Histamine and its metabolism in mammals. Part II: Catabolism of histamine and histamine liberation

Mutations in the histamine N-methyltransferase gene, HNMT, are associated with nonsyndromic autosomal recessive intellectual disability

Histamine (HA) acts as a neurotransmitter in the brain, which participates in the regulation of many biological processes including inflammation, gastric acid secretion and neuromodulation. The enzyme histamine N-methyltransferase (HNMT) inactivates HA by transferring a methyl group from S-adenosyl-l-methionine to HA, and is the only well-known pathway for termination of neurotransmission actions of HA in mammalian central nervous system. We performed autozygosity mapping followed by targeted exome sequencing and identified two homozygous HNMT alterations, p.Gly60Asp and p.Leu208Pro, in patients affected with nonsyndromic autosomal recessive intellectual disability from two unrelated consanguineous families of Turkish and Kurdish ancestry, respectively. We verified the complete absence of a functional HNMT in patients using in vitro toxicology assay. Using mutant and wild-type DNA constructs as well as in silico protein modeling, we confirmed that p.Gly60Asp disrupts the enzymatic activity of the protein, and that p.Leu208Pro results in reduced protein stability, resulting in decreased HA inactivation. Our results highlight the importance of inclusion of HNMT for genetic testing of individuals presenting with intellectual disability.

Neuroinflammatory Mechanisms of Connective Tissue Fibrosis: Targeting Neurogenic and Mast Cell Contributions

Significance: The pathogenesis of fibrogenic wound and connective tissue healing is complex and incompletely understood. Common observations across a vast array of human and animal models of fibroproliferative conditions suggest neuroinflammatory mechanisms are important upstream fibrogenic events. Recent Advances: As detailed in this review, mast cell hyperplasia is a common observation in fibrotic tissue. Recent investigations in human and preclinical models of hypertrophic wound healing and post-traumatic joint fibrosis provides evidence that fibrogenesis is governed by a maladaptive neuropeptide-mast cell-myofibroblast signaling pathway. Critical Issues: The blockade and manipulation of these factors is providing promising evidence that if timed correctly, the fibrogenic process can be appropriately regulated. Clinically, abnormal fibrogenic healing responses are not ubiquitous to all patients and the identification of those at-risk remains an area of priority. Future Directions: Ultimately, an integrated appreciation of the common pathobiology shared by many fibrogenic connective tissue conditions may provide a scientific framework to facilitate the development of novel antifibrotic prevention and treatment strategies.

Mechanistic studies of reactions catalysed by diamine oxidase using isotope effects

Diamine oxidase (DAO), the enzyme that is responsible for amine biodegradation in animals, plants and humans, catalyses the biotransformation of amines such as histamine (HA), putrescine, 1-phenylethylamine, tyrosine, tryptamine, serotonine and spermine. The kinetic and solvent isotope effects (SIEs) were applied to study the mechanism of the biotransformation using HA and its methylderivatives. The SIE for the biotransformation of HA, N(τ)-methylhistamine and N(π)-methylhistamine was found to be 3.58, 2.22 and 5.70 on Vmax, and 1.58, 1.06 and 1.14 on Vmax/KM, respectively. On the other hand, the kinetic isotope effect for oxidation of stereospecifically deuterium-labelled [(α R)-(2)H]-N(τ)-methylhistamine and [(α R)-(2)H]-N(π)-methylhistamine was 0.69 and 0.62 on Vmax, and 15.06 and 7.50 on Vmax/K(M), respectively. These results demonstrate that DAO catalyses amine biotransformation by stereospecifically cleaving the αC-H bond in the pro-S position. Moreover, the oxidation of amine to aldehyde involves several transition states, including hybridisation change from sp(3) (Schiff base) to sp(2) (imine), then back again to sp(3) to give a final product with hybridisation sp(2) (aldehyde).

Defining risk factors for red man syndrome in children and adults

BACKGROUND

Red man syndrome (RMS) is a well-known adverse reaction that occurs in pediatric patients receiving vancomycin, yet reported prevalence is varied, and characteristics and risk factors are not well understood. Our objective was to determine the prevalence, characteristics and risk factors for RMS in pediatric patients receiving vancomycin, including contributing genetic factors.

METHODS

A multicenter retrospective study of 546 subjects (0.5-21 years) who received at least 1 dose of intravenous vancomycin was conducted. Demographic and symptom data were collected through chart review and parent/nurse report. Genotype analysis included 10 single nucleotide polymorphisms in the histamine pathway.

RESULTS

RMS was observed in 77 (14%) subjects receiving vancomycin. Forty percent of subjects with RMS symptoms developed rash, pruritis and flushing, without hypotension. Antecedent antihistamine use was identified as a risk factor for RMS (P < 0.001). Multivariate regression analysis identified age > 2 years (P = 0.008), previous RMS (P < 0.001), vancomycin dose (P = 0.02) and vancomycin concentration (P = 0.017) as RMS risk factors, whereas African American race was protective (P = 0.011). We observed an apparent association between RMS and a single nucleotide polymorphism in the diamine oxidasegene (P = 0.044); however, no associations were revealed by multifactor dimensionality reduction analysis.

CONCLUSIONS

RMS is a common adverse event in children receiving vancomycin. Identified risk factors are Caucasian ethnicity, age ≥ 2 years, previous RMS history, vancomycin dose ≥ 10 mg/kg, vancomycin concentration ≥ 5 mg/mL and antecedent antihistamine use. Known genetic variants in histamine metabolism or receptors do not appear to be substantial contributors to risk of RMS.

