Search

A double-blind, placebo-controlled trial was performed to establish the duration of action of antihistamines and their ability to attenuate the adverse affects associated with histamine release. Thirty volunteers were assigned randomly to receive either placebo or a combination of the H1 blocker dimetindene maleate (0.1 mg/kg) and the H2 blocker cimetidine (5 mg/kg). A bolus dose of histamine (450 ng/kg) was given 15 minutes after antihistamine or placebo treatment and repeated after 2, 4, and 6 hours. Cardiovascular variables, plasma histamine levels, cutaneous manifestations, and objective and subjective signs and symptoms associated with histamine release were determined before and after each histamine injection. Although many of the signs of histamine release, including erythema and metallic taste, could be attenuated effectively for 6 hours with antihistamine treatment, the protection against histamine-induced flush and headache diminished after 2 hours. Statistically significant protection against histamine-mediated tachycardia persisted for only 2 hours. Antihistamine treatment significantly reduced the increase in plasma histamine levels after the first histamine injection but did not alter the levels after subsequent histamine injections. The currently recommended administration regimen for prophylaxis with antihistamines is insufficient to prevent histamine-mediated side effects, and additional doses may be required after 4 hours to achieve appropriate chemoprophylaxis.

Patients receiving intravenous morphine at doses of 0.3 and 1.0 mg/kg for general anesthesia have been reported to show significant elevations in plasma histamine that are associated with hemodynamic changes. We undertook a prospective, randomized, double-blind trial in which 0.15 mg/kg morphine or 0.3 mg/kg nalbuphine was administered intravenously to normal volunteers. Thirteen of 15 subjects receiving morphine and 10 of 14 subjects receiving nalbuphine had elevations in plasma histamine levels and symptoms of histamine release within 5 minutes of drug administration. Six subjects in the morphine group and five in the nalbuphine group exhibited levels of plasma histamine > 2.0 ng/ml, but these levels were not associated with hemodynamic changes and occurred 10 to 15 minutes after drug administration. Our study suggests that the opiate-induced elevation of plasma histamine derives from cutaneous mast cells.

Increased histamine release and formation (induced histamine) are two hypotheses considered in the pathogenesis of endotoxic shock development. To prove both hypotheses a sequence of four randomized controlled studies in rats was performed. Histamine release was measured indirectly as a decrease in tissue-histamine contents (lung, liver, spleen, stomach); histamine formation was estimated directly as an increase in histidine decarboxylase (HDC) activity in the same organs. Changes in contents and enzymatic activities were determined 4 and 8 h after shock induction; in addition, at the time of death, the activity of HDC was measured in heart, kidney, and small intestine. 4 h after shock induction, there was a significant decrease in the tissue-histamine content as measured only in the liver, with the same trend in lung and spleen. 8 h after endotoxin application, however, histamine concentration increased in the liver (significantly p < .05) and lung compared to the NaCl control group. The manifestation of changes in HDC activity in various organs was selective (i.e., not all organs showed alterations), not uniform (decreased as well as increased activities were measured), and time-dependent (no increase in HDC activity in animals dying at > 20 h). At 4 and 8 h, only the liver showed a strong increase in HDC activity which can explain the increase in histamine content. In lung, spleen, and stomach, a significant decrease occurred. The results on histamine release and formation let us conclude that histamine is involved in the pathogenesis of endotoxic shock development.

The problem of whether antihistamines (histamine H1 + H2-antagonists) should be administered prophylactically before surgical interventions rose after animal experiments with hypnotics, opioids, muscle relaxants and plasma substitutes. It could, however, not be solved by classical biomedical research, but needed a heuristic problem-solving strategy. This strategy was formalized and in this way changed into a scientific structure by the thinking-aloud technique and the building of a decision tree with 9 nodes and various study designs to answer questions at particular decision nodes. The first question, whether the incidence of the reactions was high, was answered by several controlled clinical trials. The second question of life-threatening degrees of severity in single cases, was answered by a drug surveillance study. The third question, of whether severe incidents could always be avoided was answered by medical audit. The same was the case if death had to be considered as the final therapeutic failure. The fifth question was, "are the risks of histamine release comparable to other risks in the perioperative period?" They were--if thromboembolism, infection and stress ulcers were considered. The sixth and seventh questions referred to an experimentally and clinically effective prophylaxis. They were answered by animal and clinical studies with histamine antagonists, mainly with dimetindene and cimetidine. Undesired, adverse reactions to prophylaxis are rare since the drugs are given only once. Prophylaxis was calculated to be fairly cost-effective. Problem-solving strategies are very helpful in transferring facts and conclusions from experimental basic research to clinical decision making. This was convincingly demonstrated in antihistamine prophylaxis in anaesthesia and surgery.

