Suppression of peritoneal thickening by histamine in a mouse model of peritoneal scraping.

BACKGROUND: Inflammatory reactions play an important role in peritoneal sclerosis in patients on peritoneal dialysis. Since histamine affects inflammatory reactions and immune responses, we investigated effects of intraperitoneal administration of histamine on peritonitis induced by mechanical scraping in mice. METHODS: After anesthesia, the right peritoneum was scraped 90 times over 1 min, and bilateral peritonea were observed by light microscopy after 7 days. RESULTS: Thickness of the peritoneal membrane on the right side was 174 ± 77 µm (mean ± SD, n = 8), while that on the left side was 24 ± 19 µm. Intraperitoneal administration of histamine (0.3 or 1.0 mmol/L, 0.5 mL each) twice daily for 7 days after scraping decreased thickness of the right peritoneum to 42 and 43 % of that in saline-injected animals, respectively (P < 0.01), although histamine (0.1 mmol/L) did not affect it. Promethazine (5 nmol, twice daily for 7 days), a histamine H1 receptor antagonist, abolished the amelioration caused by histamine (1.0 mmol/L). Neither ranitidine (15 nmol), a histamine H2 receptor antagonist, nor thioperamide (7.5 nmol), a histamine H3/H4 receptor antagonist, affected the outcome in histamine-treated mice. CONCLUSION: These findings indicate that histamine H1 action partly prevents the development of peritoneal fibrosis caused by mechanical scraping.

Reduction of the infarct size by simultaneous administration of L-histidine and diphenhydramine in ischaemic rat brains.

AIMS: While diphenhydramine is a histamine H(1) receptor antagonist, the agent has been shown to inhibit histamine-N-methyltransferase, a histamine inactivating enzyme in the brain. Since an increase in the brain concentration of histamine ameliorates reperfusion injury after cerebral ischaemia, effects of postischaemic administration of diphenhydramine were evaluated in rats treated with l-histidine, a precursor of histamine. METHODS: The right middle cerebral artery was occluded for 2h, and the infarct size was determined 24h after reperfusion of cerebral blood flow. Brain oedema was evaluated by comparing the area of the right hemisphere to that of the left hemisphere. RESULTS: Focal cerebral ischaemia provoked marked damage in saline-treated control rats, and infarct volumes in the striatum and cerebral cortex were 56 (49-63) mm(3) and 110 (72-148) mm(3), respectively (means and 95% confidence intervals, n=6). Administration of l-histidine (1000mg/kg, intraperitoneal) immediately after reperfusion did not affect the infarct size. Simultaneous administration of diphenhydramine (20mg/kg, intraperitoneal) with l-histidine reduced the infarct size to 25% and 21% of that in the control group, respectively. The combination therapy completely reduced ischaemia-induced brain oedema. CONCLUSION: Because histamine H(1) action does not influence ischaemic brain damage, elevation of the central histamine concentration by blockade of histamine-N-methyltransferase may be a likely mechanism responsible for the alleviation.

Soluble epoxide hydrolase inhibition and gene deletion are protective against myocardial ischemia-reperfusion injury in vivo.

Soluble epoxide hydrolase (sEH) metabolizes epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids. EETs are formed from arachidonic acid during myocardial ischemia and play a protective role against ischemic cell death. Deletion of sEH has been shown to be protective against myocardial ischemia in the isolated heart preparation. We tested the hypothesis that sEH inactivation by targeted gene deletion or pharmacological inhibition reduces infarct size (I) after regional myocardial ischemia-reperfusion injury in vivo. Male C57BL\6J wild-type or sEH knockout mice were subjected to 40 min of left coronary artery (LCA) occlusion and 2 h of reperfusion. Wild-type mice were injected intraperitoneally with 12-(3-adamantan-1-yl-ureido)-dodecanoic acid butyl ester (AUDA-BE), a sEH inhibitor, 30 min before LCA occlusion or during ischemia 10 min before reperfusion. 14,15-EET, the main substrate for sEH, was administered intravenously 15 min before LCA occlusion or during ischemia 5 min before reperfusion. The EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (EEZE) was given intravenously 15 min before reperfusion. Area at risk (AAR) and I were assessed using fluorescent microspheres and triphenyltetrazolium chloride, and I was expressed as I/AAR. I was significantly reduced in animals treated with AUDA-BE or 14,15-EET, independent of the time of administration. The cardioprotective effect of AUDA-BE was abolished by the EET antagonist 14,15-EEZE. Immunohistochemistry revealed abundant sEH protein expression in left ventricular tissue. Strategies to increase 14,15-EET, including sEH inactivation, may represent a novel therapeutic approach for cardioprotection against myocardial ischemia-reperfusion injury.