Copper, biogenic amines, and amine oxidases

Amine oxidases have been classified in the past on the basis of either (a) the structural requirements in the substrate or (b) the tissue (or species) of origin, or both. As knowledge about the chemistry of these enzymes grows, their classification on the basis of chemical structure is becoming possible. Currently, many amine oxidases can be categorized according to whether they contain riboflavin (e.g. the monoamine oxidases -- EC 1.4.3.4) or copper (e.g. the amine oxidases of plasma and the diamine oxidases EC 1.4.3.6 -- found prominently in pig kidney cortex, placenta, and pea seedlings). The copper-linked oxidases are inhibited by cyanide and by semicarbazide. The nature of the carbonyl compound(s) in the various enzyme molecules is not yet known. Nutritional deficiencies of copper and treatment of animals with copper-chelating agents are reflected in reduced activity of one or more of these enzymes. The ultimate effects of copper deficiency and copper excess on amine metabolism in vivo are described.

Histamine in food: is there anything to worry about?

Biogenic mono-, di- and poly-amines are widely distributed among living organisms. The amines fulfil many important functions in the human body both in the periphery and brain. Some authors suggest that foods rich in biogenic amines, especially histamine, present high health hazards for consumers. However, this is conditional on a range of other factors. The alimentary tract is well equipped with enzymes that inactivate amines and the blood-brain barrier prevents them entering the brain from the circulation. Oxidative deamination, methylation, acetylation and transglutamylation are the degradation pathways which operate efficiently in the stomach, intestines and liver. Particularly important is oxidative deamination. Food histamine poisoning or cheese reaction, manifested itself in patients treated with drugs that inhibit amine oxidases or in patients showing an enterocytic diamine oxidase deficit. It is rather food allergy, which should worry us more, as endogenous histamine release from mast cells is more dangerous. Preventive measures should be undertaken against increases in food allergies.

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Endogenous histamine and cortisol levels in subjects with different histamine N-methyltransferase C314T genotypes : a pilot study

BACKGROUND

Histamine N-methyltransferase (HNMT) catalyzes the methylation of histamine and plays an important role in histamine biotransformation in bronchial epithelium. Enzymatic activity of HNMT has been shown to be regulated by genetic factors, including polymorphisms in the HNMT gene. In this pilot study we determined endogenous levels of histamine and cortisol in plasma and whole blood samples from subjects with different genotypes for the HNMT C314T polymorphism, and investigated whether these parameters differed between individuals with the HNMT CC genotype and those with the CT genotype.

METHODS

Blood samples were collected from 48 unrelated volunteers (36 males, 12 females), aged 21-40 years, who participated in the study. PCR-restriction fragment length polymorphism analysis was used to determine HNMT C314T genotypes. Erythrocyte HNMT activity was determined as well as plasma and whole blood levels of histamine and cortisol. Two-group comparisons of the various parameters were analyzed by Blocked Wilcoxon test and Wilcoxon Rank Sum test as appropriate.

RESULTS

Thirty-seven subjects (24 Caucasians, three African Americans, one Middle Eastern, five Indians, three Chinese, and one Filipino) were found to have the homozygous CC genotype. Ten subjects (eight Caucasians, one Middle Eastern, and one Chinese) were heterozygous and one individual (Pakistani) was homozygous for the variant 314T allele. The frequency of HNMT CT heterozygotes in the small Caucasian cohort was 0.125. Median enzyme activity was significantly lower in subjects with the heterozygous CT genotype than in those with the homozygous CC genotype (485 vs 631 U/mL of red blood cells; p=0.023). A broad range of histamine levels in plasma and whole blood was observed for all subjects. Whereas the median plasma histamine level was found to be higher in heterozygotes for the wild-type 314C allele than homozygotes (3.32 vs 2.30 nmol/L; p=0.021), there was no difference between the two groups in histamine levels in whole blood. Cortisol levels were similar between individuals with the homozygous CC genotype and those with the heterozygous CT genotype.

CONCLUSION

Wide variability of plasma and whole-blood histamine levels was observed in subjects with different HNMT C314T genotypes. Endogenous levels of histamine are likely to be affected by various genes and polymorphisms.

Concentration of histamine in serum and tissues of the primary ductal breast cancers in women

The aim of this study was to evaluate the concentration of histamine (HA) and the activities of their enzymes, namely histidine decarboxylase (HDC) and diaminooxydase (DAO) in 95 women with ductal breast cancer and in healthy women. The control group comprised 60 women without any pathological changes in their breasts, in whom mammoplasties were performed. In women with breast cancer the concentration of HA in serum was significantly higher than in healthy controls (9.1+/-3.2 vs. 5.9+/-3.1 nmol/l; P<0.001). The concentration of HA was significantly higher in neoplasmatic tissues of women with breast cancers than in unchanged tissues of healthy subjects in the control group (14.2+/-5.1 vs. 6.3+/-9.1 nmol/g; P<0.001). HDC activity was significantly elevated in cancerous tissues of women with breast cancer relative to unchanged tissues of healthy subjects (54.7+/-17.1 vs. 39.3+/-26.9 pmol/min per mg; P<0.01). However, the activity of DAO was significantly lower (14.0+/-0.4 vs. 36.1+/-9.7 pmol/min per mg; P<0.001) in neoplasmatic tissues than in normal tissues of healthy women. The adjacent healthy tissue of cancer revealed higher concentrations of HA than were found in unchanged tissues of healthy subjects (6.3+/-9.1 vs. 7.5+/-5.4 pmol/min per mg), but this difference did not reach statistical significance. The activity of HDC did not show any significant difference between the healthy tissues adjacent to cancer foci of women with breast cancer and normal tissues obtained from healthy subjects (39.3+/-26.9 vs. 34.5+/-24.3 pmol/min per mg). However, the activity of DAO was markedly lower than in unchanged tissues of healthy women in the control group (36.1+/-9.7 vs. 14.4+/-10.9 pmol/min per mg; P<0.001). The concentration of HA in cancerous tissues was significantly higher than in adjacent healthy tissues (14.2+/-5.1 vs. 7.5+/-5.4 nmol/g; P<0.001). The activity of HDC was significantly higher in cancerous tissues than in adjacent healthy tissues (54.7+/-17.1 vs. 34.5+/-24.3 pmol/min per mg; P<0.001), but there was no difference in the activity of DAO (14.0+/-6.4 vs. 14.4+/-10.9 pmol/min per mg). The significant elevation of HA concentration in cancerous tissues of women with the ductal breast cancers is caused by the increased synthesis and decreased inactivation of HA.

