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Biomedical subjects

L R Johnson

Publications and source records attributed to L R Johnson.

At least 235 records · Page 13Linked to original sources
PubMed1979

Mucosal gastrin receptor. II. Physical characteristics of binding.

Gastrin binding to rat gastric mucosal membrane preparations revealed a linear Scatchard plot, suggesting the existence of a single class of binding sites. Further studies revealed the absence of a positive cooperative effect. Because the system appeared to satisfy the conditions for Michaelis-Menten type kinetics, the determination of a Kd of approximately 3.6 X 10(-10) M was justified. These studies also demonstrated the efficacy of the specific activity of our iodinated gastrin. Trypsin treatment abolished specific binding of gastrin to the membrane preparation, indicating the protein nature of the receptor. The importance of maintaining extremely low temperatures during the incubation and wash period is demonstrated by the decrease in both the rate and the amount of dissociation at 0 degrees C compared with 30 degrees C.

Animals↗
PubMed1979

Influence of enteric parasitism on hormone-regulated pancreatic secretion in dogs.

The objective of this study was to test the hypothesis that enteric parasites affect pancreatic secretion in their host. Pancreatic bicarbonate and protein outputs were studied in dogs with gastric and pancreatic fistulas to determine the secretory response to exogenously administered secretin and cholecystokinin and to intraduodenal stimulation with hydrochloric acid and sodium oleate to release endogenous hormones. Bicarbonate and protein concentrations in pancreatic juice were measured prior to infection with Trichinella spiralis and at various periods during primary and secondary infections. Dose-related increases in secretory activity were observed in uninfected hosts in response to all stimuli. Infected dogs responded like controls to exogenous hormones, but showed reduced secretion under duodenal stimulation during the 1st wk of primary infection. This altered response returned to normal 3 wk after primary infection and did not occur following secondary infection. Results support the conclusion that reduced pancreatic secretion is associated with enteric parasitism and is due to a defect in hormone release or in the supply of hormone available for release.

Animals↗
PubMed1979

Growth of pancreas and gastrointestinal mucosa in antrectomized and gastrin-treated rats.

Growth responses to endogenous and exogenous gastrin were examined in the pancreas and gastrointestinal tract mucosa. Rats were either antrectomized to remove the primary source of endogenous gastrin or subjected to a sham operation. Three weeks after surgery, half of the antrectomized animals were injected ip with pentagastrin (250 microgram/day) four times per day. Injections were carried out for a week. Antrectomy resulted in serum gastrin levels approximately one third of normal. DNA synthesis and DNA and RNA content of the pancreas and oxyntic gland, duodenal, and colonic mucosa were significantly reduced by antrectomy. In each case, pentagastrin treatment restored DNA synthesis and RNA and DNA levels to normal. Significant decreases in pancreatic and colonic weights in antrectomized animals were also completely prevented by pentagastrin injection. These results indicate that endogenous gastrin has an important role in the regulation of pancreatic and colonic mucosal growth, in addition to its already established similar function in oxyntic gland mucosa.

Animals↗
PubMed1979

Influence of parasitism on secretin-inhibited gastric secretion.

This study tested the hypothesis that the inhibitory action of secretin on gastrin-stimulated gastric acid and pepsin secretion is comprised in animals harboring intestinal stages of the parasite Trichinella spiralis. Pentagastrin-stimulated acid and pepsin secretion, and the influence of secretin on these processes, were measured in dogs prepared with gastric fistulas and Heidenhain pouches. Dogs were studied before and after infection with 10(4) T. spiralis larvae/kg body weight. Gastric secretion was stimulated by constant intravenous infusion of pentagastrin, 1 microgram/kg per hour. Exogenous secretin inhibited pentagastrin-stimulated acid and pepsin output from both the main stomach and Heidenhain pouch in infected as well as in the uninfected dogs. Identical inhibition was observed in uninfected dogs during duodenal infusion with HCl to release endogenous secretin. In contrast, duodenal stimulation with HCl did not inhibit acid and pepsin secretion in dogs tested during the 1st week following infection. Results support the conclusion that the regulatory effect of secretin on gastrin-stimulated gastric secretion is impaired during the early phase of infection, and is due to depressed synthesis or release of secretin from duodenal mucosa.

Animals↗
PubMed1978

Role of gastrin in mucosal DNA synthesis after vagotomy and atropine in the rat.

The purpose of this study was to examine 1) the influence of the cholinergic innervation of the stomach on the rate of DNA synthesis in the fundic mucosa of the rat and 2) the possibility that hypergastrinemia might be involved in the response. Repeated injections of atropine in fasting rats increased by 40% the rate of DNA synthesis in the oxyntic gland mucosa. Two weeks after truncal vagotomy, the DNA synthesis rate in oxyntic gland mucosa was increased 64% compared to sham-operated control animals. In the rat colon, atropine administration produced a 56% increase in DNA synthesis compared to saline-injected controls. The injection of pentagastrin in fasting rats also increased the DNA synthesis rate in both stomach and colon, but pentagastrin combined with either atropine or vagotomy stimulated DNA synthesis no more than pentagastrin alone. Cholinergic interruption by atropine or vagotomy elevated endogenous serum gastrin concentrations, indicating that the observed DNA stimulation may be mediated by hypergastrinemia.

