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Biomedical subjects

B M Peskar

Publications and source records attributed to B M Peskar.

At least 55 records · Page 3Linked to original sources
PubMed1991

Effect of carbenoxolone on the biological activity of nitric oxide: relation to gastroprotection.

1. The interactions between carbenoxolone and nitric oxide (NO) were examined by investigating their effects on human platelet aggregation, on rat aortic strips precontracted by phenylephrine and on protection of rat gastric mucosa against ethanol-induced injury. 2. Carbenoxolone (100-300 microM) caused a significant and concentration-dependent potentiation of rat peritoneal neutrophil (RPN)- 3-morpholino-syndnonimine (SIN-1)- or iloprost-induced inhibition of platelet aggregation. Higher concentrations (500 microM) of carbenoxolone alone markedly inhibited platelet aggregation. Pretreatment with carbenoxolone (100-300 microM) antagonized the reversal of the RPN- or SIN-1-induced antiaggregatory effect by oxyhaemoglobin (10 microM). 3. Rat aortic strips with intact endothelium precontracted by phenylephrine (0.1-0.3 microM) were relaxed by carbenoxolone (100-300 microM) in a concentration-dependent manner. Relaxations were abolished by mechanical removal of the endothelium or by incubation with methylene blue (10 microM) or NG-nitro-L-arginine (L-NNA, 100 microM). Sodium nitroprusside (10 nM)-induced relaxations of endothelium-denuded rat aortic strips were potentiated by carbenoxolone (100 microM). . The carbenoxolone (200 mg kg-1, p.o.)-induced gastroprotection against ethanol was antagonized by L-NNA (5-40 mg kg-1) in a dose-dependent manner. Pretreatment of rats with indomethacin (10 mg kg-1, s.c.) increased the effect of L-NNA. 5. The results suggest that the activity of carbenoxolone in the experimental systems tested is due to phosphodiesterase inhibition, although radical scavenging properties of the drug could contribute to some of the effects observed. In the rat gastric mucosa both increased prostaglandin levels and effects on the NO system could contribute to the protective action of carbenoxolone.

Animals↗
PubMed1991

Role of peptidergic sensory neurons in gastric mucosal blood flow and protection.

The present findings have revealed a new aspect of how mechanisms of gastric mucosal resistance to injury are called into effect and are coordinated by the nervous system. Capsaicin-sensitive sensory neurons in the stomach play a physiological role in monitoring acid influx into the superficial mucosa. Once activated, they strengthen gastric mucosal defense against deep injury, with a key process in this respect being an increase in blood flow through the gastric mucosa. This concept opens up completely new perspectives in the physiology and pathophysiology of the gastric mucosa if we consider that the long-term integrity of the gastric mucosa may be under the subtle control of acid-sensitive sensory neurons and that, vice versa, improper functioning of these neutral control mechanisms may predispose to gastric ulcer disease. The present observations also indicate that some of the peptides contained in gastric sensory nerve endings might fulfill a transmitter or mediator role in controlling gastric mucosal blood flow and integrity. Whereas substance P and neurokinin A are unlikely to play a role in the regulation of gastric mucosal blood flow, there is severalfold evidence that CGRP is very important in this respect. This peptide, which in the rat gastric mucosa originates exclusively from spinal sensory neurons, is released upon stimulation of sensory nerve endings and is extremely potent in facilitating gastric mucosal blood flow and in protecting the mucosa from injurious factors. Selective ablation of spinal sensory neurons containing CGRP weakens the resistance of the gastric mucosa against acid injury, which is most likely due to inhibition of protective vasodilator reflexes. We now aim at providing direct pharmacological evidence that antagonism of endogenously released CGRP results in similar pathophysiological consequences as ablation of capsaicin-sensitive sensory neurons.

Animals↗
PubMed1991

[Effect of sulfasalazine and its metabolites on prostaglandin and leukotriene liberation from human synovial tissue].