Histamine N-methyltransferase gene polymorphisms in Chinese and their relationship with enzyme activity in erythrocytes

The aim of this study was to identify polymorphisms in the histamine N-methyltransferase (HNMT) gene in Chinese and to assess their relationship with HNMT activity. One hundred and ninety-two unrelated subjects were recruited. HNMT polymorphisms were screened by direct sequencing with purified polymerase chain reaction products comprising all six exons, plus splice junctions, as well as approximately 2 kb of the 5'-flanking region (5'-FR). Erythrocyte HNMT activity was previously measured by radiochemical microassay. A total of 11 single nucleotide polymorphisms (SNPs) were identified, among which six SNPs had variant allele frequencies greater than 5%. Of the six common SNPs, three (-1637T>C, -463T>C and -411C>T) were located in 5'-FR, one (314C>T) in coding exons, and two (939A>G and 1097A>T) in the 3'-untranslated region (3'-UTR). Most of these common SNPs were in linkage disequilibrium. Genotype-phenotype correlation analyses were performed for those common SNPs in 5'-FR and 3'-UTR. In males, no significant association was found between HNMT activity and these non-coding SNPs. However, in females, the -1637T>C or -463T>C tended to be associated with decreased HNMT activity, whereas the 939A>G or 1097A>T appeared to be correlated with increased enzymatic activity. HNMT polymorphisms differ considerably between Chinese and American. The common SNPs in 5'-FR (-1637T>C and -463T>C) and 3'-UTR (939A>G and 1097A>T) might conditionally regulate the activity of HNMT, or might be genetically linked to unknown mutation(s) underlying the HNMT phenotypic variance.

Analysis of the C314T and A595G mutations in histamine N-methyltransferase gene in a Chinese population

BACKGROUND

Histamine N-methyltransferase (HNMT) plays an important role in the metabolism of histamine, a biogenic amine that has many physiologic and pathological roles in human tissues. A missense mutation C314T (Thr105Ile) in the HNMT gene has been identified to represent a common functional polymorphism in Caucasians, whereas an A595G (Ile199Val) variant has been reported in one HNMT cDNA from a Japanese subject.

METHODS

By using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay, the point mutations C314T and A595G within HNMT were both detected in 352 unrelated Chinese Han subjects.

RESULTS

None of the 352 subjects contained the A595G mutation, whereas 40 (11.6%) heterozygotes and 1 (0.3%) homozygote for the variant T314 allele were detected. The frequency of the variant T314 allele in this Chinese population was 0.060 (95% CI: 0.042-0.078), not different from Japanese but significantly lower than American Caucasians.

CONCLUSIONS

The C314T mutation represents a common functional genetic polymorphism in the Chinese Han population with a variant T314 allele frequency similar to Japanese but lower than American Caucasians, whereas the A595G mutation does not appear to exist in this population.

Histamine N-methyltransferase pharmacogenetics: association of a common functional polymorphism with asthma

Histamine is involved in the pathophysiology of asthma, and histamine N-methyltransferase (HNMT) plays the dominant role in histamine metabolism in human bronchial epithelium. Levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism within the HNMT gene results in a Thr105Ile change in encoded amino acid, and the T314 allele is associated with decreased levels of both HNMT enzymatic activity and immunoreactive protein. Therefore, presence of the T314 allele would be expected to result in reduced histamine metabolism and increased bronchoconstriction. We characterized this common, functionally significant polymorphism in DNA samples from 237 randomly selected Caucasian control subjects and 192 samples from Caucasian asthmatic patients. Allele frequencies for the T314 HNMT allele were 0.08 in the control samples and 0.14 in samples from Caucasian asthmatic patients (odds ratio = 1.9, P < 0.01), indicating a significant increase in the frequency of subjects with low HNMT activity among asthmatics. The association between a common, functionally significant genetic polymorphism for HNMT and asthma suggests that individual variation in histamine metabolism might contribute to the pathophysiology and/or response to therapy of this disease.

Methylation pharmacogenetics: catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase

Methyl conjugation is an important pathway in the biotransformation of many exogenous and endogenous compounds. Pharmacogenetic studies of methyltransferase enzymes have resulted in the identification and characterization of functionally important common genetic polymorphisms for catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase. In recent years, characterization of these genetic polymorphisms has been extended to include the cloning of cDNAs and genes, as well as a determination of the molecular basis for the effects of inheritance on these methyltransferase enzymes. The thiopurine methyltransferase genetic polymorphism is responsible for clinically significant individual variations in the toxicity and therapeutic efficacy of thiopurine drugs such as 6-mercaptopurine. Phenotyping for the thiopurine methyltransferase genetic polymorphism represents one of the first examples in which testing for a pharmacogenetic variant has entered standard clinical practice. The full functional implications of pharmacogenetic variation in the activities of catechol O-methyltransferase and histamine N-methyltransferase remain to be determined. Finally, experimental strategies used to study methylation pharmacogenetics illustrate the rapid evolution of biochemical, pharmacologic, molecular, and genomic approaches that have been used to determine the role of inheritance in variation in drug metabolism, effect, and toxicity.

