A central pathological feature of Alzheimer's disease is the profuse deposition of amyloid-beta protein (Abeta) in the brain parenchyma and vessel walls. Abeta also forms deposits in the brains of a variety of mammals, including all aged non-human primates studied to date. The sequence of Abeta in these animals is identical to that in humans. No Abeta deposits have been found in the brains of wild-type rats and mice, suggesting that the three amino acid differences between their Abeta and that of amyloid-bearing mammals impedes the fibrillogenicity of Abeta. Analysis of the primary sequence of the beta-amyloid precursor protein in tree shrews revealed a 98% similarity and 97% identity with the human protein. Furthermore, the predicted amino acid sequence of Abeta in tree shrews is identical to that in humans. However, immunohistochemical analysis failed to reveal beta-amyloid deposits in the neural parenchyma or vasculature of eight aged (7-8 years) tree shrews (Tupaia belangeri). The lack of correlation between the Abeta sequence and amyloid formation suggests that other factors contribute to cerebral amyloid deposition in aged animals.

Aging↗

PubMedDate not supplied

Expression of cyclooxygenase (COX)-1 and COX-2 in adaptive cytoprotection induced by mild stress.

Prostaglandins (PG) derived from COX-1 play an important role in the maintenance of mucosal integrity but the role of COX-2-derived products in mucosal defence mechanism has not been fully explained. Mild stress is known to prevent gastric mucosal lesions induced by severe stress via the phenomenon of adaptive cytoprotection but it remains unknown which COX is involved in this adaptation. In this study, the mucosal expression of COX-1 and COX-2 was examined and the inhibitors of these enzymes were used to determine the contribution of these enzymes in adaptive cytoprotection induced by mild stress. Male Wistar rats were exposed to mild water immersion and restraint stress (WRS) at various time intervals ranging from 5 min up to 2 h followed 1 h later by exposure to severe 3.5 h WRS with or without pretreatment with: 1) NS-398 (10 mg x kg(-1) i.g.), a selective COX-2 inhibitor; 2) resveratrol (5 mg x kg(-1) i.g.), a selective COX-1 inhibitor; 3) meloxicam (2 mg x kg(-1) i.g.), preferential COX-2 inhibitor; and 4) indomethacin (5 mg x kg(-1) i.p), non-selective inhibitor of COX. The number of WRS lesions was counted, gastric blood flow (GBF) was measured by H2-gas clearance technique, mucosal biopsy samples were taken for the assessment of PGE2 by radioimmunoassay, and the expression of COX-1 and COX-2 mRNA by RT-PCR. WRS for 3.5 h produced numerous gastric lesions, decreased GBF by 48% and inhibited formation of PGE2 by 68% as compared to intact mucosa. Exposure to mild WRS during 5-30 min by itself failed to affect mucosal integrity but significantly attenuated gastric lesions induced by exposure to severe 3.5 h stress; the maximal protective effect being achieved with mild WRS during 15 min. This protective effect was accompanied by the rise in GBF and the generation of PGE2 in the gastric mucosa. After extension of mild WRS from 15 min up to 1 or 2 h before more severe 3.5 h WRS, the loss of cytoprotective effect of mild WRS against severe stress accompanied by significant fall in the GBF were observed. Pretreatment with NS-398 (10 mg x kg(-1) i.g.) that failed to affect mucosal PGE2 generation, reduced significantly the protection and accompanying rise in GBF produced by mild WRS whereas resveratrol partly reduced the protection and the rise in GBF induced by mild WRS. Meloxicam or indomethacin significantly inhibited PGE2 generation and completely abolished the hyperemia and protection induced by mild WRS against more severe stress. The protective and hyperemic effects of mild WRS were completely restored by the addition of 16,16 dm PGE2 (5 microg x kg(-1) i.g.) to NS-398 or resveratrol, while the deleterious effects of meloxicam and indomethacin were significantly attenuated by the concomitant treatment with this PGE2 analogue. We conclude that PG derived from both, COX-1 and COX-2 appear to be involved in adaptive cytoprotection developed in response to mild stressors.

