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L R Johnson

Publications and source records attributed to L R Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1987

Hormonal effects on development of the secretory apparatus of chief cells.

We used light microscopy, transmission electron microscopy, and stereological point-counting methods to investigate the response of rat gastric chief cells to corticosterone and thyroxine during postnatal development. Administration of corticosterone or thyroxine to normal animals in the first two postnatal weeks increased relative numbers of chief cells in the fundic mucosa but did not change the absolute number of total cells in each gland. The chief cells displayed more rough endoplasmic reticulum, zymogen granules, and Golgi saccules in corticosterone- or thyroxine-injected rats than in normal control rats. When rats were either adrenalectomized or made hypothyroid using propylthiouracil, the number of chief cells dramatically decreased. Ultrastructural studies of chief cells from adrenalectomized or hypothyroid rats showed retarded differentiation as indicated by increased free ribosomes, less rough endoplasmic reticulum, fewer zymogen granules, and poorly developed Golgi apparatuses. In adrenalectomized animals, thyroxine replacement alone failed to induce the histological maturation of chief cells, but addition of corticosterone stimulated chief cell differentiation. In hypothyroid animals, either thyroxine or corticosterone replacement restored the differentiation of chief cells to normal levels. Our data indicate that 1) corticosterone is necessary for gastric chief cell maturation during postnatal development, 2) a decrease or loss in either corticosterone and/or thyroxine results in retarded chief cell differentiation and functional activity, and 3) the effect of thyroxine on chief cell development is secondary to an accompanying increase in serum corticosterone.

Adrenalectomy↗
PubMed1987

Hormonal effects on development of the secretory apparatus of parietal cells.

The effect of corticosterone and thyroxine on the development of parietal cells was studied in 20-day-old rats. Either corticosterone or thyroxine injection significantly increased the amount of mitochondria, tubulovesicles, and intracellular canaliculi in normal rat pup parietal cells. However, the ultrastructure of parietal cells did not change when rats were adrenalectomized or made hypothyroid by propylthiouracil (PTU) during the first week of life. Corticosterone had the same effect in hypothyroid rats as in normal rats, increasing the volume fraction of mitochondria and the surface density of tubulovesicles and intracellular canaliculi in the parietal cell. However, thyroxine failed to do so in adrenalectomized animals. When 20-day-old adrenalectomized or hypothyroid rats were challenged with secretagogues, there was no increase in maximal acid output over the basal secretory rate, while normal rats showed a 40-50% increase. We conclude that 1) normal parietal cells respond to additional thyroxine or corticosterone with increases in volume fraction of mitochondria and surface density of tubulovesicles and intracellular canaliculi; 2) the dramatic decreases in acid secretion observed in adrenalectomized or PTU-treated rats are not explained by the morphology of parietal cells that remains normal; 3) the effect of thyroxine on the development of acid secretion is mediated by corticosterone; and 4) unlike chief cells the morphological development of parietal cells does not appear to depend on corticosterone or thyroxine after postnatal day 7.

Adrenalectomy↗
PubMed1987

Stimulation of ornithine decarboxylase activity in digestive tract mucosa.

Refeeding fasted rats with normal rat food and with a variety of amino acids increases ornithine decarboxylase (ODC) activity considerably. The time course of that increase, the areas of the digestive tract directly affected, and the effective concentrations of stimulants are unknown. By use of isolated 5-cm segments of rat jejunum, we determined that maximal activation of ODC occurred after a 2-h exposure to 0.6 M glycine. Increased activity was first apparent after a 1-h exposure to glycine and was significant after a 2-h exposure to 0.05 M glycine. ODC activity increased the most in segments of jejunum, followed by segments of ileum and then duodenum. Glycine (0.4 M) failed to increase ODC activity in gastric and colonic mucosa. Interestingly, D-alanine was more effective than L-alanine in stimulating ODC activity in the jejunum. Enzyme activity was not dependent on osmotic activity of the test substances. Glucose increased enzyme activity, but mannitol and fructose were without effect. The effects of glycine were significantly greater than those of glucose. In summary, ODC of the small intestinal mucosa is increased by direct contact with amino acids and glucose within 2 h after exposure. Increased enzyme activity depends on the nature of the stimulant rather than the osmotic activity of the solution in contact with the mucosa.

