Biomedical subjects

K E Hejtmancik

Publications and source records attributed to K E Hejtmancik.

9 recordsLinked to original sources

PubMed1981

Hormone-stimulated release of pancreatic polypeptide before and after vagotomy in dogs.

Concentrations of pancreatic polypeptide (PP) in peripheral blood were measured before, during, and after infusions of graded doses of synthetic human gastrin I (SHG-I), cholecystokinin 99% pure (CCK-99%), CCK octapeptide (CCK-OP), and pure natural porcine secretin in six dogs with gastric and duodenal fistulas. Studies were repeated after truncal vagotomy. Significant increases in concentrations of PP were found with 1 microgram . kg-1 . h-1 of SHG-I, 0.25 and 1.0 microgram . kg-1 . h-1 of CCK-99%, and 0.06 and 0.25 micrograms . kg-1 . h-1 of CCK-OP. Significant increases persisted after vagotomy, except at the lower dose of CCK-OP. Postvagotomy responses were significantly less than prevagotomy, except at the higher doses of CCK-99% and CCK-OP. Pure secretin did not change concentrations of PP in blood before or after vagotomy. The most potent stimulant for PP release on a molar basis was CCI-99%, followed by CCK-OP and SHG-I. The results suggest that cholinergic and humoral agents of the gastrin-cholecystokinin family interact in the normal physiological response of PP to food and that, in dogs, CCK-like peptides are more potent than gastrin.

Animals↗

PubMed1981

Action of pancreatic polypeptide on exocrine pancreas and on release of cholecystokinin and secretin.

We have studied the effect of exogenous porcine pancreatic polypeptide (PP; 0.8 and 2.1 microgram/kg . h, iv) on endogenously stimulated pancreatic exocrine secretion in five pancreatic-fistula dogs. Plasma levels of cholecystokinin (CCK), secretin, and PP were measured in addition to pancreatic secretion of water, bicarbonate, and protein. Intraduodenal infusions of acid and a mixture of phenylalanine and tryptophan were used to stimulate hormone release. PP caused a dose-dependent inhibition of endogenously stimulated pancreatic secretion, whereas the release of CCK and secretin was not affected. Duodenal acidification and intraduodenal infusion of phenylalanine and tryptophan caused a significant release of PP. This study shows that: 1) PP suppresses pancreatic secretion by means of a mechanism that is probably direct; this effect is not mediated through inhibition of release of CCK or secretin, and 2) phenylalanine and tryptophan, both strong stimulants of CCK release, cause a substantial rise in PP in peripheral blood. The mechanism of PP release may involve CCK (in previous studies, we have shown a rise in circulating PP levels after iv CCK infusion).

Animals↗

PubMed1980

Role of gastrin in vagally-stimulated pancreatic secretion.

In an attempt to clarify the contribution of antral gastrin to the vaginal stimulation of pancreatic secretion, we have measured the effect of total excision of the antral mucosa on pancreatic secretion induced by electrical vagal stimulation in eight anesthetized dogs. Stimulation was done before excision of the mucosa, and after excision, with and without a gastrin background. Mucosal excision reduced pancreatic volume response to 25% and pancreatic protein response to 32% of the respective responses obtained before excision; gastrin release in response to vagal stimulation was completely abolished. With a gastrin background (0.5 microgram/kg-hr of synthetic human gastrin-17-I), which resulted in serum gastrin concentrations higher than those obtained by vagal stimulation before excision of antral mucosa, the pancreatic volume and protein response showed only partial restoration. These studies provide evidence that vagal pancreatic secretion is only partially gastrin-dependent, and that other antral factors, probably vagally modulated intramural cholinergic pathways, are involved.

Animals↗

PubMed1980

Effects of gastrin on circulating levels of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in dogs.

