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Notes: Abstract The influence of imidazole compounds (histamine analogues and H2-receptor antagonists) and of the specific histamine H2-receptor agonist dimaprit on histamine methyltransferase (HMT) from pig gastric mucosa was investigated. By their effect on HMT two groups of substituted imidazole compounds could be differentiated. Some were pure inhibitors of the enzyme, whereas others were inhibitors only in high concentrations (〉10−3 M) and activators of the enzyme in low concentrations. The strongest inhibitor of all the histamine analogues tested was 2-methylhistamine (I.D.50=0.6×10−4 M), whereas the strongest activation was exerted by 4-[(2-amino-ethylmercapto)-methyl]-5-methylimidazole (57% increase of enzymic activity at 10−4 M concentration). From the group of histamine H2-receptor antagonists only burimamide was an inhibitor (I.D.50=1.6×10−4 M) whereas metiamide and cimetidine belonged to the strongest activators of the enzyme (179% enzymic activity at 10−4 M concentration of metiamide). The strongest activator of all the substances tested in this series of compounds, however, was the non-imidazole compound dimaprit, which increased enzymic activity by 86% in as small a concentration as 10−5 M. For substituted imidazole ring systems an attempt is made to evaluate the structural requirements of the single compound to classify it as a pure inhibitor or a concentration-dependent inhibitor/activator of HMT.

Notes: Conclusions None of the synthetic analogues ofS-adenosyl-l-homocysteine was a more potent inhibitor of the enzyme thanS-adenosyl-l-homocysteine itself. Several requirements very probably had to be fulfilled for inhibition of gastric histamine methyltransferase by compounds similar in structure to S-adenosyl-l-homocysteine: (1) The side chain linked to the 5′-position of ribose must bear an amino acid residue; (2) the chain-length of this residue must be the same as that of homocysteine; (3) the heterocyclic base has to be a purine base with a nucleophilic center at position 6; (4) this nucleophilic center must not be sterically hindered by substitutes; (5) the purine base must have a nitrogen atom in position 3. These requirements indicate, that the binding sites, proposed byZappia et al. [2] for various methyltransferases were identical with those found for the fixation ofS-adenosyl-l-homocysteine or its analogues to histamine methyltransferase.

Notes: Abstract Histamine concentrations in canine whole blood and plasma were determined under several pharmacological, pathophysiological, and clinical conditions, using fluorometric methods. The specificity of the assay for whole-blood histamine was investigated by comparing 3 purification procedures for the isolation of histamine from whole blood including butanol extraction (Shore), ion-exchange chromatography on Dowex 50 W-X 8, and the combination of these 2 methods (Lorenz). Histamine in whole blood was identified in analytical and preparative samples by fluorescence spectra, thin-layer chromatography, degradation by diamine oxidase from pig kidney and inactivation by histamine methyltransferase from guinea-pig brain as well as by biological tests on the isolated guinea-pig ileum. Since butanol extraction resulted in significantly higher ‘histamine’ values than the other two purification procedures, ion-exchange chromatography on Dowex 50 was recommended as the method of choice for the specific determination of histamine in dog's whole blood. Normal values of histamine concentrations in canine plasma were tentatively estimated. They depended on the time between pretreatment of the animals (anaesthesia, operation) and the collection of blood and showed an approximately logarithmic normal distribution. The median, the lower/upper quartiles and the range of the plasma histamine levels obtained 30 minutes after the end of pretreatment were 0.2, 0–0.4 and 0–1.2 ng/ml, respectively. Nearly 50% of the values were zero (below 0.1 ng according to the sensitivity of the method), only 1% of them exceeded slightly 1 ng/ml. Thus histamine release by drugs or by other medical treatments was only stated, when plasma histamine levels exceeded 1 ng/ml and decreased in a way to give an elimination curve of approximately first-order kinetics (Bateman function). Histamine concentrations in dog's whole blood showed approximately a logarithmic normal distribution. The median, lower/upper quartiles and range were 47, 34/75 and 13–209 ng/ml respectively. The histamine levels in the whole blood of four circulatory regions did not show any significant differences. The plasma histamine concentrations in the portal vein were slightly higher than in the hepatic veins. The injection of exogenous histamine and the concomitant determination of plasma and whole-blood histamine levels in four circulatory regions showed that the plasma histamine determination was the more sensitive method for measuring histamine elimination curves than the whole-blood histamine assay. The elimination of exogenous histamine administered intravenously was influenced by several drugs including inhibitors of histamine inactivation and histamine receptor antagonists. Aminoguanidine and the H2-receptor antagonist burimamide slowed down the disappearance of histamine from the plasma, the H1-receptor antagonist dimethpyrindene enhanced it, but amodiaquine had no significant effects. Dimethpyrindene and burimamide were capable of releasing histamine in dogs, in some cases to a considerable extent. The plasma substitute Haemaccel®, a chemically modified gelatin, released histamine in dogs. Using batch 3000, from 27 animals investigated, 15 animals showed elevated plasma histamine levels and a hypotensive blood pressure response, whereas in 12 of the dogs it did not show an effect on these parameters. The plasma histamine levels at the time of maximum hypotension showed an approximately logarithmic normal distribution. This frequency distribution in combination with the varying incidence of anaphylactoid reactions depending on the batches used seemed very important for the interpretation of clinical reactions to Haemaccel in human test persons and patients. By histamine determinations in plasma and whole blood of several circulatory regions and in various tissues before and after infusion of Haemaccel it could be demonstrated that the sites of histamine release by Haemaccel in dogs were especially the skin of the upper hemisphere of the body and the liver, whereas the gastro-intestinal tract took up histamine from the circulation. These numerous results under various experimental conditions may be considered as an evidence for the high quality and reliability of the method to study histamine release in the whole animal or in human subjects by evaluating histamine elimination curves in plasma.

