Search PubMed⌕ Search

Biomedical subjects

L F Johnson

Publications and source records attributed to L F Johnson.

At least 199 records · Page 11Linked to original sources
PubMed1977

The relative amounts of the cytoplasmic RNA species in normal, transformed and senescent cultured cell lines.

We have examined the relative quantities of 18S and 28S rRNA, 4S RNA and poly (A) + mRNA in the following cultured cells: the mouse fibroblast lines 3T3 and 3T6 in the resting (contact inhibited) and growing (sparse) states, 3T3 clones transformed with SV40 (SV3T3) and with both SV40 and polyoma SV-Py 3T3), hamster lung fibrobalsts (v79), human cervical carcinoma cells (HeLa), and human diploid fibroblasts at early and late passage. The relative quantities of the RNA species were determined by labeling the cells to equilibrium with 32PO4 and measuring the amount of label in each RNA species. The ratio of mRNA to rRNA varied form 1.1% to 2.7% in the different cell lines, the more rapidly growing cell lines usually giving a higher ratio. In cells experiencing growth limitation either by contact inhibition or due to senescence, the ratio of mRNA to rRNA was about 30% lower than in the corresponding cells in the growing state. In most cell lines the ratio of 4S RNA to 18S rRNA was between 0.8 and 1.2, but in seescent fibroblasts, this ratio increased to greater than 1.7. Senescent fibroblasts also contained much more total RNA per unit of DNA than the same cells at early passage or than 3T6 or 3T3 cells.

Animals↗
PubMed1976

Changes in RNA in relation to growth of the fibroblast. IV. Alterations in theproduction and processing of mRNA and rRNA in resting and growing cells.

In previous reports, it was shown that both the concentration and rate of production of rRNA and mRNA were greater in growing than in resting 3T6 fibroblasts. Studies on isolated nuclei indicated that ribosomal RNA production is apparently controlled at the level of transcription. In contrast, hnRNA, the putative precursor of mRNA, appeared to be synthesized at the same rate in resting and growing cells. This finding was unexpected and has been tested in several ways. In this report, we show by an independent method that the relative rate of production of mRNA compared to hnRNA is several-fold higher in growing than in resting cells. However, the kinetics of processing of mRNA appear unchanged. This result suggests either that mRNA arises from a small subfraction of hnRNA or that the efficiency of processing of the hnRNA precursor is an important control mechanism which determines mRNA production ingrowing and resting states. Comparison of the initial rates of labeling of hnRNA and cytoplasmic message gives the efficiency with which the cytoplasmic mRNA is produced from nucleoplasmic RNA. The very low efficiency (3-4% in growing and 1-2% in resting cells) suggests that not every hnRNA molecule gives rise to a cytoplasmic message. In contrast to the similar kinetics of mRNA production in resting and growing states, processing of ribosomal RNA is much slower in the resting state and the emergence time for 28S RNA from nucleolus is greatly lengthened.

Cell Division↗
PubMed1976

Patterns of gastroesophageal reflux in health and disease.

Twenty-four pH monitoring the distal esophagus quantitates gastroesophageal reflux in a near physiologic setting by measuring the frequency and duration of acid exposure to the esophageal mucosa. Fifteen asymptomatic volunteers were studies with 24-hour pH and esophageal manometry. The normal cardia was more competent supine than in the upright position. Physiologic reflux was unaffected by age, rarely occurred during slumber, and was the rule after alimentation. One hundred symptomatic pateitns with an abnormal 24-hour pH record (2 S.D. above the mean of controls) could be divided into three patterns of pathological reflux: those who refluxed only in the upright position (9), only in the supine position (37), and in both positions (54). Upright differed from supine refluxers by excessive aerophagia causing reflux episodes by repetitive belching. Compared to controls, they had excessive post-prandial reflux, lower DES pressure, and less DES exposed to the positive pressure of the abdomen. Supine differed from upright refluxers by having a higher incidence of esophagitis and an inability to clear the esophagus of acid after a supine reflux episode. Compared to controls, they had only a lower DES pressure. Combined refluxers had a higher incidence of esophagitis than supine refluxers. Stricture (15%) was seen only in this group. They were similar to supine refluxers in their inability to clear a supine reflux episode. Compared to controls, they had a lower DES pressure and less DES exposed to the positive pressure of the abdomen. Forty of the 100 patients had an antireflux procedure (4 upright, 8 supine, 28 combined). The most severe postoperative flatus and abdominal distention was seen in the upright refluxers. It is concluded that minimal reflux is physiological. Patients with pathological reflux all have lower DES pressure. Patients with upright reflux have less of their DES exposed to the positive pressure environment of the abdomen. Patients with supine reflux have an inability to clear the esophagus of reflux acid and are prone to develop esophagitis. Patients with both upright and supine reflux have the most severe disease and are at risk in developing strictures. In patients with only upright reflux, aerophagia and delayed gastric emptying may be an important etiological factor.

