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Biomedical subjects

R Ahmed

Publications and source records attributed to R Ahmed.

At least 199 records · Page 11Linked to original sources
PubMed1988

Reliability of QT intervals as indicators of clinical hypercalcemia.

Reliability of corrected QT intervals (QoTc, QaTc, and QeTc) as indicators of clinical hypercalcemia was assessed in 14 hypercalcemic patients. Hypercalcemia was severe to extreme (serum calcium 14.9 to 22.8 mg/dl) in 11, moderate (13.4 mg/dl) in 1, and mild (12.2 and 11.8 mg/dl) in 2 patients. QT intervals during hypercalcemia were compared with those during normocalcemia either before or after development of hypercalcemia. QeTc interval showed neither significant correlation with serum calcium nor any consistent pattern of change with development of hypercalcemia or normalization of serum calcium. In contrast, QoTc and QaTc intervals shortened with development of hypercalcemia and returned toward normal with normalization of serum calcium in all the patients, and showed significant correlation with serum calcium (QoTc: r = -0.77, p less than 0.001, n = 35; QaTc: r = 0.82, p less than 0.001, n = 35). QaTc was short (less than 0.30 s) in all the ECGs in severe and moderate hypercalcemia and in 2 of the 5 ECGs in mild hypercalcemia. Combination of short QoTc (less than 0.18 s) and short QaTc was found to be highly specific for, and was present in 65% of ECGs, in moderate and severe hypercalcemia. Combination of normal QoTc (greater than 0.18 s) and normal QaTc (greater than 0.30 s) was not observed in moderate or severe hypercalcemia. We conclude that QoTc and QaTc intervals are reliable indicators of clinical hypercalcemia.

Adult↗
PubMed1988

T-cell tolerance: exposure to virus in utero does not cause a permanent deletion of specific T cells.

This study documents the curing of a congenitally acquired chronic viral infection and the acquisition of T-cell competence by a previously tolerant host. Infection of mice with lymphocytic choriomeningitis virus (LCMV) is a classic model of viral persistence and antigen-specific T-cell unresponsiveness. Mice infected at birth or in utero become lifelong carriers with no detectable virus-specific cytotoxic T lymphocyte (CTL) responses. This chronic infection can be eliminated by adoptive transfer of Lyt-2+ T cells from LCMV-immune mice. To determine whether these cured carriers were capable of generating their own LCMV-specific CTL response, mice congenic at the Thy-1 locus (Thy-1.1 and Thy-1.2) were used in the adoptive transfer experiments. Host-derived T-cell responses were checked after treating the cured carriers with a monoclonal antibody to deplete the immune donor T cells. Such cured carrier mice were able to generate a host-derived virus-specific CTL response and resisted a second LCMV challenge in the absence of any donor T cells. In addition, bone marrow cells from these cured carriers could functionally reconstitute irradiated mice. Thus this report demonstrates the acquisition of LCMV-specific T-cell competence by previously unresponsive carrier mice infected in utero. These results show that exposure to a virus even during embryonic life does not cause a permanent deletion of specific T cells. These findings are of significance to the understanding of tolerance mechanisms and have implications for the treatment of chronic viral infections.

Animals↗
PubMed1988

Characterization of Escherichia coli serotype O157:H7.

A total of 174 strains of Escherichia coli serotype O157:H7 representing human isolates obtained from outbreaks and sporadic cases of hemorrhagic colitis, hemolytic-uremic syndrome, and nonbloody diarrheal illnesses as well as from asymptomatic carriers across Canada and the United States were examined. E. coli serotype O157:H7 possessed distinct biochemical markers, a 100% negative reaction for beta-glucuronidase and sorbitol, and a 100% positive reaction for raffinose and dulcitol; all strains otherwise were biochemically typical of E. coli. The vast majority (97%) of the strains were susceptible to commonly used antimicrobial agents. All strains produced readily detectable levels of Verotoxin; however, with polymyxin extraction, nearly 50% of the strains showed up to a 10-fold increase in the toxin level. None were found to mediate hemagglutination of human group A erythrocytes with or without D-mannose. The majority (approximately 70%) of the strains showed localized and diffuse adherence to HEp-2 cells and Henle 407 cells, and the adherence patterns were not very different from those observed among other E. coli strains. Twenty phage types were recognized, with phage types 1 and 2 accounting for 65% of the test strains. Plasmid analysis indicated three basic plasmid profiles: profile I was characterized by 68.7- and 4.2-megadalton (MDa) plasmids (62% of strains), profile II was characterized by 66.2- and 1.8-MDa plasmids (20% of strains), and profile III was characterized by a 62.5-MDa plasmid (18% of strains). A small number (19%) of the strains carried at least one additional plasmid over the basic complements, and these could be considered to constitute a miscellaneous category. None of the above-described characteristics of E. coli serotype O157:H7 could be directly correlated with one another, with the nature of infection, or with the geographical distribution of strains.

