Potentiation of the Action of Histamine by Semicarbazide

Preparation of a carboxylated single-walled carbon-nanotube-chitosan functional layer and its application to a molecularly imprinted electrochemical sensor to quantify semicarbazide

Semicarbazide (SEM) is a protein-bound nitrofurazone metabolite that is detrimental to human health. Therefore, to ensure food safety, it is necessary to detect SEM in food samples. To this end, we developed a novel electrochemical sensor to detect SEM by using a molecularly imprinted polymer (MIP) as the recognition element. Computer-aided molecular modelling was performed to guide the synthesis of the MIP, and subsequently, MIP/carboxylated single-walled carbon-nanotubes/chitosan (MIP/SWNTs-COOH/CS) was prepared as the sensing platform to develop the electrochemical sensor. The linear range of the sensor was 0.04-7.6 ng mL^-1, with a detection limit of 0.025 ng mL^-1. The sensor was successfully applied to detect SEM in four different real samples, with recoveries ranging from 83.16% to 93.40%. The results indicated that the fabricated electrochemical sensor can be widely applied to detect SEM in the environment and in agri-food products.

Attenuation of Weight Gain and Prevention of Associated Pathologies by Inhibiting SSAO

Obesity is a worldwide prevalent metabolic disorder that is associated with diabetes, among many other diseases. Bearing this in mind, prevention and treatment ways need to be improved. Notably, activity of the enzyme semicarbazide-sensitive amine oxidase (SSAO) is found to be elevated in overweight subjects. Moreover, SSAO inhibition has resulted in an increase of histamine activity in adipose tissue and the limitation of body fat. The current review aims to overview the risks of obesity, rationalize the molecular ways of SSAO activity, and outline the strategies of inhibiting upregulated enzyme levels. It describes the differences between SSAO inhibitors and advances the prospective agents. Based on evidence, caffeine is proposed as an effective, safe, and reliable choice to inhibit SSAO activity. Furthermore, the histamine in adipocytes has been associated with SSAO activity. Therefore, it is suggested as one of the key compounds to be studied for obesity management. To conclude, inhibiting SSAO may attenuate weight gain and prevent related diseases.

Release of mast cell mediators, vasoconstriction and edema in the isolated, perfused head of the rat following intracarotid infusion of neurotensin

Intracarotid infusions of neurotensin (NT) into the isolated, perfused head of rats trigger concentration-dependent histamine and 5-hydroxytryptamine (5-HT) release from the perfused organ. The secretory event was accompanied by a concentration-dependent rise in perfusion pressure and facilitation of edema formation. The three NT effects were markedly reduced in heads derived from rats pretreated with high doses of compound 48/80 to produce mast cell depletion. The vasoconstrictor response to NT was greatly attenuated by the 5-HT receptor antagonist methysergide but unaffected by antihistaminic drugs. The results were interpreted as an indication that NT stimulates histamine and 5-HT release from mast cells of the rat perfused head. The results also suggest that the vasoconstrictor response to NT in the rat head is mediated by mast cell 5-HT. The potentiation of edema formation by NT was attributed to the action of mast cell mediators (most likely histamine and 5-HT) released by NT on microvessels.

Neurotensin stimulates histamine release from the isolated, spontaneously beating heart of rats

Neurotensin (NT) evoked a transient, dose-dependent histamine release (ED50 170 ng ml-1) from the rat perfused heart. Histamine release by NT occurred within seconds and lasted less than 2 min. The histamine releasing effect of NT was followed by a dose-dependent increase of the perfusion pressure and a slight tachycardia. The histamine releasing effect of NT was completely abolished in hearts derived from rats pretreated for 3 days with high doses of compound 48/80. The coronary vasoconstrictor effect of NT was increased in hearts derived from compound 48/80-pretreated rats. The mast cell inhibitor cromoglycate markedly inhibited NT-induced histamine release without affecting the coronary vasoconstrictor effect of NT. The histamine releasing effect of NT was inhibited, while its coronary vasoconstrictor effect was markedly potentiated, in hearts derived from rats pretreated with the antiallergic and antiinflammatory steroid dexamethasone. The increase of perfusion pressure evoked by NT was not modified by antihistamine drugs. Infusions of exogenous histamine (10(-6)-10(-5) g ml-1) caused a dose-dependent coronary vasodilation in the rat perfused heart. The results suggest that NT stimulates histamine release from cardiac mast cells. These results together with those obtained in previous studies suggest that mast cell mediators (particularly histamine and serotonin) are unlikely to be responsible for the coronary vasoconstrictor effect of NT in the rat perfused heart.