Human histamine N-methyltransferase pharmacogenetics: common genetic polymorphisms that alter activity

Histamine N-methyltransferase (HNMT) catalyzes a major pathway in histamine metabolism. Levels of HNMT activity in humans are regulated by inheritance. We set out to study the molecular basis for this genetic regulation. Northern blot analysis showed that HNMT is highly expressed in the kidney, so we determined levels of enzyme activity and thermal stability in 127 human renal biopsy samples. DNA was isolated from 12 kidney samples with widely different HNMT phenotypes, and exons of the HNMT gene were amplified with the polymerase chain reaction. In these 12 samples, we observed a C314T transition that resulted in a Thr105Ile change in encoded amino acid, as well as an A939G transition within the 3'-untranslated region. All remaining renal biopsy samples then were genotyped for these two variant sequences. Frequencies of the alleles encoding Thr105 and Ile105 in the 114 samples studied were 0.90 and 0.10, respectively, whereas frequencies for the nucleotide A939 and G alleles were 0.79 and 0.21, respectively. Kidney samples with the allele encoding Ile105 had significantly lower levels of HNMT activity and thermal stability than did those with the allele that encoded Thr105. These observations were confirmed by transient expression in COS-1 cells of constructs that contained all four alleles for these two polymorphisms. COS-1 cells transfected with the Ile105 allele had significantly lower HNMT activity and immunoreactive HNMT protein than did those transfected with the Thr105 allele. These observations will make it possible to test the hypothesis that genetic polymorphisms for HNMT may play a role in the pathophysiology of human disease.

Synthesis of tritium-labelled N tau-methylhistamine for the improvement of extraction efficiency of N tau-methylhistamine from biological fluids

In order to trace the loss of N tau-methylhistamine, a principal metabolite of histamine, during extraction and purification from human plasma and urine samples, N tau-[3H]methylhistamine was prepared in two steps from N alpha t-butoxycarbonylhistamine (II). In the first step, compound II was deprotonated with NaH in an aprotic solvent and treated with [3H]methyl iodide. The products, N alpha t-butoxycarbonyl-N tau-[3H]methylhistamine (III) and N alpha t-butoxycarbonyl-N pi-[3H]methylhistamine (IV), were then hydrolysed with iodotrimethylsilane under mild and short reaction conditions. Facile purification with Sep-Pak silica cartridges gave the combined two isomers of N tau-[3H]methylhistamine and N pi-[3H]methylhistamine in 10.7% radiochemical yield with a radiochemical purity of > 94% and a ratio of approximately 2:1. Improvements in the extraction of methylhistamine using chromatography on Sep-Pak silica cartridges led to an overall recovery of 82.5 +/- 0.3% (n = 3) based upon total [3H]methylhistamine from normal human plasma.

Determination of plasma Ntau-methylhistamine in vivo by isotope dilution using benchtop gas chromatography-mass spectrometry

A practical sensitive and specific method for determination of the stable metabolite of histamine, Ntau-methylhistamine, in human plasma using benchtop gas chromatography-stable isotope dilution mass spectrometry has been developed. Ntau-Methylhistamine, a principal metabolite of histamine in humans, was extracted and purified from human plasma using a two-step procedure with Sep-Pak silica cartridges. Quantitation of Ntau-methylhistamine was made possible by the synthesis of Ntau-[2H3]methylhistamine used as an internal standard. Derivatization with pentafluoropropionyl anhydride of extracts of human plasma yielded the bis-pentafluoropropionyl derivative of Ntau-methylhistamine for measurement using selected ion monitoring of the m/z 417/420 ion pair after electron impact on a benchtop gas chromatography-mass spectrometry (GC-MS). By improvements in the plasma extraction technique, inclusion of a synthetic internal standard and the development of a sensitive and stable derivative of the histamine metabolite, Ntau-methylhistamine was found to be significantly elevated in the plasma of patients with the dermal fibroproliferative disorder, hypertrophic scarring as compared to age-matched normal volunteers (98.5+/-29.5 pg/ml, n=9, versus 43.3+/-16.5 pg/ml, n=8, p<0.05). As such, this method affords a sensitive, specific and practical approach to measurement of histamine metabolites in plasma and other biological fluids.

Histamine N-methyltransferase: inhibition by monoamine oxidase inhibitors

Histamine N-methyltransferase (HNMT) catalyzes the N tau-methylation of histamine. N tau-Methylhistamine can then undergo oxidation catalyzed by the mitochondrial enzyme monoamine oxidase (MAO). Addition of an MAO inhibitor such as pargyline to tissue preparations can increase the HNMT activity assayed --presumably as a result of inhibition of N tau-methylhistamine metabolism by MAO. However, pargyline-dependent "activation" of HNMT may also occur in tissue preparations that lack mitochondria. Our experiments were performed to determine whether MAO inhibitors, like many other amine compounds, could directly increase the activity of partially purified HNMT, and, if so, to study the mechanism of activation. Human kidney HNMT was partially purified by sequential ion exchange and gel filtration chromatography. The activity of the purified HNMT was increased approximately 50% in the presence of pargyline. However, enzyme kinetic experiments showed that pargyline, like many other amines, was a competitive inhibitor of HNMT. Apparent activation of the enzyme resulted from sequential shifts of histamine substrate curves to higher Vmax values in the presence of increasing concentrations of pargyline. Other acetylenic MAO inhibitors, clorgyline and the two stereoisomers of deprenyl, were also competitive inhibitors of purified human kidney HNMT. Inhibition kinetic experiments performed in the presence of varying concentrations of histamine demonstrated that Kis values for pargyline, clorgyline, (R)-deprenyl and (S)-deprenyl were 0.126, 0.144, 0.217, and 0.627 mM, respectively. When the concentration of the cosubstrate for the reaction, S-adenosyl-L-methionine, was varied in the presence of variable concentrations of pargyline, inhibition of HNMT by pargyline was noncompetitive with regard to the methyl donor, with Kii and Kis values of 1.23 and 0.95 mM, respectively. Finally, several amine compounds related structurally to pargyline were also found to be inhibitors of HNMT.