Bacterial Adhesion↗
PubMed1988

T4+ T helper cell function in vivo: differential requirement for induction of antiviral cytotoxic T-cell and antibody responses.

This study documents the differential requirements of T4+ T helper cells in the induction of virus-specific cytotoxic T-lymphocyte (CTL) and antibody responses during acute lymphocytic choriomeningitis virus infection. Two monoclonal antibodies (GK1.5 and RL172.4) directed against the L3T4 (T4) molecule were used for depleting T helper cells from mice. Depletion of T4+ cells caused a pronounced suppression of antiviral antibody response (20-fold decrease) but had minimal effect on virus-specific CTL response (less than 2-fold reduction). Despite the elimination of greater than 90% of T helper cells, anti-L3T4-treated mice were able to generate a CTL response of sufficient magnitude to control the viral infection. In contrast, depletion of Lyt2+ T cells abrogated the CTL response and the ability to eliminate virus. Thus, our results underscore the importance of the Lyt2+ T-cell subset in controlling infection with this virus and show that a deficiency of T4+ T cells is likely to have a more severe effect on antibody production than on CTL responses.

Animals↗
PubMed1988

Genetic analysis of in vivo-selected viral variants causing chronic infection: importance of mutation in the L RNA segment of lymphocytic choriomeningitis virus.

Viral variants with different biological properties are present in the central nervous systems (CNS) and lymphoid tissues of mice persistently infected with lymphocytic choriomeningitis virus (LCMV). Viral isolates from the CNS are similar to the original Armstrong LCMV strain and induce potent virus-specific T-cell responses in adult mice, and the infection is rapidly cleared. In contrast, LCMV isolates derived from spleens of carrier mice cause persistent infections in adult mice. This chronic infection is associated with low levels of antiviral T-cell responses. In this study, we genetically characterized two independently derived spleen variants by making recombinants (reassortants) between the spleen isolates and wild-type (wt) LCMV and showed that the ability to persist in adult mice and the associated suppression of T-cell responses segregates with the large (L) RNA segment. In addition, we analyzed a revertant (isolated from the CNS) derived from one of the spleen variants. By comparing the biological properties of three reassortants that contained the same S segment but had the L segment of either the original wt Armstrong LCMV, the spleen variant derived from it, or the CNS revertant derived from the spleen variant, we were able to show unequivocally that biologically relevant mutations occurred in the L segment not only during generation of the spleen variant from wt LCMV but also in reversion of the spleen variant to the wt phenotype. Thus, our results showed that (i) genetic alterations in the L genomic segment were involved in organ-specific selection of viral variants, and (ii) these mutations profoundly affected the ability of LCMV to cause chronic infections in adult mice.

Animals↗
PubMed1988

Reactions of sterols with pyridinium chlorochromate.

Reaction of pyridinium chlorochromate with cyclohexanol and several C(3)-sterols have been investigated. It has been found that the equatorieal C(3)-sterols axe easily oxidised in good yield to give corresponding ketosteioids while the axial sterols give poor yields.

Journal Article↗
PubMed1987

Failure to preserve fertility in patients with Hodgkin's disease.

