Irreversible Inhibitor Of Histidine Decarboxylase Research Articles

Carnosine protects brain microvascular endothelial cells against rotenone‐induced oxidative stress injury through histamine H1 and H2 receptors in vitro

Although it is believed that carnosine has protective effects on various cell types, its effect on microvascular endothelial cells has not been well defined. In the present study, we investigated the protective effects of carnosine in microvascular endothelial cells using an in vitro rotenone-induced oxidative stress model. Mouse brain microvascular endothelial cells were exposed to 1μmol/L rotenone for 18h. In some experiments, carnosine (100nmol/L-1mmol/L) was added 30min prior to rotenone exposure. When used, histamine receptor antagonists (100nmol/L-10μmol/L) were added 15min before carnosine treatment. After rotenone exposure, apoptosis of microvascular cells was analysed by Hoechst 33342 staining, whereas mitochondrial membrane potential was assessed by JC-1 staining. Intracellular carnosine and histamine levels were determined using HPLC or ultra-HPLC. Over the range 1μmol/L-1mmol/L, carnosine concentration-dependently decreased the number of apoptotic cells after 18h exposure to rotenone. This effect was reversed by the histamine H1 receptor antagonists pyrilamine and diphenhydramine (1 and 10μmol/L) and the H2 receptor antagonists cimetidine (100nmol/L-10μmol/L) and zolatidine (10μmol/L). α-Fluoromethylhistidine (100μmol/L), a selective and irreversible inhibitor of histidine decarboxylase, also significantly inhibited the protective effects of carnosine. At 0.1mmol/L, carnosine restored the decrease in mitochondrial membrane potential after 6h exposure to 1μmol/L rotenone and this effect was also reversed by the H1 and H2 receptor antagonists. Moreover, intracellular carnosine levels increased as early as 1h after carnosine treatment, whereas intracellular histamine levels increased 18h after carnosine treatment. The results of the present study indicate that carnosine protects brain microvascular endothelial cells against rotenone-induced oxidative stress injury via histamine H1 and H2 receptors. The findings suggest that carnosine may be beneficial in the treatment of microvascular endothelial dysfunction induced by oxidative stress.

Apomorphine-induced turning behavior in 6-hydroxydopamine lesioned rats is increased by histidine and decreased by histidine decarboxylase, histamine H 1 and H 2 receptor antagonists, and an H 3 receptor agonist

The role of histamine and its receptors in basal ganglia neurocircuitry was assessed in apomorphine-induced turning behavior. Rats with unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta and medial forebrain bundle were administered histaminergic agents, and apomorphine-induced turning behavior was tested on Days 7 and 14 post-lesion. Compared with saline-treated rats, histidine (500 mg/kg, i.p.), a precursor of histamine, increased turning behavior ( p < 0.05), while α-fluoromethylhistidine (α-FMH, 25 μg, i.c.v.), an irreversible inhibitor of histidine decarboxylase, decreased turning behavior ( p < 0.05) but only on Day 14 post-lesion. Both the histamine H 1 receptor antagonist pyrilamine (10 and 50 μg, i.c.v.) and the H 2 receptor antagonist cimetidine (10 and 50 μg, i.c.v.) significantly decreased turning behavior on Days 7 and 14 post-lesion. The histamine H 3 receptor agonist immepip (10 μg, i.c.v.) decreased turning behavior ( p < 0.05) on Day 14 post-lesion. The present findings indicate the complex interactions of histamine on basal ganglia function.

Carnosine protects against Abeta42-induced neurotoxicity in differentiated rat PC12 cells.