Alanine↗
PubMed1987

The role of food intake on gastric mucosal growth and gastrin receptors during pregnancy and lactation.

We examined the effects of pregnancy and lactation on mucosal growth and the numbers and affinity of gastrin receptors in the oxyntic gland mucosa in rats and compared these with changes in serum gastrin levels and food consumption. Gastric mucosal DNA, RNA, and protein contents were significantly increased during lactation. These changes were not observed in either pregnant or nonlactating rats which had given birth at the same time as the lactating animals. The gastrin-binding capacity of a membrane fraction of the oxyntic mucosa was also increased at the corresponding periods in lactating rats (Days 7, 15, 20). Scatchard plot analysis revealed that the number of gastrin receptors was significantly increased without any change in affinity. Food consumption and levels of serum gastrin remained unaltered in pregnant and non-lactating rats compared to virgin controls, but were significantly increased in lactating rats. Increased serum gastrin levels and gastrin binding capacities in lactating rats (Day 15) were abolished by preventing increased food consumption by means of pair feeding. The results demonstrate that the number of gastrin receptors in the oxyntic mucosa increases during lactation in rats. This increase is probably due to hypergastrinemia caused by increased food intake. The increased number of gastrin receptors may be involved in the mechanism of hypertrophic responses of the gastric mucosa in lactating rats.

Animals↗
PubMed1987

Dual fluorometric/colorimetric detection system for an automated random-access instrument utilizing standard polystyrene test tubes as precision cuvettes.

To attain the optical precision necessary to precisely quantify fluorescent or colorimetric signals, analytical systems have typically included quality-controlled cuvettes, flow cells, or dual-beam reference systems. We describe a system where a fluorescence or transmittance signal is quantified in single, standard, 12-mm-diameter polystyrene test tubes. Tube-to-tube variation is minimized by referencing the primary signal to a second reference signal. The tube is carefully oriented within a positioner that allows for the precise placement of the tube within a light path 7.6 mm in diameter. The detection system allows for use of either four pairs of fluorescence excitation/emission wavelengths or eight transmittance wavelengths, which are selected by using specific interference filters. The impact of temperature, tube imperfections, surface flaws, and distortions is minimized by using a reference ratio. Fluorescence is measured with an orthogonal photomultiplier tube, and transmittance with a photodiode; both are illuminated with an ordinary long-life tungsten-halogen lamp. This system is used with the Becton Dickinson AFFINITY system, an automated random-access analyzer with analyte-specific unit-package reagents. The polystyrene tube of the reagent package, which has an antibody-absorbed surface, serves as both the cuvette and the separation medium. Use of the reference ratio method reduces intertube imprecision of fluorometric or transmittance signals, for more precise quantification of various analytes.

Autoanalysis↗
PubMed1986

Does corticosterone affect gastric mucosal cell growth during development?

The effect of corticosterone on the growth of the gastric mucosa was investigated during development. The weight of the mucosa and DNA, RNA, and protein content were used as parameters of growth. The pepsinogen content of the oxyntic gland was examined as an indicator of the biological action of corticosterone on development. Corticosterone-treated animals had lower body weights than control animals on days 10-20. This difference was not seen on day 25. Corticosterone administration during the first and second postnatal weeks induced the precocious appearance of pepsinogen in the oxyntic gland mucosa and increased basal acid output. These effects disappeared by day 25. The weight of the mucosa and DNA, RNA, and protein content of the oxyntic gland and antrum increased with age, but corticosterone had no effect on any of these parameters. We conclude that the induction of precocious development of the gastric mucosa by corticosterone is not due to the stimulation of growth.

Animals↗
PubMed1986

Effect of refeeding on polyamine biosynthesis in isolated enterocytes.

