Search PubMed⌕ Search

Biomedical subjects

D L Hamilton

Publications and source records attributed to D L Hamilton.

At least 73 records · Page 4Linked to original sources
PubMed1978

The effect of cholera toxin and heat labile and heat stable Escherichia coli enterotoxin on cyclic AMP concentrations in small intestinal mucosa of pig and rabbit.

The effect of cholera toxin, heat labile and heat stable Escherichia coli enterotoxin on mucosal cyclic AMP concentrations was determined on the proximal jejunum of weanling pigs and young rabbits. Ligated loops were injected with solutions containing no enterotoxin for control and either cholera toxin, heat labile or heat stable E. coli enterotoxin. The loops were drained after either two, four or six hours incubation at which time accumulated fluid was recorded and mucosal samples removed for determination of cyclic AMP concentration. In the rabbit, cholera toxin and heat labile, but not heat stable E. coli enterotoxin stimulated intestinal secretion while in the pig all three enterotoxins induced net fluid accumulation. Cholera toxin and heat labile, but not heat stable E. coli enterotoxin elevated rabbit mucosal cyclic AMP concentrations. In the pig these enterotoxins had no significant effect on mucosal cyclic AMP concentrations. The results are inconsistent with the hypothesis that the adenyl cyclase system is an essential step for enterotoxin induced intestinal secretion. The activation of intestinal adenyl cyclase by bacterial enterotoxins may only be an associated and not a necessary event for the stimulation of intestinal secretion.

Animals↗
PubMed1978

Effects of intraluminal glucose on intestinal secretion induced by heat stable and heat labile Escherichia coli enterotoxin, cholera toxin and theophylline.

Glucose, l-alanine, l-aspartate, l-methionine and glycine enhanced net fluid and electrolyte absorption in acute isolated loops of the proximal jejunum of weanling swine. The effect of glucose on intestinal secretion induced by heat stable and heat labile Escherichia coli entero-toxin, cholera toxin and theophylline was examined in both the proximal and distal jejunum of weanling swine. In the proximal jejunum glucose enhanced the rate of net fluid and electrolyte absorption. This increase was accompanied by an increase in unidirectional dosium absorption. In loops exposed to either heat stable or heat labile enterotoxins, glucose significantly decreased the rate of net fluid and electrolyte secretion. The magnitude of glucose enhancement in loops exposed to heat stable and heat labile enterotoxins was similar to adjacent control loops. However, glucose enhancement did not occur in loops exposed previously to cholera toxin or concurrently to theophylline. Therefore, cholera toxin and theophylline may inhibit substrate dependent sodium absorption in the proximal jejunum. In the distal jejunum glucose enhancement did occur but the rate of enhancement was less than in the proximal jejunum. In this region glucose enhancement was not evident in loops exposed to either theophylline, heat stable, heat labile or cholera toxin.

Amino Acids↗
PubMed1978

Effect of heat stable and heat labile Escherichia coli enterotoxins and cholera toxin in combination with theophylline on unidirectional sodium and chloride flux in the small intestine of weanling swine.

The effect of heat stable and heat labile Escherichia coli enterotoxins or cholera toxin in combination with theophylline on net water, sodium and chloride and unidirectional sodium and chloride fluxes was examined in acute isolated loops of jejunum of weanling swine. The effect of heat stable enterotoxin in combination with theophylline was determined in loops located in the proximal jejunum, while combinations of theophylline and either heat labile enterotoxin or cholera toxin were studied in the distal jejunum. In each situation the addition of theophylline resulted in an additive rather than a synergistic increment of intestinal secretory activity. This study implies that the intestinal adenyl cyclase system and enterotoxin induced intestinal secretion may not be directly related in the swine small intestine.

Animals↗
PubMed1977

Electrolyte levels and net fluid and electrolyte movements in the gastrointestinal tract of weanling swine.

Electrolyte concentrations, osmolality and pH were determined in conventionally raised weanling swine fed a liquid diet. Incorporation of a dilution marker into the diet in combination with frequent feeding enabled estimations as to the sites of relative fluid and electrolyte absorption and secretion along the gastrointestinal tract. Unlike many other species the weanling pig depends largely on its large intestine for absorption of fluid and electrolytes with small changes in net fluid movement occurring along the jejunal and ileal segments. Additional observations included the absorption of water by the porcine stomach which increased dilution marker concentration by approximately twofold and the high osmolality values recorded in the small and large intestine. The implications of these observations are discussed with regard to pathogenesis of colibacillary diarrhea in the weanling pig.

Animals↗
PubMed1977

Effect of heat stable and heat labile Escherichia coli enterotoxins, cholera toxin and theophylline on unidirectional sodium and chloride fluxes in the proximal and distal jejunum of weanling swine.

Acute, isolated loops of proximal and distal jejunum of weanling swine were exposed to either heat stable porcine Escherichia coli enterotoxin, heat labile porcine Escherichia coli enterotoxin, cholera toxin or theophylline. Unidirectional sodium fluxes in response to heat stable in the proximal jejunum were dependent on the length of time that the intestinal mucosae was exposed to the enterotoxin. Net water, sodium and chloride and unidirectional sodium and chloride flux measurements in the proximal jejunum in response to each agent uniformly indicated that net secretion of fluid and electrolytes was the result of increased unidirectional sodium secretion or blood-to-lumen flux and decreased unidirectional chloride absorption or lumen-to-blood flux. In addition heat stable cholera toxin and theophylline but not heat labile decreased unidirectional chloride secretion a small but significant amount in the proximal jejunum. Sodium and chloride flux measurements in the distal jejunum demonstrated that all four secretory agents could stimulate net secretion of water, sodium and chloride in that region. The response to these secretory agents as measured by sodium and chloride unidirectional flux rates was not similar to changes observed in the proximal jejunum. In the distal small intestine, whereas heat labile cholera toxin and theophylline induced similar qualitative changes in unidirectional sodium and chloride fluxes, that induced by heat stable differed.