(1) The present study was designed to investigate whether histamine is involved in the protective effect of carnosine on Abeta42-induced impairment in differentiated PC12 cells. (2) PC12 cells were exposed to Abeta42 (5 muM) for 24 h after carnosine (5 mM) applied for 18 h. Histamine receptor antagonists (diphenhydramine, zolantidine, thioperamide, clobenpropit) or histidine decarboxylase inhibitor (alpha-fluoromethylhistidine) were added 15 min before carnosine. Cell viability, glutamate release or cell surface expression of NMDA receptor was examined. (3) Abeta42 caused a concentration-dependent reduction of viability in PC12 cells and pretreatment with carnosine ameliorated this impairment. This amelioration was reversed by the H(3) receptor antagonists thioperamide and clobenpropit, but not by either the H(1) receptor antagonist diphenhydramine or the H(2) receptor antagonist zolantidine. Further, alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, also had no effect. In the presence of Abeta42, carnosine significantly decreased glutamate release and carnosine increased the surface expression of NMDA receptor. (4) These results indicate that the mechanism by which carnosine attenuates Abeta42-induced neurotoxicity is independent of the carnosine-histidine-histamine pathway, but may act through regulation of glutamate release and NMDA receptor trafficking.

Involvement of brain endogenous histamine in the degeneration of dopaminergic neurons in 6-hydroxydopamine-lesioned rats

Previous studies have suggested that brain histamine is involved in the pathogenesis of Parkinson's disease (PD), but the role of endogenous histamine in the degeneration of dopaminergic neurons in the substantia nigra pars compact (SNpc) remains unclear. We aimed to investigate this issue by changing the brain histamine levels by giving histaminergic agents, and administrating histamine receptor antagonists in the PD animal model, i.e. the 6-hydroxydopamine (6-OHDA)-lesioned rat. In saline-treated animals, 6-OHDA infusion produced a progressive increase in apomorphine-induced turning rate and a loss of tyrosine hydroxylase immunoreactive (TH-ir) neurons in the SNpc. Histaminergic agents were given prior and daily for 1, 7 or 14 days after 6-OHDA infusion. Histidine (500 mg/kg, i.p.), a precursor of histamine, increased the turning rate (27% on day 7 and 26% on day 14, respectively; P < 0.05) and also the loss of TH-ir neurons, but only on day 1 and 7 (67% vs 47% and 90.4% vs 74% loss, respectively; P < 0.05). In contrast, α-fluoromethylhistidine (α-FMH, 25 μg, i.c.v.), an irreversible inhibitor of histidine decarboxylase (HDC), significantly decreased the turning rate (25% on day 7 and 26% on day 14, respectively; P < 0.05) and prevented the loss of TH-ir neurons, also only on day 1 and day 7 (28% vs 47% and 58% vs 74% loss, respectively; P < 0.05). In addition, the histamine H 1 receptor antagonist pyrilamine (5 μg, i.c.v.), but not the H 2 receptor antagonist cimetidine (5 μg, i.c.v.), also decreased the turning rate (38% on day 7 and 21% on day 14, respectively; P < 0.05) and prevented the loss of TH-ir neurons on day 1 and day 7 (38% vs 51% and 60% vs 78% loss, respectively; P < 0.05). On day 14 after 6-OHDA lesion, there were no significant differences in the number of TH-ir neurons among all the different treatment groups. Taken together, these findings indicate that endogenous histamine may accelerate the degeneration of dopaminergic neurons via its H 1 receptor, while attenuation of histamine transmission may play a protective role on it in the early stage of development of 6-OHDA lesioned PD rats.

Carnosine protects against NMDA-induced neurotoxicity in differentiated rat PC12 cells through carnosine-histidine-histamine pathway and H 1/H 3 receptors

