluating hepatic functional reserve. We assessed the clinical usefulness of this technique, including its value in establishing a prognosis, in patients with cirrhosis of the liver. METHODS: Scintigraphy with 99mTc-GSA was performed in 10 healthy subjects, 42 patients with chronic hepatitis and 158 patients with cirrhosis. Computer acquisition of gamma camera data were started just before the injection of 99mTc-GSA. Time-activity curves for the heart and liver were generated from regions of interest (ROIs) for the heart and the entire liver. A receptor index was calculated by dividing the radioactivity of the liver ROI by that of the liver-plus-heart ROI 15 min after the injection. An index of blood clearance was calculated by dividing the radioactivity of the heart ROI at 15 min by that of the heart ROI at 3 min. RESULTS: The median receptor index was lower in patients with cirrhosis than in patients with chronic hepatitis or in healthy subjects, and the median index of blood clearance was higher. The receptor index was significantly lower when a complication (varices, ascites) was present. The index of blood clearance was significantly higher when a complication (varices and ascites) was present. Correlation of the two indices with classic indicators for functional reserve was significant. On the basis of the receptor index, the patients with cirrhosis were divided into two groups of roughly equal size: group A, receptor index over 0.85, and group B, receptor index 0.85 or less. On the basis of the index of blood clearance, the patients with cirrhosis were divided into two groups of roughly equal size: group A, index of blood clearance < 0.70, and group B, index of blood clearance > or = 0.70. The cumulative survival rates were lower in group B than in group A. CONCLUSION: Scintigraphy with 99mTc-GSA is clinically useful, especially in establishing the prognosis of patients with cirrhosis of the liver.

Multiplicity in type V adenylylcyclase: type V-a and type V-b.

Type V mammalian adenylylcyclase cDNA was originally isolated from two animal species, the dog and rat. The amino acid sequences from the two species are highly homologous, but completely different in the putative N-terminal, cytoplasmic region. Northern blot analysis using oligonucleotide probes unique to either of the two clones has revealed that the two forms of type V adenylylcyclase mRNA, canine form (= type V-a) and rat form (= type V-b), are co-expressed as splicing variants in both species. Genomic Southern blot analysis has suggested that the two forms are the products of a single gene. When overexpressed, however, deletion of the N-terminal domain did not alter any biochemical properties. Thus multiple splicing variants with unique N-terminal amino acid sequences of type V adenylylcyclase can be generated from a single gene, however, biochemical properties of these variants may not be different.

Changes in caveolin subtype protein expression in aging rat organs.

It is now accepted that caveolin plays a key role in signal transduction by directly binding to and regulating the function of molecules involved in transmembrane signaling, such as ras, suggesting that the amount of caveolin within cells may be an important factor in determining the cellular signaling. We investigated the ontogenic changes in the protein amount of caveolin subtypes, as well as ras protein expression in various organs (the heart, lungs, and muscles) obtained from aging rats (neonates, young and old adults). Our results demonstrated that caveolin protein expression changed ontogenically in a subtype-dependent manner. In lungs, for example, caveolin-1 expression changed in an opposite manner to caveolin-3 expression, while in the heart caveolin-1 and -3 changed in parallel. Ras expression showed an ontogenic increase in lungs and a decrease in muscles, which were both parallel to caveolin-1 expression. Our results suggest that the regulation of transmembrane signaling by caveolin may differ among developmental stages and caveolin subtypes.

Prognostic predictive value of 18F-fluorodeoxyglucose positron emission tomography for patients with pancreatic cancer.

18Fluorine-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) is a unique imaging diagnostic tool to evaluate glucose metabolism and hexokinase activity which may reflect the aggressiveness of a tumor. Thirty-seven patients with primary pancreatic cancer were evaluated with 18F-FDG-PET. Thirteen patients underwent resection for the pancreatic cancer and 24 patients had unresectable tumors. The standardized uptake values (SUV) of 18F-FDG in the primary tumors were calculated. No correlations were found between the SUV in the tumors and the metastatic status to the peritoneal/liver, TNM factors/stage, or resectability. The patients were divided into 2 groups with high and low SUV, with the cut-off value being 3.0 (median SUV value of 37 cases). No differences in the probability of survival were observed between the 2 groups in the patients with resectable tumors. However, in the patients with unresectable tumors, those in the high SUV group had a significantly shorter prognosis than those in the low SUV group. Moreover, a multivariate analysis of survival indicated that SUV is an independent prognostic factor for patients with unresectable pancreatic cancer.