Notes: Abstract In 9 dogs, whose maximum gastric acid response to pentagastrin was evoked by 6 μg/kg, the total gastric secretion as well as the peak gastric secretion was enhanced by amodiaquine. The optimum dose of this antimalarial drug was 2 mg/kg, whereas 0.25 mg/kg were without effect and 3 mg/kg reduced already the augmentation of gastric secretion by this substance. The increase in acid output by amodiaquine was greater than that in volume. The total secretion was more enhanced than the peak secretion, which means a longer duration of the amodiaquine potentiated gastric secretion elicited by pentagastrin, than that without application of amodiaquine contrary to that stimulated by exogenous histamine. Amodiaquine itself did not stimulate gastric acid secretion, in contrast to prostigmine and carbachol. Thus amodiaquine seemed not to enhance gastric secretion by a direct or indirect parasympathomimetic action. The question whether amodiaquine acted on gastric secretion in a specific way and not by parasympathomimetic effects, led to investigations in several exocrine glands. In salivary glands, amodiaquine did neither stimulate the secretion in all doses investigated nor did it enhance the pilocarpine and acetylcholine induced salivation with any significance and regularity. Also the pancreatic and biliary secretion was neither stimulated by amodiaquine nor was the secretin induced secretion of the pancreas and liver augmented by amodiaquine. Thus the enhancing effect of this drug on the histamine and pentagastrin stimulated gastric secretion was very likely specific for the gastric mucosa and not due to a parasympathomimetic action of the drug. In contrast to the findings in various exocrine glands of the gastrointestinal tract, the arterial hypotension following the i.v. injection of acetylcholine was increased specifically by a preceeding i.v. injection of amodiaquine, whereas the equi-effective actions of histamine, serotonin and bradykinin as well as the hypertension by epinephrine and norepinephrine were not influenced by amodiaquine. This specific effect of the antimalarial drug very probably was not caused by an inhibition of the unspecific choline esterase in the blood. Since in exocrine glands no evidence could be found for a parasympathomimetic action or other modes of action of amodiaquine, it seemed probable that amodiaquine potentiated the histamine and pentagastrin stimulated gastric secretion by an inhibition of histamine methyltransferase in vivo.

Notes: Conclusion These results indicate that even small alterations of the incubation procedure witho-phthaldialdehyde may considerably influence the specificity of the fluorometric histamine assay. Tests for identification of this amine are always necessary in studies on histamine in body fluids or following the administration of drugs.

Notes: Abstract Histamine methyltransferase (HMT) activity was determined by a modified isotope assay in biopsy specimens from gastric mucosa of control subjects, duodenal ulcer patients and after various gastric operations. Enzymic activity of male control subjects who were ‘healthy’ with respect to their upper gastrointestinal tract was 70.4±12.8 pmol/(min×mg protein). In male duodenal ulcer patients HMT-activity was significantly lowered by 15%; following selective vagotomy with pyloroplasty a significant increase of 14% was observed as compared to controls. The difference between values before (59.9±13.3) and after (80.4±11.7) this operation was highly significant (p〈0.001). Experiments in a small number of patients showed that after other modifications of vagotomy elevated HMT-activities were also found, whereas after resection procedures such changes of enzymic activity did not occur. According to these results the low gastric HMT-activity of duodenal ulcer patients could play a role in the pathogenesis of a chronic peptic ulcer by being responsible for reduced histamine inactivation and — as a consequence —enhanced acid secretion. Furthermore, vagotomy seemed to influence acid secretion in human subjects not only by direct effects on the parietal cells, but also by an activation of histamine catabolism. One patient, who despite complete vagotomy showed both no reduction in acid secretion and a low gastric HMT-activity, may be the representative of a new population of peptic ulcer patients.

