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L R Johnson

Publications and source records attributed to L R Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1985

Ultrastructure of transganglionic HRP transport in cat trigeminal system.

The ultrastructure of transganglionic transport of horseradish peroxidase (HRP) from the inferior alveolar (IA) nerve to the brainstem is being studied in the cat. The IA nerve was soaked in an HRP solution and following a two-day survival the animal was perfused transcardially with a paraformaldehyde-glutaraldehyde solution. The tissue was immediately dissected and postfixed for 1-3 h in perfusate. Sections of 75 micron thickness were cut with a Vibratome and reacted utilizing tetramethyl benzidine (TMB) as the chromagen. Optimum results for electron microscopy were obtained by osmication in a pH 6.0, 1% osmium tetroxide solution for 45 min at 45 degrees C, followed by rapid dehydration and embedment in Epon. The resulting HRP-TMB reaction product was characterized and identified ultrastructurally in ganglion cells, peripheral and central axons and in brainstem terminals. The HRP-TMB reaction product varied in density but had consistent crystalline-like laminations of a repeating unit and characterized by a membrane 4-5 nm in diameter. Some of the HRP-TMB reaction product found in terminals and axons was below the limit of resolution of the light microscope.

Animals↗
PubMed1985

Erythrocyte cytosolic free Ca2+ and plasma membrane Ca2+-ATPase activity in cystic fibrosis.

The properties of the Ca2+, Mg2+-ATPase of erythrocyte membranes from patients with cystic fibrosis (CF) were extensively compared to that of healthy controls. Following removal of an endogenous membrane inhibitor of the ATPase, activation of the enzyme by Ca2+, calmodulin, limited tryptic digestion or oleic acid, as well as inhibition by trifluoperazine, were studied. The only properties found to be significantly different (CF cells vs controls) were calmodulin-stimulated peak activity (90 vs 101, P less than 0.02) and trypsin-activated peak activity (92 vs 102, P less than 0.02). No significant difference could be measured in the steady-state Ca2+-dependent phosphorylation of CF and control erythrocyte membranes indicating similar numbers of enzyme molecules per cell. The functional state of Ca2+ homeostasis in intact erythrocytes was investigated by measuring the resting cytosolic free Ca2+ levels using quin-2. Both CF and control erythrocytes maintained cytosolic free Ca2+ between 20 to 30 nM. Addition of 50 uM trifluoperazine resulted in an increase in erythrocyte cytosolic free Ca2+ to about 50 nM in both CF and control cells. Estimates of erythrocyte membrane permeability using the steady-state uptake of 45Ca into intact erythrocytes revealed no differences between CF and control cells. These results confirm that there is a small decrease in the calmodulin-stimulated activity of the erythrocyte Ca2+, Mg2+-ATPase in CF. However, this deficit is apparently not large enough to impair the ability of the CF erythrocyte to maintain normal resting levels of cytosolic free Ca2+.

Calcium↗
PubMed1985

Functional development of the stomach.

Large increases in gastric acid and pepsin secretion, antral gastrin concentration, and decreases in serum gastrin occur during the third week of life in the neonatal rat. At the same time gastrin receptors appear and gastrin release becomes sensitive to somatostatin, indicating that absence and then appearance of specific hormone receptors may be responsible for some of the ontogenic pattern. At this time the mucosa also begins to grow rapidly, with a greater proportion of cells leaving the proliferative pool and differentiating. For the first 2.5-3 weeks these ontogenic changes can be triggered by corticosterone. Their full expression depends on dietary changes associated with weaning. Neither hormones, dietary changes, nor the weaning process itself is essential for development, because in the absence of these, all of the changes still occur--although they may be delayed or be smaller in magnitude. Figure 1 provides a generalized summary of the normal functional development of the stomach and how it is altered by changes in corticosterone levels and the absence of weaning. These findings indicate that ontogeny is genetically programmed and that the full expression of this program depends on hormones, luminal contents, and other environmental factors. In comparison with the small intestine, for example, gastric ontogeny has not received adequate attention. There are essentially no studies directed toward understanding changes in motility during this period. There is really only one study examining the growth pattern of the mucosa during development, and this study is aimed at changes in DNA synthesis and cell loss. Experiments involving the cell cycle are needed to understand whether existing cells mature and differentiate or whether newly created cells suddenly leave the proliferative pool to differentiate. There have been no experiments in which the effects of thyroid hormone on gastric development have been adequately examined. In addition, little or nothing is known about EGF in the ontogenic process. Studies implanting fetal tissue into adult hosts are needed to determine which gastric functions can develop in the absence of luminal stimulation and hormone changes. The cell biology of the gastric mucosa is difficult to examine--especially that involving the cells concerned with growth and differentiation. The stem cells are dispersed throughout the tissue and are a small portion of the cell population. These have never been isolated for study. In vitro culture of mucosal cells, however, is a technique that can possibly be used to examine development at the cellular and molecular level.