Since the histidine-containing dipeptide carnosine (β-alanyl- l-histidine) is believed to have many physiological functions in the brain, we investigated the neuroprotective effects of carnosine and its mechanisms of action in an in vitro model of neurotoxicity induced by N-methyl- d-aspartate (NMDA) in differentiated PC12 cells. Pretreatment with carnosine increased the viability and decreased the number of apoptotic and necrotic cells measured by MTT and Hoechst 33342 and propidium iodide (PI) double staining assays. Carnosine also can inhibite the glutamate release and increase HDC activity and the intracellular and extracellular contents of carnosine, histidine and histamine detected by high-performance liquid chromatography (HPLC). The protection by carnosine was reversed by α- fluoromethylhistidine, a selective and irreversible inhibitor of histidine decarboxylase (HDC). Pyrilamine and thioperamide, selective central histamine H 1 and H 3 antagonists also significantly reversed the protection of carnosine. Further, the inhibition of glutamate release by carnosine was reversed by thioperamide. Therefore, the protective mechanism of carnosine may not only involve the carnosine-histidine-histamine pathway, but also H 1/H 3 receptors and the effective inhibition of glutamate release. This study indicates that carnosine may be an endogenous protective factor and calls for its further study as a new antiexcitotoxic agent.

Ischemia of rat stomach mobilizes ECL cell histamine

Microdialysis was used to study how ischemia-evoked gastric mucosal injury affects rat stomach histamine, which resides in enterochromaffin-like (ECL) cells and mast cells. A microdialysis probe was inserted into the gastric submucosa, and the celiac artery was clamped (30 min), followed by removal of the clamp. Microdialysate histamine was determined by enzyme-linked immunosorbent assay. In addition, we studied the long-term effects of ischemia on the oxyntic mucosal histidine decarboxylase activity in omeprazole-treated rats. Gastric mucosal lesions induced by the ischemia were enlarged on removal of the clamp. The microdialysate histamine concentration increased immediately on clamping (50-fold rise within 30 min) and declined promptly after the clamp was removed. In contrast, histidine decarboxylase activity of the ECL cells was lowered by the ischemia and returned to preischemic values 9 days later. Mast cell-deficient rats responded to ischemia-reperfusion much like wild-type rats with respect to histamine mobilization. Pretreatment with the irreversible inhibitor of histidine decarboxylase, alpha-fluoromethylhistidine, which is known to eliminate histamine from ECL cells, prevented the rise in microdialysate histamine. Pharmacological blockade of acid secretion (cimetidine or omeprazole) prevented the lesions induced by ischemia-reperfusion insult but not the mobilization of histamine. In conclusion, ischemia of the celiac artery mobilizes large amounts of histamine from ECL cells, which occurs independently of the gross mucosal lesions. The prompt reduction of the mucosal histidine decarboxylase activity in response to ischemia probably reflects ECL cell damage. The lesions develop not because of mobilization of histamine per se but because of ischemia plus reperfusion plus gastric acid.

Involvement of the Histaminergic System in Leptin-Induced Suppression of Food Intake

The ob gene product leptin is secreted from white adipose tissue, and may regulate food intake by acting on the hypothalamus in the central nervous system. But the mechanism of this effect is still unclear. The central histaminergic system has been suggested to participate in the control of various physiological functions, particularly in feeding behavior, as it mediates anorectic signals like leptin. Thus, we hypothesized that the central histaminergic system is a target for leptin in its control of feeding. To prove this, we first examined the effect of i.p. administration of α-fluoromethylhistidine (FMH), a specific and irreversible inhibitor of histidine decarboxylase, on leptin-induced suppression of food intake in normal C57BL strain mice. Leptin treatment (1.3 mg/kg, i.p.) significantly reduced food intake by 60% of that of control at 6 h and by 84% at 24 h compared with control. When mice were injected with FMH (100 mg/kg, i.p.) before being given leptin, leptin-induced suppression of food intake was abolished and there was no significant difference compared with that of control. Additionally, we further examined the effects of leptin on food intake in mutant mice lacking histamine H 1 receptors (H1R-KO mice). Leptin injection significantly reduced food intake by 56% of that of control at 6 h and by 79% at 24 h in wild-type mice (WT mice), but not in H1R-KO mice. This finding suggests that leptin affects the feeding behavior through activation of the central histaminergic system via histamine H 1 receptors.

Induction by interleukin-1, tumor necrosis factor and lipopolysaccharides of histidine decarboxylase in the stomach and prolonged accumulation of gastric acid.