The hypothesis that the "down-regulated" gonad is less vulnerable to the effects of cytotoxic chemotherapy for advanced Hodgkin's disease has been investigated. Thirty men and eighteen women were randomly allocated to receive an agonist analogue of gonadotrophin-releasing hormone prior to, and for the duration of, cytotoxic chemotherapy. Buserelin (d-Ser-[TBU]6 LHRH ethylamide) was prescribed in two different dosage schedules to twenty men, and in a single dosage schedule to eight women. A standard gonadotrophin-releasing hormone test (GnRH 100 micrograms) was performed 1 week prior to and on day 1 of each cycle of chemotherapy. In all patients peak luteinizing hormone responses to GnRH were suppressed throughout treatment. The higher of the two dosage schedules used in the men caused more effective suppression of luteinizing hormone, and both regimens led to an initial suppression of peak follicle-stimulating hormone responses to GnRH, which was not maintained. At follow-up assessment up to 3 years from the completion of treatment, all men treated with buserelin were profoundly oligospermic and four of the eight women were amenorrhoeic. All ten male controls were profoundly oligospermic, and six of nine female controls were amenorrhoeic. In the dosages and schedules investigated, buserelin was ineffective in conserving fertility.

Amenorrhea↗
PubMed1987

Determination of lead and cadmium in milk by electrothermal atomic absorption spectrophotometry.

The concentration of lead and cadmium in different kinds of milk samples (powdered, infant formula, market, buffalo, condensed and human) were determined using electrothermal atomic absorption spectrophotometric technique. Among all the varieties of milk analysed, condensed milk was found to contain much higher amount of lead. Human milk as expected was found to have lowest concentration of these elements. The results were compared with the reported values of other countries. Daily intake of these toxic elements by adults and babies up to the age of six months through the consumption of various types of milk was estimated and compared with the tolerance levels.

Animals↗
PubMed1987

Immune therapy of a persistent and disseminated viral infection.

The mechanism of viral clearance was studied by using the mouse model of chronic infection with lymphocytic choriomeningitis virus. Distinct patterns of viral clearance and histopathology were observed in different organs after adoptive immune therapy of persistently infected (carrier) mice. Clearance from the liver occurred within 30 days and was accompanied by extensive mononuclear cell infiltrates and necrosis of hepatocytes. Infectious virus and viral antigen were eliminated concurrently. This pattern of viral clearance was also seen in most other tissues (i.e., lung, spleen, lymph nodes, pancreas, etc.). In contrast, a different pattern of clearance was observed in the brain. Infectious virus was eliminated within 30 days, but viral antigen persisted in the central nervous systems of treated carrier mice for up to 90 days. The urinary system was the most resistant to immune therapy. Elimination of infectious virus and viral antigen from the kidney took greater than 200 days and even then was not complete; trace levels of infectious virus were still present in the kidneys of some treated carrier mice. After immune therapy, viral antigen in the kidney was located within renal tubules that costained for intracellular mouse immunoglobulin G. This unusual staining pattern, coupled with the observation of large numbers of plasma cells within the kidney, suggests that virus-immunoglobulin G complexes found in the tubules may represent in situ immune complex formation as opposed to deposition of circulating immune complexes. In conclusion, these results suggest that the site (organ) of viral persistence is an important consideration in developing treatment strategies for controlling chronic viral infections.

Animals↗
PubMed1987

Effective clearance of a persistent viral infection requires cooperation between virus-specific Lyt2+ T cells and nonspecific bone marrow-derived cells.

The lifelong chronic lymphocytic choriomeningitis virus (LCMV) infection established in neonatally or congenitally infected mice can be eliminated by adoptive transfer of lymphoid cells from LCMV-immune mice. In this study, we have identified the effector cells mediating the clearance of persistent and disseminated LCMV infection. Using mice that are recombinant in the H-2 region and by selective depletion of lymphocyte subpopulations, we show that viral clearance was mediated by LCMV-specific Lyt2+ L3T4- T cells that are restricted to the class I genes of the major histocompatibility complex. In addition, our results show a requirement for host-derived bone marrow cells for the effective elimination of virus from the liver. These studies emphasize the importance of virus-specific T cells and an intact bone marrow function in viral clearance.

Animals↗
PubMed1987

Virus-lymphocyte interaction: T cells of the helper subset are infected with lymphocytic choriomeningitis virus during persistent infection in vivo.