Animals↗
PubMed1985

Induction in vitro of a specific pattern of jejunal propulsive behavior by cholecystokinin.

Experiments were conducted in vitro to determine whether arterial infusion of the C-terminal octapeptide of cholecystokinin (CCK-8) into cat jejunal segments could elicit propulsive behavior when a segment must do hydrostatic work to expel fluid. Oral and aboral ends of jejunal segments, 17 cm in length, were connected to a propulsion evaluation system that imposed input-output conditions of constant capacitance and negligible resistance. Infusion of 1 X 10(-10) to 3 X 10(-9) M CCK-8 produced an initial simultaneous ejection of approximately equal volumes of fluid from both ends of the segments. This reduction in luminal volume lasted for approximately 4 min. Concurrent with this initial reduction in luminal volume were phasic ejections of fluid that often did not occur simultaneously or with equal magnitude from both ends of a segment. This pattern persisted throughout the period of CCK-8 infusion. Arterial infusion of atropine sulfate (10(-6) M) or hexamethonium sulfate (2.8 X 10(-7) M) prevented the induction of propulsive behavior by CCK-8. These results indicate that arterial infusion of CCK-8 can induce a specific pattern of jejunal propulsive behavior by triggering neural activity in the enteric nervous system and that CCK-8 may have a physiological role in regulating propulsion.

Animals↗
PubMed1985

Attenuation of trophic response to gastrin after inhibition of ornithine decarboxylase.

The mechanism by which the hormone gastrin induces growth of the gastrointestinal mucosa is unknown. Many hormones are inducers of ornithine decarboxylase (ODC), the rate-limiting enzyme in the synthesis of the polyamines putrescine, spermidine, and spermine. Although the exact biochemical function of the polyamines is not completely understood, they appear to be required for normal cell growth and differentiation. Rats were maintained on a liquid diet for 5 days and treated with difluoromethylornithine (DFMO, 200 mg/kg ip, 3 times/day), a selective, irreversible inhibitor of ODC, for 5 days. Half of these animals also received pentagastrin (250 mg/kg ip) during the final 3 days of the treatment schedule. DFMO alone had no effect on body weight or mucosal growth. Pentagastrin increased total RNA, DNA, and protein in the oxyntic gland and duodenal and colonic mucosa. Concurrent treatment with DFMO completely inhibited the trophic response to pentagastrin in the oxyntic gland area of the stomach and the duodenal mucosa. In contrast, DFMO was without effect on response of the colonic mucosa to pentagastrin. Pentagastrin treatment did not induce the mucosal ODC activity of the oxyntic gland area of the stomach, the duodenum, the ileum, or the proximal colon of either animals fasted for 48 h or animals maintained on a liquid diet. ODC activity was measured at 4, 8, 12, and 24 h after administration of hormone. These results suggest that, in at least the proximal bowel, the stimulation by gastrin of nucleic acid and protein synthesis requires intact polyamine synthesis but that gastrin itself does not induce ODC.

Adenosylmethionine Decarboxylase↗
PubMed1985

Effect of proglumide on rat pancreatic growth.

Proglumide, a glutaramic acid derivative, is a specific competitive inhibitor of gastrin and cholecystokinin (CCK) receptors. As such, it blocks gastrin-stimulated acid secretion, the trophic effect of gastrin, and CCK-stimulated smooth muscle contraction and acinar cell secretion. In the current study we have demonstrated that proglumide (100 mg/kg three times per day) blocks the trophic effect of a low dose of CCK octapeptide (300 ng/kg) given three times a day for 2 days. The same dose of proglumide when given alone for 6 days, however, resulted in a significant stimulation of pancreatic growth. Proglumide had no effect on the trophic response to a high dose of CCK-OP (5 micrograms/kg) administered for either 2 or 6 days. These results indicate that given over a period of several days proglumide behaves like a partial agonist of pancreatic growth.