1. Injection of interleukin-1 (IL-1) into pylorus-ligated rats has been shown strongly to inhibit gastric secretion. However, in the present study, we found that an intraperitoneal injection of IL-1 into intact (non-pylorus-ligated) fasted mice rapidly (within 30 min) induced an accumulation of gastric acid ('early response'). When the dose of IL-1 was larger, the accumulation lasted for a longer period. 2. Injection of IL-1 also caused a later elevation of the activity of histidine decarboxylase (HDC), the histamine-forming enzyme, in the stomach ('later response'). 3. Cimetidine, an antagonist of histamine H2-receptors, suppressed the accumulation of gastric acid in both the early and later periods. An irreversible inhibitor of HDC, alpha-fluoromethylhistidine, partially inhibited the accumulation in the later period. 4. IL-1, when injected 1 h after feeding in mice fasted overnight, markedly retarded gastric emptying. 5. Tumour necrosis factor (TNF) and lipopolysaccharide (LPS) or endotoxin from E. coli both had IL-1-like effects on the stomach, and their effects are presumably mediated by IL-1. 6. These results support the idea that an inhibition of gastric emptying and an elevation of HDC activity in the stomach may explain the findings that a long-lasting accumulation of gastric acid is induced by IL-1 despite its potent inhibition of gastric acid secretion. 7. On the basis of these results, and in the light of the known actions of histamine, the possible roles of IL-1 in gastric inflammation and ulceration are discussed.

Interactions between neuronal histamine and halothane anesthesia in rats.

Using an in vivo microdialysis method, we measured the release of histamine in the anterior hypothalamic area (AHy) of rats under several concentrations of halothane anesthesia (1, 0.5, and 0.2%). The release of histamine increased to 341 and 325% at halothane concentrations of 0.5 and 0.2%, compared with the basal level at anesthesia induced by 1% halothane. alpha-Fluoromethylhistidine (100 mg/kg i.v.), a specific and irreversible inhibitor of histidine decarboxylase, reduced the histamine release to <35% of the basal value at 1% halothane anesthesia in the AHy, and also decreased the anesthetic requirement for halothane, evaluated as the minimum alveolar concentration (MAC), by 26%. Furthermore, pyrilamine (20 mg/kg i.v.), a brain-penetrating H1 antagonist, and zolantidine (20 mg/kg i.v.), a brain-penetrating H2 antagonist, reduced the MAC for halothane by 28.5 and 16%, respectively. Although thioperamide (5 mg/kg i.v.), an antagonist of presynaptic H3 autoreceptor, induced an approximate twofold increase in the level of histamine release in conscious freely moving rats, the same dose of thioperamide had little effect on the release of histamine under 1% halothane anesthesia in the AHy. Furthermore, thioperamide did not change the anesthetic requirement (MAC) for halothane. The present findings indicate that halothane anesthesia inhibits the release of neuronal histamine and that histaminergic neuron activities change the anesthetic requirement (MAC) for halothane through H1 as well as H2 receptors.

Effect of alpha-fluoromethylhistidine-evoked histamine depletion on ultrastructure of endocrine cells in acid-producing mucosa of stomach in mouse, rat and hamster.

The oxyntic mucosa of the mammalian stomach is rich in endocrine cells, such as ECL cells, A-like cells, somatostatin cells, D1/P cells and, in some species, enterochromaffin cells. The various endocrine cell types can be distinguished on the basis of their characteristic cytoplasmic granules and vesicles. The ECL cells contain numerous large secretory vesicles and relatively few, small electron-dense granules and small clear microvesicles. We have suggested that in the rat the ECL cells contain most of the gastric histamine with the secretory vesicles as the major histamine storage site in these cells. alpha-Fluoromethylhistidine is an irreversible inhibitor of histidine decarboxylase, the histamine-forming enzyme. We have previously shown that this enzyme inhibitor depletes histamine from the ECL cells in the rat and reduces the number of secretory vesicles in the cytoplasm. In the present study, we have examined whether alpha-fluoromethylhistidine affects the ECL cells in other species and whether it affects other types of endocrine cells in the oxyntic mucosa of the rat. Mice, rats and hamsters were treated with the inhibitor (3 mg/kg per h) via minipumps subcutaneously for 24 h. This treatment lowered the oxyntic mucosal histamine concentration by 65-90% and the number and volume density of the secretory vesicles by 85-95% in the ECL cells of the three species examined. In contrast, the number and volume density of granules and microvesicles were not greatly affected. No evidence was found for an effect of alpha-fluoromethylhistidine on A-like cells, somatostatin cells or D1/P cells of the rat stomach, suggesting that, unlike the ECL cells, they do not contain histamine.