The lifelong persistence of lymphocytic choriomeningitis virus (LCMV) in neonatally or congenitally infected mice is accompanied by a suppression of virus-specific T-cell responses. In this study, we identified the subset of T cells infected with LCMV during persistent infection in vivo. Using specific monoclonal antibodies to separate the different lymphocyte cell populations and employing both an infectious center assay and immunofluorescence to detect the virus, we found that infection is confined primarily to T cells of the helper subset (L3T4+ Lyt2-), with minimal involvement of cytotoxic T cells (Lyt2+ L3T4-) and mature B cells. About 0.54 to 1.1% of L3T4+ T cells were producing the virus, as determined by the infectious center assay. In contrast, 9.1 to 12.2% of these L3T4+ T cells contained viral antigen, as shown by immunofluorescence studies. This finding suggested that, at any given time, a substantial number of infected T cells were not producing infectious virus. This infection of T helper cells may be involved in the suppression of LCMV-specific T-cell responses observed in persistently infected mice.

Animals↗
PubMed1987

Effects of combined changes in serum calcium and potassium on QT interval. A study by Holter electrocardiographic monitoring during hemodialysis.

Holter electrocardiographic recordings were performed for 24 hours in 20 patients on chronic hemodialysis to evaluate the effect of changes in serum calcium and potassium during a 5-hour hemodialysis period on the QT interval. Hemodialysis caused an acute increase in serum calcium from a predialysis value of 9.6 +/- 1.3 mg/dl to 11.5 +/- 1.2 mg/dl and a decrease in serum potassium from 4.9 +/- 0.6 mEq/L to 3.5 +/- 0.4 mEq/L. The Q-oTc interval shortened from a predialysis value of 0.240 +/- 0.023 sec to a minimum of 0.215 +/- 0.022 sec during the 5th hour of hemodialysis. This Q-oTc interval shortening was correlated strongly with an increase in serum calcium and was statistically significant only in subjects showing an increase in serum calcium of more than 2 mg/dl (p less than 0.05). The Q-eTc interval increased from a predialysis value of 0.392 +/- 0.030 sec to 0.414 +/- 0.024 sec during the 4th hour of hemodialysis. This Q-eTc interval prolongation was correlated with a decrease in serum potassium. It was concluded that increased serum calcium during hemodialysis caused shortening of the Q-oTc interval, that the degree of shortening was proportional to the magnitude of increase in serum calcium, and that changes in serum calcium and the Q-oTc interval were concurrent. It was also concluded that hemodialysis resulted in prolongation of the Q-eTc interval. This change was possibly caused by a decrease in the level of serum potassium during the procedure.

Adult↗
PubMed1987

Influence of collateral flow reduction on electrophysiologic properties of preexisting ischemic area and inducibility of ventricular arrhythmias in the dog.

Electrophysiologic properties of the left ventricle, vulnerability to ventricular arrhythmias and regional myocardial blood flow (RMBF) of the left ventricle were examined during superposition of acute ischemia on a healed myocardial infarction. The left circumflex coronary artery (LCX) was ligated in 13 dogs with a 28-day-old anteroapical infarction. Six (46%) of 13 dogs had reproducible ventricular tachycardia in response to programmed ventricular stimulation before LCX ligation. Ventricular fibrillation could be induced in 2 of these 6 dogs. After LCX ligation, 11 (85%) of 13 dogs had ventricular arrhythmias induced by ventricular stimulation. Nine of 13 dogs had ventricular tachycardia and 7 of 13 dogs had ventricular fibrillation. The heterogeneity of the effective refractory period (delta ERP) and the local intraventricular conduction time (LIVCT) in the border and the infarct zones of the left ventricle increased significantly after LCX ligation. RMBF in the border and the infarct zones were markedly decreased by LCX ligation. The magnitude of reduction of RMBF was correlated significantly with the prolongation of LIVCT. In conclusion, acute critical reduction of the collateral blood supply causes a more heterogeneous refractory period and conduction delay in the preexisting ischemic area of the heart, increasing the vulnerability to lethal ventricular arrhythmias.

Animals↗