The effects of sulfasalazine (SASP) and its metabolites sulfapyridine (SP) and 5-aminosalicylic acid (5-ASA) were investigated on release of prostaglandins (PG) and leukotrienes (LT) from synovial tissue of 37 patients with osteoarthritis, chondrocalcinosis and rheumatoid arthritis. Calcium ionophore A23187 significantly increased the release of PGE2, 6-keto-PGF1 alpha, LTB4, and LTC4 from human synovial tissue irrespective of the underlying joint disease. SASP inhibited release of LTC4 and increased release of PGE2. On the other hand, 5-ASA and SP inhibited the release of all eicosanoids measured. The effective concentrations of SASP and SP were found to be in the range which can be reached during SASP therapy. On the other hand, blood and synovial fluid levels of 5-ASA are considerably lower than those which inhibit eicosanoid synthesis in vitro. While nonsteroidal anti-inflammatory drugs, which are used for symptomatic therapy of rheumatoid arthritis, inhibit cyclooxygenase only, SP, the active metabolite of the second line anti-rheumatic drug SASP, inhibits both PG and LT release. Inhibition of LT synthesis by SASP and SP could contribute to the second line efficacy of SASP therapy in rheumatoid arthritis.

6-Ketoprostaglandin F1 alpha↗
PubMed1991

Leukotrienes in mucosal damage and protection.

Exposure of the rat gastric mucosa to ethanol stimulates the generation of leukotriene (LTC4) and 15-hydroxyeicosatetraenoic acid, but not of thromboxanes and prostaglandins. Lipoxygenase activation is not found with other topical irritants or nonsteroidal anti-inflammatory drugs. A number of gastroprotective drugs dose-dependently inhibit the stimulatory action of ethanol on mucosal LTC4 formation closely parallel to their protective activity suggesting that ethanol-induced damage and activation of lipoxygenases may involve common targets which are simultaneously counteracted by certain types of protective agents. Selective inhibition of 5-lipoxygenase, however, does not confer protection against gastric mucosal damage caused by topical irritants or non-steroidal anti-inflammatory drugs. Thus, although leukotrienes may mediate certain reactions elicited by gastric ulcerogens such as submucosal venular constriction and mucosal microvascular engorgement, they do not appear to be major mediators of ulcerogen-induced tissue necrosis. The contribution of other products of the various pathways of arachidonic acid metabolism to gastric mucosal injury and the mechanism underlying the close interrelationship between protection and inhibition of LTC4 formation observed with certain compounds remains to be investigated.

Animals↗
PubMed1990

Release of calcitonin gene-related peptide induced by capsaicin in the vascularly perfused rat stomach.

It has been suggested that capsaicin-induced gastric mucosal protection results from the local release of vasodilator peptides such as calcitonin gene-related peptide (CGRP) from afferent nerve endings within the stomach, since CGRP is able to reduce gastric lesion formation. This concept is supported by the present finding that capsaicin (10(-5) M), administered to the vascularly perfused stomach of the rat, produces a more than 30-fold rise of the CGRP content of the venous effluent. High-pressure liquid chromatography revealed only one peak of immunoreactivity coeluting with synthetic CGRP.

Animals↗
PubMed1990

Afferent nerve-mediated protection against deep mucosal damage in the rat stomach.

Intragastric capsaicin protects against ethanol-induced gross mucosal lesion formation by stimulation of afferent nerve endings in the rat stomach. The aims of the present study were to examine histologically the protective effect of capsaicin and to test whether this effect is related to changes in mucosal eicosanoid formation and mucosal blood flow. Intragastric capsaicin (160 microM) significantly reduced gross mucosal lesion formation induced by 25% ethanol. Light microscopy revealed that the depth of erosions was attenuated likewise. However, capsaicin did not prevent ethanol from causing superficial damage to the mucosa as observed by light and scanning electron microscopy. The protective action of capsaicin against ethanol remained unchanged by a dose of indomethacin that reduced the ex vivo formation of prostaglandin E2 and 6-oxo-prostaglandin F1 alpha in the gastric mucosa by about 90%. Capsaicin alone did not affect the ex vivo formation of these prostaglandins and of leukotriene C4. Intragastric capsaicin (160 microM) enhanced gastric mucosal blood flow by 89% as measured by the hydrogen gas clearance technique. This effect was also observed when capsaicin was administered together with 25% ethanol. These data indicate that afferent nerve stimulation by intragastric capsaicin protects against deep mucosal damage in response to ethanol, an effect that seems related to an increase in mucosal blood flow but not to eicosanoid formation.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

The effects of platelet-activating factor on flow rate and eicosanoid release in the isolated perfused rat gastric vascular bed.