Characterization of basal and morphine-induced histamine release in the rat periaqueductal gray.

Previous studies have shown that antinociceptive doses of systemic morphine increase extracellular histamine (HA) levels in the rat periaqueductal gray (PAG), although the cellular origin of basal and morphine-induced HA release in the PAG is unknown. Treatment with alpha-fluoromethylhistidine (FMH; 100 mg/kg, i.p.), the irreversible inhibitor of histidine decarboxylase, decreased basal HA release by a maximum of 80% and prevented morphine-induced HA release in the PAG. In addition, perfusion of this area with the sodium channel blocker tetrodotoxin (10(-6) M) decreased basal HA release by a maximum of 57% from baseline levels. When the perfusion medium was modified by substitution of magnesium for calcium, extracellular HA levels in the PAG decreased by a maximum of 72%, and morphine-induced HA release was prevented. Thioperamide (5 mg/kg, i.p.), an H3 antagonist, increased HA release in the PAG to a maximum of 249% within the first 30-60-min period. Taken together, these results suggest that basal and morphine-induced HA release in the rat PAG have a neuronal origin.

Regulation of hypothalamic preprogrowth hormone-releasing factor messenger ribonucleic acid expression in food-deprived rats: a role for histaminergic neurotransmission.

To determine the component(s) of dietary protein that regulates GH-releasing factor (GRF) synthesis, we measured hypothalamic prepro-GRF mRNA by solution hybridization/nuclease protection analysis in food-deprived rats refed protein-free diets (PF) supplemented with individual amino acids. Adult male Sprague-Dawley rats were allowed free access to food (Fed), food deprived for 72 h (FD), or FD then refed for 72 h with a normal (NF) diet, a protein-free (PF) diet, or PF diets containing tyrosine, tryptophan (Trp), glutamic acid, or histidine (His). Food-deprived rats displayed the expected 80% reduction in hypothalamic prepro-GRF mRNA. Upon refeeding, levels were normalized in rats refed a normal diet, but not in those refed a PF diet alone or with tyrosine, Trp, or glutamic acid. In contrast, prepro-GRF mRNA was restored to 70% of Fed values by a PF diet with His. Supplementing a PF diet with His was sufficient to maintain hypothalamic prepro-GRF mRNA expression, as 3 days of feeding replete rats with PF diet or PF diet with added Trp resulted in a 50% reduction in prepro-GRF mRNA, whereas levels were reduced 25% by feeding animals a PF diet with His. Groups of rats allowed free access to food were treated for 72 h with two daily injections of 100 mg/kg alpha-fluoremethylhistidine, a specific irreversible inhibitor of histidine decarboxylase, to determine if the effect of His on prepro-GRF mRNA depended on neural conversion to histamine. alpha-Fluoremethylhistidine-treated rats showed a 40% reduction in hypothalamic prepro-GRF mRNA, with no concomitant change in preproneuropeptide-Y or preprosomatostatin. These data indicate that decreased hypothalamic prepro-GRF mRNA in FD rats is due in part to the lack of dietary and provide clear evidence for a role of the histaminergic neural system in the regulation of hypothalamic GRF expression.

