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Biomedical subjects

S Stern

Publications and source records attributed to S Stern.

At least 127 records · Page 7Linked to original sources
PubMed1989

Comparison of 60-Hz electric fields and incandescent light as aversive stimuli controlling the behavior of rats.

Rats were exposed to two procedures which enabled them to press a lever to turn off a 90 or 100 kV/m 60-Hz electric field or, later in the study, illumination from an incandescent lamp. Under one procedure, a response turned off the stimulus for a fixed duration, after which the stimulus was turned on again. A response during the off-period restarted the fixed duration. None of the rats turned the field off reliably. Next, under an alternative procedure, pressing one lever turned the field off; pressing the other lever turned it back on; responding under those conditions differed little from that seen at 0 kV/m. Under both procedures, when illumination from an incandescent lamp served as the stimulus, each rat did turn the stimulus off, and performances varied with stimulus intensity. The results show that a 100 kV/m 60-Hz electric field is not sufficient to function as an aversive stimulus under two procedures where illumination from a lamp does function as an aversive stimulus.

Animals↗
PubMed1989

Residual left ventricular function and prognosis of patients with asymmetric septal hypertrophy recovering from acute myocardial infarction.

The prognosis of patients recovering from acute myocardial infarction (MI) depends mainly on their residual left ventricular (LV) function. In patients with asymmetric septal hypertrophy (ASH) who are recovering from MI, a larger functioning myocardial mass may remain. However, the frequency of ASH in these patients has not yet been described. Predischarge echocardiography, radionuclide ventriculography, and treadmill stress tests were performed in 403 consecutive patients who had recovered from acute MI. Eighty-eight patients (22%) had ASH with septal thickness greater than or equal to 1.3, and 32 (8%) had septal thickness greater than or equal to 1.5 cm. One hundred thirty-six patients who had recovered from a first MI and had no ASH served as control subjects. Left ventricular ejection fraction (LVEF) in the group with ASH was significantly higher than in control subjects (61% vs 50%; p = 0.0001). LV end-diastolic diameter (LVD(d] and E point septal separation (EPSS) were smaller in the group with ASH (4.9 cm and 5.4 mm) than in the control group (5.5 cm and 10.5 mm). The frequency of positive treadmill test results, angina pectoris, recurrent MI, heart failure, and death during a 22-month follow-up period was similar in both groups. Fifty subjects in the control group were matched with 50 patients from the group with ASH on the basis of maximal level of creatine phosphokinase, location of infarct, and presence or absence of hypertension, and the difference between the two groups was even more marked (LVEF 48% vs 61%, respectively; p = 0.0004).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Model for the three-dimensional folding of 16 S ribosomal RNA.

We have derived a model for the three-dimensional folding of Escherichia coli 16 S ribosomal RNA, using interactive computer graphic methods. It is based on (1) the secondary structure derived from comparative sequence analysis, (2) the three-dimensional co-ordinates for the centers of mass of the 30 S subunit proteins, and (3) the locations of sites in 16 S rRNA that interact with specific ribosomal proteins, from footprinting and crosslinking studies. We present a detailed description of the derivation of the model. About 75% of the RNA chain is sufficiently constrained to provide a useful model. This contains most of the universally conserved core of the molecule. In all but a few instances, protected and crosslinked sites can be placed within or very close to their cognate proteins, while obeying stereochemical rules. The overall shape of the model and locations of specific regions of the RNA correspond well to data derived from electron micrographs of 30 S subunits, although such data were not used to construct the model. Phylogenetic variations in the structure are readily accommodated; as an example, we have modeled the 950-nucleotide mammalian mitochondrial 12 S rRNA by superimposing it on the E. coli structure. The three major RNA domains, as defined by secondary structure, appear to exist as autonomous structural units in three dimensions, for the most part. There is an extensive interface between the 5' and central domains, whereas the 3' major domain has relatively little apparent contact with the rest of the structure. The 5', central and 3' major domains form structures that resemble the body, platform and head, respectively, seen in electron micrographs of 30 S subunits. We discuss possible roles for the ribosomal proteins in stabilizing specific structural features of the RNA during ribosome assembly. The decoding site, as deduced from footprinting and crosslinking studies involving the tRNA anticodon stem-loop, is well-localized. Bases protected from chemical probing by the anticodon stem-loop line the cleft of the subunit. The conserved loop at position 530, which contains some of the bases protected by A site-bound tRNA, is remote (approx. 80 A) from the decoding site. Protection of these bases by the anticodon stem-loop is thus unlikely to be due to direct contact.

