PubMed Health⌕ Search

Biomedical subjects

H Najafi

Publications and source records attributed to H Najafi.

At least 19 recordsLinked to original sources
PubMed1992

Expression and function of GLUT-1 and GLUT-2 glucose transporter isoforms in cells of cultured rat pancreatic islets.

We have previously investigated glucose induction of glucokinase, glucose usage and insulin release in isolated cultured rat pancreatic islets (Liang, Y., Najafit, H., Smith, R. M., Zimmerman, E. C., Magnuson, M. A., Tal, M., and Mastchinsky, F. M. (1992) Diabetes (1992) 41, 792-806). Here we studied the expression and function of GLUT-1 and GLUT-2 glucose transporter isoforms, using the same system, i.e. isolated pancreatic rat islets immediately after isolation or cultured in the presence of 3 or 30 mM glucose for as long as 10 days. We found by immunofluorescence microscopy and Western and Northern blot analysis of islet extracts that GLUT-1 expression was induced in islet beta-cells in tissue culture both with low or high glucose present. The induction of GLUT-1 was specific to beta-cells but was not present in all beta-cells and was not detected in alpha-cells. GLUT-2 expression was also specific for beta-cells and was not observed in all beta-cells. Some beta-cells in culture coexpressed GLUT-1 and GLUT-2. The expression of the two glucose transporters was regulated in the opposite direction in response to glucose concentration in the culture medium. GLUT-1 was more effectively induced when glucose was low, and GLUT-2 expression was more pronounced when glucose was high in the culture media. Another difference between the two glucose transporters was that GLUT-2 expression was increased while GLUT-1 expression was decreased as culturing continued as long as 7 days. Thus, after 7 days of culture GLUT-2 expression in beta-cells was nearly the same at low and high glucose, whereas GLUT-1 was practically absent no matter what the glucose level was. In attempts to correlate GLUT-1 and GLUT-2 expression to beta-cell function glucose uptake and glucose-stimulated insulin release in fresh and cultured islets were measured. In freshly isolated islet glucose uptake was estimated to be 100-fold in excess of actual glucose use. Glucose uptake was reduced by 7-day culture to about one-third of that observed in freshly isolated islets no matter what the glucose concentration of the culture media. We conclude that in the present experimental system GLUT-1 and GLUT-2 expression and function are not closely associated with glucose usage rates or the secretory function of beta-cells.

Animals↗
PubMed1992

Identification of glucose response proteins in two biological models of beta-cell adaptation to chronic high glucose exposure.

High resolution 2-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) combined with computerized analysis of gel images was used to search for proteins whose biosynthesis was induced or repressed in pancreatic islet cells chronically exposed to high glucose in an in situ and a tissue culture model of islet cell adaptation to excessive fuel load. The in situ model involved a 4-day intravenous infusion of either 50% glucose or 0.45% saline solution, followed by islet isolation, [35S]methionine labeling at 3 and 18 mM glucose for both groups, and protein analysis by 2-dimensional SDS-PAGE. The tissue culture model involved a 7-day culture of isolated rat islets in RPMI 1640 with 10% fetal calf serum containing either 3 or 30 mM glucose, followed by radiolabeling and 2-dimensional PAGE of proteins as in the in situ model. A small fraction of about 1.5% of the approximately 2000 identifiable proteins can be characterized as adaptive proteins. Of these altogether 58 proteins in the two models, 5 proteins were demonstrable in both models and two of these (proteins 1526 and 7622) are particularly noteworthy. Protein 1526 (Mr 57,000; pI 5.09) showed the same response pattern in both models and its expression was most enhanced when islets from chronically glucose-infused animals or those cultured for 7 days at 30 mM were radiolabeled at 18 mM glucose. Protein 7622 (Mr 68,000; pI 6.50) (also known as GSP-65; Collins, H.W., Buettger, C., and Matschinsky, F.M. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 5494-5498) showed a different labeling pattern in the two models: stimulation of [35S]methionine incorporation by 18 mM glucose both in control and experimental islets from the infusion study, but lack of such stimulation of radiolabeling in islets cultured for 7 days at 30 mM glucose in contrast to islets cultured at 3 mM. The experimental strategy and the methodology are evaluated and the significance of the results is discussed. Potentials of the approach and plans for future experiments are considered.