Direct Evidence for Increased Continuous Histamine Release in the Striatum of Conscious Freely Moving Rats Produced by Middle Cerebral Artery Occlusion

Extracellular histamine in the stratum of conscious freely moving rats collected by intracerebral microdialysis 1 day after implantation of a U-shaped dialysis probe was measured by HPLC coupled with postcolumn o-phthalaldehyde derivatization fluorometry. The basal fractional histamine outputs were almost constant from 1 to 7 h after the start of perfusion (5.9-8.4 pg/30 min). Depolarization by perfusion with a high K+ (100 mM)-containing medium produced a significant (124%) increase and neuronal blockade by perfusion with a tetrodotoxin (1 microM)-containing medium resulted in a 68% reduction in the histamine output. The histamine output was markedly reduced by intraperitoneal injection of alpha-fluoromethylhistidine (100 mg/kg), an irreversible inhibitor of histidine decarboxylase, or (R)-alpha-methylhistamine (5 mg/kg), a potent and specific H3-receptor agonist. After middle cerebral artery (MCA) occlusion, the histamine output gradually increased, and reached four times the control value 8 h later. When rats were pretreated with metoprine (10 mg/kg), a histamine N-methyltransferase inhibitor, there was no significant difference in the histamine output between the MCA-occluded and the sham-operated groups during the first 3.5 h after the operation, but the histamine output gradually increased thereafter in the MCA-occluded group. In rats treated with alpha-fluoromethylhistidine, MCA occlusion failed to cause an increase in the histamine output. These results demonstrate that MCA occlusion induces a long-lasting increase in neuronal histamine release in the rat striatum.

Further investigations on the antipropulsive effect of centrally administered histamine and its relation with morphine

The effect of intracerebroventricularly (i.c.v.) administered histamine (100 μg/rat) on intestinal myoelectrical activity was investigated in the jejunum of fasted rats. Histamine caused the disappearance of phase III and a partial reduction of phase II of migrating myoelectric complexes. This effect was antagonized by i.c.v. pretreatment with mepyramine (10 μg/rat), an H 1 receptor antagonist. Lesions of central noradrenergic neurons by i.c.v. injection of the neurotoxin 6-hydroxydopamine strongly reduced both the inhibition of intestinal propulsion and the migrating myoelectric complexes profile induced by i.c.v. histamine, whereas pretreatment with p-chlorophenylalanine, a selective depletor of serotonin stores, had no effect. It thus appears that aminergic pathways are involved in the visceral effects of central histamine. Mepyramine (200 μg/rat i.c.v.) partially reduced the slowing of intestinal transit induced by high doses of morphine. Pretreatment with compound 48/80 (10 μg/rat i.c.v.), a mast cell degranulator, but not with α-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, reduced the antipropulsive action of i.c.v. morphine to the same extent as mepyramine, suggesting that histamine released from cerebral mast cells by high doses of morphine could contribute to the intestinal inhibition by morphine.

Histamine and calcium are independently regulated intracellular mediators of lymphocyte mitogenesis

In addition to cytosolic calcium ([Ca 2+] i), intracellular histamine has been implicated as a mediator of mitogenesis in normal mouse spleen cells stimulated by the plant lectin, concanavalin (Con) A. We have linked the growth-promoting action of this amine with its binding to distinct intracellular sites, designated H IC, in microsomes and nuclei and shown that the proliferative response of lymphocytes can be blocked by antagonizing the binding of histamine to H IC by N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine. HCl (DPPE), or by depleting intracellular histamine levels by the specific irreversible inhibitor of histidine decarboxylase, α-FMH. We now demonstrate that, at a concentration which completely inhibits both 3H-histamine binding to H IC and 3H-thymidine incorporation into DNA, DPPE fails to block the acute (30 seconds) rise in [Ca 2+] i in spleen cells exposed to Con A. Conversely, the calcium channel antagonist, verapamil, suppresses the Con A-induced rise in [Ca 2+] i at a concentration which correlates with its inhibition of thymidine incorporation into DNA, but does not prevent histamine synthesis or bind to H IC. Thus, in Con A-stimulated lymphocytes, intracellular histamine and calcium appear to be independently regulated, but essential, mediators of the proliferative response.