High technology plays an important role in surgery, either to expand surgical procedures or to reduce tissue trauma, which is a main goal of minimum invasive surgery. Due to the tremendous increase of costs the problem of technology assessment will not only be solved by statistical methods, but also by biomedical considerations and laboratory tests. Histamine release could be an indication for tissue trauma, which is caused directly by tissue damage or indirectly by infection or hypoxia. Therefore histamine release was investigated during different phases of operation in two clinically very important and complex situations: resection of liver metastases of colorectal carcinoma and resection of the oesophagus because of an oesophageal carcinoma. To model this situation in animal experiments, two randomized controlled studies were conducted in sheep. Traditional techniques were compared with techniques of minimum invasive surgery. Plasma histamine levels were determined at well-defined phases of the operation. Histamine release was demonstrated at distinct phases of operation indicating considerable specificity of this parameter, if sensitivity is guaranteed by advanced tests. Incision of the liver capsule by thermocauterization, liver ischaemia, tissue trauma in more extended disruption of perioesophageal tissue were causes of more extended histamine release. It is concluded that measurement of plasma histamine is a suitable indicator for discriminating between extended and minimum invasive surgery. The consequence of considering this parameter may be less complications in the post-operative period and a short hospital stay with better quality of life.

Histamine assays in gastroduodenal tissues and body fluids are not an absolute objective of scientific interest but are related to the role of histamine in health and disease. Hence, the reliability of histamine assays has to be assessed in relation to this aim. Sensitivity and specificity of the chemical histamine assays are similar in tissues and body fluids. The modern developments in a fluorometric-fluoroenzymatic assay guarantee the highest sensitivity and specificity, especially by tests that monitor specificity in each single run of histamine determinations. Precision and accuracy of histamine measurement were especially investigated for the fluorometric assay. They included tests on the coefficient of variation over the whole concentration range, long-term precision with double-sample standard control charts, comparison of several methods for histamine assay including bioassay, and long-term accuracy with the use of Cusum charts. Finally, appropriate sample preparation, sample-taking, relevant body fluids and tissues, and the right time for sample-taking were evaluated in extended methodologic studies. Histamine assays are not just methods for a normal routine laboratory. Extended knowledge about histamine release and metabolism will be necessary to analyse data in this particular field with reasonable validity.

The problem of a preoperative histamine H1- + H2 - prophylaxis was tackled by a group of new studies including randomized controlled clinical trials and cross-sectional studies with plasma histamine measurements and administration of H1- + H2 - antagonists to a control group. The first study demonstrated serial histamine release in the induction of anaesthesia up to 4 times in a single patient. Basal plasma histamine levels in resting subjects fell below 100 pg/ml during the time necessary for preparation of the surgical patient. Hence, spikes of elevated plasma histamine concentrations corresponded to histamine release. Although this histamine release very often was less than 1 ng/ml plasma histamine, it created systemic reactions after atracurium. The cut-off point of 1 ng/ml for such anaphylactoid reactions does no longer exist, also lower plasma levels are of patho-physiological significance. The clinical signs of histamine release in the induction of anaesthesia vary from drug to drug. Sometimes tachycardia and hypertension produce the highest likelihood ratio, sometimes tachy- and bradycardia, but no changes in blood pressure as in the case of atracurium. It is concluded that the reasons why histamine release in anaesthesia and surgery is so much underreported and under-estimated include the present paradigms about plasma histamine levels and the "classical picture" of histamine release. Both are no longer valid and need a re-assessment.

