Inhibition of histamine methylation in vivo by drugs

Mind molecules

Scientific styles vary tremendously. For me, research is largely about the unfettered pursuit of novel ideas and experiments that can test multiple ideas in a day, not a year, an approach that I learned from my mentor Julius "Julie" Axelrod. This focus on creative conceptualizations has been my métier since working in the summers during medical school at the National Institutes of Health, during my two years in the Axelrod laboratory, and throughout my forty-five years at Johns Hopkins University School of Medicine. Equally important has been the "high" that emerges from brainstorming with my students. Nothing can compare with the eureka moments when, together, we sense new insights and, better yet, when high-risk, high-payoff experiments succeed. Although I have studied many different questions over the years, a common theme emerges: simple biochemical approaches to understanding molecular messengers, usually small molecules. Equally important has been identifying, purifying, and cloning the messengers' relevant biosynthetic, degradative, or target proteins, at all times seeking potential therapeutic relevance in the form of drugs. In the interests of brevity, this Reflections article is highly selective, and, with a few exceptions, literature citations are only of findings of our laboratory that illustrate notable themes.

Concentration of histamine in different parts of the brain and hypophysis of rabbit: effect of treatment with histidine, certain other amino acids and histamine

1. Estimates have been obtained by biological assay of the histamine concentration in different parts of the rabbit brain and hypophysis.2. Mean values (ng/g) for the brain were: hypothalamus, 660; central grey matter and medial thalamus, 275; tegmental region of mid-brain, the hind-brain and caudate nucleus, 140 to 170; hippocampus and cerebral cortex, 90 to 110; cerebellum (vermis), 60.3. The mean value (ng/g) for the anterior lobe of the hypophysis was 650; for the posterior lobe, 400.4. In conscious rabbits, intravenous infusion of histidine in the dose range 62 to 1,500 mg/kg, raised significantly (P<0.01) the concentration of histamine in all regions of the brain examined, the pattern of distribution remaining unchanged. The largest increases occurred in the mid brain (90 to 320%) and in the hypothalamus (50 to 250%); in these areas the higher doses produced higher concentrations. Elsewhere in the brain the concentration rose in response to the lowest dose of histidine, but was not increased when higher doses were given. Concentrations in the anterior lobe of the hypophysis were unaltered.5. The infusion of histidine, unlike that of amino acid precursors, of the monoamines, produced no obvious disturbance in the animals.6. The rise in brain histamine after dosage with histidine persisted for several hours, depending on the dose; with 500 mg/kg, the rise was virtually unchanged after 16 hours.7. Histamine (5 mg/kg by intravenous infusion) raised the concentration of histamine in the hypophysis but not in the brain.8. After the infusion of DOPA, alpha-methyldopa or 5-hydroxytryptophan, the histamine concentration rose in the mid-brain but not in other parts of the brain.9. These amino acids, when infused singly with histidine, did not interfere with the histidine-induced rise of brain histamine.

In vivo studies on histamine catabolism and its inhibition

1. Histamine catabolism in vivo was studied in mice subjected to various forms of pretreatment; tissues from mice killed 2.5 min after intravenous injection of (14)C-histamine were assayed for (14)C-histamine, (14)C-methylhistamine and total (14)C.2. Pretreatment of mice with aminoguanidine, an inhibitor of diamine oxidase, strongly increased levels of (14)C-histamine in intestine; pretreatment with aminoguanidine plus a monoamine oxidase inhibitor strongly increased levels of (14)C-methylhistamine in liver. Effects in other tissues are reported and discussed.3. Pretreatment of mice with non-isotopic methylhistamine increased levels of (14)C-histamine in liver. Methylhistamine is the first known inhibitor of histamine-methylation in vivo.4. Pretreatment of mice with inhibitors of protein synthesis, drugs which reduce the basal activity of histidine decarboxylase and which block its activation, failed to affect histamine catabolism.5. Pretreatment of mice with endotoxin or with Freund's adjuvant, irritants known to cause activation of histidine decarboxylase, failed to affect histamine catabolism.6. There was no evidence of parallelism between the histamine-destroying enzymes and the histamine-forming enzyme, histidine decarboxylase, either in distribution or ability to undergo changes in activity. No support was obtained for the view that histamine-catabolizing enzymes play a role in the local control of responses to newly formed histamine.

The possible role of histamine in the coritsone induced gastric acid hypersecretion of the guinea-pig

1. The effects of cortisone treatment combined with agents influencing histamine metabolism were studied on the free and total acid output in pylorus ligated guinea-pigs.2. It was found that reduction in the synthesis of histamine produced by the administration of alpha-methylDOPA significantly inhibited the acid response to cortisone.3. Enhancement of the oxidative deamination of histamine brought about by the administration of diamine oxidase or heparin inhibited cortisone induced acid hypersecretion significantly.4. Inhibition of the oxidative deamination of histamine by aminoguanidine and iproniazid resulted in a significant increase of the cortisone induced acid hypersecretory response.5. Inhibition of the methylation of histamine by chlorpromazine or 1,4-methylhistamine inhibited the cortisone induced hypersecretory response significantly.6. Studies with labelled histamine indicated that cortisone increases the sequestration of histamine to the stomach.