Essential fatty acid-deficient diet modifies PAF levels in stomach and duodenum of endotoxin-treated rats

Platelet-activating factor (PAF) is thought to play an important role in pathogenesis of endotoxin shock. Here, using essential fatty acid deficient (EFAD) rats, we have evaluated changes in mean arterial blood pressure, PAF levels and damage in both stomach and duodenum following intravenous administration of endotoxin (LPS). In EFAD rats the second phase of LPS-induced hypotension was strongly reduced. Similarly, PAF levels in stomach and duodenum of EFAD rats were also reduced and correlated to the diminished damage. Our study confirms a direct involvement of PAF in LPS-induced gastrointestinal damage.

Nitric oxide and castor oil-induced diarrhea

The effect of NG-nitro-L-arginine methyl ester (L-NAME) on castor oil-induced diarrhea was studied in control rats and those treated with isosorbide dinitrate or isosorbide-5-mononitrate. Castor oil (2 ml) produced diarrhea that lasted at least 8 h. Pretreatment of the rats with L-NAME (1-25 mg/kg i.p.) 15 min before castor oil did not block the castor oil-induced diarrhea beyond 3 h after challenge but delayed its appearance (P < .05-.001). However, diarrhea was inhibited (P < .01-.001) during the entire 8 h if rats were treated twice with L-NAME (25 mg/kg) (15 min before and 3 h after castor oil). These findings suggest that L-NAME, once administered, loses its activity 3 h after its administration. The nitric oxide synthase substrate, L-arginine (150-600 mg/kg), reversed (P < .05-.01) the inhibitory effect of L-NAME on diarrhea induced by castor oil. This effect is enantiomer-specific because D-arginine (900 mg/kg) was without an effect. These results suggest that castor oil-induced diarrhea in rats involves the L-arginine nitric oxide pathway. This is further supported by the effect of isosorbide dinitrate (0.6-120 mg/kg) and isosorbide-5-mononitrate (0.6-120 mg/kg). When administered to castor oil-treated rats, these two nitric oxide-generating agents prevented in a dose-dependent fashion (P < .01-.001) the inhibitory effect of L-NAME (25 mg/kg).

Inhibition of intestinal motility and secretion by flavonoids in mice and rats: structure-activity relationships

Intraperitoneal administration of some flavonoids (apigenin, flavone, kaempferol, morin, myricetin, naringin and rutin; 12.5-50 mg kg-1) significantly (P < 0.05-0.01) reduced small (28-69%) and large (83-134%) intestinal transit in mice. Other flavonoids (naringenin, silibinin, silymarin and taxifolin, 100-200 mg kg-1) reduced (23-41%; P < 0.05-0.01) intestinal transit at doses of 100-200 mg kg-1 while hesperitin, catechin and phloridzin (up to 200 mg kg-1) had no effect. This effect was antagonized by yohimbine (87-96%) and phentolamine (87-91%) but not by prazosin, propranolol, atropine, hexamethonium, mepyramine, cyproheptadine and naloxone. Yohimbine (92-96%) also antagonized the inhibitory effect of flavonols (12.5-50 mg kg-1) (P < 0.05-0.01) on intraluminal accumulation of fluid and diarrhoea induced by castor oil. By contrast, verapamil potentiated the flavonol effect. It is suggested that these effects, influenced by the structure of the molecules, are mediated by alpha 2-adrenergic receptors and calcium.

Inhibitors of nitric oxide synthase enhance rat ileum contractions induced by ricinoleic acid in vitro

The effects of NG-nitro-L-arginine methyl ester (L-NAME) and NG-monomethyl-L-arginine (L-NMMA), inhibitors of nitric oxide (NO) synthase, were studied on ricinoleic acid-evoked contractions in rat isolated ileum. Ricinoleic acid (10(-5) to 10(-4) M) caused a concentration-dependent contraction. Addition of L-NAME (30-300 microM) or L-NMMA (30-300 microM) to the Tyrode's solution increased in a concentration-dependent fashion the amplitude of the ricinoleic acid-evoked responses. L-Arginine (900 microM), a natural substrate of NO synthase, but not D-arginine (900 microM), counteracted the effect of L-NAME (300 microM). The potentiating effect of L-NAME was also prevented by sodium nitroprusside (0.1-1 microM), a generator of NO. These results provide evidence that endogenous NO may modulate the contraction of rat ileum induced by ricinoleic acid. As the contraction induced by ricinoleic acid is not blocked by tetrodotoxin (0.6 and 6.0 microM) the contractile effect of ricinoleic acid results mainly from a direct action on the smooth muscle.

Increased ex-vivo colonic generation of PAF induced by diphenylmethane stimulant laxatives in rats, mice, guinea-pigs and rabbits

The effects of in-vivo treatment with bisacodyl, phenolphthalein, picosulphate, sulphosuccinate, mannitol and lactulose laxatives were examined on the ex-vivo formation of platelet-activating factor (PAF) by duodenum and colon of rat, mouse, guinea-pig and rabbit. Bisacodyl (10 mg kg-1), phenolphthalein (20 mg kg-1) and picosulphate (10 mg kg-1), but not sulphosuccinate (40 mg kg-1), mannitol (50 mg kg-1) or lactulose (50 mg kg-1), at doses that all caused laxation, markedly increased PAF in the colon (P < 0.01) but not in the duodenum. Intraluminal release of acid phosphatase was also significantly increased in the colon of rats treated with bisacodyl, phenolphthalein and picosulphate, but not in colons of animals treated with sulphosuccinate, mannitol or lactulose. The data show that enhanced generation of PAF is associated with the colonic damage induced by diphenylmethane laxatives, but do not show whether this is a cause or a consequence of the pathophysiological changes.