Animals↗
PubMed1978

Automated measurement of serum thyroxine with the "ARIA II," as compared with competitive protein binding and radioimmunoassay.

Two conventional serum thyroxine assays, run in separate laboratories, one by competitive protein binding and one by radioimmunoassay, were used to evaluate the automated ARIA II (Becton Dickinson Immunodiagnostics) serum thyroxine assay. Competitive protein binding as compared to ARIA II with 111 clinical serum samples gave a slope of 1.04 and a correlation coefficient of 0.94. The radioimmunoassay comparison to ARIA II with 53 clinical serum samples gave a slope of 1.05 and a correlation coefficient of 0.92. The ARIA II inter-assay coefficient of variation for 10 replicates of low, medium, and high thyroxine serum samples was 6.2, 6.0, and 2.9%, respectively, with an inter-assay coefficient of variation among 15 different assays of 15.5, 10.1, and 7.9%. The automated ARIA II, with a 2.2-min cycle per sample, gives results that compare well with those by manual methodology.

Antibody Specificity↗
PubMed1977

Effect of long-term parenteral feeding on gastric secretion in dogs.

Three dogs were surgically prepared with gastric fistulas and Heidenhain (vagally denervated) pouches. Acid and pepsin responses to pentagastrin and food were determined before, at the end of a 1-mo period of total parenteral feeding, and 1 mo after the resumption of a normal oral diet. Acid and pepsin output from the denervated pouch in response to pentagastrin and food decreased significantly (P less than 0.001) after parenteral feeding and returned to control levels after the dogs resumed a normal diet. Secretory outputs from the gastric fistula in response to pentagastrin remained unchanged throughout the experiment. Basal serum gastrin levels decreased 50% during the period of intravenous feeding and returned to levels approximately twice the control levels following resumption of normal oral food intake. Serum gastrin responses to a meal also decreased during intravenous alimentation and returned to higher than normal levels following a 1-mo period of oral intake. These studies indicate that the absence of oral food intake in the dog does not result in decreased acid secretion from the innervated stomach. Vagal innervation in some way is responsible for the preservation of normal secretion during the absence of food from the gastrointestinal tract of the dog.

Animals↗
PubMed1977

Effect of cholecystokinin on myoelectric activity of small bowel of the dog.

The effect of cholecystokinin on the myoelectric activity of the small intestine was determined in conscious dogs. Six animals were implanted with electrodes along the small intestine, and a cannula was placed in the stomach. A second cannula was inserted into the duodenum in three animals, and a pancreatic fistula was prepared in three animals. Recordings were made in the fasted state, during the intravenous infusion of either saline or cholecystokinin-octapeptide (CCK-OP), during the intraduodenal infusion of either saline or L-tryptophan, and during the fed state. CCK-OP disrupted the fasted pattern of myoelectric activity, caused a dose-dependent increase in spike potentials, and caused a dose-dependent increases in pancreatic protein secretion. Stimulation of myoelectric activity occurred at doses that produced submaximal protein secretion; however, the stimulation was not identical to that seen with feeding. Intraduodenal infusion of L-tryptophan increased pancreatic protein secretion, interrupted the fasted pattern of motility, and induced a pattern similar to that seen with feeding. We conclude that CCK alters small intestinal motility and may play a role in the changes in small-bowel motility caused by the ingestion of food.

Action Potentials↗
PubMed1977

Changes in protein and nucleic acid synthesis in rat gastric mucosa after pentagastrin.

The trophic effects of gastrin on gastrointestinal tissues have been shown to be physiologically important. This study was designed to investigate the sequence of changes in macromolecular synthesis in the rat gastric mucosa following a single dose of pentagastrin. The earliest response was an increase at 1-2 h of poly (A) messenger RNA (mRNA). This increase dropped after 4 h but remained slightly elevated even 12 h after pentagastrin. By 6 h there was a large increase in protein synthesis that lasted until 12 h. Accompanying this rise in protein synthesis was a large increase in ribosomal (rRNA) and transfer RNA (tRNA), which peaked at 12 h. The changes in both fractions of RNA and protein were over by 18 h. No significant increase in secreted protein was noted, but there was a slight, transient decrease at 1 h. Pentagastrin stimulated all forms of RNA, but the largest increase was seen in the rRNA fraction. After multiple doses, parallel increases in rRNA and tRNA were seen. The stimulation of protein synthesis could be abolished by actinomycin D, and was, therefore, RNA dependent.

Animals↗