A free-radical hypothesis for the instability and evolution of genotype and phenotype in vitro

It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., an in vitro evolution, which includes crisis, spontaneous transformation ('immortalization'), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by the in vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause of in vitro evolution. We propose an oxyradical hypothesis to explain each of the stages of in vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.

Opiates, mast cells and histamine release

Opiates have long been known to cause the release of histamine from mast cells, resulting in several undesirable effects, such as hypotension, urticaria, pruritus, and tachycardia. The mechanism of this opiate response has remained unclear, although it is known to be non-immunological in nature. A survey of the histamine-releasing properties of a variety of opiates shows that the pharmacology of opiate-induced histamine release from mast cells is distinct from that of known opiate receptors. Although functional opiate receptors may exist on mast cells and may be capable of modulating IgE-mediated histamine release, there is no evidence that these receptors account for opiate-induced histamine release. Since other basic compounds have been suggested to release histamine from mast cells by directly activating G-proteins, it seems possible that morphine and endogenous opiates may also share this mechanism.

Diamine oxidase activity and related substrates in rat liver after chronic ethanol feeding

Chronic ethanol feeding as 12% or 36% of total calories caused a dose-dependent diminution of diamine oxidase activity in rat liver. Hepatic cadaverine and histamine levels were unmodified by ethanol, whereas putrescine increased, partially in relation to the decrease in diamine oxidase activity. Such results may be of interest in view of an aggravation of ethanol-induced hepatic damage when exogenous diamines and polyamines reach the liver in potentially toxic amounts.

Effects of aminoguanidine on pre- and post-irradiation regional cerebral blood flow, systemic blood pressure and plasma histamine levels in the primate

Exposure to ionizing radiation causes hypotension, cerebral ischemia and release of histamine (HA). To investigate the relationship among these three responses, rhesus monkeys (Macaca mulatta) received aminoguanidine (AG) (1 mg/kg), then were given either 50 Gy whole-body irradiation or sham-irradiation. Monkeys receiving AG had lower mean arterial blood pressure (MABP) than saline-treated controls. Compared to controls, rCBF was lower in irradiated monkeys but pre-treatment with AG did not influence this effect. Among untreated, irradiated monkeys, HA levels were increased only at two minutes post-irradiation, but among AG-treated, irradiated monkeys, HA levels were higher at all times postirradiation. Radiation-induced release of HA may be associated with radiation-induced hypotension and reduced rCBF, but failure of AG to alter rCBF suggests that released HA may not be the sole mediator of these effects. Because elevations in plasma HA are probably due to HA derived from degranulation of mast cells, release of other bioactive substances from mast cells may also influence these cardiovascular effects. Surprisingly, in sham-irradiated monkeys, AG alone had a slight but significant hypotensive effect.

Intestinal diamine oxidases and enteral-induced histaminosis: studies on three prognostic variables in an epidemiological model

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.

Assay for N tau-methylimidazoleacetic acid, a major metabolite of histamine, in urine and plasma using capillary column gas chromatography-negative ion mass spectrometry

A gas chromatographic-mass spectrometric assay has been developed for the measurement of N tau-methylimidazoleacetic acid in urine and plasma. The method uses the isopropyul ester 3,5-bistrifluoromethylbenzoyl derivative of N tau-methylimidazoleacetic acid and electron capture negative ion chemical ionisation mass spectrometry. The derivative has very good chromatographic properties and a negative ion mass spectrum which contains only a molecular ion at m/z 422. When this ion is specifically monitored, an amount of derivative equivalent to 1 pg of parent compound can be detected. A deuterated analogue of N tau-methylimidazoleacetic acid was synthesised for use as an internal standard and this allowed the development of an assay for N tau-methylimidazoleacetic acid, in urine with a precision of 2.9% and in plasma with a precision of 1.5%.

Analysis of histamine and N tau-methylhistamine in plasma by gas chromatography-negative ion-chemical ionization mass spectrometry

Current methods of quantitation of histamine and its major metabolite N tau-methylhistamine are inaccurate and insensitive to the very low concentrations that exist in plasma samples. Therefore, an accurate and sensitive method for quantification in plasma has been developed using the stable isotope dilution assay with negative ion-chemical ionization mass spectrometry. For histamine, after the addition of [2H4]histamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the pentafluorobenzyl derivative (CH2C6F5)3-histamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 430/434. For N tau-methylhistamine, after the addition of N tau-[2H3]methylhistamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the heptafluorobutyryl derivative (C3F7CO2)2-N tau-methylhistamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 497/500. The precision of the histamine assay is 3.1% and the accuracy is 95.5 +/- 2.5% while the precision of the N tau-methylhistamine assay is 1.9% and the accuracy is 106.8 +/- 1.9%. The lower limits of sensitivity are 1 pg for histamine and 6 pg for N tau-methylhistamine injected on column. Using the assay in three normal human volunteers, plasma concentrations of histamine were 130, 92, and 85 pg/ml, and of N tau-methylhistamine were 229, 228, and 216 pg/ml. This assay provides a very sensitive and accurate method of quantitation of histamine and N tau-methylhistamine in plasma samples.

Analysis of N tau-methyl imidazole acetic acid by electron impact gas chromatography/mass spectrometry

A method for the quantitative analysis of N tau-methyl imidazole acetic acid, a major urinary metabolite of histamine, using electron impact gas chromatography/mass spectrometry is described, as are the results of its application to a problem of clinical interest.