Ornithine decarboxylase (ODC) activity has been found to be preferentially associated with small intestinal villus cells rather than crypt cells in the rat. In the present study, ODC, S-adenosylmethionine decarboxylase (SAMDC), and polyamines were measured in isolated enterocytes to determine which cell populations increased polyamine biosynthetic activity after refeeding. Two hours following refeeding, significant increases in ODC were observed in villus tip (10 times) and midvillus (20 times) enterocytes. No increase in ODC activity was found in isolated crypt cells. A similar pattern was observed for SAMDC. Enzyme activity increased in villus tip (2 times) and midvillus (27 times) cells but not in crypt enterocytes. Putrescine contents were increased following refeeding in midvillus enterocytes (P less than 0.05) and in crypt cells (P less than 0.05). The accumulation of putrescine in midvillus cells occurs via ODC-induced biosynthesis, whereas in crypt enterocytes it may be due to putrescine uptake. The lack of induction of ODC and SAMDC in crypt enterocytes following acute refeeding suggests these enzymes are apparently not involved in the initiation of cell proliferation known to occur under this condition.

Adenosylmethionine Decarboxylase↗
PubMed1986

Role of thyroxine in functional gastric development.

The role of thyroxine (T4) on the functional development of chief and parietal cells was studied in the rat. Daily injection of thyroxine (0.1 microgram/g body wt) resulted in the precocious appearance of pepsinogen in the oxyntic gland mucosa and an increase in basal acid output. Thyroxine had no effect in adrenalectomized rats. In propylthiouracil-induced hypothyroid pups, pepsinogen content and basal acid secretion were low. Corticosterone acetate (200 micrograms/g body wt) injection increased pepsinogen content and basal acid secretion in the absence of normal levels of thyroid hormones. We conclude that the effect of thyroxine on the development of chief and parietal cells is primarily due to accompanying changes in serum corticosterone.

Adrenal Glands↗
PubMed1986

Ornithine decarboxylase and mucosal growth in response to feeding.

The purpose of this study was to examine the role of ornithine decarboxylase (ODC) in the stimulation of the growth of gastrointestinal mucosa following feeding. Rats were divided into five groups: 1) fasted for 2 days, 2) fasted for 2 days and refed for 2 days, 3) fasted for 2 days and refed with the addition of 5% difluoromethylornithine (DFMO) to the drinking water, 4) normally fed, and 5) normally fed plus 5% DFMO in the drinking water. In general the results show a significant dissociation between ODC activity and growth of gastrointestinal mucosa in response to feeding. In the gastric mucosa, growth was inhibited by fasting and DFMO and stimulated by feeding, but there were no significant changes in ODC activity in any of the five groups. In the ileum ODC activity increased dramatically in refed rats and was essentially eliminated in rats fed DFMO. DFMO, however, had no effect on mucosal growth in fed rats and only prevented part of the trophic response to refeeding. The results in the colon were much the same as in the ileum, except that DFMO prevented even less of the trophic response to refeeding, despite total inhibition of ODC. These data suggest that polyamines necessary for growth of gastrointestinal mucosa following feeding are not supplied by the rapid activation of mucosal ornithine decarboxylase.

Animals↗
PubMed1986

Mechanism of induction of mucosal ornithine decarboxylase by food.

Refeeding fasted rats dramatically increases ornithine decarboxylase (ODC) activity in the mucosa of the small intestine and colon. The agents responsible for that activation and pathways leading to activation, however, have not been identified. The current work examines whether stimulation of ODC activity is mediated humorally or directly and whether dietary amines might be in part responsible for activation. Male Sprague-Dawley rats were used 1 wk after they were surgically prepared with Thiry-Vella jejunal loops. Two hours after refeeding rats fasted for 48 h, ODC activity increased 40-fold in mucosa from the intact jejunum and 4-fold in the mucosa of the bypassed segments. The injection of intestinal contents (obtained from additional fed rats) into the bypassed loop caused a 10-fold increase in ODC activity in the loop measured 2 h later. Injection of gut contents, lyophilized to remove dietary amines, produced no change in enzyme activity. The addition of 400 mol dimethylamine to lyophilized gut contents restored enzyme activation to 80% of the previous level. These data allow the following conclusions: following a meal mucosal ODC is activated by both humoral and direct mechanisms, direct stimulation by dietary constituents appears to be the predominant mechanism involved, and dietary amines may be one of the agents involved in directly increasing enzyme activity.