Base Sequence↗
PubMed1988

Prognostic significance of ischemic episodes in patients with previous myocardial infarction.

This study assessed the prognostic significance of ischemic changes during daily activity as recorded by ambulatory electrocardiographic monitoring in a group of 224 low-risk postinfarction patients. Of the 224 patients studied, 74 (33%) had transient ischemic episodes on Holter monitoring. During the 28 months of follow-up the frequency of cardiac events (cardiac death, reinfarction, hospitalization for unstable angina, balloon angioplasty or coronary bypass surgery) was 51% among those with ischemic episodes on Holter monitoring, compared with 12% in those without such changes (p less than 0.0001). The 74 patients with positive results in their exercise tests and Holter monitoring had a 51% event rate, compared with 20% among the 44 patients with a positive exercise test result but negative Holter results (p less than 0.001). The event rate in those without ischemic changes either on the exercise test or on Holter was only 8.5%. Among patients with good (greater than 40%) or reduced (less than 40%) left ventricular ejection fraction, those with transient ST depression on Holter had a significantly higher cardiac event rate compared with those without it. A similar event rate was found in patients with only silent, only symptomatic and with silent and symptomatic ischemic episodes.

Activities of Daily Living↗
PubMed1988

Interaction of ribosomal proteins S5, S6, S11, S12, S18 and S21 with 16 S rRNA.

We have examined the effects of assembly of ribosomal proteins S5, S6, S11, S12, S18 and S21 on the reactivities of residues in 16 S rRNA towards chemical probes. The results show that S6, S18 and S11 interact with the 690-720 and 790 loop regions of 16 S rRNA in a highly co-operative manner, that is consistent with the previously defined assembly map relationships among these proteins. The results also indicate that these proteins, one of which (S18) has previously been implicated as a component of the ribosomal P-site, interact with residues near some of the recently defined P-site (class II tRNA protection) nucleotides in 16 S rRNA. In addition, assembly of protein S12 has been found to result in the protection of residues in both the 530 stem/loop and the 900 stem regions; the latter group is closely juxtaposed to a segment of 16 S rRNA recently shown to be protected from chemical probes by streptomycin. Interestingly, both S5 and S12 appear to protect, to differing degrees, a well-defined set of residues in the 900 stem/loop and 5'-terminal regions. These observations are discussed in terms of the effects of S5 and S12 on streptomycin binding, and in terms of the class III tRNA protection found in the 900 stem of 16 S rRNA. Altogether these results show that many of the small subunit proteins, which have previously been shown to be functionally important, appear to be associated with functionally implicated segments of 16 S rRNA.

Autoradiography↗
PubMed1988

Probing the assembly of the 3' major domain of 16 S rRNA. Interactions involving ribosomal proteins S2, S3, S10, S13 and S14.

We have used rapid probing methods to follow the changes in reactivity of residues in 16 S rRNA to chemical and enzymatic probes as ribosomal proteins S2, S3, S10, S13 and S14 are assembled into 30 S subunits. Effects observed are confined to the 3' major domain of the RNA and comprise three general classes. (1) Monospecific effects, which are attributable to a single protein. Proteins S13 and S14 each affect the reactivities of different residues which are adjacent to regions previously found protected by S19. S10 effects are located in two separate regions of the domain, the 1120/1150 stem and the 1280 loop; both of these regions are near nucleotides previously found protected by S9. Both S2 and S3 protect different nucleotides between positions 1070 and 1112. In addition, S2 protects residues in the 1160/1170 stem-loop. (2) Co-operative effects, which include residues dependent on the simultaneous presence of both proteins S2 and S3 for their reactivities to appear similar to those observed in native 30 S subunits. (3) Polyspecific effects, where proteins S3 and S2 independently afford the same protection and enhancement pattern in three distal regions of the domain: the 960 stem-loop, the 1050/1200 stem and in the upper part of the domain (nucleotides 1070 to 1190). Proteins S14 and S10 also weakly affect the reactivities of several residues in these regions. We believe that several of the protected residues of the first class are likely sites for protein-RNA contact while the third class is indicative of conformational rearrangement in the RNA during assembly. These results, in combination with the results from our previous study of proteins S7, S9 and S19, are discussed in terms of the assembly, topography and involvement in ribosomal function of the 3' major domain.