Mechanism of hematocrit increase induced by the combined administration of morphine and adriamycin: role of histamine release

The mechanism by which morphine interacts with Adriamycin to increase hematocrit has been investigated in mice. Treatment with Adriamycin (12.8 mg/kg, iv) or morphine (20 mg/kg, sc) resulted in slight increases in hematocrit 30 min postdose, while animals given sc morphine 30 min prior to iv Adriamycin exhibited significant increases in hematocrit as early as 1 min post-Adriamycin. The hematocrit increase reached maximal levels 12 min post-Adriamycin and returned to basal values 4 hr postdose. Splenectomizing animals prior to morphine and Adriamycin treatment had no effect on the drug-induced hematocrit increase. This indicates that red cell release from splenic contracture is not the mechanism for the hematocrit increase. Measurement of plasma histamine levels following drug treatment demonstrated a marked and rapid rise in plasma histamine levels reaching maximal values 1 min post-Adriamycin. Adriamycin alone triggered this release; however, morphine pretreatment resulted in a higher maximum and more prolonged elevation of plasma histamine levels. Treatment with pyrilamine (3.1-50 mg/kg, ip) prior to morphine and Adriamycin administration partially reversed drug-induced hematocrit increase and protected against resultant lethality. Cimetidine (50-200 mg/kg, ip) treatment was not effective. The temporal relationship between hematocrit and histamine increases suggests a cause/effect relationship between released histamine and hematocrit elevation. Protection by pyrilamine and not cimetidine further supports this cause/effect relationship and indicates the effects is mediated via histamine type 1 receptors.

Effect of acute ethanol administration on diamine oxidase activity in maternal, embryonal and fetal tissues

Pregnant rats were acutely treated with ethanol to study the influence of this drug on diamine oxidase activity of maternal, embryonal, and fetal tissues. When ethanol was given on day 12 of gestation, enzyme activity was unmodified in placenta and embryo, whereas it was reduced by 38 and 31%, respectively, in maternal liver and plasma at 3 h. When ethanol was given on day 18 of gestation, diamine oxidase activity diminished in maternal liver, plasma and placenta by about 35-40% at 6 h. Moreover, in the fetus ethanol caused a 35% diminution of enzyme activity in liver at 6 h and a 45% stimulation in brain at 3 h, and of about 65% at 6-12 h. These data may be of interest in view of the physiological role of diamine oxidase in the oxidation of the large amounts of amines produced during pregnancy.

Histamine food poisoning: toxicology and clinical aspects

Histamine poisoning can result from the ingestion of food containing unusually high levels of histamine. Fish are most commonly involved in incidents of histamine poisoning, although cheese has also been implicated on occasion. The historic involvement of tuna and mackerel in histamine poisoning led to the longtime usage of the term, scombroid fish poisoning, to describe this food-borne illness. Histamine poisoning is characterized by a short incubation period, a short duration, and symptoms resembling those associated with allergic reactions. The evidence supporting the role of histamine as the causative agent is compelling. The efficacy of antihistamine therapy, the allergic-like symptomology, and the finding of high levels of histamine in the implicated food suggest strongly that histamine is the causative agent. However, histamine ingested with spoiled fish appears to be much more toxic than histamine ingested in an aqueous solution. The presence of potentiators of histamine toxicity in the spoiled fish may account for this difference in toxicity. Several potentiators including other putrefactive amines such as putrescine and cadaverine have been identified. Pharmacologic potentiators may also exist; aminoguanidine and isoniazid are examples. The mechanism of action of these potentiators appears to be the inhibition of intestinal histamine-metabolizing enzymes. This enzyme inhibition causes a decrease in histamine detoxification in the intestinal mucosa and results in increased intestinal uptake and urinary excretion of unmetabolized histamine.

Metabolism of N tau-methylhistidine by mice

Mice and rats were injected with tracer doses of radioactive N tau-[Me-14C]methylhistidine in order to determine the recovery of the injected radioactivity and the extent of the metabolism of N tau-methylhistidine. In the first 27 h after injection, 96.3, 78.0 and 97.5% of radioactivity was excreted by female mice, male mice and male rats respectively. Recovery after 5 days of collection was 98.4 and 92.8% for female and male mice respectively. However, radioactivity associated with N tau-methylhistidine or its acetylated derivative accounted for 44, 86.5 and 96.0% of the excreted radioactivity for female mice, male mice and rats respectively. In female mice the remaining excreted radioactivity was associated with four major peaks of activity when the metabolites were separated by cation-exchange chromatography. In male mice there were only three of these metabolites present. After chromatographic purification, one metabolite was identified by mass spectroscopy to be 1-methylimidazole-4-acetic acid. Examination of the possible sources of this metabolite indicates that, in mice, N tau-methylhistidine is decarboxylated and enters the chain of reactions common to histamine metabolism. Such extensive metabolism precludes the use of N tau-methylhistidine excretion as an index of myofibrillar protein breakdown in mice.

Measurement of imidazoleacetic acid in urine by gas chromatography-mass spectrometry

Imidazoleacetic acid (IAA), a histamine and histidine metabolite, was quantified in human urine by gas chromatography-mass spectrometry (GC-MS). The acid was separated by ion-exchange chromatography, derivatized as the n-butyl ester with boron trifluoride-butanol and the derivative extracted with chloroform. GC-MS analysis was carried out by selected-ion monitoring of ions m/z 81 and m/z 83 corresponding, respectively, to IAA and [15N,15N']IAA used as internal standard. The mean IAA content in urine was about 8.02 nmol/mg of creatinine. The specificity of measurement was rigorously established by GC retention time, peak shape, ion abundance ratios, and recovery experiments. The method is capable of quantifying IAA in 0.05 ml of urine and in amounts as low as 0.20 nmol.

Growth of pulmonary metastases of B16 melanoma in mast cell-free mice

The relationship of mast cells to tumor growth has been debated but not elucidated. The existence of a mast cell-free animal, the W/Wv mouse, provides a model in which tumor metastasis can be studied with special reference to host tissues and their mast cell content rather than to the adhesiveness of the tumor cell itself. Both hind footpads of 30 W/Wv mice and 30 control mice (+/+) were injected with 2 X 10(5) cells of B16-F10 melanoma cells. The left paw received 1000 rads orthovoltage radiation 12 hr before tumor inoculation. Growth of tumors in both paws was recorded. Ten animals from each group were killed on Day 31 after tumor inoculation, and the remaining animals were kept until they died. Autopsy was performed in all animals, and patterns of metastasis were recorded. Results showed that (1) preinoculation radiation significantly slowed tumor growth in the left paw (P = 0.0009), and (2) lung metastases were present in 4 of 10 W/Wv mice, but in none of 10 +/+ mice killed after 31 days (P = 0.05). Overall, 17 of 25 W/Wv mice and 8 of 26 +/+ mice had lung metastases (P = 0.008).