Animals↗
PubMed1986

Stimulation of growth of a colon cancer cell line by gastrin.

The trophic effects of the hormone gastrin-17 were examined on a human colon cancer cell line. LoVo cells were obtained from the American Type Culture Collection and grown in minimal essential medium in the presence of 10% bovine fetal serum. To demonstrate the trophic effect of gastrin, synchronization was necessary. The effect of gastrin was optimal after 26-h exposure to 0.6 mM thymidine. In the presence of serum the optimal dose of gastrin for stimulation of DNA synthesis was 7.2 X 10(-10) M. Under these conditions gastrin caused a 220% increase in [3H]thymidine incorporation. In the absence of serum the optimal dose of gastrin (3.6 X 10(-9) M) increased DNA synthesis approximately 200%. Twenty-four hours after gastrin treatment (1.8 X 10(-10) M gastrin 17) cell numbers increased 50.8% compared with control. At 48 h this increase was maintained at 44%. Maximum stimulation by gastrin occurred 7-8 h after release from synchronization and exposure to gastrin. This corresponded to the S phase of the cell cycle. Significant stimulation occurred a second time at 22-24 h, presumably during the second S phase in a still synchronous or partially synchronous cell population. These data demonstrate that physiological concentrations of gastrin-17 can stimulate the growth of a human cancer cell line and that some degree of synchronization may be necessary to demonstrate similar effects in other cell lines. Such cell lines may provide a source of rapidly growing cells in which the mechanisms of the trophic effect of gastrin can be examined.

Adenocarcinoma↗
PubMed1986

Effect of cell proliferation on healing of gastric and duodenal ulcers in rats.

The healing of acetic acid-induced gastric and duodenal ulcers was examined together with the biochemical indices of growth in gastric and duodenal mucosa in the following three groups of rats: (a) chow-fed, (b) fed an isocaloric liquid diet, (c) fed the liquid diet plus pentagastrin injections (250 micrograms/kg, 3 times/day). Animals received the diet regimen for 10 days from 1 day after induction of ulcer (day 0). Following the feeding regimens, serum gastrin levels, oxyntic gland mucosal DNA synthesis, and gastric secretory function were significantly lowered in the rats fed liquid diets. DNA synthesis in the duodenal mucosa was not different from the pre-ulcer levels. Pentagastrin significantly restored the DNA synthetic and gastric secretory activity of the liquid diet-fed rats toward the levels in the chow-fed group. In the latter group, a significant increase in DNA synthesis and levels of serum gastrin was found at day 6 (after 5 days feeding), which corresponded with a rapid, spontaneous healing of ulcers. Feeding rats liquid diet significantly delayed the healing of gastric, but not duodenal ulcers. Repeated administration of pentagastrin accelerated gastric ulcer healing in the liquid diet group toward the rate observed in the chow-fed group, but had no effect on the healing of duodenal ulcers. These results indicate that cell proliferation is an important factor in the healing of gastric ulcers.

Animals↗
PubMed1986

A four-year prospective study of the respiratory effects of volcanic ash from Mt. St. Helens.

This report describes the 4-yr follow-up of 712 loggers exposed over an extended period to varying levels of fresh volcanic ash from the 1980 eruptions of Mt. St. Helens. Concerns related to the irritant effect the ash might have on the airways and also to its fibrogenic potential if exposures were intense and continued over many years. Our subjects were divided into 3 groups: high, low, and no exposure. Baseline testing was begun in June 1980, 1 month after the major eruption, and follow-up testing continued on an annual basis through 1984; 88% of the loggers have been tested at least 3 times. Analysis of lung function data showed that a significant, exposure-related decline in FEV1 occurred during the first year after the eruption. The decline was short-lived, however, and by 1984 the differences between exposure groups were no longer significant. Self-reported symptoms of cough, phlegm, and wheeze showed a similar pattern. No ash-related changes were seen in chest roentgenograms taken in 1980 and in 1984. Our findings are consistent with the hypothesis that the inhaled ash caused mucus hypersecretion and/or airway inflammation that reversed when the exposure levels decreased. The ash levels to which the loggers were exposed were low compared with permissible occupational levels for nuisance dusts, but generally higher than the total suspended particulate levels permissible in ambient air.