Animals↗
PubMed1977

Effects of immune-mediated enteroluminal neltrophil emigration on intestinal function in pigs.

Intestinal function was assessed in cannulated loops of porcine proximal jejunum during immune-mediated emigration of neutrophils into the intestine. Net water, net sodium, net chloride, undirectional sodium and unidirectional chloride fluxes were measured before and after intestinal exposure to an antigen in both sensitized and nonsensitized pigs. Neutrophil emigration was assessed histologically. The results indicate that fluid and electrolyte movements in the intestine are not significantly altered during immune-mediated enteroluminal neutrophil emigration suggesting that the neutrophil response does not interfere with intestinal function.

Animals↗
PubMed1976

Bacteriophage T4 head morphogenesis. VII. Terminal stages of head maturation.

Several aspects of the terminal stages of T4 head maturation were investigated using ts and am mutants blocked at single steps of the assembly pathway. We had previously found that cells infected with mutants of gene 13, e.g., tsN38 and amE609, accumulated both stable (10 to 20%)- and fragile (80%)-filled head precursors (Hamilton and Luftig, 1972). Here we showed the following for such gene 13-defective, mutant-infected cells. (i) Using thin-section analysis the pool of phage precursor structures observed under nonpermissive conditions was one-third of that observed when the cells were cultured under permissive conditions. (ii) In order for complete conversion of the precursors into viable phage to occur, there were apparent requirements of metabolic energy, protein, and DNA synthesis. (iii) The intracellular DNA pool under nonpermissive conditions exhibited a 50% distribution between 63S (mature size) and 200 S (concatenate size) DNA, with the latter DNA serving as a precursor pool. Further, this DNA pool when spread onto a protein monolayer exhibited a dispersed array of DNA, strands around a core, which was less dense than that found for the greater than 1,000S DNA concatenate isolated from gene 49-defective infected cells. (iv) When precuations were taken to stabilize the head precursors, such as lysis of the cells into glutaraldehyde, there was a 30% increase in the yield of 1,200S filled heads. Correlating these results and previous results concerning gene 49-defective unfilled heads, we propose that there are several forms of gene 13 fragile head precursors which serve as intermediates between gene 49 unfilled heads and gene 13 stable filled heads. We cannot, however, rule out the possibility that all gene 13-defective heads represent a single class of unstable particles, which decay slowly. In either case, we have shown that gene 13-defective particles are unstable to some degree inside the cell and are highly unstable outside the cell; yet all particles can still be efficiently converted to phage in vivo.

Chloramphenicol↗
PubMed1976

Gastrointestinal metabolism of cadmium in experimental iron deficiency;.

The average gastrointestinal uptake 4 h after an intragastric dose of 400 nmol of cadmium chloride labeled with 109CdCl2 in iron-deficient mice, 25%, was significantly greater than the result, 16%, in iron-normal animals, and more cadmium entered the body of the former, 3.8%, than the latter, 2% (P less than 0.05). Between 4 and 72 h, gastrointestinal radioactivity declined without further increase in body activity; however, more radiocadmium remained in the duodenum of iron-deficient than iron-normal animals (P less than 0.05). The radiocadmium sequestered in the duodenum was bound to a protein with a molecular weight of about 12,000. After subcutaneous injection of radiocadmium, the rate of excretion of radioactivity from the body was similar in iron-normal and iron-deficient mice; however, a greater proportion of the injected dose accumulated in the duodenum of the iron-deficient animals (P less than 0.05). Thus, the intestinal adapative response to iron deficiency may enhance cadmium toxicity, whereas sequestration and subsequent excretion of cadmium by the intestinal mucosa serves to protect the body against toxic effects. The duodenum, particularly in iron-deficient mice, is especially vulnerable to the toxic effects of cadmium.

Animals↗
PubMed1975

Continuing dental education: reasonable answers to unreasonable questions.

Increasing government involvement in health care, interest in consumerism, and improved instructional technology have raised new challenges for continuing dental education. Arguments from educational research and evaluation theory are used to show the potential dangers involved in compulsory, mass-media continuing education with pre- and posttest measures of success.

Behavior↗
PubMed1972

Bacteriophage T4 head morphogenesis. 3. Some novel properties of gene 13-defective heads.

The nature of phage precursors in gene 13-defective infected cells was studied by electron microscopy and pulse-chase isotopic labeling experiments. Our results suggest that both stable (20%) and fragile (70%) filled-head precursors accumulated in the absence of gene 13 product. Upon extraction, the fragile heads were found to lose most of their deoxyribonucleic acid and appeared unfilled with an average density of 1.34 g/cm(3) and a sedimentation coefficient of 300S. These unfilled heads differed from empty gene 13-defective heads which did not have any associated deoxyribonucleic acid and banded at an average density of 1.31 g/cm(3). Furthermore, it was found that a tsN38 (temperature-sensitive mutant in gene 13)- infected culture maintained at 41.5 C for increasing times led to a decrease in specific infectivity of 1,000S phagelike particles. Electron microscopy of these particles revealed that the decreased infectivity was due to an improper union of head and tails.

Carbon Isotopes↗