A sensitive double isotopic, chromatographic method for the determination of histamine. I: Studies with authentic histamine

This paper presents a method for the determination of histamine using an internal standard of 14C-labelled histamine, which together with an unknown sample of unlabelled histamine is dansylated with 3H-labelled dansyl chloride. The products of this dansylation are then separated on thin-layer-chromatographic plates coated with micropolyamide. The spot of dansylhistamine is scraped off and the content of histamine in the unknown sample is calculated from the 3H/14C-ratio in the spot.

Compound 48/80 and the healing of wounds in rats. The effect of timing of drug injections

Wound breaking strength was measured in Long-Evans rats in two settings: in one experiment animals received Compound 48/80 i.p. for 8 consecutive days, starting 1 day before infliction of wound and in the second experiment 48/80 was given for 6 days before wounding. Wound breaking strength was always measured on the seventh day after wounding. There was a significant increase in wound breaking strength in animals treated before incision was made, as compared to controls, saline-treated animals (p less than 0.01). When 48/80 was given one day before incision was made, the breaking strength was significantly decreased (p less than 0.0002). Possible explanation for these opposite results is discussed.

Clearance of histamine from the peritoneal cavity of rats

To study the clearance of histamine from the peritoneal cavity of rats, histamine was either injected i.p. or released locally by the injection of compound 48/80. At various intervals peritoneal fluid was removed and analysed for histamine concentration by a fluorometric assay. Exogenous and endogenous histamine were cleared from the peritoneal cavity at the same rate with a half life of 20 minutes. The rate was not altered by different histamine concentrations, by injection of heparin, and by the removal of peritoneal leukocytes. Repeated injections of large amounts of histamine resulted in a decreased clearance. The results suggest that histamine concentrations above the physiological level are quickly degraded. Activities of histamine as an inflammatory mediator are likely to be of short duration.

Effects of histamine agonists and antagonists on luminol-dependent chemiluminescence of granulocytes

Histamine inhibited luminol-dependent chemiluminescence (CL) of granulocytes in a dose-dependent manner, with an ID50 of about 3 X 10(-5) M. Dimaprit, a selective H2-agonist, produced a histamine-like effect. Furthermore, cimetidine, ranitidine, and TZU 0460, which are selective H2-antagonists, but not mepyramine, a selective H1-antagonist, blocked the inhibitory effect of histamine on CL. Thus it may be concluded that the inhibitory effect of histamine is mediated via histamine H2-receptors. H1- and H2-antagonists per se, except at extremely high concentrations, had no effect on CL of granulocytes.

Histamine content, diamine oxidase activity and histamine methyltransferase activity in human tissues: fact or fictions?

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.

Histamine and its catabolism in tumour-bearing rat and mouse

The hypothesis that failure of histamine (Hi)-mediated inter and intracellular cell-cell communication may be involved in the control of cellular growth has been tested in leukaemia-bearing mice and fibrosarcoma-bearing rats. In all examined tissues of mice bearing leukaemia L1210 cells and rats bearing methylcholanthrene fibrosarcoma histamine content was higher than in controls. Tissues of fibrosarcoma-bearing rats more intensively metabolized 14C-Hi and oxidative pathway was predominant. Histamine metabolic activity as well as histamine catabolic pathways do not differ in leukaemic mice as compared with the controls.

Presence and measurement of tele-methylhistamine in mast cells

The histamine metabolite tele-methylhistamine (t-MH) was identified and measured in crude and purified peritoneal mast cells (MCs). Peritoneal dialysates, peritoneal cells, and purified MCs all contained t-MH in concentrations representing about 0.2% of the corresponding histamine (HA) levels. T-MH levels in crude cells represented about 70% of the total dialysate levels, indicating the presence of extracellular as well as intracellular t-MH. T-MH levels per MC in purified fractions were similar to those of crude fractions, indicating a MC origin for the intracellular t-MH. Histamine methyltransferase activity was not detected in crude or purified MC fractions, and incubations with the monoamine oxidase inhibitor pargyline failed to increase the content or release of t-MH in either fraction, suggesting a very slow or non-existent histamine methylation in MCs. Compound 48/80 produced a temperature-dependent release of HA and t-MH in crude and purified preparations, and Triton X-100 also released both amines. In all cases, the degree of release of both amines was correlated, consistent with a granular origin for t-MH in MCs. The low concentrations of t-MH in MCs do not necessarily indicate a role for MCs in HA metabolism, but suggest that t-MH may be a valuable marker for non-MC HA.

Effects of pargyline on tele-methylhistamine and histamine in rat brain

Rapid and complete inhibition of brain MAO produced linear increases in brain t-MH levels from 30 min to 4 hr after drug treatment at a rate of 0.26 nmole/g X hr, resulting in a 3-fold increase which persisted for at least 12 hr. HA levels were slightly elevated 1 and 2 hr after drug administration but quickly returned to control levels, suggestive of sensitive regulatory mechanisms in brain. Although the slight change in HA levels precludes steady-state assumptions, the rate of increase in brain t-MH levels after MAO inhibition provides a novel estimate of the half-life of endogenous brain HA (50 min). Despite the transient effect of pargyline on brain HA content, the effect of pargyline on brain t-MH levels suggests that MAO inhibitors may produce long-term alterations in brain histaminergic dynamics.