Notes: Conclusion The strong raise in histamine content during the first day of experimental hydronephrosis seemed to induce a slow increase of histamine methyltransferase activity, the only histamine metabolizing enzyme in rabbit kidney [4]. This process of adaptation can be interpreted as a defence mechanism against the formation and the release of high amounts of histamine.

Notes: Abstract Histamine assays can be unreliable in individual subjects or samples even though the particular method is in general working very well. Therefore the specificity and accuracy of histamine determination in the gastric aspirate of individual duodenal ulcer patients was thoroughly examined and shown to be satisfactory. Pitfalls of the fluorometric assay were investigated. A native (non-histamine) fluorescence in gastric aspirate which occurs before the addition of OPT was not removed by the original Shore procedure. In the combined assay (Dowex 50+ butanol extraction) this fluorescence no longer interferes with the assay. For the identification of histamine in a single gastric aspirate of an individual duodenal ulcer patient, the reversed blank (3M HCl added to the reaction mixture before OPT instead after OPT), excitation and fluorescence spectra, the heating test with spectra recorded and the HMT test were found to be reliable. The formaldehyde test and the heating test without recording the spectra were useless since they gave false negative results. Since the HMT test was regarded as a reference method it was thoroughly investigated both by theoretical considerations (enzyme kinetics) and by a series of measurements in a single patient as well as in a group of nine subjects. Samples from the period of peak acid output in response to pentagastrin showed an average histamine concentration of about 8 ng/ml and a histamine output of 1.5 μg/30 min.

Notes: Abstract After an i.v. application of 100 mg tramadol in 13 healthy volunteers (1) no change in plasma histamine concentration could be detected, (2) systemic anaphylactoid reactions did not occur, (3) cutaneous reactions were not rated as anaphylactoid since itching and erythema were seen only once after tramadol whereas erythema was also observed twice after saline, (4) blood pressure and heart rate were only very slightly and transiently elevated without any abnormalities in ECG-readings and (5) only side effects typical for opioid therapy were observed.

Notes: Abstract Besides DiGeorge, velocardiofacial and conotruncal anomaly face syndromes, some of the isolated congenital heart diseases have also been associated with a chromosomal deletion in 22q11. These disease entities, which had originally been considered to have a different genetic background, are now included in the CATCH-22 microdeletion complex. CATCH 22 is an acronym for cardiac defect, abnormal facies, thymic hypoplasia or aplasia and T-cell deficiency, cleft palate, hypoparathyroidism, and hypocalcemia. In the present study, we focused on the complex cardiovascular defects (CCVD) and screened 40 patients for a microdeletion of 22q11 by fluorescence in situ hybridization using the D22S75 DNA probe and for associated CATCH features. The patients were from genetic counseling (n = 15) or fetopathology (n = 3) of the Clinical Genetics Department in Marburg and from the Pediatric Cardiology Department (n = 22) in Mainz. Monosomy 22q11 was detected in 9 cases (= 22.5%). Familial transmission with one mildly affected parent and one affected sib each was proven in two cases. The CCVDs comprised complex conotruncal defects such as tetralogy of Fallot, double outlet right ventricle, transposition of great arteries and truncus arteriosus communis, or anomalies of the derivatives of the branchial arch arteries in association with a ventricular septal defect, including one case of atresia of the ductus arteriosus with pulmonary artery aneurysm and resulting in fetal hydrops. All 13 patients with a deletion of 22q11 showed at least one additional CATCH symptom. Most consistently, facial dysmorphy was apparent (92%), while hypocalcemia, mostly at threshold values, was present in 62% and thymic hypoplasia including borderline low T-lymphocyte numbers was observed in 41%. None of the patients presented with a cleft palate. A high intrafamilial variability in expression was also evident with respect to the CCVD. Our findings indicate that seemingly isolated complex cardiovascular defects associated with a 22q11 microdeletion most probably do not represent a distinct subgroup within the CATCH-22 complex but are syndromal in nature with extracardiac features that are often overlooked.