Suppression of ischaemia-induced cytokine release by dimaprit and amelioration of liver injury in rats.

Inflammatory reactions play an important role in ischaemia/reperfusion injury in various organs. Since histamine H(4) action has been shown to prevent the development of ischaemia/reperfusion liver injury, we examined the effects of dimaprit, a histamine H(2)/H(4) receptor agonist, on ischaemia-induced cytokine release and liver damage. Male Wistar rats (300 g) were subjected to warm ischaemia for 30 min. by occlusion of the left portal vein and hepatic artery under halothane anaesthesia. Saline or dimaprit (20 mg/kg, subcutaneously) was injected immediately after reperfusion of blood flow. Transient ischaemia provoked severe liver damage 24 hr after reperfusion, and the plasma concentrations of alanine transaminase and aspartate transaminase were 4600 IU/l and 13,200 IU/l, respectively. The values in the dimaprit group were 55% and 46% of those in control animals, respectively. Dimaprit also reduced the infarct size to 50%. Liver ischaemia markedly increased interleukin-12 levels 2-24 hr after reperfusion. The dimaprit treatment depressed the values to 40-64% of those in the corresponding control group 4-24 hr after reperfusion. Since interleukin-12 facilitates cell-mediated cytotoxicity, the protective effect of dimaprit may be attributed to regulation of cytokine release during reperfusion.

Recovery of brain dopamine metabolism by branched-chain amino acids in rats with acute hepatic failure.

A decrease in the serum ratio of branched-chain amino acids (BCAAs) to aromatic amino acids (Fischer ratio) reflects the severity of hepatic encephalopathy, and clinical improvement by dietary augmentation with BCAAs has been demonstrated. As behavioral alteration results from changes in central neurotransmission, we investigated the role of BCAA administration on changes in the levels of central neurotransmitters in acute liver injury. Male Wistar rats were subjected to liver ischemia by occluding the left portal vein and hepatic artery for 90 minutes. A 4% BCAA solution containing valine, leucine, and isoleucine was intraperitoneally administered 3 times (8 mL/kg, each) at 1 hour, 6 hours, and 24 hours after vascular reperfusion, and changes in the extracellular concentrations of neurotransmitter amino acids, monoamines, and their metabolites were evaluated in the striatum by a microdialysis procedure. Although the extracellular concentration of dopamine was affected by neither liver ischemia nor BCAA injections, the level of 3,4-dihydroxyphenylacetic acid, a metabolite of dopamine, decreased to 34% in the ischemic group 24 hours after reperfusion. The 3,4-dihydroxyphenylacetic acid level was normalized by treatments with BCAAs. The improvement of deranged cerebral dopaminergic activity may be a contributing factor in the improvement of hepatic encephalopathy by BCAAs.

A comparison of protective effects between L-histidine and hypothermia against ischemia-induced neuronal damage in gerbil hippocampus.