Adaptation, Physiological↗

PubMedDate not supplied

Involvement of gastrin in gastric secretory and protective actions of N-alpha-methyl histamine.

N alpha-methylhistamine (N alpha-MH) is one of an unusual metabolite of histamine that was found in Helicobacter pylori-infected stomachs and is believed to interact with specific histamine H(1), H(2) and H(3)-receptors to stimulate gastric acid secretion and gastrin release from isolated G-cells but the effects of N alpha-MH on gastric mucosal integrity have been little studied. This study was designed; (1) to compare the effect of exogenous N alpha-MH with that of standard histamine on gastric secretion and plasma gastrin levels in rats equipped with gastric fistula (series A); and (2) to assess the action of N alpha-MH on gastric lesions induced by 100% ethanol (series B) in rats with or without removal of antral portion of the stomach (antrectomy). Rats of series B were pretreated intragastrically (i.g.) or intraperitoneally (i.p.) with N alpha-MH or histamine (0.1-2 mg/kg) 30 min prior to 100% ethanol (1.5 ml, i.g.) with or without: (1) vehicle (saline); (2) RPR 102681 (30 mg/kg i.p.), to block CCK-B/gastrin receptors; and (3) ranitidine (40 mg/kg s.c.) to inhibit histamine H(2)-receptors. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H(2)-gas clearance method and venous blood was collected for determination of plasma gastrin levels by radioimmunoassay (RIA). N alpha-MH and histamine dose-dependently increased gastric acid output (series A); the dose increasing this secretion by 50% (ED(50)) being 2 and 5 mg/kg i.g or i.p., respectively, and this effect was accompanied by a significant rise in plasma gastrin levels. Both, N alpha-MH and histamine attenuated dose-dependently the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. These secretory, protective, hipergastrinemic and hyperemic effects of N alpha-MH and histamine were completely abolished by antrectomy, whereas pretreatment with RPR 102681 attenuated significantly the N alpha-MH and histamine-induced protection against ethanol damage and accompanying hyperemia. Ranitidine, that produced achlorhydria and a further increase in plasma gastrin levels, failed to influence the N alpha-MH- and histamine-induced protection and accompanying rise in the GBF. We conclude that (1) N alpha-MH stimulates gastric acid secretion and exhibit gastroprotective activity against acid-independent noxious agents in the manner similar to that afforded by histamine; and (2) this protection involves an enhancement in the gastric microcirculation and release of gastrin acting via specific CCK-B/gastrin receptors but unexpectedly, appears to be unrelated to histamine H(2)-receptors.

Animals↗

PubMedDate not supplied

Gastric preconditioning induced by short ischemia: the role of prostaglandins, nitric oxide and adenosine.