There is an increasing interest in measuring human plasma histamine levels in various clinical conditions. A variety of 'old' and newly developed techniques are applied to meet this demand. However, the discrepancy between reported reference values for histamine in human plasma measured using this variety of techniques, suggests the existence of a certain degree of inaccuracy and imprecision. We therefore organized an external quality control study on the reliability of current histamine determinations in European laboratories. Three lyophilized plasma quality control samples, in duplicate, covering the normal and pathological range of histamine concentrations (0-45 nmol/l), two different aqueous histamine standard samples and one solvent sample were sent to 10 laboratories for the analysis of their histamine content. The following methods were used: gas chromatography-mass spectrometry (n = 2), enzymatic single isotopic assay (n = 1), fluorometric-fluoroenzymatic assay (n = 3), radioimmunoassay (n = 3) and high performance liquid chromatography (n = 2). The study was performed and evaluated according to the approved recommendations (1983) of the International Federation of Clinical Chemistry (IFCC). The target values +/- s.d. of the three plasma samples were: 39.5 +/- 4.6 nmol/l (CV = 11.6%), 2.3 +/- 2.2 nmol/l (CV = 96%) and 8.9 +/- 1.5 nmol/l (CV = 17%), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

In a prospective clinical trial, plasma histamine levels were measured in 28 polytrauma patients on day 1, 5 and 14 after trauma. Only those subjects who died were drop-outs. All patients had severe polytrauma with at least 3 body regions involved. The median plasma histamine levels at all three time points were significantly higher than in patients with single trauma of the extremities or before selective orthopaedic surgery but still in the normal range (less than 1 ng/ml). However, all patients with plasma levels above 1 ng/ml on days 1 and 5 died, as did all patients with levels above 0.5 ng/ml on day 1. Thus the elevation of plasma histamine levels, for whatever reason, appears to be a prognostic factor for bad outcome in polytrauma patients.

The increasing importance of measuring histamine in many clinical conditions and the variety of currently used techniques enforced us to organize an external quality control study (ring study) on the reliability of histamine measurements in European laboratories. Three plasma quality control samples in duplicate (lyophilized) with different amounts of histamine (0-5 ng/ml), two different aqueous histamine standard samples and one solvent sample were sent to 10 laboratories for analysis of their histamine content. The following methods were used: gas chromatographic-mass-spectrometric technique (n = 2), single isotope assay (n = 1), fluorometric-fluoroenzymatic assay (n = 3), radioimmunoassay (n = 3), HPLC technique (n = 2). The study was performed and evaluated according to the approved recommendation (1983) of the International Federation of Clinical Chemistry (IFCC). This first report of the study is concentrated on the imprecision and inaccuracy of the different principal methods and laboratories by comparing two unrelated plasma histamine samples of different analyte concentrations (target values and SD: 4.39 +/- 0.51 ng/ml and 0.99 +/- 0.17 ng/ml). This study showed a fairly good agreement between most participants. 7/11 results obtained with 4 different methods were accurate and precise in the plasma range of histamine (Youden plot). Results outside the borderlines turned out to be a problem of the analyst rather than the method itself. It is suggested to define reference values for plasma histamine and to establish reference laboratories and methods according to the IFCC-guidelines.

The danger of luminal histamine administered orally or formed in the intestinal fluid by bacteria has long been neglected. However, the demonstration of blocking intestinal diamine oxidase (DAO) by a variety of common drugs has revived the discussion and has created a new disease concept: enteral-induced histaminosis. In an animal model the three central prognostic variables of this disease concept (large amounts of histamine in food to make the individual ill, blocking of DAO by commonly used drugs, and the relationship between increased plasma histamine levels and disease manifestation by exogenous histamine application) were tested with randomized trials in vivo and biochemical tests in vitro using semipurified enzymes from pig and man. In the first trials authentic histamine in quantities similar to that in normal amounts of food or cheese bought from a supermarket produced life-threatening reactions if the DAO was inhibited by pretreatment with aminoguanidine. In the second series of experiments in vitro a numerous commonly used drugs was shown to inhibit both the porcine and human enzyme. Some of the inhibitors were really strong, such as dihydralazine, chloroquine, pentamidine, cycloserine, clavulanic acid, dobutamine, pancuronium and others. The type of inhibition was sometimes competitive as in the case of dihydralazine and pancuronium, sometimes non competitive (e.g. pentamidine) which may be important for long-term treatment. In the third group of experiments a relationship between the dose of i.v. injected histamine and the elevation in plasma histamine levels and clinical symptoms in pigs was demonstrated. Hence, elevated plasma histamine in pigs acts as a pathogenetic factor for the disease manifestation. It is concluded that after modelling enteral-induced histaminosis in an animal the trias of variables shown in this study should be consequently investigated in man.