Autoradiography↗
PubMed1988

Characteristics of silent and symptomatic myocardial ischemia during daily activities.

In 191 patients with proven coronary artery disease, 24-hour Holter monitoring detected 587 transient episodes of ST depression during daily activities. Of that total, 424 episodes were silent (72.3%) and 163 were symptomatic (27.7%). There were no statistically significant differences between silent and symptomatic episodes as to their mean duration (15.1 vs 14.3 minutes, respectively), heart rate at onset of ST depression (93 vs 96 beats/min, respectively), heart rate at the time of maximal ST depression (114 beats/min, both) and mean maximal ST depression (1.9 vs 2.0 mm, respectively). Of the 191 patients, 104 (55%) had only silent episodes, 33 (17%) only symptomatic episodes and 54 (28%) had both types ("mixed"). All patients, regardless of episode type, were of similar age, received comparable medical therapy, had a similar extent of angiographically documented coronary artery disease and similar episode characteristics. However, mixed-episode patients had significantly more ischemic episodes per day (4.8) than silent-episode (2.6) and symptomatic-episode (1.9) patients (p less than 0.001 for both) and a longer total period of daily ischemia (60 minutes), than the other 2 groups (36 and 28 minutes, respectively, p less than 0.001 for both). Of the 191 patients, 97 (51%) had had a previous myocardial infarction. The characteristics of their silent and symptomatic episodes were similar to the 94 (49%) patients without infarction, except for a longer duration of the silent episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Activities of Daily Living↗
PubMed1988

Clinical outcome of silent myocardial ischemia.

Asymptomatic coronary artery disease can be detected by an abnormal electrocardiogram at rest, by a positive exercise test result unaccompanied by pain, or by the demonstration of silent ischemic episodes during daily activities. However, the clinical outcome of patients with silent myocardial ischemia has not yet been clearly defined. In a study of 356 patients with documented coronary disease--211 of whom had previous myocardial infarction--the prognostic information of spontaneous ST-segment depression was found to be independent of that associated with a positive exercise test result, ejection fraction, and extent of arteriographically documented coronary artery disease. Patients with asymptomatic ischemia had a higher coronary event rate than those without ischemia. Cardiac event rates followed a similar pattern for patients with silent, symptomatic and mixed ischemia--whether or not there was previous myocardial infarction.

Activities of Daily Living↗
PubMed1988

Interaction of proteins S16, S17 and S20 with 16 S ribosomal RNA.

We have used rapid chemical probing methods to examine the effect of assembly of ribosomal proteins S16, S17 and S20 on the reactivity of individual residues of 16 S rRNA. Protein S17 strongly protects a compact region of the RNA between positions 245 and 281, a site previously assigned to binding of S20. Protein S20 also protects many of these same positions, albeit more weakly than S17. Strong S20-dependent protections are seen elsewhere in the 5' domain, most notably at positions 108, and in the 160-200 and 330 loop regions. Enenpectedly, S20 also causes protection of several bases in the 1430-1450 region, in the 3' minor domain. In the presence of the primary binding proteins S4, S8 and S20, we observe a variety of effects that result from assembly of the secondary binding protein S16. Most strongly protected are nucleotides around positions 50, 120, 300 to 330 and 360 in the 5' domain, and positions 606 to 630 in the central domain. In addition, numerous nucleotides in the 5' and central domains exhibit enhanced reactivity in response to S16. Interestingly, the strength of the S20-dependent effects in the 1430-1450 region is attenuated in the presence of S4 + S8 + S20, and restored in the presence of S4 + S8 + S20 + S16. Finally, the previously observed rearrangement of the 300 region stem-loop that occurs during assembly is shown to be an S16-dependent event. We discuss these findings with respect to assignment of RNA binding sites for these proteins, and in regard to the co-operativity of ribosome assembly.

