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Biomedical subjects

J R Roberts

Publications and source records attributed to J R Roberts.

At least 145 records · Page 8Linked to original sources
PubMed1986

Evidence for dual modulation of pepsinogen secretion using isoproterenol, carbachol, CCK-8, forskolin, 8 bromo-cAMP, and A23187 probes.

The cellular mechanisms by which pepsinogen (PNG) secretion is controlled are not understood. The aim of this study was to explore whether modulation of PNG secretion is mediated by cAMP or calcium-calmodulin (C-C). PNG secretion in isolated rabbit gastric fundic glands (IGG) was tested, using agents believed to act via cAMP or C-C. IGG were stimulated for 30 minutes with histamine (H) 10(-5) M, isoproterenol (I) 10(-5) M, carbachol (C) 10(-5) M, cholecystokinin-octapeptide (CCK-8) 10(-7) M, forskolin (F) 10(-5) M, 8 bromo-cAMP (8B) 10(-3) M, and A23187 (A) 10(-6) M. PNG levels were determined by spectrophotometric assay of hemoglobin digestion products. PNG amounts secreted were (mean per cent above basal levels of total IGG PNG units +/- SEM): H, -0.02 +/- 0.30%; I, 3.5 +/- 0.9%; C, 5.1 +/- 2.2%; CCK-8, 5.3 +/- 1.5%; F, 10.6 +/- 3.8%; 8B, 13.8 +/- 4.5%; A, 2.1 +/- 1.1%. All secretagogues except H stimulated PNG release significantly above basal levels (p less than 0.05). A primary histaminergic mechanism for pepsinogen secretion is unlikely. Since two other adenylate cyclase activators, isoproterenol and forskolin and the 3':5'-cyclic adenosine monophosphate analog 8-bromo cAMP stimulated pepsinogen secretion, cAMP-dependence is probable. Since carbachol, CCK-8, and A23187, which are believed to act via calcium-calmodulin, also stimulated pepsinogen secretion, this system, too, presumably plays a substantial role. Thus the data support a dual 3':5'-cyclic adenosine monophosphate/calcium-calmodulin modulation of pepsinogen secretion.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1985

Localization of human factor FVIII inhibitor epitopes to two polypeptide fragments.

Epitopes for 22 alloantibodies that inhibit factor VIII procoagulant protein (FVIII) from multitransfused individuals with severe hemophilia A and three autoantibodies from nonhemophilic individuals appeared to be restricted to two specific regions of the FVIII molecule. Immunoblotting of purified FVIII and purified thrombin-degraded FVIII, followed by reaction with inhibitor plasma samples, monoclonal anti-human IgG3 and IgG4 antibodies, and radiolabeled affinity-purified rabbit anti-mouse IgG, revealed that inhibitor epitopes could be localized to the Mr 72,000 and Mr 44,000 thrombin fragments of FVIII. These two chains are located at the carboxyl terminus and near the amino terminus of the FVIII molecule, respectively. The pattern of reactivity of the inhibitor alloantibodies could be divided into three types: 10 reacted with the Mr 72,000 chain, 3 reacted with the Mr 44,000 chain, and 9 reacted with both of these chains. Among the 3 inhibitor autoantibodies, 1 of each type was found. Ten normal plasmas, as well as 14 plasmas from multitransfused individuals with severe hemophilia A and no inhibitor, were not reactive with the FVIII immunoblots. However, one multitransfused individual with severe hemophilia A and no detectable inhibitor revealed the presence of an antibody reactive with the middle section of the FVIII molecule. The existence of FVIII inhibitor epitopes on both the Mr 72,000 and Mr 44,000 chains raises the possibility that these epitopes might be further restricted to regions of homology between the two chains. These data suggest the possibility of designing inhibitor blocking polypeptides for use as therapeutic agents.

Autoantibodies↗
PubMed1985

Human factor VIII procoagulant protein. Monoclonal antibodies define precursor-product relationships and functional epitopes.