Animals↗
PubMed1985

Ileal mucosal growth during intraluminal infusion of ethylamine or putrescine.

Either ethylamine or the diamine putrescine was infused at the rate of 1 mumol/h for 66 h into the ileal lumen of rats. Total mucosal RNA, DNA, and protein content was greater in amine-treated rats than in rats receiving 0.9% NaCl. Growth was greatest in the mucosa surrounding the tip of the infusion catheter but was also observed 9 cm proximal and distal to the catheter tip. Infusion of these amines induced the activity of the enzymes ornithine and S-adenosylmethionine decarboxylase. Ornithine decarboxylase activity was increased 2- and 6-fold and S-adenosylmethionine decarboxylase activity 10- and 5-fold by putrescine and ethylamine, respectively. Induction of the polyamine biosynthetic enzymes was not accompanied by increases in the tissue content of polyamines. Putrescine, spermidine, and spermine content of the ileal mucosa surrounding the catheter tip was the same in 0.9% NaCl-, ethylamine-, and putrescine-treated animals. Finally, ethylamine was without effect on serum gastrin concentration in these experiments. The results suggest that amines regulate mucosal growth and may do so by modulating the activity of the enzymes involved in the synthesis of the polyamines.

Adenosylmethionine Decarboxylase↗
PubMed1985

Relationship of response to a bronchodilator and decline in forced expiratory volume in one second in population studies.

To study the question of bronchial responsiveness as a risk factor for chronic air-flow limitation, we measured the response to inhaled isoproterenol in 795 subjects drawn from 2 cohorts that have been followed over a 9 to 11-yr period. A matched analysis was also performed comparing 44 responsive subjects from these cohorts with 132 nonresponsive control subjects. In both cohorts, level of response to isoproterenol was associated with rate of decline of FEV1 only among "responsive" subjects. These results were confirmed by the matched analysis in which rate of decline of FEV1 among responsive subjects was significantly greater than that observed in their matched controls. These differences were present among smokers as well as nonsmokers and among subjects with and without doctor-diagnosed chronic bronchitis and asthma. We conclude that bronchial hyperresponsiveness is associated with an accelerated decline of FEV1 in nonsmokers and ex-smokers as well as in smokers, and that the relationship exists before clinical disease is manifest. Further work needs to be done to determine whether the association is causal or merely indirect.

Adult↗
PubMed1985

Enhanced ultrastructural visualization of the horseradish peroxidase-tetramethylbenzidine reaction product.

Ultrastructural visualization of the horseradish peroxidase-tetramethylbenzidine (HRP-TMB) reaction product within trigeminal ganglion cells and brain stem axons and terminals following HRP injections into the pulpal chambers of cat teeth is enhanced by utilization of a modified osmication procedure that converts the reaction product to a markedly stable and electron-dense form. The results following the use of the modified osmication procedure (pH 5.0 phosphate buffer at 20 degrees C for 12 hours) are compared to results obtained by following Carson's osmication protocol (Carson KA, Mesulam M-M: J Histochem Cytochem 30:425, 1982; Carson KA, Mesulam M-M: In Tracing Neural Connections with Horseradish Peroxidase. Edited by M-M Mesulam. J Wiley, Chichester, England, 1982, p 153-184) (pH 6.0 phosphate buffer at 45 degrees C for 45 min). The results suggest that the conversion of the HRP-TMB reaction product to an electron-dense form during osmication is intimately associated with the pH of the phosphate buffer and the total time of osmication.

Animals↗
PubMed1985

Effect of epidermal growth factor on the development of rat gastric mucosa.

Epidermal growth factor (EGF) has been shown to stimulate the growth of adult rat gastric mucosa and to increase DNA synthesis of mouse small and large intestinal mucosa. This study examines whether EGF affects the functional and structural development of the rat gastric mucosa. Rats were injected with 20 micrograms/kg EGF three times/day for 5 days beginning on the 10th day after birth. A control group of animals received saline injections of identical volume. All rats were killed on day 15. EGF significantly increased the weight of the whole stomach and the DNA, RNA, and protein content of the oxyntic gland mucosa, but had no effect on the RNA/DNA ratio, or antral and serum gastrin levels. Two groups of similarly treated rats, were anesthetized with ether, pylorus-ligated, and injected with either saline or pentagastrin (250 micrograms/kg) after they had recovered from anesthesia. EGF-treated rats had significantly higher rates of basal acid secretion and pentagastrin-stimulated acid secretion than the saline-treated controls. EGF, however, did not alter basal or pentagastrin-stimulated pepsin secretion nor did it change mucosal pepsinogen content. These results indicate that EGF stimulates oxyntic mucosal growth in unweaned rats but that it does not lead to precocious maturation or functional development.