In a prospective study the histamine content of the mucosa of the body of the stomach was measured in 100 patients consisting of control subjects, patients with duodenal ulcer and patients suffering from various gastrointestinal diseases. The histamine content was found to be 43 mug/g in male control subjects (median) while in duodenal ulcer patients levels attained were significantly lower by about 30 per cent. In all the other groups of patients histamine concentrations in gastric mucosa were found to be "normal". Since in most species it is extremely diffcult to alter the mucosal histamine concentration by any form of treatment, the diminished histamine content of the gastric mucosa in patients with duodenal ulcer seems remarkable. Among several possible explanations offered for this finding we think the most likely is that histamine release is increased in duodenal ulcer disease.

High activities of diamine oxidase (EC 1.4.3.6) were measured in the intestinal tract of human subjects and of several mammalian species. The enzyme was localized in the mucosa and was distributed primarily in the cytoplasm; the only exception being the guinea-pig where it was located in the particulate fraction. Despite its instability the enzyme from human colonic mucosa was purified 80-fold. During the purification a soluble monoamine oxidase (EC 1.4.3.4) was separated from diamine oxidase. The pH optima of diamine oxidase for putrescine and histamine were 6.6-7.0 and 6.4-6.6, respectively. Short-chain aliphatic diamines were deaminated with the highest reaction velocity, but histamine and N tau-methylhistamine were also excellent substrates. The Km for putrescine was 8.3 x 10(-5) M, for histamine 1.9 x 10(-5) M and for N tau-methylhistamine 9.7 x 10(-5) M. Typical substrates of monoamine oxidase were not deaminated by the enzyme. Aminoguanidine strongly inhibited human intestinal diamine oxidase (IC50 = 1.1 x 10(-8) M). Because of its properties the intestinal diamine oxidase is considered to play a protective role against histamine in diseases such as ischaemic bowel syndrome, mesenteric infarction and ulcerative colitis.

Acute haemorrhagic lesions in the oesophagus, stomach and duodenum ('stress ulcers') occur relatively often under clinical conditions and are always dangerous to the patient (lethality rate about 70%). Since conservative and surgical treatment are without significant success up to now, prevention by adaptation to stressors or by administration of drugs seems mandatory. An improved technique for producing acute gastric lesions in rats by immobilization and a new method for assessing this disease in the animals is presented in this communication. High precision is obtained within a single experimental series especially from day to day. Since histamine was suggested to be involved in the pathogenesis of stress ulcer disease, (+)-catechin, a rather specific inhibitor of specific histidine decarboxylase from rat stomach, was tested in immobilized rats. It prevented the formation of acute gastric lesions by 80% in seven series of experiments lasting for half a year. Since the drug has low toxicity in man, it is recommended for clinical trials.

A prospective controlled clinical trial was conducted on changes in plasma histamine and catecholamine levels during 5 standard operations. This communication, as the first part of the trial, deals only with the feasibility of such a trial and the changes in plasma histamine levels. Elevated histamine concentrations corresponding to histamine-release responses of greater than 1 ng/ml occurred in 8 of 25 operations. In an explorative analysis these responses were associated with distinct phases of anaesthesia or the surgical procedure. Blood transfusion carried the risk of infusion of "free histamine" into the patient--especially when administered under pressure. Since during operations "free histamine" enters the circulation with a rather high incidence and may cause harmful effects, premedication with H1-+H2-receptor antagonists seems worth consideration.