The human Factor VIII procoagulant protein (VIII:C) purified from commercial Factor VIII concentrate consisted of a polypeptide doublet of 80,000 mol wt, a 92,000-mol wt polypeptide, and additional polypeptides of up to 188,000 mol wt. Thrombin digests contained a doublet of 72,000 mol wt, as well as 54,000- and 44,000-mol wt fragments. Proteolysis studies of purified VIII:C using thrombin and activated protein C have suggested that the 92,000- and 80,000 (or 72,000)-mol wt polypeptides comprise activated VIII:C. We have now used seven monoclonal antibodies raised against purified VIII:C to construct a preliminary epitope map of these VIII:C polypeptides. The specific VIII:C polypeptides with which the monoclonal antibodies reacted were determined by immunoblotting of VIII:C onto nitrocellulose sheets after reduced NaDodSO4-polyacrylamide gel electrophoresis. A minimum of five distinct epitopes were defined by these monoclonal anti-VIII:C antibodies. Identification of polypeptides bearing these epitopes allowed localization of distinct thrombin cleavage sites to the 92,000- and 80,000-mol wt chains, helped define polypeptide chain precursor-product relationships, and suggested that both the 92,000- and 80,000-mol wt polypeptides are necessary for VIII:C function. These data and their interpretation are consistent with the published description of the complete primary structure of VIII:C and its thrombin cleavage products. The 92,000- and 80,000-mol wt chains have been located at the amino- and carboxy-terminal ends of the molecule, respectively.

Antibodies, Monoclonal↗
PubMed1985

Independent modulation of von Willebrand factor and fibrinogen binding to the platelet membrane glycoprotein IIb/IIIa complex as demonstrated by monoclonal antibody.

In this study we have used two new monoclonal antibodies, designated LJP5 and LJP9, as well as a previously described one, AP2, all specific for the platelet membrane glycoprotein (GP)IIb/IIIa complex. None of them reacted with dissociated GPIIb or GPIIIa. The monovalent Fab fragment of both LJP5 and LJP9 bound to unstimulated platelets in a saturable manner, but binding was markedly decreased after platelets had been incubated at 37 degrees C in the absence of added extracellular calcium. The binding of LJP9 was not affected by AP2, but was blocked by excess LJP5. On the contrary, the binding of LJP5 was blocked in the presence of both AP2 and LJP9. Thus, these antibodies bound to distinct epitopes of GPIIb/IIIa. At saturation, the binding to unstimulated platelets was between 2.41 and 10.9 X 10(4) molecules/platelet for LJP5 and between 3.47 and 9.1 X 10(4) molecules/platelet for LJP9 (range of 11 and 10 experiments, respectively). Binding increased up to 50% after thrombin stimulation. The estimated association constant, Ka, was 2.7 X 10(7) M-1 for LJP5 and 3.85 X 10(7) M-1 for LJP9. Both LJP5 and LJP9 partially inhibited the association of 45Ca2+ with the surface of unstimulated platelets. Moreover, both antibodies blocked the binding of von Willebrand factor (vWF) to stimulated platelets, whereas only LJP9, but not LJP5, blocked fibrinogen binding. LJP9 was also a potent inhibitor of platelet aggregation, whereas LJP5 was without effect in this regard. The results of the present study demonstrate that independent modulation of vWF and fibrinogen binding to stimulated platelets can be attained with monoclonal antibodies directed against distinct epitopes of GPIIb/IIIa.

Adenosine Diphosphate↗
PubMed1985

The effects of cholecystokinin on parietal cell secretion in isolated gastric glands.