Animals↗
PubMed1992

Morbidity and duration of ICU stay after cardiac surgery. A model for preoperative risk assessment.

Although risk factors for mortality after cardiac surgery have been identified, there is no widely applicable method for readily determining risk of postoperative morbidity based on preoperative severity of illness. The goal of this study was to develop a model for stratifying the risk of serious morbidity after adult cardiac surgery using readily available and objective clinical data. After univariate analysis of risk factors in 3,156 operations, 11 variables were identified as important predictors by logistic regression (LR) analysis and used to construct an additive model to calculate the probability of serious morbidity. Reliable correlation was found between a simplified additive model for clinical use and the LR model. The clinical and logistic models were then tested prospectively in 394 patients and demonstrated a pattern of increasing morbidity with ascending scores similar to that predicted by the reference group. Increasing clinical risk score was also associated with a greater frequency of individual complications as well as prolongation of ICU stay. This study demonstrates that it is feasible to design a simple method to stratify the risk of serious morbidity after adult cardiac surgery. With further prospective multicenter refinement and testing, such a model is likely to be useful for adjusting severity of illness when reporting outcome statistics as well as planning resource utilization.

Aged↗
PubMed1992

Concordant glucose induction of glucokinase, glucose usage, and glucose-stimulated insulin release in pancreatic islets maintained in organ culture.

Using cultured islets as the experimental system, this study established dosage-response and time-dependency curves of the inductive glucose effect on glucose-stimulated insulin release, glucose usage, and glucokinase activity. Glucose-stimulated insulin release in islets cultured for 1, 2, or 7 days was increased as a function of glucose concentration in the culture medium and as a function of time. Glucose usage in the cultured islets showed a close relationship with glucose concentration in the culture medium at both 2 and 7 days of culture. Glucokinase activity increased in islets cultured for 1, 2, or 7 days as a function of increasing glucose concentrations in the culture medium and as a function of time. The V(max) of glucokinase in islets cultured for 7 days in medium containing 30 mM glucose was twice the value of freshly isolated islets and was almost fivefold higher than that in islets cultured for 7 days in 3 mM glucose. The glucose induction of glucose-stimulated insulin release, of glucose usage, and of glucokinase activity were tightly correlated. The biochemical mechanisms of glucose induction of islet glucokinase were further studied. Immunoblotting with an antibody against C-terminal peptide of glucokinase showed that densities of a 52,000-kD protein band from tissue extracts of islets cultured for 7 days in 3, 12, and 30 mM glucose were 25, 44, and 270% compared with that of extract from freshly isolated islets (100%). RNA blot analysis of glucokinase mRNA demonstrated virtually the same levels in fresh islets and islets after 7 days of culture in 3 or 30 mM glucose. The adaptive response of glucokinase to glucose appears therefore to be occurring at a translational or posttranslational site in cultured islets. These data greatly strengthen the concept that glucose is the regulator that induces the activity of glucokinase, which in turn determines the rate change of glucose usage as well as glucose-stimulated insulin release from beta-cells. Thus, the hypothesis that glucokinase is the glucose sensor of beta-cells is strengthened further.

Animals↗
PubMed1992

Differential effects of advanced age on neurologic and cardiac risks of coronary artery operations.

Two thousand patients undergoing coronary artery bypass grafting with cardiopulmonary bypass were prospectively studied to compare the influence of age on the incidence of neurologic, cardiac, and other complications. Postoperative neurologic events were found in 56 (2.8%) patients, with an incidence in patients > or = 75 years (8.9%) more than twice that of patients 65 to 74 (3.6%) and nine times larger than in patients < 65 (0.9%). Cardiac complications did not differ between age groups except for low cardiac output state, which occurred 1.7 times more frequently in patients > or = 75 years compared with those < 65. Patients with postoperative neurologic events had a ninefold increase in mortality--35.7% versus 4.0%. Logistic regression analysis demonstrate the most important predictors of a postoperative neurologic event to be age, preoperative neurologic abnormality, recent myocardial infarction, and duration of cardiopulmonary bypass. The risk of neurologic complications increases disproportionately to the risk of cardiac complications in the elderly undergoing coronary artery bypass grafting with cardiopulmonary bypass. Despite neurologic improvement (32 of 56 patients), a postoperative neurologic event was second only to low cardiac output state as the postoperative complication most highly associated with in-hospital death. These results are important for decisions regarding selection of candidates for coronary artery bypass grafting and for prediction of surgical outcome.