A high histamine content was found in all areas of human gastric and duodenal mucosa. In single subjects there was no general preference of histamine being located predominantly in fundus and corpus. In biopsy specimens of human corpus mucosa many histamine-containing O-PD reactive cells could be identified. In the sections treated previously with O-PD also many toluidine blue staining cells (mast cells) could be visualized. As shown by a transcription technique their place and number was the same as those of O-PD reacting cells. It is concluded that histamine in human corpus mucosa is localized exclusively in mast cells which seem to participate in acid secretion and in duodenal ulcer disease in man.

This randomized study compared the effects of the emulsion formulation of propofol with those of the Cremophor-containing agent Althesin. Plasma histamine concentration, immunoglobulin levels, total complement C3 and complement C3 conversion were measured prior to and following induction of anaesthesia in 32 male volunteers with either 2 mg/kg propofol or 0.05 ml/kg Althesin. In only one volunteer, in the Althesin group, was an increase in plasma histamine to a value greater than 1 ng/ml associated with a relatively large increase over the base line value. Cutaneous signs, such as flushing, did not correlate with the plasma concentrations of histamine. No changes consistent with a propensity to produce anaphylactoid reactions could be seen from measurements of immunoglobulin levels, complement C3 or plasma histamine concentration in the propofol treated subjects.

In human kidney allotransplantation, elevated plasma histamine levels were measured before surgery, following revascularization, and in single cases also several days after surgery. The maximum extent of this histamine release must be tested with respect to time and to localization. Its significance must be established. The intermittently increasing plasma histamine levels (greater than 1 ng/ml) must be considered as a possible risk regarding stress ulcer pathogenesis.

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 (3 M 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 microgram/30 min.

The ability of the gut to inactivate various amines by oxidative deamination was tested with a 130-fold purified amine oxidase preparation from dog small intestine. Of 34 amines tested, putrescine, benzylamine, cadaverine, and serotonin were the most favourable substrates. Histamine was inactivated rapidly by this enzyme preparation, too. Histamine derivatives methylated at the imidazole nucleus were also deaminated, whereas Nalpha-methylhistamine was only a poor substrate and Nalpha, Nalpha-dimethylhistamine was not a substrate at all. Using a second procedure for the purification of amine oxidases from gut, the separation of a soluble monoamine oxidase from diamine oxidase was achieved by gel filtration on Sephadex G-200. The diamine oxidase deaminated putrescine (Km = 1.3 x 10(-4)M) and histamine (Km = 6.6 x 10(-5)M), but not serotonin, and was inhibited by aminoguanidine, but not by pargyline. The soluble monoamine oxidase inactivated serotonin (Km = 4.5 x 10(-4)M), but not histamine and putrescine and was inhibited by pargyline, but not by aminoguanidine. It was concluded that in dog small intestine (as well as in rabbit small intestine) only diamine oxidase was capable of inactivating histamine by oxidative deamination.

Following superior mesenteric artery occlusion and revascularization in dogs all animals died in a circulatory collapse state. However, pretreatment by aminoguanidine, the strong and specific inhibitor of diamine oxidase, accelerated the circulatory break-down significantly and increased the venous plasma histamine concentrattions up to levels which also in normal dogs are effective in the circulatory system. Furthermore, the haematocrit increased significantly more in the aminoguanidine-treated animals than in the dogs treated by saline. No changes in plasma diamine oxidase activity were observed in saline-treated animals during intestinal ischemia and following revascularization. In aminoguanidine-treated animals no enzymic activity could be measured. The results were interpreted by a protective role of intestinal diamine oxidase in intestinal ischemia. Enhancement of the enzymic activity in patients, for instance by heparin, may be helpful in mesenteric infarction disease.