Animals↗
PubMed1984

Ultrastructure of transganglionic degeneration in brain stem trigeminal nuclei during normal primary tooth exfoliation and permanent tooth eruption in the cat.

Electron microscopy is used to study changes in the axons and terminals in the cat brain stem trigeminal nuclei, main sensory, and partes interpolaris and caudalis, during the process of natural tooth shedding. Areas previously showing light optical argyrophilic degeneration products and adjacent areas lacking this degeneration are included. Various types of alteration occur early during tooth loss, including increased presumed glycogen, increased cytoplasmic density, flocculence, lucency, and neurofilamentous hyperplasia. By the stage of maximum exfoliation, terminals and axons of marked density become prominent in areas showing argyrophilia, whereas nondense forms occur elsewhere. By late eruption ages, all forms of degenerated terminals and axons are rare, but phagocytes are heavily laden with similar forms of debris. The sequence of ultrastructural events is discussed in light of recent studies of transganglionic degeneration, their correlation with light microscopic findings, and the potential implications for central plasticity in this system.

Age Factors↗
PubMed1984

Proglumide inhibition of trophic action of pentagastrin.

Proglumide, a glutaramic acid derivative, inhibits the acid secretory effects of gastrin and is said to be a specific gastrin receptor blocking agent. In the current study we have shown that proglumide inhibits the binding of gastrin to its receptor in rat oxyntic gland mucosa and tested whether this receptor is also responsible for the trophic effect of gastrin. In the first study 400 mg/kg proglumide injected with 250 micrograms/kg pentagastrin every 8 h for 48 h totally prevented the trophic effects of pentagastrin in rat oxyntic gland mucosa. Parameters measured included DNA synthesis and DNA, RNA, and protein content. In a second study the lowest maximally effective dose of proglumide was determined to be 100 mg/kg. The trophic effect of pentagastrin was inhibited in duodenal mucosa, colonic mucosa, and pancreas as well as oxyntic gland mucosa. These data demonstrate that proglumide blocks the trophic action of exogenous gastrin and suggest that the trophic effect of gastrin is mediated by the gastrin receptor.

Animals↗
PubMed1984

Ontogeny of gastric mucosal muscarinic receptor and sensitivity to carbachol.

Development of the muscarinic cholinergic receptor and sensitivity of oxyntic gland mucosa to a muscarinic agonist were studied in rats of various ages. The gastric lumen of the fetal rat at the 20th day of gestation contained a statistically significant amount of basal pepsin, which increased log linearly over the first 30 days of life. Carbachol was effective in stimulating the secretion of pepsin as early as 12 h after birth. Basal acid could be measured in the gastric lumen 12 h after birth. The secretion of basal acid increased log linearly over the first 30 days of life. Carbachol was an effective secretagogue even in the fetal rat. The density of the muscarinic cholinergic receptor of the adult rat oxyntic gland mucosa was 99.3 fmol/mg protein with an apparent equilibrium dissociation constant for quinuclidinyl benzilate of 0.40 nM. The receptor was well developed even in the fetal rat, which bound 79.6 fmol/mg protein with an apparent equilibrium dissociation constant of 0.26 nM. Except for immediately after birth, receptor density was maintained between 70 and 90% of the adult level over the first 30 days of life. These results suggest that cholinergic regulation of gastric acid and pepsin secretion is probably functional by either late gestation or at least immediately after birth.

Aging↗
PubMed1984

Polyamines in the response to intestinal obstruction.