Age Factors↗
PubMed1991

Effects of alternate RNA splicing on glucokinase isoform activities in the pancreatic islet, liver, and pituitary.

Different glucokinase isoforms are produced by tissue-specific alternative RNA splicing in the liver and pancreatic islet, the only tissues in which glucokinase activity has been detected. To determine whether differences in protein structure brought about by alternative RNA splicing have an effect on glucose phosphorylating activity, we expressed cDNAs encoding four different hepatic and islet glucokinase isoforms and determined the Km and Vmax of each. When the glucokinase B1 and L1 isoforms were expressed in eukaryotic cells, both high Km glucose phosphorylating activity and immunoreactive protein were detected. However, when the glucokinase B2 and L2 isoforms were expressed, both of which differ by deletion of 17 amino acids in a region between the putative glucose and ATP-binding domains, no high Km glucose phosphorylating activity and much less immunoreactive protein were detected. When the glucokinase B1 and B2 isoforms were expressed in Escherichia coli as fusion proteins with glutathione S-transferase, affinity-purified B1 fusion protein was able to phosphorylate glucose whereas the B2 fusion protein was not, thus indicating that the lack of glucose phosphorylating activity from both the B2 and L2 isoforms is due to lack of intrinsic activity in addition to accumulation of less protein. The Km values of the B1 and L1 isoforms, which differ from each other by 15 amino acids at the NH2 terminus, were similar, but the Vmax of the B1 isoform was 2.8-fold higher than that of the L1 isoform. Mutagenesis of the first two potential initiation codons in the glucokinase B1 cDNA from ATG to GTC (methionine to valine) indicated that the first ATG was crucial for activity and is, therefore, the likely translation initiation codon. Messenger RNAs encoding both the B2 and L2 isoforms of glucokinase were detected in islet and liver by polymerase chain reaction amplification of total cDNA, indicating that mRNAs utilizing this weak alternate splice acceptor site in the fourth exon are normally present in both the liver and islet but as minor components. A regulatory role for weak alternate splice acceptor and donor sites in the glucokinase gene was suggested by examining the expression of the gene in the pituitary and in AtT-20 cells. Interestingly, although glucokinase mRNAs of appropriate sizes were detected in both the AtT-20 cells and rat pituitaries, neither exhibited any detectable high Km glucose phosphorylating activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Glucose regulates glucokinase activity in cultured islets from rat pancreas.

In this study, we have used isolated pancreatic islets cultured for 7 days in 3 or 30 mM glucose to explore whether glucokinase is induced or activated by high glucose concentrations and has related enzyme activity to glucose-stimulated insulin release. Islets cultured in low glucose medium or low glucose medium plus 350 ng/ml insulin did not respond to high glucose stimulation. Islets cultured in medium containing high glucose concentrations showed a high rate of basal insulin secretion when perifused with 5 mM glucose, and the insulin release was greatly augmented in a biphasic secretion profile when the glucose concentration was raised to 16 mM. Islet glucokinase and hexokinase activities were determined by a sensitive and specific fluorometric method. Glucokinase activity was reduced to approximately 50% in islets cultured in low glucose medium with or without insulin present compared to results with fresh islets. However, islets cultured in 30 mM glucose showed that glucokinase activity was elevated to 236% compared to results with fresh islets. It is concluded that (a) glucose is the physiological regulator of glucokinase in the islet of Langerhans and that (b) the activity of glucokinase plays a crucial role in glucose-induced insulin secretion.

Animals↗
PubMed1977

Coronary obstruction secondary to direct cannulation.

Four patients are reported with obstruction of the proximal left main coronary artery that developed following prosthetic replacement of the aortic valve. Angina pectoris and ventricular arrhythmias were the presenting clinical manifestations. Anterior descending coronary artery bypass was used in 3 of the patients and vein patch angioplasty in the fourth. One patient died in the hospital. The 3 survivors achieved reflief from angina and ventricular arrhythmias. One patient died from nephropathy 2 1/2 years later. Two patients remained asymptomatic 1 1/2 and 3 years later, respectively. This review emphasizes the need for prompt coronary angiography in patients experiencing angina pectoris after aortic valve replacement, and it shows that coronary revascularization can be performed with satisfactory results.