In a randomized controlled trial, 30 pigs were orally treated with histamine (60 mg). In addition, half of the animals underwent a specific blockade of the enzyme diamine oxidase (DAO), which is the main histamine catabolising enzyme in the intestinal tract. Only these DAO-blocked animals exhibited severe clinical symptoms (e.g. hypotension, flush, vomiting) and, in parallel, showed tremendous elevations of plasma histamine levels of up to 160 ng/ml. 3 out of 15 animals in this group died within the experimental period. In contrast, the control animals neither exhibited plasma histamine levels above 5 ng/ml nor had any clinical reactions. These results contradict the current opinion that oral histamine intake in food is not clinically relevant, especially since many commonly used drugs are DAO-inhibitors and approximately 20% of our population take these drugs. Apart from drugs, some other factors (alcohol, spoilt food etc.) can also function via a blockade of DAO as an additional risk. DAO-blockade is therefore a real epidemiological problem. Evidence is presented here for the new disease concept: Food-Induced Histaminosis.

In a control group (n = 12) the histamine content of the liver was 1.42 microgram/g tissue and the activity of the histamine-degradating enzyme, HMT, 421.5 pmol/(min . mg protein). In patients with affections of the biliary tract (n = 12) the histamine content was significantly raised to 3.09 microgram/g tissue and the HMT activity slightly diminished [349 pmol/(min . mg protein)]. The lowest values of HMT activity were found in the livers of those patients with histologically proven damage of liver cells.

One of the frequently reported side effects following epidural morphine administration in clinical trials is a generalized pruritus of several hours duration. Since histamine can elicit pruritus we investigated the plasma histamine levels following epidurally applied morphine (0.05 mg/kg) in 10 urological patients. Plasma histamine levels were determined as an indicator of histamine release. Indeed, in 2 of 10 patients plasma histamine concentrations rose to 2 ng/ml. 5 of 6 criteria for establishing histamine release were fulfilled in both cases. Minor clinical symptoms appeared only in one patient (one single wheal of 1 cm diameter, metallic taste), but no symptoms at all in the other. Considering the low dose of the analgesic and the relatively high incidence of histamine release (2/10) the result of this prospective study seems worth to be emphasisized and followed-up in further studies. Pruritus did not occur in any of the patients, the role of histamine in its pathogenesis is now becoming more doubtful.

In shock produced by temporary superior mesenteric artery occlusion the plasma histamine concentration was enhanced following release of the mesenteric blockade. Furthermore, an inhibition of the diamine oxidase catalysed histamine inactivation resulted in an aggravation of the shock development. These processes, already shown in dogs and mini pigs, were also observed in rabbits. Histamine receptor antagonists abolished the effect of the enhanced histamine concentration appearing in the circulation following inhibition of diamine oxidase. In human intestinal tract a fairly similar distribution of histamine and diamine oxidase was found as in the mammals studied. Thus the indicated pathobiochemical processes should be reckoned with in patients suffering from circulatory disorders of the intestinal tract.

The importance of intestinal diamine oxidase in histamine catabolism was proved in several series of experiments. However, intestinal monoamine oxidase might also be involved in histamine degradation either by direct deamination or by the deamination of methylated products. The soluble fraction of intestinal monoamine oxidase was purified and tested for the properties and substrate specificity by three different methods which are described in detail. Using 0.15 M phosphate buffer the optimum pH was 7.4--7.6. The Km values for serotonin and tyramine were 0.2 and 0.3 X 10(-3) M. The most favoured substrates of the enzyme were tyramine, tryptamine and serotonin, but it was not possible to classify the enzyme as a type A or B monoamine oxidase only by its substrate specificity. Histamine and ring methylated derivatives were not attacked by intestinal monoamine oxidase. This means that in the intestinal mucosa by the oxidative pathway of histamine is completely catalysed by diamine oxidase.

Plasma histamine assay in man is indicated for the diagnosis of histamine release, as well as the elucidation of the mechanisms of adverse drug reactions, and the identification of clinical situations in anaesthesia and surgery where a pathological plasma histamine level may occur. Normal and pathological plasma histamine levels vary considerably in the literature. Data from various studies, especially one involving 300 patients in Heidelberg (G.F.R.), allow us to define the normal range for human plasma histamine as 0-1.0 ng . ml-1 . Values greater than 1 ng . ml-1 have to be considered as pathological. The problems related to blood collection and plasma preparation are considered here. Any judgement concerning the method described in the test must take into consideration our long experience of 15 years with it, its reliability in clinical conditions, its practicability, its relatively low cost, and finally, the absence of radioisotopes.