The gastrointestinal mucosa immediately proximal to an intestinal obstruction becomes hyperplastic. Since mucosa that is distal to an obstruction atrophies, it appears that the adaptational response to obstruction is regulated by local factors. The hypothesis tested in these studies is that increased polyamine metabolism in the gut proximal to an obstruction is a required local event in the hyperplastic process. Ligation of either rat ileum or colon resulted within 66 h in a doubling of total RNA, DNA, and protein content in the 2 cm of mucosa immediately proximal to the tie. The trophic response was accompanied by an increase in primary amine content of the intestinal chyme in the segment of gut under investigation. These amines were not removed from intestinal chyme by 24 h of lyophilization, suggesting that the more volatile short-carbon-chain aliphatic amines were of limited importance. Subsequent studies focused on polyamine metabolism. Ornithine decarboxylase (ODC) activity was increased in the mucosa proximal to obstruction. In the ileum, ODC activity was increased 10-fold over control values and in the colon about 2-fold. Increased ODC activity was accompanied by corresponding increases in mucosal polyamine content. Finally, treatment of rats with difluoromethylornithine, a selective, irreversible inhibitor of ODC, partially prevented the trophic response to intestinal obstruction.

Animals↗
PubMed1984

Stimulation of mucosal growth by a dietary amine.

Nutrients are believed to have a direct trophic effect on the cells of the gastrointestinal mucosa. However, no normal constituent of the diet has ever been shown to stimulate mucosal growth when administered orally. Sham-operated and antrectomized rats were fed 20 g of powdered commercial rat pellets daily or 20 g of food containing dimethylamine (100 mumol/g food). After 7 days rats were killed and growth of the mucosa of the oxyntic gland portion of the stomach and 2-cm segments of duodenum, jejunum, and proximal colon was determined. Antrectomy resulted in significant decreases in the weight and the DNA, RNA, and protein content of all four tissues and serum gastrin levels. Feeding amines abolished the differences in the oxyntic gland and duodenal mucosa. In general, the effect of amines decreased distally. Feeding amines did not significantly alter serum gastrin levels. These data indicate that dietary amines may directly stimulate the growth of gastrointestinal mucosa. These results may explain some of the proximal-to-distal gradients described for the growth of the mucosa.

Amines↗
PubMed1984

Calcium-ATPase activity in cystic fibrosis erythrocyte membranes: decreased activity in patients with pancreatic insufficiency.

The activity of Ca-ATPase (Ca2+,Mg2+-ATPase, ATP phosphohydrolase, EC 3.6.1.3) was measured in erythrocyte membrane preparations from 37 cystic fibrosis patients, 27 with pancreatic insufficiency and 10 with pancreatic sufficiency, and from 24 healthy controls. The mean maximal calcium-stimulated specific activities, in the absence and presence of purified calmodulin, of the pancreatic sufficient patients (34.3 +/- 4.2 and 75.9 +/- 6.9 nmol/min/mg) was indistinguishable from that of controls (35.8 +/- 2.6 and 84.3 +/- 4.7 nmol/min/mg), while both activities of patients with pancreatic insufficiency were significantly decreased (28.9 +/- 1.3, p less than 0.02; 65.2 +/- 3.0, p less than 0.001) compared to the control group. Similarly, the mean erythrocyte membrane (Na + K)ATPase activity was decreased only for those patients with a history of steatorrhea and who clinically required pancreatic enzyme therapy and had low immunoreactive trypsin levels (10.6 +/- 0.8 versus control, 13.4 +/- 1.1, and pancreatic sufficient patients, 13.3 +/- 1.4 nmol/min/mg; p less than 0.025). No correlation was found between any of the ATPase activities and the clinical scores of the patients, suggesting the lack of significant contribution of general clinical status to the activities of those cation transporters.

Adolescent↗
PubMed1984

Effects of somatostatin and acid on inhibition of gastrin release in newborn rats.

Newborn dogs, humans, and rats have elevated gastric luminal pH values and significantly elevated serum gastrin levels compared to adults. In the adult, acidification of the antral mucosa to pH 3.0 or lower inhibits gastrin release. Somatostatin is released by acid and may mediate this effect. We examined the effects of gastric acidification and somatostatin injection in rats aged 10 days to adult. Gastric gavage with 0.15 M HCl significantly lowered serum gastrin in animals of all ages. Somatostatin injection (400 micrograms/kg) significantly decreased serum gastrin in rats aged 18 days or older, but not in 10- and 15-day-old animals. These data indicate that 1) the mechanism whereby antral acidification inhibits gastrin release is at least partially developed in unweaned rats, 2) somatostatin is not a necessary mediator of the inhibition of gastrin release, and 3) at least part of the hypergastrinemia found in newborn animals is of antral origin.

Aging↗