Lovastatin prevents angiotensin II-induced cardiac hypertrophy in cultured neonatal rat heart cells.

Angiotensin II activates p21ras, and mediates cardiac hypertrophic growth through the type 1 angiotensin II receptor in cardiac myocytes. An inhibitor of 3-hydroxy-3-methyglutaryl-coenzyme A (HMG-CoA) reductase has been shown to block the post-translational farnesylation of p21ras and inhibit protein synthesis in several cell types. Primary cultures of neonatal cardiac myocytes were used to determine whether HMG-CoA reductase inhibitors, lovastatin, simvastatin and pravastatin inhibit the angiotensin II-induced hypertrophic growth. Angiotensin II (10(-6) M) significantly increased protein-DNA ratio, RNA-DNA ratio, ratios of protein synthesis and mitogen-activated protein (MAP) kinase activity. Lipid-soluble HMG-CoA reductase inhibitors, lovastatin (10(-6) M) and simvastatin (10(-6) M) partially and significantly inhibited the angiotensin II-induced increases in these parameters, but a water-soluble HMG-CoA reductase inhibitor, pravastatin (10(-6) M) did not. Mevalonate (10(-4) M) overcame the inhibitory effects of lovastatin and simvastatin on angiotensin II-induced increases in these parameters. A selective protein kinase C inhibitor, calphostin C (10(-6) M) partially and significantly prevented angiotensin II-induced increases in these parameters, and treatment with both lovastatin and calphostin C inhibited completely. Angiotensin II increased p21ras activity and membrane association, and lovastatin inhibited them. These studies demonstrate that a lipid-soluble HMG-CoA reductase inhibitor, lovastatin, may prevent angiotensin II-induced cardiac hypertrophy, at least in part, through p21ras/MAP kinase pathway, which is linked to mevalonate metabolism.

Diagnosis of metastasis of ovarian clear cell carcinoma to the peritoneum of the abdominal wall by positron emission tomography with (fluorine-18)-2-deoxyglucose.

A 43-year old woman, operated on for ovarian clear cell carcinoma (stage IIc) four years previously was found to have a small mass under the abdominal wall in the right lower quadrant of the abdomen. Neither diagnostic imaging (ultrasonography and MRI) nor tumor markers showed any evidence of recurrence, but positron emission tomography revealed a hot spot area, and it was diagnosed as recurrence of the ovarian carcinoma. The postoperative histopathological diagnosis was metastasis of ovarian carcinoma to the peritoneal wall.

The role of 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG-PET) in the diagnosis of recurrence and lymph node metastasis of cervical cancer.

The usefulness of positron emission tomography with 2-[18F]-fluoro-2-deoxy-D-glucose (FDG-PET) in diagnosing recurrence and lymph node metastasis of uterine cervical cancer was evaluated as a preliminary study. The FDG uptake of 13 cervical cancer patients, including 4 patients with recurrence, was evaluated. The FDG uptake of the cervices of 5 patients who underwent PET studies for non-cervical tumors were used as control. In 2 patients who had undergone radical hysterectomy, we compared the diagnosis of lymph node metastasis based on FDG-PET and magnetic resonance imaging. The FDG uptake in the 9 primary cervical cancers was greater than that in normal cervices (p=0.025). Examination of the 4 recurrent tumors revealed a higher FDG uptake than that in normal cervices (p=0.0022). Metastatic lesions in lymph nodes showed an accumulation of FDG on the PET scan. In conclusion, FDG-PET may be an effective diagnostic tool for detecting recurrence and lymph node metastasis of uterine cervical cancers.