Does brain histamine contribute to the development of hypertension in spontaneously hypertensive rats?

Histaminergic neurons of the brain have been implicated in genetic hypertension. We investigated the effect of inhibition of histamine synthesis by alpha-fluoromethylhistidine (alpha-FMH), the irreversible inhibitor of histidine decarboxylase, on the development and maintenance of hypertension in spontaneously hypertensive rats. Young (3-week-old) and adult (7-week-old) rats were treated with alpha-fluoromethylhistidine for 29 and 13 days, respectively. Treatment of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats with alpha-fluoromethylhistidine led to a pronounced decrease in the histidine decarboxylase activity and in the histamine concentration in the brain (hypothalamus, brainstem, cortex-midbrain). In adult spontaneously hypertensive rats, the development of hypertension was not influenced by alpha-fluoromethylhistidine. In young spontaneously hypertensive rats, alpha-fluoromethylhistidine led to a transient delay in the development of hypertension which was followed by a transient tendency to increased blood pressure. It is concluded that histaminergic neurons of the brain play only a subordinate role, if any at all, in the development of hypertension in spontaneously hypertensive rats.

Modification of rat thermal responses to morphine by α-FMH suggests a role for neural histamine in morphine tolerance

In rats, morphine may either raise or lower body temperature depending on the dose. A morphine dose of 50 mg/kg, i.p., consistently produced a nearly maximal hypothermic response in non tolerant rats, whereas this dosage induced an elevation of body temperature in tolerant rats. In rats pretreated with alpha-fluoromethylhistidine (alpha-FMH), an irreversible inhibitor of histidine decarboxylase which induces a reduction in brain histamine synthesis, this morphine dose of 50 mg/kg, i.p. produced an elevation of rectal temperature resembling that observed in morphine-tolerant rats. To confirm the suggestion that hyperthermic effects of the higher dose of morphine in morphine-tolerant rats or in alpha-FMH-pretreated rats could be related to a possible involvement of mediators of fever, e.g. prostaglandins, animals were pretreated with acetylsalicylic acid (aspirin, Bayer) 30 mg/kg, i.p., 60 min before morphine. Results showed that acetylsalicylic acid prevented the hyperthermic response of morphine, resulting in a fall in body temperature. Since morphine releases histamine and alpha-FMH inhibits histamine synthesis, our data demonstrating that an inhibitor of prostaglandin-synthetase showed efficacy only in animals responding with fever to the higher dose of the opiate, suggests a physiological antagonism between histamine and prostaglandins on mechanisms underlying hyper/hypothermic responses to morphine.

Histamine-producing cell-stimulating activity. Interleukin 3 and granulocyte-macrophage colony-stimulating factor induce de novo synthesis of histidine decarboxylase in hemopoietic progenitor cells.