Deglutition Disorders↗
PubMed1976

Diagnostic accuracy of fiberoptic panendoscopy and visceral angiography in acute upper gastrointestinal bleeding.

Emergency fiberoptic panendoscopy and visceral angiography both had comparable diagnostic accuracy in our series of 55 patients with actively bleeding upper gastrointestinal lesions. The diagnostic accuracy of the barium meal was found inferior to both fiberoptic panendoscopy and visceral angiography. Panendoscopy proved capable of quickly and safely diagnosing site and source of the active bleeding lesion. Visceral angiography requiring additional time, expense and personnel commitment proved an effective back-up procedure when panendoscopy was unsuccessful or contradictions existed. Emergency angiography was well tolerated by gravely ill patients. The therapeutic advantage of angiography with infusion of vasopressin upon completion of the diagnostic study remains to be shown as an advantage over panendoscopy.

Acute Disease↗
PubMed1975

Increasing content of poly A(+) mRNA of serum-stimulated cells in the absence of ribosome synthesis.

When 3T6 cells undergo a serum-induced transition from resting to growing state, the number of ribosomes and the amounts of mRNA increase as the cells prepare for DNA synthesis. We have examined the effect of preventing ribosome synthesis during this transition. When resting cells are stimulated to grow in the presence of 5-fluorouridine, mRNA accumulates normally during the first eight hours, though new ribosome formation is completely blocked by the drug. At later times, mRNA continues to accumulate, but at a reduced rate. The ratio of poly A(+) mRNA to rRNA increases from the value characteristic of resting 3T6 (1.8%) to that of growing 3T6 (2.7%) by five hours, and continues to increase to abnormally high values after this time. Although labelling of tRNA is not affected after brief exposure of cells to fluorouridine, the drug prevents the later accumulation of tRNA that ordinarily occurs following serum stimulation of resting cells. This failure of accumulation is not the result of increased lability of fluorinated tRNA, but is probably due to failure of the transcription rate of pre-tRNA to increase. It is possible that this effect might be due to a regulatory system coupling tRNA content to ribosome content. In cultures stimulated with serum in the presence of fluorouridine the rate of protein synthesis increases with poly A(+) mRNA content during the first eight hours; it then fails to increase further, possibly because ribosomes become rate-limiting.

Blood↗
PubMed1975

Evaluation of the Nissen antireflux procedure by esophageal manometry and twenty-four hour pH monitoring.

Fifteen normal volunteers without symptoms of gastroesophageal reflux and sixteen patients with symptoms of gastroesophageal reflux unresponsive to medical management and having endoscopic esophagitis had esophageal manometry and twenty-four hour pH monitoring of the distal esophagus. The symptomatic patients underwent a Nissen antireflux procedure and were restudied at four months. After surgery, patients had less reflux, a higher sphincteric pressure, and an equal amount of sphincter within the abdomen as did asymptomatic control subjects.

Deglutition Disorders↗
PubMed1975

Changes in RNA in relation to growth of the fibroblast. III. Posttranscriptional regulation of mRNA formation in resting and growing cells.