Combined diagnostic imaging for retroperitoneal schwannoma.

Retroperitoneal tumors are occasionally encountered by gynecologists, and differential diagnosis from adnexal tumors is important, however, it is difficult in many cases. We report a case in which we preoperatively diagnosed a benign solid tumor in the retroperitoneum of the pelvic cavity on the basis of a variety of diagnostic images, including FDG-PET. Postoperative histological examination showed a benign schwannoma in the pelvis. We discuss the usefulness of FDG-PET combined with MRI and other diagnostic images as a means of differentiating between the characteristics of retroperitoneal tumors.

Early diagnosis and evaluation of therapy in postoperative recurrent cervical cancers by positron emission tomography.

Positron emission tomography (PET) using 2-[18F]fluoro-2 deoxy-D-glucose (FDG) was performed on two uterine cervical cancer patients in whom recurrent tumors, one pelvic and the other at the vaginal wall had not been precisely diagnosed using the usual imaging examinations. One recurrence was confirmed by the acccumulation of FDG to the pelvic mass as detected by magnetic resonance imaging (MRI). During chemotherapy, changes in FDG-PET findings were detected earlier than those in MRI. In the other, PET detected a recurrent tumor that could not be found by MRI, and was also useful for evaluating chemotherapeutic effects. These cases suggest that PET with FDG can be a useful examination not only for diagnosing recurrent cervical cancer after radical hysterectomy, especially pelvic recurrence, but also for evaluating chemotherapeutic effects on recurrent cancers.

A case of oophoritis detected by gallium-67-citrate scintigraphy.

A 39-year-old woman with fever of unknown origin was admitted to our hospital. Whole body scintigrams with 67Ga-citrate showed an abnormal accumulation of radioactivity in the pelvic cavity. Cystadenocarcinoma of the ovary was suspected on the basis of findings obtained by abdominal computed tomography and magnetic resonance imaging. Left oophorectomy was performed, and oophoritis was diagnosed. We would like to propose that 67Ga-citrate scintigraphy may be useful for the diagnosis of oophoritis as well as gynecologic malignant tumors.

Usefulness of per-rectal portal scintigraphy with Tc-99m pertechnetate for galactosemia in infants.

Galactosemia discovered by newborn screening is rarely caused by enzyme deficiency. It has recently been reported that among patients without enzyme deficiency portosystemic shunting may be a cause of galactosemia in some patients. We did per-rectal portal scintigraphy in patients with such galactosemia detected during screening of newborns to examine the usefulness of this method for the diagnosis of portosystemic shunts via the inferior mesenteric vein. The subjects were eight neonates with galactosemia without enzyme deficiency detected during screening. A solution containing technetium-99m pertechnetate was instilled into the rectum, and serial scintigrams were taken while radioactivity curves for the liver and heart were recorded sequentially. The per-rectal portal shunt index was determined by calculating the ratio for counts of the liver to counts for the heart integrated for 24 seconds immediately after the appearance of the liver time-activity curve. A portosystemic shunt was detected in both of the patients with a shunt index of 30% or more, but not in the six patients with a shunt index less than 30%. The blood galactose levels of these six patients later entered the reference range. This method is noninvasive and there is little exposure to the radionuclide. It seemed to be useful for the diagnosis of portosystemic shunt in newborns with galactosemia without enzyme deficiency.

Clinical usefulness of positron emission tomography with fluorine-18-fluorodeoxyglucose in the diagnosis of liver tumors.