The effect of synthetic human gastrin I, infused at two doses, on the concentrations of somatostatin, pancreatic polypeptide, and vasoactive intestinal peptide in portal and systemic blood was studied in six anesthetized dogs. Intragastric pH was maintained at 5.5, and acid output was measured by intragastric titration. Significant increases in somatostatin and pancreatic polypeptide concentrations in portal blood were found with the lower dose of gastrin (0.5 microgram/kg . h) infused for 40 min. When gastrin was infused at 1.5 microgram/kg . h for 100 min, both portal and systemic blood concentrations of somatostatin and pancreatic polypeptide rose significantly. Cimetidine (300 mg, as an iv bolus), given 40 min after the beginning of the second infusion, did not affect gastrin-stimulated release of somatostatin and pancreatic polypeptide, whereas acid output was completely abolished. Vasoactive intestinal peptide concentrations did not change with the infusion of either dose of gastrin. This daily shows that gastrin releases somatostatin and pancreatic polypeptide in a dose-dependent fashion, and since this release was not acid mediated, it appears likely to be a direct action of gastrin.

Animals↗

PubMed1980

Release of pancreatic polypeptide in humans by infusion of cholecystokinin.

Plasma levels of pancreatic polypeptide were measured after a test meal and after infusion of graded doses of 99% pure cholecystokinin in 6 healthy volunteers. Initial attempts at sterilization of 99% pure cholecystokinin resulted in complete inactivation. Successful sterilization was accomplished by filtration by using specially treated silver-coated filters. Biologic activity of sterilized material was confirmed with cholecystokinin bioassay, and plasma levels of sterilized cholecystokinin achieved by exogenous infusions were measured with a specific cholecystokinin radioimmunoassay. Significant increases in plasma levels of pancreatic polypeptide were found with a test meal and with infusions of 0.25 and 0.5 micrograms/kg-hr of 99% pure cholecystokinin. Integrated values of pancreatic polypeptide released by the low-dose and the high-dose infusions of 99% pure cholecystokinin were 59% and 50% of that obtained by food, respectively. Integrated levels of cholecystokinin after 45 min of infusion of 0.25 micrograms/kg-hr were equal to those after a standard meal. Cholecystokinin, therefore, is an effective humoral releaser of pancreatic polypeptide in humans and may play an important role in the intestinal phase of release of pancreatic polypeptide.

Adult↗

PubMed1979

Structure, function, and antigenicity of cholera toxin.

Chemical modification of intact cholera toxin or its B subunit by either partial nitration or reduction and alkylation did not result in significant loss of biological activity as determined by measurement of cyclic AMP in Chinese hamster ovary cells. Complete nitration or succinylation in the presence of guanidine hydrochloride resulted in complete loss of biological activity and significantly affected the immunoreactivity of the toxin and B subunit. Compositional analyses of both the isolated alpha and gamma chains of the toxin were typical of globular proteins and did not reveal significant hydrophobicity. Analysis of antigenic relationships by radioimmunoassay indicated a partial crossreactivity between the alpha chain and the B subunit of cholera toxin. Since previous structural studies of the beta chain of cholera toxin indicated chemical similarity with the glycoprotein hormones [Kurosky et al. Science 195:299 (1977)], radioimmunoassay procedures were employed to investigate for possible crossreactivity. No evidence of crossreactivity between cholera toxin subunits and subunits of ovine luteinizing hormone was found.

Alkylation↗

PubMed1979

Antigenic specificity of neutralizing antibody to cholera toxin.

Selected rabbit antisera to cholera toxin antigens and convalescent cholera patient sera were analyzed using the permeability factor neutralization test and two sensitive in vitro serological assays specific for cholera toxin, cholera toxin A subunit, and cholera toxin B subunit. The results indicated that antisera to cholera toxin contained toxin-neutralizing activity as well as antibodies specific for both the A subunit and B subunit. It was clearly established that antisera to B subunit, devoid of significant anti-A subunit activity, neutralized the vascular permeability activity of cholera toxin. Antisera to A subunit contained neutralizing antibodies and antibodies to both A and B subunits. Absorption with B subunit removed both the toxin-neutralizing and anti-B subunit activities, while the anti-A activity was unaffected. Neutralizing antibody titers of rabbits immunized with B subunit were also observed to be significantly higher than neutralizing antibody titers of sera from A subunit-immunized rabbits, despite the overall similarity in anti-B subunit titers as determined by passive hemagglutination and radioimmunoassay of sera from the two groups of rabbits. Anti-alpha chain sera neither neutralized cholera toxin nor possessed significant antitoxin or anti-B subunit titers as determined by passive hemagglutination and radioimmunoassay. The anti-alpha chain sera contained high levels of antibody specific for A subunit, which is consistent with the hypothesis that the alpha chain is part of the A subunit structure. In contrast, the gamma chain was not shown to be antigenic. Sera from convalescent cholera patients possessed toxin-neutralizing antibody as well as passive hemagglutination and radioimmunoassay antibody against both A and B subunits.