To understand the role of histamine in the aetiology and pathogenesis of human diseases reliable data are urgently needed for the histamine content and for the activities of histamine-forming and -inactivating enzymes in human tissues. In order to make a substantial progress toward this aim a tissue-sampling programme during surgical interventions was carefully conceived and conducted. From March 1982 until January 1983 106 tissue specimens were taken from 56 patients who underwent surgery. Only healthy tissues, not injured or oedematous, and without adherent structures were taken by only one surgeon who was interested in this research and experienced in tissue preparation procedures in biochemistry. The times of 'warm' ischaemia during the operative procedures were visually estimated, the times between resection of the organs or specimens and deep-freezing of the tissues were precisely recorded. Compared to previous work in the literature and especially to our own work using the same assays for determination higher histamine contents were found in this study in most of the tissues, in particular in the gastrointestinal tract. Also the diamine oxidase activities were considerably higher in many organs, e.g. 3-4 times higher in the gastrointestinal tract when compared with those in publications of our group who used always the same analytical test. However, the histamine methyltransferase activities in this study were not at variance to those determined in previous investigations. Many of them were reported in this communication for the first time. Since the methods for histamine determination and those for measuring enzymic activities were not different in this study and in previous communications of our group we are convinced that the optimized tissue-sampling and -preparation techniques were responsible for the higher values in this communication. But the problem of the 'warm' ischaemia period could not be solved by sample-taking procedures of this type during operations. There are good reasons to prefer biopsy specimens for the analysis of histamine storage and metabolism in human tissues in health and disease, but - unfortunately - they are not always available.

Elevated histamine concentrations of pathophysiological significance could be determined in plasma of dogs suffering from acute pancreatitis according to Pfeffer. This result was also obtained in dogs treated with aminoguanidine, a very effective diamine oxidase blocker, in addition to the duodenal blind loop preparation. Elevated histamine concentrations were found in nine out of ten dogs.

From a methodological point of view the relevance of clinical-biochemical trials depends on the answers to mainly four complexes of questions: (1) the reliability of the assays in the clinical situation to be tested, (2) the precision and accuracy of sample-taking, (3) the qualification of the design and the protocols in the clinical part of the trial and (4) the usefulness of the time concepts in the trial concerning biorhythms, seasonal influences, psychological trauma of diagnostic procedures and treatment. In this study mainly the second complex of questions was studied intensely. The precision of the fluorometric histamine assay in biopsy specimens from human gastric mucosa depended on several conditions: Biochemical technique, sample preparation and removal of biopsies from gastric mucosa via endoscopy. The CV% of the whole procedure was about 8-times higher than that of the biochemical technique. In clinical-biochemical studies on the significance of histamine or any other hormone (such as gastrin) in any disease (uch as duodenal ulcer) it seems therefore useless to describe the precision of an assay only by the variance of the biochemical technique. Calculation of the histamine content as mean of 3 samples reduced the CV% from 27.2 to 14.9% and should therefore be recommended.

The authors studied the variations in histaminaemia in the plasma on the one hand, and in whole blood on the other hand: In volunteers:-after administration of histamine in an intravenous infusion ranging from 18 to 90 ng/min/kg;-after administration of thiopental, methohexital and propanidide. In volunteers, by means of the different parameters measured, the authors found that the mean plasma concentration was 0.69 +/- 0.26 ng/ml. In the whole blood, the histaminaemia was 54 +/- 18 ng/ml. The perfusion of histamine up to 45 ng/kg/min led to no symptomatology in 3 volunteers. Propanidide led to an average increase of 350 p. 100 in the initial normal figure of plasma histaminaemia approximately 5 minutes after the beginning of the injection. But there is no agreement between the figures obtained and the clinical signs (tachycardia, mild hypotension). The injection of thiopental led to an analagous symptomatology: i.e. tachycardia and mild hypotension, arising before the maximum increase in plasma histaminaemia. Methohexital, and althesin are also histamine-liberators. Only estomidate, a new pure hypnotic product as yet not commercialised, did not lead to histamine-liberation.