BACKGROUND: Various organs including heart, kidneys, liver or brain respond to brief exposures to ischemia with an increased resistance to severe ischemia and this phenomenon is called 'preconditioning'. No study so for has been undertaken to check whether such short, repeated gastric ischemic episodes protect gastric mucosa against the damage caused by subsequent prolonged ischemia-reperfusion or necrotizing substances. MATERIAL AND METHODS: In this study, cyclooxygenase (COX)-1, COX-2, nitric oxide (NO) and adenosine receptors inhibitors were used to determine the possible involvement of endogenous prostaglandin, NO and adenosine in the mechanism of gastric preconditioning. This ischemic preconditioning was induced by short episodes of occlusion of celiac artery from 1 to 5 times, for 5 min each applied 30 min before prolonged (30 min) ischemia followed by 3 h of reperfusion (I/R) or 30 min before topical application of strong mucosal irritants such as 100% ethanol, 25% NaCl or 80 mM taurocholate. RESULTS: Exposure to regular I/R produced numerous gastric lesions and significant fall in the gastric blood flow and PGE2 generation. Short (5 min) ischemic episodes even induced several times (1-5 times) by itself failed to cause any gastric lesions but significantly attenuated those produced by I/R and this protective effect reached maximum with two 5 min ischemic episodes and this preconditioning was considered as standard. The protective effects of standard ischemic preconditioning against gastric lesions induced by I/R was accompanied by a reversal of the fall in the gastric blood flow and PGE2 generation and resembled those induced by classic gastric mild irritants such as 20% ethanol, 5% NaCl and 5 mM taurocholate. These protective and hyperemic effects of standard preconditioning, lasted up to 6-8 h, and were significantly attenuated by pretreatment with specific COX-1 and COX-2 inhibitors such as Vioxx (5 mg/kg i.g.) and resveratrol (10 mg/kg i.g.) that failed to affect PGE2 generation in intact gastric mucosa but attenuated significantly that in preconditioned gastric mucosa. Non-specific COX-inhibitor indomethacin (5 mg/kg i.p.), that suppressed the PGE2 generation by approximately 90% and non-specific NO synthase inhibitor L-NNA (20 mg/kg i. p.), that significantly suppressed NO production, significantly inhibited the protection and the rise in GBF induced by standard preconditioning and these effects were restored by addition of 16,16 dm PGE2 (1 Kg/kg i.g.) or L-arginine (200 mg/kg i.g.), a substrate for NO-synthase, to indomethacin or L-NAME, respectively. Pretreatment with adenosine (10 mg/kg i.g.) also reduced the lesions induced by I/R and increased the gastric blood flow with the extent similar to that observed with standard ischemic preconditioning, while an antagonist of adenosine receptors, 8-phenyl theophylline (SPT, 10 mg/kg i.g.) attenuated significantly the gastroprotection afforded by the preconditioning. Gene expression of COX-1 but not COX-2 was detected by RT-PCR in intact gastric mucosa and in that exposed to I/R with or without ischemic preconditioning, whereas COX-2 was overexpressed only in preconditioned mucosa. CONCLUSIONS: 1) gastric ischemic preconditioning represents one of the most powerful protective intervention against the mucosal damage induced by severe I/R as well as by topical mucosal irritants in the stomach; 2) this protection, involving several mediators such as PG derived from COX-1 and COX-2, NO originating from NO-synthase and adenosine, appear to play a key mechanism of gastric ischemic preconditioning.

Adenosine↗

PubMedDate not supplied

Quantitative autoradiography of [3H]norharman [( 3H]beta-carboline) binding sites in the rat brain.

The anatomical distribution of [3H]norharman binding sites was determined by quantitative autoradiography in rat brain slices. They are enriched in hypothalamic, thalamic, accumbens and amygdaloid nuclei as well as in hippocampal, neocortical and olfactory-related structures. The distribution pattern differs from that of other previously described receptors or binding sites (e.g. monoamine oxidase, benzodiazepine, tryptamine, 5-hydroxytryptamine receptors (5-HT1A, 5-HT1B, 5-HT1C, 5HT2], which suggests that a unique class of [3H]norharman binding sites exists in the rat brain. The findings are consistent with previous experiments which showed high affinity binding sites for [3H]norharman in rat brain membranes (KD 1.552 nM; autoradiography KD 5.5 nM). A correspondence in the displacing activity of drugs was found for both methods (crude membrane fraction: harman much greater than tryptamine much greater than 5-hydroxytryptamine greater than N-methyl-beta-carboline-3-carboxamide (FG 7142) = diazepam; autoradiography: harman much greater than tryptamine much greater than FG 7142 greater than 5-hydroxytryptamine greater than diazepam). Provided that the binding sites represent functional receptors, the present anatomical findings may explain the biological effects of norharman, e. g. pro-conflict behaviour (limbic-hypothalamic structures), tonic-clonic convulsions (limbic-cortical structures) and alterations of locomotor activity (accumbens nucleus).

Alkaloids↗