In the isolated rat stomach perfused via the vasculature in situ under constant pressure bolus injections of platelet-activating factor (PAF, 3, 16, or 50 ng) induced dose-dependent, long-lasting reductions of flow rates and simultaneously significant increases in the release of cysteinyl-leukotrienes (cys-LT), thromboxane (TX) B2 and 6-keto-prostaglandin (PG) F1 alpha. Reversed phase high pressure liquid chromatography demonstrated the release of a mixture of comparable amounts of LTC4, LTD4 and LTE4 by PAF. Inhibition of cys-LT synthesis by the lipoxygenase inhibitors nordihydroguaiaretic acid (NDGA) and L-651,896 did not significantly affect PAF-induced flow reduction indicating that endogenous cys-LT are of minor importance for the PAF effect on gastric vascular flow. This conclusion is supported by the fact that the cys-LT receptor antagonist FPL 55712 in a concentration (1 x 10(-6) M) that completely antagonized gastric flow reduction by exogenous LTC4 (1 x 10(-7) M) had no effect on the PAF-induced reduction of flow. The cyclooxygenase inhibitor indomethacin aggravated the PAF-induced flow reduction suggesting that the endogenous vasodilator PGI2 might act as a functional PAF antagonist in the rat gastric vascular bed. In contrast to FPL 55712 the PAF antagonist BN 52021 significantly and concentration-dependently antagonized the PAF effect on gastric vascular flow. The results demonstrate that PAF and LTC4 induce flow reductions in the rat gastric vascular bed by activating different receptors and that endogenous eicosanoids released by PAF do not contribute significantly to the PAF effect on gastric vascular flow.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

Effects of non-steroidal anti-inflammatory drugs on rat gastric mucosal leukotriene C4 and prostanoid release: relation to ethanol-induced injury.

1. The effects of oral and subcutaneous administration of the non-steroidal anti-inflammatory drugs sodium salicylate, aspirin and indomethacin on ex vivo gastric mucosal release of leukotriene C4 (LTC4) prostaglandin E2 (PGE2), 6-oxo-PGF1 alpha and thromboxane B2 (TXB2) were investigated in rats under basal conditions as well as after challenge with ethanol. 2. Basal release of PGE2, 6-oxo-PGF1 alpha and TXB2 was inhibited by oral administration of aspirin (0.6-400 mgkg-1) and indomethacin (4 or 20 mgkg-1), but not by sodium salicylate (up to 400 mgkg-1), in a dose-dependent manner. Oral administration of aspirin in the dose range 3.2-400 mgkg-1 and of indomethacin (20 mgkg-1) additionally inhibited release of LTC4, while sodium salicylate (up to 400 mgkg-1) had no effect. Indomethacin (20 mgkg-1) and aspirin (400 mgkg-1) administered subcutaneously inhibited generation of cyclo-oxygenase products of arachidonate metabolism, but did not significantly affect LTC4 synthesis. 3. Oral instillation of ethanol caused gastric mucosal damage and simultaneously induced a selective increase in the ex vivo release of LTC4 from rat gastric mucosa, while release of cyclo-oxygenase products of arachidonate metabolism was not significantly affected. Oral pretreatment of rats with sodium salicylate protected the gastric mucosa and simultaneously inhibited the ethanol-stimulated gastric mucosal LTC4 release in a dose-dependent manner. Sodium salicylate had no effects on the release of PGE2 and TXB2, while that of 6-oxo-PGF1 alpha was slightly increased. 4. Pretreatment with indomethacin (4 or 20mg kg- p.o.) or aspirin in doses up to 25mg kg-1 p.o. prior to oral instillation of ethanol did not inhibit gastric mucosal damage and had no effect on the stimulatory action of ethanol on LTC4 release. Higher doses of aspirin (100mgkg-1 or 400mgkg-1 p.o.) reduced the mucosal damaging effect of ethanol and simultaneously inhibited LTC4 release. 5. The results suggest that aspirin and indomethacin in concentrations higher than those necessary to inhibit the cyclo-oxygenase pathway of arachidonate metabolism additionally inhibit gastric mucosal LTC4 synthesis under basal conditions, while sodium salicylate has no such effect. On the other hand, sodium salicylate, but not indomethacin or low doses of aspirin (up to 25mg kg 1), by an unknown mechanism inhibits stimulation of LTC4 biosynthesis by ethanol and simultaneously protects the gastric mucosa against ethanol-induced damage. Similar effects of high oral doses (> 100mgkg- 1) of aspirin might be due to significant formation of salicylate. These results suggest that there is a causal relationship between enhanced LTC4 biosynthesis and the development of ethanol-induced gastric injury.