Histamine release by neurotensin in the rat hindquarter: structure-activity studies

Histamine releasing effects of neurotensin (NT) and several NT fragments and structural analogues were measured in the rat perfused hindquarter. The results show that the chemical groups responsible for histamine release are located in the C-terminal sequence Arg9-Pro10-Tyr11-Ile12-Leu13-OH. Both the spatial configuration and positive charge of Arg8 and Arg9 appear to contribute to the histamine releasing effect of NT. Optimization of the histamine releasing effect of NT requires both a free C-terminal carboxyl group and the presence in position 11 of NT of an aromatic residue, with the L-configuration, bearing an heteroatom capable of hydrogen bonding with the receptor. The results indicate that the structural requirements of NT to induce histamine release from the rat perfused hindquarter are similar to those involved in other peripheral biological actions of NT.

Influence of various drugs on the variations of blood pressure, hematocrit and plasma histamine caused by neurotensin and compound 48/80 in rats

Intravenous injections of neurotensin (NT) (0.5, 1 and 2 nmoles kg-1) evoked dose-dependent increases in histaminemia and hematocrit, and marked hypotensive effect, in anesthetized rats. The increase of plasma histamine was rapid in onset (within sec), peak plasma histamine being reached in less than 2 min. The decline of plasma histamine was gradual and almost complete 15 min after injection of NT. The hematocrit increased slowly, maximum values being obtained 5-10 min after injection of NT, and it persisted throughout the period of observation. The hypotensive effect of NT was rapid in onset and of prolonged duration. Compound 48/80, a well known histamine liberator and mast cell depletor, produced variations of blood pressure, of hematocrit and of plasma histamine very similar to those elicited by NT. Pretreatment of rats with cromoglycate, a well known mast cell stabilizer, or with dexamethasone, inhibited markedly the changes of histaminemia, of hematocrit and of blood pressure evoked by NT and compound 48/80. The results clearly suggest that the effects of NT on blood pressure and on vascular permeability in rats are mediated to some extent by mast cell histamine. Hexamethonium, a ganglion blocker, inhibited slightly the effect of NT on histaminemia but it did not block NT-induced changes of hematocrit. However, the hypotensive effect of NT was severely blocked in hexamethonium-treated rats. These results were interpretated as an indication that hexamethonium prevents NT-induced hypotension not merely by reducing the mobilization of mast cell histamine by NT but most likely by interfering with the mechanism by which NT and/or its mast cell mediators produce their effects on blood pressure.

Diamine oxydase in rabbit small intestine: separations from a soluble monoamine oxidase, properties and pathophysiological significance in intestinal ischemia

From all mammals investigated so far only in rabbits diamine oxidase could not be detected in any tissue except the gut. Thus this species was chosen for studying the physiological and pathophysiological function of this enzyme in the gastrointestinal tract. By gel filtration on Sephadex G 50 and G 200 the enzyme was purified 100-fold, separated from a soluble monoamine oxidase, and the properties of the two enzymes were determined. Diamine oxidase from rabbit small intestine deaminated putrecine (Km = 1.3 times 10(-4) M, pH-optimum 6.4-6.9) and histamine (Km = 8 times 10(-5) M, pH-optimum 7.5), but not serotonin, and was inhibited by aminoguanidine, but not by pargyline. Soluble monoamine oxidase from rabbit small intestine catabolized serotonin (Km = 1.8 times 10(-4) M, pH-optimum 8.8) but not putrescine and histamine, and was inhibited by pargyline, but not by aminoguanidine. Based on its properties in vitro intestinal diamine oxidase could inactivate the vasoactive biogenic amine histamine in vivo. To confirm this hypothesis, in rabbits the small intestine was damaged severely by inducing total intestinal ischemia, which occurs as mesenteric infarction also in human subjects and is accompanied by histamine release. Treatment with aminoguanidine and ischemia killed the animals 3-times faster than ischemia alone, which supported our hypothesis on a protective role of intestinal diamine oxidase against histamine.