Both interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) induce increased histamine production by murine hemopoietic cells. Histidine-free culture conditions or addition of alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, completely abrogate this phenomenon, indicating that increased histamine levels result from an augmentation of the rate of its synthesis. L-Histidine decarboxylase (HDC) (EC 4.1.1.22) activity is detected in normal bone marrow cell lysates. It is markedly increased following incubation of the cells with IL-3 or GM-CSF. The cells responding by the most important enhancement of HDC activity are located in the less dense layers of a discontinuous Ficoll gradient containing the majority of the hemopoietic progenitor cell types, such as colony-forming units (spleen), granulocyte-macrophage colony-forming cells, and mast cell precursors. In comparison with other HDC-containing cell populations tested, the enzymatic activity contained in these cells is particularly high after IL-3 or GM-CSF treatment and similar to the HDC levels observed in murine fetal liver. The time course of IL-3 and GM-CSF-induced HDC activation at comparable concentrations is slightly different. In response to GM-CSF, HDC activation is more rapid, with a significant enhancement after 4 hr of incubation, as compared with IL-3-induced HDC activation. Moreover, in the latter case the activation increases more progressively up to 48 hr of incubation, whereas GM-CSF-induced increase of HDC activity reaches a plateau more rapidly. In addition, maximal increase in histamine production in response to IL-3 is always higher than in response to GM-CSF. Moreover, the simultaneous presence of both factors at optimal concentration induces only a partially cumulative effect. These results suggest that IL-3 and GM-CSF induce HDC activation in two distinct ways, possibly reflecting the involvement of distinct target cells. However, both mediators act by inducing the transcription of the HDC gene and de novo synthesis of this enzyme since actinomycin D or cycloheximide abolish GM-CSF-or IL-3-induced histamine-producing cell-stimulating activity. This synthesis is independent from cell proliferation as demonstrated by the lack of effect of bone marrow cell irradiation. Finally, the observation that cholera toxin, prostaglandin E2, and N6,2'-O-dibutyryl adenosine 3',5'-cyclic monophosphate mimic the effects of IL-3 and GM-CSF on bone marrow cell HDC suggests an involvement of cyclic adenosine monophosphate in factor-induced histamine-producing cell-stimulating activity.

Histaminergic neuromodulation of the release of vasopressin.

In an attempt to clarify the nature of histaminergic neuromodulation of the vasopressinergic system, several studies under different experimental paradigms were carried out. L-Histidine loads (8 mmol/kg, i.p.) induced a marked increase in histamine (HA) in the anterior (AHR) and posterior (PHR) hypothalamic regions, the median eminence (ME) and adenohypophysis (Ah) with no apparent effect on the concentration of HA in the neurohypophysis (Nh), as measured by high-performance liquid chromatography. These findings correlated with decreases in vasopressin (VP) levels in the AHR and ME, accompanied by increases of the neuropeptide in the PHR and Ah. Intraperitoneal injections of HA (6 mumol/kg), resulted in a significant (p less than 0.005) rise in VP levels in the PHR, ME and Ah. HA induced an elevation of VP in the prefrontal cortex (PFC) from 6.23 +/- 2.02 to 43 +/- 4.05 microU/mg, as well as a 60% reduction in neurohypophyseal VP. These HA-induced VP responses were abolished by both mepyramine (3 mumol/kg) and famotidine (4 mumol/kg) in the PHR and PFC. Mepyramine suppressed the HA-induced VP response in the Ah and enhanced it in the Nh, while famotidine did the opposite. When alpha-fluoromethylhistidine (FMH), an irreversible inhibitor of histidine decarboxylase, was administered at doses of 100 mg/kg/day (i.p.), hypothalamic HA levels fell by 40-45% after 1 h, by 50% after 3 h, and by 65-80% after 24 h in adrenalectomized rats. In the same conditions, but after a week of treatment with FMH, the VP response to adrenalectomy was clearly impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

Histamine and increased ovarian blood flow mediate LH-induced superovulation in the cyclic hamster.

Constant infusion of LH (400 micrograms NIH-S24) through an osmotic minipump inserted on Day 1 (oestrus) of the cycle in the hamster resulted in spontaneous superovulation (approximately equal to 29 ova) at the next expected oestrus, increased blood flow (P less than 0.001) to the ovary on Day 3, and slight depletion (0.1 greater than P greater than 0.05) of histamine in the ovary. Treatment with antihistamine (alpha-fluoromethylhistidine, an irreversible inhibitor of histidine decarboxylase, or cimetidine, an H2 blocker) by injections or by infusion using separate osmotic minipumps significantly (P less than 0.01) reduced the number of ova shed in the LH-treated hamsters. Infusion of LH with alpha-fluoromethylhistidine in the same osmotic minipump reduced the bioactivity of the LH. Infusion of antihistamine alone did not alter the normal number of ova shed. The results suggest that the LH-induced superovulation involves stimulation of histamine release; the histamine than may increase ovarian blood flow thus allowing more gonadotrophins to reach the ovary.