The proportion of hnRNA processed into cytoplasmic mRNA in resting and growing 3T3 and 3T6 cells has been investigated by measuring the efficiency of transfer of nuclear poly(A) to the cytoplasm. When nuclear poly(A) is either labeled continuously with precursor or pulse labeled and then chased with cordycepin, growing cells transfer approximately twice as much of the poly(A) from the nucleus to the cytoplasm as do resting cells. When cells undergo a serum-induced transition from the resting to growing state, the efficiency of poly(A) transfer is increased to that characteristic of growing cells by 3 hr after the addition of the serum. On the other hand, the proportion of hnRNA which is polyadenylated and the total nuclear poly(A) content are the same in resting and growing cells. It appears that the principal means by which the cell regulates its poly(A)+ mRNA content in the growing and resting states is by regulating the efficiency which nuclear poly(A)+ RNA is converted to cytoplasmic mRNA.

Adenine↗
PubMed1975

Gastroesophageal dynamics during immersion in water to the neck.

This investigation was undertaken to study the effect of hydrostatic pressure on gastroesophageal dynamics during immersion in thermoneutral water to the neck. In 5 healthy male subjects (normal end-expiratory), gastric pressure (PG), esophageal pressure (PE), location and pressure of distal esophageal sphincter (des), location of respiratory inversion point (RIP), and gastroesophageal pH gradient were measured standing in air (A), standing in water to the neck (B), and standing in air with abdominal compression (C). The pressure was measured with a Honeywell esophageal catheter (model 31) with built-in pressure transducer. A Beckman stomach pH electrode (no. 39042) was positioned adjacent to the pressure transducer. PG increased from 4.6 +/- 0.6 (SE) mmHg in A to nearly 20 mmHg in B and C, while PE increased from -6.0 +/- 0.8 mmHg in A to -0.8 +/- 1.0 and -3.4 +/- 0.9 mmHg in B and C, respectively. However, PDES was always 11-15 mmHg higher than PG. The superior limit of DES was displaced cephalad by indicating a stretching of DES and a shortening of the esophagus. Qualitatively similar findings were obtained in C. In all experiments, the esophageal pH remained above 6, and no alteration in the amplitude of primary peristaltic waves was seen. It is concluded that a head-out immersion with increased gastroesophageal pressure gradient predisposes to gastric reflux in the absence of a competent DES mechanism.

Adult↗
PubMed1974

Evaluation of current operations for the prevention of gastroesophageal reflux.

A prospective randomized study was done on 45 patients to evaluate the effectiveness of the Hill, Nissen or Belsey anti-reflux procedure. All patients had symptoms of GE reflux unresponsive to medical therapy, a + standard acid reflux test (SART), and esophagitis (38/45) or + Burnstein test (7/45). Esophageal symptomatic, radiographic, manometric and pH (SART and 24-hr monitoring) evaluation was done pre- and 154 days (ave.) postsurgery. All procedures improved the symptoms of pyrosis. The best improvement was seen after the Nissen repair. All procedures increased the distal esophageal sphincter (DES) pressures over preoperative levels. The Nissen and Belsey increased it more than the Hill. Sphincter length and dynamics remained unchanged. The Nissen procedure placed more of the manometric sphincter below the respiratory inversion point in the positive pressure environment of the abdomen. The esophageal length was increased by the Nissen and Hill repairs. This was thought to account for the high incidence of temporary postsurgery dysphagia following the Nissen and Hill repairs and the lower incidence following the Belsey repair. Reflux was most effectively prevented by the Nissen repair, as shown by the SART and the 24-hr esophageal pH monitoring, a sensitive measurement of frequency and duration of reflux. The average length of hospital stay was 20 days for Belsey and 12 days for both Nissen and Hill procedure. Postsurgery complications were more common following the thoracic than the abdominal approach. Ability to vomit postrepair was greatest with the Hill and least with the Belsey and Nissen repair. All procedures temporarily increased amount of flatus. It is concluded that the Nissen repair best controls reflux and its symptoms by providing the greatest increase in DES pressure and placing more of the sphincter in the positive abdominal environment. This is accomplished with the lowest morbidity but at the expense of temporary postoperative dysphagia and a 50% chance of being unable to vomit after the repair.

Deglutition Disorders↗