Adult↗
PubMed1977

Permanent transvenous balloon occlusion of the inferior vena cava: experience with 60 patients.

Traditional operations to obstruct the IVC are often unsatisfactory because the morbidity and mortality is appreciable: poor risk patients do not tolerate surgical and anesthetic trauma. Furthermore, if the patient is anticoagulated, an operation requires that such desirable treatment be stopped. Ten years ago a study was begun to develop a transvenous method of IVC occlusion in the awake anticoagulated patient. Animal studies were done prior to patient application. A technique was evolved wherein IVC interruption could be accomplished with a balloon bearing catheter inserted through the jugular vein. The balloon was positioned with venography and after inflation held in place by lateral pressure in the distensible IVC. The catheter was then removed, leaving the balloon in position. Balloon occlusion has been used in the management of 60 selected patients since 1970. Twenty-nine patients were simultaneously anticoagulated without complication. Very sick patients tolerated the procedure well. No patient experienced further pulmonary emboli. Nine hospital deaths occurred from a variety of causes, none related to the balloon catheter. Late follow-up shows that the occluding balloon gradually deflates in about 12 months. The remnant has remained stable in all patients, contained in a scar that permanently interrupts the IVC.

Adolescent↗
PubMed1976

Carotid body tumor: resection or reflection.

We have studied a series of 24 cases of carotid body tumor, comprising our total experience during the past two decades. Twelve patients had symptoms related to compression or invasion of the surrounding structures. Two patients had malignant changes, while three individuals had bilateral lesions. Thirteen patients underwent neck exploration for diagnosis or attempt at surgical removal of the tumor prior to admission to our institution. Definitive procedures in 24 cases resulted in one postoperative death, a rate of 4%. Internal carotid flow was preserved in every case. Intraluminal shunting was employed during the last decade, and no instance of cerebral damage was encountered. It is our intention to emphasize the importance of an accurate diagnosis by carotid angiography prior to surgical management. We also wish to encourage routine excision of these tumors as they are diagnosed, before they reach an enormous size.

Adult↗
PubMed1976

Abdominal aortic resection in thoracic dissection.

Dissection nearly always begins in the thorax, but it commonly extends into the abdominal aorta, which may become the focal point of the disease. We report five patients who illustrate the surgical management of this disease variant. Clinical manifestations included retroperitoneal rupture, expanding false aneurysm, and lower aortic occlusion. All patients had an aortic bifurcation graft, with reentry of the false lumen at the renal level. Two patients also had thoracic-aortic resection or plasty or both. Although one patient had thoracic aortic rupture at the five-year interval, these abdominal aortic resections provided effective palliation in all. This successful experience in managing complex dissections shows that when aortic dissection extends into the abdomen, resection of the distal aorta with a reentry procedure may be appropriate therapy.

Adult↗
PubMed1976

Aortic valve replacement without left heart decompression.

Conventionally, during aortic valve replacement the left ventricle is vented to achieve a dry field, remove air, and prevent ventricular distention. This report demonstrates the feasibility of performing aortic valve replacement without cannulation of either the left ventricle or the left atrium. The technique has been utilized in 54 patients with 1 early death due to pulmonary embolism and 1 late death presumably secondary to ventricular arrhythmias.

Adolescent↗
PubMed1975

Late thrombosis affecting one limb of aortic bifurcation graft.

Late unilateral limb thrombosis was encountered in 45 of 601 patients discharged from the hospital with functioning aortic bifurcation grafts, an incidence of 7.5%. It was invariably associated with clinical manifestations of arterial insufficiency to the affected limb more serious than those of the extremity prior to the initial operation. Although the specific cause could not be determined, it was usually due to either progression of the disease distal to the reconstructed segment or to certain compromises at the time of the first operation or both. Among several procedures employed, unilateral reconstruction of the thrombosed limb is the procedure of choice. The reoperation was successful in 75% of the patients.

Adult↗