An increase in the histamine concentration in the brain has been demonstrated to provide protective effects against ischemia/reperfusion brain injury. Since hypothermia and barbiturates are also regarded to protect ischemic brains, effects of postischemic treatments were compared in gerbils between mild hypothermia and intraperitoneal administration of L-histidine, a precursor of histamine. Furthermore, effects of thioperamide, a histamine H(3) receptor antagonist, were evaluated in histidine-treated gerbils after 60 days. Transient forebrain ischemia for 4 min at 37 degrees C provoked severe neuronal damage in the hippocampal CA1 pyramidal cells after 7 days. Postischemic hypothermia (33 degrees C) for 3 h under pentobarbital anesthesia alleviated neuronal death, and the number of preserved neurons was 77+/-56/mm (mean+/-S.D., n=14). The effect of L-histidine injected three times, immediately, 6 h, and 24 h after reperfusion (1,000 mg/kg, i.p., each), was more prominent than that of hypothermia, and the number of preserved neurons was 142+/-55/mm (n=14). When the histologic outcome was evaluated after 60 days, most neurons were damaged in both the hypothermic and histidine groups. The improvement of the histologic outcome was observed even after 60 days in animals injected with thioperamide, immediately and 6 h after reperfusion (5 mg/kg, s.c., each), with three injections of l-histidine. The number of preserved neurons was 133+/-88/mm (n=10), while that in the hypothermic group was 7+/-15 (n=10). Activation of the central histaminergic system provides beneficial effects against cerebral ischemia.

Suppression of ischemia/reperfusion liver injury by histamine H4 receptor stimulation in rats.

Inflammatory reactions play an important role in ischemia/reperfusion injury in various organs. Since histamine is closely related to inflammatory reactions and immune responses, effects of postischemic administration of histaminergic ligands on ischemia-induced liver injury were examined in rats. Animals were subjected to warm ischemia for 30 min by occlusion of the left portal vein and hepatic artery under halothane anesthesia, and liver damage was evaluated by assessing plasma concentrations of transaminases after 24 h. Warm ischemia for 30 min provoked severe liver damage after 24 h, and the plasma concentrations of alanine transaminase (ALT) and aspartate transaminase (AST) were 8600 I.U./l and 13100 I.U./l, respectively. Subcutaneous injections of histamine twice, immediately and 6 h after reperfusion (20 mg/kg, each), alleviated liver damage. The plasma concentrations of ALT and AST in the histamine group were 35% and 24% of those in the control group, respectively. Neither mepyramine (3 mg/kg x 2), an H1 antagonist, nor cimetidine (15 mg/kg x 2), an H2 antagonist, affected the outcome in histamine-treated rats. However, thioperamide (5 mg/kg x 2), an H3/H4 antagonist, completely abolished the alleviation caused by histamine. Administration of dimaprit (1-10 mg/kg x 2), an H2/H4 agonist, mimicked the protective effect of histamine, and the effect of dimaprit is reversed by thioperamide, whereas neither H1 nor H2 antagonists altered the outcome caused by dimaprit. Clozapine (15 mg/kg x 2), an H4 agonist, also mimicked the protective effect of histamine. These findings indicate that stimulation of histamine H4 receptors after ischemic events prevents development of reperfusion injury in the liver.

Reduction in brain infarction by augmentation of central histaminergic activity in rats.

Inflammation is a factor in the aggravation of reperfusion injury after cerebral ischemia. Since histamine H(2) receptor stimulation suppresses inflammatory reactions, effects of the central histaminergic activation on brain infarction were examined in rats. Focal cerebral ischemia for 2 h was provoked by transient occlusion of the right middle cerebral artery, and the infarct size was determined by 2,3,5-triphenyltetrazolium chloride stain after 24 h. Effects of postischemic administration of thioperamide, an H(3) antagonist, and metoprine, an inhibitor of histamine-N-methyltransferase, were evaluated in rats treated with l-histidine, a precursor of histamine. Furthermore, effects of these agents on changes in the striatal histamine level were examined by a microdialysis procedure. Focal ischemia provoked marked damage in rats treated with l-histidine (1000 mg/kg) alone. Administration of l-histidine (1000 mg/kg) with either thioperamide (5 mg/kg) or metoprine (10 mg/kg) alleviated brain infarction. The size of brain infarction was 27% and 10% of that in animals treated solely with l-histidine, respectively. The combination treatment with thioperamide and metoprine decreased the size of brain infarction in rats given l-histidine (500 mg/kg), although protective effects were not clear without l-histidine. A marked increase in the histamine concentration was observed in the histidine plus metoprine group, the value being 363% of that in the saline-injected group after 2-3 h. The histamine concentrations in the histidine group and histidine plus thioperamide group were 188% and 248%, respectively. These findings indicate that facilitation of central histaminergic activity reduced the brain infarction.