Animals↗

PubMed1979

Characterization of the antigenic determinants of cholera toxin subunits.

The antigenic specificity of purified preparations of A subunit, B subunit, alpha chain, and gamma chain of cholera toxin was studied by double immunodiffusion and radioimmunoassay with antisera produced in rabbits and mice. Rabbits immunized with A subunit produced serum antibodies which were capable of binding radiolabeled A subunit, alpha chain, and B subunit. Rabbits immunized with alpha chain produced serum antibodies that would bind radiolabeled alpha chain and A subunit. Rabbits immunized with the B subunit produced serum antibodies monospecific for the B subunit. The gamma chain did not elicit measurable antibodies in rabbits or mice as evidenced by radioimmunoassay or double immunodiffusion. A sensitive competitive radioimmunoassay was developed in which the B subunit could inhibit binding of radiolabeled A subunit and alpha chain with either antisera prepared against A subunit or alpha chain. Neither the A subunit nor the alpha chain could inhibit binding of B subunit with the antiserum prepared against B subunit. In addition, selected elution fractions obtained during A- and B-subunit purification were used to immunize groups of mice. Mice responded to immunization with the elution fractions of A subunit by producing anti-A-subunit and anti-B-subunit serum antibody responses, whereas mice immunized with elution fractions of B subunit produced only antibodies specific for the B subunit. An equimolar amount of the two resulting protein peaks was used to immunize two groups of rabbits. Rabbits immunized with A subunit, produced a serum anti-B subunit response equal to that of rabbits immunized with the B subunit. Rabbits immunized with equimolar concentrations of A and B subunits were observed to be equally protected against intestinal loop challenge with Vibrio cholerae Inaba V86. The A subunit, not the B subunit, was biologically active when tested by the S49 mouse lymphosarcoma cell test. These studies provide additional evidence supporting the hypothesis that the A subunit, specifically of alpha chain, of cholera toxin contains antigenic determinants in common with the B subunit.

Animals↗

PubMed1977

Radioimmunoassay for the antigenic determinants of cholera toxin and its components.

A radioimmunoassay procedure is described for the detection of cholera toxin and its component polypeptide chains. Cholera toxin, A subunit, B subunit, alpha chain, and gamma chain were iodinated by the chloramine T procedure. Radiolabeling did not significantly alter the polyacrylamide electrophoretic migration patterns of the toxin or its components. Moreover, radiolabeled toxin, B subunit, and alpha chain preparations retained substantial ability to bind to intestinal mucosal homogenates. The minimal amount of antitoxin detectable with radiolabeled toxin was 0.04 antitoxin units/ml. Substitution of radiolabeled B subunit, A subunit, and alpha chain for radiolabeled toxin decreased the sensitivity of the test. Radiolabeled gamma chain did not bind to the antitoxin preparation. Competitive inhibition studies, with titrated anti-choleragen serum and radiolabeled toxin or components, indicated that the minimum concentration of toxin detectable was 7.0 x 10(-8) mumol/ml at a 90% inhibition level. The A subunit and alpha chain preparations inhibited the binding of the radiolabeled B subunit to antitoxin sites. Conversely, B subunit inhibited the binding of radiolabeled A subunit and alpha chain to antitoxin. The gamma chain did not show any reaction with antitoxin or cross-reaction with either whole toxin or its components. These results strongly suggest that the A subunit and the alpha chain contain antigenic determinant(s) that are common to the B subunit. The B subunit (beta chain) and the alpha chain of cholera toxin may therefore contain region(s) of chemical similarity.

Antigens, Bacterial↗