Cholecystokinin (CCK), a peptide hormone found in both gut and brain, shares amino acid homologies with gastrin and has previously been shown to stimulate gastric acid secretion in whole animal experiments. To investigate possible direct effects of CCK apart from extrinsic neural and hormonal influences, we have investigated the effects of the sulfated octapeptide of CCK (CCK-8) in rabbit isolated gastric glands using 14C-aminopyrine accumulation and intrinsic factor (IF) secretion as markers of parietal cell function. CCK-8 stimulated a significant increase (p less than 0.05) in IF secretion and 14C-aminopyrine accumulation. IF secretion was dose dependent for CCK concentrations from 10(-10)M to 10(-6)M. The combination of CCK (10(-6)M) and histamine (5 X 10(-5)M) elicited IF secretion greater than that of either agent alone. These results are similar to those observed for pentagastrin (10(-7)M), suggesting that the effects of CCK on parietal cell secretion may be due at least in part to a direct receptor-mediated parietal cell response to this agent.

Aminopyrine↗
PubMed1984

Successful use of emergency transthoracic pacing in bradyasystolic cardiac arrest.

We present the document successful resuscitation of six patients using emergency transthoracic pacing. Two patients were resuscitated from asystole, one had a slow supraventricular bradycardia following head trauma and spinal shock, and three patients had cardiovascular collapse secondary to complete A-V dissociation. One patient developed a non-fatal pericardial tamponade, but there were no cases of pneumothorax. All patients failed to respond to standard medical therapy. We believe that the initially successful resuscitation of these patients was related directly to the pacing procedure. Three patients had underlying pathology that did not allow longterm survival. Three patients were discharged from the hospital without neurologic sequelae. Although emergency transthoracic pacing has a relatively low success rate in bradyasystolic cardiac arrest and may be associated with serious complications, the procedure may be life-saving in selected cases.

Aged↗
PubMed1984

Saline acclimation and water and sodium transport across avian small intestine.

The uptake of sodium and water across everted sacs of the jejunum and ileum of Pekin ducklings, nestling Glaucous-winged gulls, and adult Japanese quail was measured in both freshwater- and saltwater-acclimated birds to assess the importance of the avian small intestine in salt and water balance after a salt load. The jejunum and ileum together were divided into segments I-V in ducklings and gulls and segments I-IV in Japanese quail. Acclimation to sodium chloride solutions increased the uptake of sodium and water, per unit dry weight of tissue, across segments II and IV in larger ducklings, although no significant differences were observed in smaller ducklings. Sodium and water transport were significantly greater across the posterior region of the small intestine of saltwater-acclimated gulls. In Japanese quail acclimated to sodium chloride solutions, mean values for sodium and water uptake were decreased, compared with fresh-water-acclimated birds, but were not statistically significantly different. Increased uptake of water and sodium after saline acclimation appears to be correlated with the presence of functional salt glands.

Animals↗
PubMed1983

Thrombin proteolysis of purified factor viii procoagulant protein: correlation of activation with generation of a specific polypeptide.

Factor VIII procoagulant protein (VIII:C) purified from commercial factor VIII concentrate contained multiple polypeptides ranging in mol wt from 79,000 to 188,000, all of which were removed from solution by a monoclonal anti-VIII:C antibody specific for a thrombin-sensitive epitope. In a time-course digest of the purified VIII:C using a trace amount of purified human alpha-thrombin, changes occurred in all VIII:C polypeptides during the activation and inactivation of VIII:C activity. The generation and destruction of a mol wt 92,000 polypeptide paralleled the increase and decrease in VIII:C activity, suggesting that this polypeptide represents an activated form. These results provide the basis for a working hypothesis for the mechanism of thrombin activation of VIII:C.

Antibodies, Monoclonal↗
PubMed1982

Endotracheal administration of atropine sulfate.

Atropine sulfate was successfully administered endotracheally to a 74-year-old patient suffering profound bradycardic cardiovascular collapse. Ninety seconds following endotracheal atropine administration, normal blood pressure and pulse were established. Therapeutic blood levels of atropine were documented following endotracheal administration. The endotracheal route for atropine administration appears to provide an effective alternative route of administration when intravenous access is difficult or impossible to establish rapidly.

Aged↗