We studied various liver tumors by positron emission tomography with fluorine-18 fluorodeoxyglucose (FDG-PET) to examine the diagnostic usefulness of this technique. We also examined the relation between findings on FDG-PET and the characteristics of hepatocellular carcinoma. FDG-PET was performed in 78 patients with liver tumors, including 53 with primary liver cancer [48 hepatocellular carcinomas (HCC) and 5 cholangiocellular carcinomas (CCC)], 20 with metastatic liver cancer, 2 with liver hemangioma, and 3 with focal nodular hyperplasia. For quantitative evaluation, a region of interest (ROI) was placed over the entire tumor region, at the level of the maximum diameter of the tumor. A background ROI was then placed over the non-tumor region of the liver. The average activity within each ROI was subsequently corrected for radioactive decay, and the standardized uptake value (SUV) was calculated by dividing the tissue activity by the injected dose of radioactivity per unit body weight. SUV ratio was expressed as the tumor-to-non-tumor ratio of the SUV. The median SUV was significantly lower in HCC than in metastatic live cancer or CCC, and the median SUV ratio was significantly lower in HCC than in metastatic liver cancer or CCC. The median SUV was not higher in multiple HCC than in single HCC, but the median SUV ratio was significantly higher in multiple HCC than in single HCC. The median SUV and the median SUV ratio were significantly higher in the presence of portal vein thrombosis than in the absence of such thrombosis. The Cancer of the Liver Italian Program score and the alpha-fetoprotein value correlated significantly with both the SUV and SUV ratio. These results suggest that FDG-PET is clinically useful not only for the differential diagnosis of liver tumors but also for evaluation of the clinical characteristics of HCC.

Diagnostic usefulness of FDG PET for pancreatic mass lesions.

UNLABELLED: The purpose of this study was to investigate the feasibility of [18F]2-deoxy-2-fluoro-D-glucose (FDG) positron emission tomography (PET) in patients with a pancreatic mass by comparing the results with those of X-ray computed tomography (CT) and magnetic resonance (MR) imaging. METHODS: Eighty-six patients with pancreatic lesions, included 65 malignant tumors and 21 benign masses (55 masses were proven histologically and the others were diagnosed clinically), were studied. The diagnostic factors of CT and MR imaging were evaluated, and those of FDG PET were also evaluated for malignant and benign masses by visual interpretation and quantitative interpretation with the standardized uptake value (SUV) and SUVgluc which was designed to reduce the effects of a high blood sugar level. Visual interpretations were evaluated only in FDG PET images, and quantitative interpretations were evaluated by referring to CT and/or MR imaging. The correlation between SUV and the degree of histological differentiation in pancreatic ductal adenocarcinoma was investigated. RESULTS: Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy for CT imaging were 91, 62, 88, 68 and 84%, and for MR imaging 78, 70, 88, 54 and 76%, respectively. In visual interpretation of FDG PET images, the sensitivity, specificity, PPV, NPV and accuracy were 82, 81, 93, 59 and 81%, respectively. Significant differences between malignant and benign lesions existed in SUV and SUVgluc (p < 0.0001, each). With the cutoff value of SUV as 2.1 and SUVgluc as 2.2, the accuracy of diagnosis was maximal. With that cutoff value, the sensitivity, specificity, PPV, NPV and accuracy for SUV were 89, 76, 92, 70 and 86%, and for SUVgluc 91, 76, 92, 73 and 87%, respectively. The sensitivity and NPV of SUVgluc were higher than those of SUV, which suggests that SUVgluc may be more useful in reducing the number of overlooked malignant tumors. The specificity and PPV of FDG PET were superior to those of CT and MR imaging. There were no significant differences between the SUVs of moderately differentiated adenocarcinomas and those of well differentiated adenocarcinomas. CONCLUSION: To improve the diagnostic procedure for classifying masses, FDG PET with not only SUV but also SUV corrected by the blood sugar level is required in addition to morphological diagnosis by CT and/or MR imaging.

Thallium and FDG uptake by atelectasis with bronchogenic carcinoma.

We report a case of bronchogenic carcinoma with atelectasis studied by T1-SPECT and FDG-PET. In the carcinoma, abnormally high uptake of T1 and FDG were detected, but in the region of atelectasis, an abnormally high uptake of T1 with a relatively low uptake of FDG were observed. On quantitative analyses, the T1 retention indexes of the tumor and atelectasis were 29.7 and 42.0. The mean SUVs of FDG of the tumor and the atelectasis were 8.92 and 1.28. T1-SPECT could not distinguish the atelectasis from the carcinoma. FDG-PET was superior to T1-SPECT in this case in detecting malignancy and distinguishing it from atelectasis.