Adolescent↗
PubMed1986

Relationship between serum IgE and cross-sectional and longitudinal FEV1 in two cohort studies.

Evidence is accumulating that elevated levels of serum IgE may play a role in the pathogenesis of chronic airflow obstruction. We examined this question using data on 863 subjects drawn from two cohort studies which we have followed over a period of nine to 11 years. One, the Portland cohort, represents a working population aged 25 to 55 years at baseline. The second, the Screening Center cohort, spans a wider age range (18 to 87 years at baseline) and is biased towards respiratory disease. Spirometric tests and respiratory symptom questionnaires have been administered five times over a nine-year period for the Portland cohort, and over an 11-year period for the Screening Center cohort. IgE was measured one time towards the end of the follow-up. Our data confirm the finding that smokers tend to have higher IgE levels than nonsmokers. For the combined sample, geometric mean levels of IgE were 31.0 IU/ml among smokers and 17.4 IU/ml among nonsmokers. Levels among ex-smokers were intermediate. Among smokers, IgE was not related to either amount smoked or pack-years. Cross-sectionally, FEV1 was inversely related to IgE in the Screening Center cohort, but not in the Portland cohort study. Among smokers, this association was only present for those subjects with symptoms of chronic bronchitis (chronic cough/sputum production). We found no association of IgE with longitudinal rate of decline of FEV1 in either cohort. These findings are consistent with other studies and support the hypothesis that serum IgE is inversely related to function level cross-sectionally, but is not predictive of rate of decline of lung function.

Adult↗
PubMed1986

Light- and electron-microscopic localization of primary dental afferents to medullary dorsal horn (pars caudalis).

Light-microscopic (LM) and ultrastructural (electron-microscopic, or EM) identification of primary dental afferents to medullary dorsal horn (MDH) was demonstrated in the cat following injections of horseradish peroxidase (HRP) into pulpal chambers of unilateral maxillary and mandibular posterior teeth, including the cuspids. Use of a new osmication protocol improved and simplified the EM localization of reaction product within the brain stem terminals. LM examination showed that the projection pattern varied between the different levels of MDH. At caudal levels, the labeling was primarily confined to a narrow band consisting of a dense projection to the dorsomedial portion of laminae I and superficial II and a less intense projection to lamina V. The pattern to rostral levels became increasingly more dense and extensive within these same laminae. LM examination of the tooth apex region showed that a limited spread to the periodontal ligament occurred in some cases. EM investigation of the ipsilateral MDH demonstrated reaction product in terminals with synaptic vesicles that are presynaptic to small and medium-sized dendrites. Labeled axonal endings in close association with cell bodies were also observed. No labeled structures were identified in the contralateral MDH. Some of the reaction product found with EM was below the LM limit of resolution, and thus ultrastructural investigation is necessary for a complete analysis of any pathway when using HRP.

Animals↗
PubMed1986

Thin layer chromatography of commercial samples of amido black 10B.

The tannic acid-phosphomolybdic acid-amido black (TPA) stain has been used primarily for staining hemoglobin. That different dye lots of amido black cause variable staining is documented in the literature. Nine commercial samples of amido black were investigated using thin layer chromatography; all of these dyes contained colored contaminants. Separation of contaminants was achieved using silica gel thin layer chromatography and a solvent system of 95% ethanol:90% phenol:concentrated NH4OH, 12:9:3. TPA staining of red blood cells was improved by using purified amido black.

Amido Black↗
PubMed1985

Toxic ricin demonstrates a dual dental projection.

Toxic ricin was used to study the central distribution of dental afferents in the cat. Following intrapulpal ricin injections ganglion cell degeneration is seen in the II and III ganglion divisions. Central argyrophilic degeneration occurs in the dorsal portion of all ipsilateral trigeminal nuclei. Ventral degeneration is seen in the pars interpolaris and pars caudalis. No contralateral degeneration was observed. The results are discussed with regard to previous studies of the central location of dental afferents.

Animals↗