Effect of senna is not mediated by platelet-activating factor

The effect of in vivo treatment with senna was examined on the ex vivo formation of platelet-activating factor (PAF) by small and large intestine of rat, mouse and guinea pig. A single or a prolonged oral administration of senna (60-240 mg/kg) to animals did not increase intestinal PAF content. Nor did senna increase the intraluminal release of acid phosphatase. A similar result was obtained in the colonic tissue of rat perfused in vitro with rhein (1-500 micrograms/ml) or rhein anthrone (1-500 micrograms/ml). In contrast, a single oral administration of phenolphthalein (20 mg/kg), bile salts (20 mg/kg) or magnesium sulfate (30 mg/kg) to rats increased intestinal PAF content. Magnesium sulfate also increased the intraluminal release of acid phosphatase. Colonic tissue of rats perfused in vitro with calcium ionophore A23187 (10 micrograms/ml) formed large amounts of PAF and acid phosphatase. PAF stimulates intestinal motility and secretion and mediates gut damage while acid phosphatase is a marker of cellular damage. Therefore, our data suggest that senna is well tolerated in animals and PAF does not mediate senna-induced laxation.

Platelet activating factor and the responses of rat isolated stomach strip to prostaglandin E2

The effect of platelet activating factor (PAF) on contractions evoked by acetylcholine, 5-hydroxytryptamine (5-HT) and prostaglandin E2 (PGE2) was studied in-vitro on rat stomach strip. Addition of PAF to the organ bath increased PGE- but not 5-HT- or acetylcholine-evoked responses. The effect of PAF was unaffected by atropine, methysergide or indomethacin, but prevented by a specific PAF receptor antagonist BN 52021. The data support a specific interaction between PAF and PGE2 on rat stomach strip.

Inhibitors of nitric oxide synthetase prevent castor-oil-induced diarrhoea in the rat

1. Castor oil (2 ml orally) produced copious diarrhoea in rats 3 h after its administration. 2. Pretreatment (intraperitoneal, i.p.) of rats with the NO synthesis inhibitors NG-nitro-L-arginine methyl ester (L-NAME, 1-25 mg kg-1) and NG-monomethyl-L-arginine (L-NMMA, 2.5-100 mg kg-1) inhibited or prevented castor-oil-induced diarrhoea. L-Arginine (150-600 mg kg-1, i.p.) administered to rats pretreated with L-NAME 10 mg kg-1, drastically reduced the antidiarrhoeal activity of L-NAME in a dose-related manner. D-Arginine (900 mg kg-1) did not modify the protection by L-NAME. 3. Pretreatment (i.p.) of rats with L-NAME (2.5-25 mg kg-1) decreased the intestinal fluid accumulation and Na+ secretion induced by castor oil. L-Arginine (600 mg kg-1) but not D-arginine (900 mg kg-1) counteracted the inhibitory effect of L-NAME (10 mg kg-1). 4. L-NAME (10 and 25 mg kg-1) had no significant effect on the intestinal transit in normal rats or those given castor oil. 5. These results provide evidence that nitric oxide (NO) could play an important role in castor-oil-induced diarrhoea.

Research on heterocyclic compounds, XXIX. Synthesis and antiinflammatory activity of imidazo[1,2-a]pyrazine derivatives

The reaction in anhydrous ethanol of some substituted 2-aminopyrazines with ethyl 2-benzoyl-2-bromoacetate or with ethyl 3-bromo-4-oxopentanoate afforded a group of ethyl 2-phenylimidazo[1,2-a]pyrazine-3-carboxylates and a group of ethyl 2-methylimidazo[1,2-a]pyrazine-3-acetates, respectively. The corresponding acids obtained via alkaline hydrolysis were subjected to pharmacological testing in vivo in order to evaluate their antiinflammatory activity.

Perfusion of rat colon with sennosides, rhein and rheinanthrone. Concentration-related histamine release

Rat colon perfused intraluminally in vitro and in vivo released histamine into the perfusates. Histamine release was increased by rhein 0.1-10 micrograms/ml and much more by rheinanthrone 0.1-10 micrograms/ml but not by sennosides A or B 1-10 micrograms/ml. The effect of rhein and rheinanthrone was reduced by tritoqualine 20 mg/kg. This raises the possibility that laxation by senna and its derivatives involves histamine formation.

Preliminary studies on antipyretic and analgesic properties of Taverniera abyssinica

In an attempt to ascertain the pharmacological basis of the use of the marketed traditional drug Taverniera abyssinica A. Rich. (Amharic name Dingetegna), crude extracts as well as purified substances of this plant were tested for their antipyretic and analgesic properties. Antipyretic activity was determined on rats made hyperthermic by yeast injection and analgesic activity was determined by the hot plate, as well as the acetic acid induced writhing, methods. The study showed that the plant possesses significant antipyretic and analgesic activities.