Animals↗
PubMed1988

Quantitative determination of eicosanoids in biological material.

Radioimmunoassay is the most widely used method for determination of eicosanoids in biological material. Although this technique is, in principle, simple, radioimmunological data generally require extensive validation procedures. Here some examples for such methods are presented with special emphasis on the determination of cysteinyl-leukotrienes.

Animals↗
PubMed1988

Release of cysteinyl-leukotrienes is of minor importance in PAF induced reduction of perfusion rate in the gastric vascular bed.

In the isolated rat gastric vascular bed, PAF dosedependently decreased the perfusion rate and increased the formation of cysteinyl-leukotrienes, TXB2 and 6-keto F1 alpha (measured by radioimmunoassay). Inhibition of cysteinyl-leukotrienes biosynthesis by NDGA or antagonism of cysteinyl-leukotrienes receptors by FPL 55712 did not prevent the PAF induced reduction of gastric flow. Inhibition of cyclooxygenase by indomethacin aggravated the PFA-induced reduction of flow, however in the later period of experiment. BN 552021 - the PAF receptor antagonist, completely prevented the release of cysteinyl-leukotrienes, TXB2 and 6-keto F1 alpha into perfusate, however was not able to prevent completely the PAF induced reduction of gastric flow. We conclude that the reduction of flow observed after PAF administration seems to be related rather to the vasocongestion induced by PAF itself.

Animals↗
PubMed1987

Possible mode of action of 5-aminosalicylic acid.

Despite the extensive use of sulfasalazine (SAS) and/or 5-aminosalicylic acid (5-ASA) in patients with inflammatory bowel disease and, more recently, rheumatoid arthritis, their mode of action has not been elucidated so far. None of the numerous pharmacological and biochemical effects described, including immunosuppressive, antifolate, and modulatory actions on lymphocyte and leukocyte functions, could be defined unequivocally as mediating their beneficial activity. Recently, interest has focused on actions of SAS and 5-ASA on the various enzymes of the arachidonic acid cascade. Mucosa of patients with inflammatory bowel disease generates excessive amounts of cyclooxygenase products such as prostaglandins (PG) as well as 5-lipoxygenase products such as leukotriene (LT) B4 and sulfidopeptide-LT. Both PG and LT exert proinflammatory actions and are potentially important mediators of mucosal inflammation. SAS and 5-ASA, however, have been found to inhibit PG synthesis under certain experimental conditions only, while increasing PG formation under other conditions. While SAS was found to inhibit colonic LTB4 synthesis, 5-ASA was reported to selectively affect the cyclooxygenase pathway of arachidonate metabolism in this tissue. Our results demonstrate that, like the parent compound, the metabolite 5-ASA in a dose-dependent manner inhibits release of LTB4 and sulfidopeptide-LT from normal human colonic mucosa (IC50 3.5 and 3.7 mmol/liter, respectively). Indomethacin, which has no efficacy in the treatment of patients with inflammatory bowel disease, on the other hand, selectively inhibited PGE2 formation in normal and inflamed colonic mucosa (IC50 1.7 and 1.0 mmol/liter, respectively) without reducing synthesis of LTB4 or sulfidopeptide-LT.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminosalicylic Acids↗
PubMed1987

Formation of cysteinyl-containing leukotrienes by human arterial tissues.

Human arterial rings incubated in modified Tyrode solution released small amounts of leukotriene (LT) C4-like material spontaneously and larger amounts upon stimulation with the ionophore A23187 as determined by radioimmunoassay. By reversed phase high pressure liquid chromatography (HPLC) LTC4-like material was found to comigrate with authentic LTC4, LTD4 and LTE4. Nordihydroguaiaretic acid (NDGA) significantly inhibited the ionophore A23187-induced release of LTC4-like material, while indomethacin was without effect. Simultaneously the arterial rings released much larger amounts of 6-keto-prostaglandin (PG) F1 alpha, which were significantly decreased by indomethacin. The results demonstrate that human arterial tissue has the capacity to synthesize cysteinyl-containing LT from endogenous arachidonic acid.

Adult↗