Aldehydes↗
PubMed1988

Haemophilus influenzae meningitis in the presence of cerebrospinal fluid shunts.

Haemophilus influenzae is an uncommon pathogen in shunted patients and there is uncertainty about optimal management. We report here two cases which were managed differently, with different outcomes. The first case was treated with chloramphenicol and the shunt was not removed. Although there were subsequent episodes of respiratory infection, the outcome was satisfactory. The second case was treated with cefuroxime and the shunt was exteriorized. Re-shunting was followed by relapse and further shunt removal. This and other case reports suggest that in Haemophilus meningitis in shunted patients treatment need not involve shunt removal, but that this is so only if appropriate antimicrobials such as chloramphenicol are used.

Cefuroxime↗
PubMed1988

Sinus node and atrioventricular nodal function in 220 patients recovering from acute myocardial infarction.

Sinus node and atriventricular (A-V) nodal functions were evaluated by right atrial pacing in 220 consecutive patients recovering from acute myocardial infarction (AMI), 10-28 days after the infarct (mean = 14 days). In the 188 patients in whom a pacing rate of 120 beats/min could be achieved, sinus node recovery time, corrected sinus node recovery time (CSNRT) and total recovery time were correlated to infarct site and the presence or absence of myocardial ischemia. Sinus node recovery time and total recovery time were significantly longer in patients with inferior (1,153 + 28 and 3,129 + 179 ms, respectively) or non-Q-wave infarct (1,112 + 28 and 3,730 + 266 ms, respectively), than in patients with anterior infarct (1,044 + 20 and 1,153 + 28 ms, respectively). The parameters were within the reported normal range. When corrected for heart rate (CSNRT), these differences were no longer present. The presence or site of residual ischemia during right atrial pacing did not affect the sinus nodes parameters. A-V nodal function, studied in all 220 patients, was assessed by the appearance of second-degree A-V block at pacing rates below 120 beats/min and by measuring the shortest atrially paced cycle length with 1:1 A-V conduction. Second-degree A-V block appeared at a similar frequency in different AMI locations. Thus, sinus and A-V node functional status in patients recovering from AMI are not affected by infarct site or by the presence or absence of residual myocardial ischemia.

Adult↗
PubMed1988

Use of streptokinase for lysis of a mobile left ventricular thrombus--report of a case and review of the literature.

One-third of patients with acute anterior wall infarction develop left ventricular apical thrombi. Mobile thrombi carry the highest risk of systemic embolization, particularly in the early phase after the acute infarction. We report here on a young patient in whom a protruding and mobile left ventricular thrombus was detected on two-dimensional echocardiogram 1 week after an acute antero-septal infarction. Intravenous administration of relatively low doses of streptokinase was followed within 14 h by complication-free resolution and disappearance of the thrombus.

Echocardiography↗
PubMed1988

Treatment of torsade de pointes with magnesium sulfate.

Twelve consecutive patients who developed torsade de pointes (polymorphous ventricular tachycardia with marked QT prolongation, TdP) over a 4 year period were treated with intravenous injections of magnesium sulfate. In nine of the patients a single bolus of 2 g completely abolished the TdP within 1 to 5 min, and in three others complete abolition of the TdP was achieved after a second bolus was given 5 to 15 min later. Nine of the patients also received continuous infusion of MgSO4 (3 to 20 mg/min) for 7 to 48 hr until the QT interval was below 0.50 sec. In nine of the 12 patients the TdP was induced by antiarrhythmic agents. The QT interval preceding TdP ranged from 0.54 to 0.72 sec. After the MgSO4 bolus, which prevented the recurrence of TdP, no significant changes were observed in the QT interval. There were no side effects of this treatment. In eight of the 12 patients potassium levels before the TdP were below 3.5 meq/liter; magnesium levels were available in eight patients before TdP, and were normal in all. Five additional patients with polymorphous ventricular tachycardia but normal QT intervals (non-TdP patients) received two to three boluses of MgSO4. This treatment was ineffective in all, but they responded to conventional antiarrhythmic therapy. Thus, MgSO4 is a very effective and safe treatment for TdP, and its application is rapid and simple. Its use is therefore recommended as the first line of therapy for TdP.

Aged↗