Determination of N tau-methylimidazoleacetic acid (a histamine metabolite) in urine by gas chromatography using nitrogen-phosphorus detection

N tau-Methylimidazoleacetic acid, the quantitatively most important metabolite of histamine, was isolated from urine by ion exchange chromatography. After esterification with 2-propanol and extraction, N tao-methylimidazoleacetic acid was analyzed by capillary gas chromatography with nitrogen-phosphorus detection, using N tao-ethylimidazoleacetic acid as internal standard. The synthesis of this internal standard is described. In contrast to the methods hitherto described, this method is appropriate for use in clinical chemical laboratories. Normal 24-h excretion ranged from 8.3 to 18.5 mumol (n = 20). Five patients with mastocytosis, a patient with chronic myelocytic leukemia and a patient after an anaphylactoid reaction on acetylsalicylic acid showed highly elevated values.

Dynamics of renal histamine in normal rat kidney and in nephrosis induced by aminonucleoside of puromycin

Histamine is known to have a profound effect on capillary permeability in nonrenal tissues and this effect is presumably mediated by cyclic (c)AMP. Because in our previous experiments we found that histamine stimulates cAMP accumulation in glomeruli (Torres, V. E., T. E. Northryn, R. M. Edwards, S. V. Shah, and T. P. Dousa. 1978. Modulation of cyclic nucleotides in isolated rat glomeruli. J. Clin. Invest.62: 1334.), we now explored whether this amine is formed in renal tissue, namely in glomeruli, and whether its renal metabolism is altered in experimental nephrosis induced by puromycin aminonucleoside (PA) in rats. In normal rats, histamine content was higher (Delta + 240%) in cortex than in medulla. In glomeruli isolated from renal cortex, histamine content was significantly higher (Delta + 260%) than in tubules. Incubation of isolated glomeruli with l-histidine resulted in a time-dependent increase of histamine content in glomeruli, but no change was found in tubules. The increase in glomerular histamine was blocked by the histidine decarboxylase inhibitor bromocresine. In rats with PA nephrosis induced by a single intraperitoneal injection of PA (15 mg/100 g body wt) urinary excretion of histamine was markedly increased (>Delta + 200%), but control rats did not differ from rats with PA nephrosis in urinary excretions of l-histidine and of creatinine. At the peak of proteinuria (day 9 after injection of PA) the plasma level of histamine was slightly elevated, and plasma histidine slightly decreased in animals that developed PA nephrosis. The content of histamine was markedly higher and the level of histidine was significantly lower in the renal cortex of PA-nephrotic rats as compared with controls; PA-nephrotic and control rats did not differ in the content of histidine and histamine in the liver. In addition, the content of histamine was higher in glomeruli isolated from PA-nephrotic rats; lesser difference was found in cortical tubules. The results further indicate that PA-nephrotic rats have higher content of histamine in the renal cortex, predominently in glomeruli with increased urinary histamine excretion. The elevated renal cortical histamine is not due to higher availability of histamine precursor l-histidine. Results thus show that glomeruli are a major site of intrarenal histamine synthesis and accumulation, and also suggest that abnormal renal metabolism of this amine in PA nephrosis may be related, as a cause or as a consequence, to the pathogenesis of this disease.

Equine immunology 2: immunopharmacology--biochemical basis of hypersensitivity

In general, 4 types of hypersensitivity reactions can be defined according to their immunological basis and clinical appearance. The differing mechanisms of these responses are described with particular reference to chemical mediators which through their pharmacological actions contribute to the clinical manifestations of hypersensitivity. Chemical mediators may exert their influence locally or systemically through their action on effector, tissues or organs and in addition, may be involved in the recruitment of cells of specific type to the site of the reaction. The possible role of these mediators in hypersensitivity in the equine species is discussed to provide a background for a subsequent paper which will be concerned with the therapy of hypersensitivity conditions.

Determination of N tau-methylhistamine in plasma and urine by isotope dilution mass fragmentography

The determination in N tau-methylhistamine by gas chromatography-mass spectrometry is described using bis-heptafluorobutyryl derivatives and deuterium labelled N tau-methylhistamine as internal standard. A description of the synthesis of the internal standard, N tau-trideuteromethylhistamine, is given. Normal concentrations for plasma were 1.4 +/- 0.4 microgram/l (mean +/- 1 S.D., n = 10). The normal values for urine ranged from 60 to 280 microgram/24 h (n = 20). Five asthmatic patients showed above-normal plasma concentrations.

Putrescine metabolism and the study of diamine oxidase activity in vivo

The catabolism of 14C-putrescine (1,4-tetramethylene-diamine) to labeled CO2 in small laboratory animals has been studied extensively in order to establish the influence of nutritional, endocrine and other factors on this process. Special attention has been paid to treatments that are known to affect the activity of diamine oxidase (DAO, histaminase, EC, 1.4.3.6), a copper-containing enzyme characteristically inhibited by semicarbazide. Thus, copper-deficient rats metabolize putrescine more slowly than their controls. Antimalarial drugs that inhibit histamine N-methyltransferase also inhibit putrescine catabolism in vivo and DAO activity in vitro. Adrenalectomized rats metabolize the diamine at a reduced rate, a result consistent with the previously demonstrated decrease of DAO in the tissues of several species of animal. There is no effect on the rate of catabolism of putrescine when thyroid state is altered. Heparin (up to 15,000 U/kg), which releases DAO from the small (0.1 mg/kg), intestine, and aminoguanidine (0.1 mg/kg), which inhibits the enzyme powerfully, both cause decreased rates of catabolism of the diamine in rats. The putrescine-catabolizing ability returns with a half-time of recovery of 15-18 h, corresponding to the estimates of SHAFF and BEAVEN [36] for recovery of intestinal DAO activity following administration of heparin or cycloheximide. Together with out other results this suggests that what is being measured by putrescine catabolism depends to a significant extent on the activity of DAO in vitro.