Effect of diazoxide and hydralazine on intestinal transit and blood pressure in the rat

Anorectic Toxicity of Dih Ydroartemisinin, Artemether, and Arteether in Rats Following Multiple Intramuscular Doses

During studies of arteether (AE), artemether (AM), and dihydroartemisinin (DQHS) neurotoxicity, the effect of 7 daily intramuscular doses (25, 50, and 100 mg/ kg/d) of those antimalarial drugs on gastrointestinal function was investigated in rats. A modified Nichols' method was used to measure daily food and water consumption. To estimate gastric transit, the total length amaranth (administered 40 minutes prior to sacrifice) dye traveled through small intestine were measured, and to determine gastric retention, the tied-off stomach pouch was removed and the contents weighed 24 hours after the last dose or when a rat became moribund or died. AM and AE dose solutions were prepared using sesame oil, whereas 50% dimethylacetamide (DMAC) sesame oil was used for DQHS. The results showed that after dosing with 50 mg/ kg for 7 days, 50% inhibition of food consumption (ID50) occurred at 1.9 days for DQHS, 3.9 days for AM, and 4.1 days for AE. Similar data were observed for water intake. After 100 mg/kg dosing, the ID50 s for food and water consumption decreased to 2.8-2.9 days for AM and 3.1-3.7 days for AE. Food consumption and body weights were decreased following all three treatments, and rats exhibited neurologic symptoms at 25-100 mg/kg dose of DQHS and 50-100 mg/kg dose of AM and AE. In addition, the results constituted a 53% and 82% inhibition of gastric transit for AM and AE, respectively, at 25 mg/kg animals compared to control, and 100% inhibition was found in high doses (50 and 100 mg/kg) for all the three drugs. The gastric retention ratio (controls equal 1.0) was 26.0 for DQHS, 5.8 with AE, and 2.3 for AM rats following 50 mg/kg dosing. When the 100 mg/kg dose was administered, the gastric retention ratio doubled for AE (11.6) and AM (4.3). The consumption data indicated that DQHS was about 2-3 times more toxic to the anorexia than AM and AE at 25 and 50 mg/kg/day dose levels. Significant differences in gastric emptying and gastric transit activities between AE and AM were observed. Data demonstrated that after multiple intramuscular doses of DQHS, AM, or AE in rats, food consumption and gastric emptying were decreased, gastric transit was inhibited, as reflected in a significant body weight reduction and death. Since an exhibition of the anorectic symptoms of AM and AE was at a lower dose than the neurologic signs in rats, the anorexia could be an early portent or prediction of the neurotoxicity in animals or humans.

Diazoxide attenuates indomethacin-induced small intestinal damage in the rat

ATP-sensitive potassium (K(ATP)) channel openers have been shown to protect against cellular damage in neurons, cardiac muscle, and kidney and to effectively reduce nonsteroidal anti-inflammatory drug (NSAID)-induced gastric damage in rats. We investigated the effects of K(ATP) channel opener diazoxide on small intestinal injury induced in rats by indomethacin administration. The effect of glibenclamide, a K(ATP) channel blocker, was also evaluated. Diazoxide (15, 45 and 135mg/kg) or glibenclamide (18mg/kg), were given by oral gavage 1h before and 6h after indomethacin treatment (20mg/kg p.o.). After 24h, macroscopic and histologic lesions, myeloperoxidase (MPO) activity and lipid peroxidation levels were evaluated. Diazoxide at 15mg/kg was ineffective, while at doses of 45mg/kg and 135mg/kg was able to significantly improve all damage parameters. Glibenclamide administration enhanced intestinal injury. These results show for the first time a beneficial effect of diazoxide in indomethacin-induced enteritis in the rat. Several mechanisms, such as oxidative phosphorylation uncoupling and hypermotility seem particularly important in NSAID-induced intestinal injury. Such events lead to increased mucosal permeability and to penetration of noxious lumen components, which ignite the inflammatory response. Since K(ATP) channel openers were shown to protect against mitochondrial damage, to reduce intercellular permeability and to relax smooth muscle, we suggest that diazoxide could exert its beneficial effects by one or more of these actions.

Comparison between phenylpropanolamine and structurally related compounds on gastric transit in the rat

Our laboratory previously reported several pharmacological differences between phenylpropanolamine [PPA; (+/-)-norephedrine] and its structurally related compounds in regard to their activity on cardiovascular and appetite-suppressant parameters. The present study investigates the pharmacological differences between PPA, [1R,2R]-(-)-norephedrine [(-)-NOR], [1S,2S]-(+)-norephedrine [(+)-NOR], [1R,2S]-(-)-ephedrine [(-)-EPH], [1S,2R]-(+)-ephedrine [(+)-EPH], [1R,2S]-(-)-norpseudoephedrine [(-)-NORP], [1S,2R]-(+)-norpseudoephedrine [(+)-NORP], [1R,2R]-(-)-pseudoephedrine [(-)-PSE], and [1S,2S]-(+)-pseudoephedrine [(+)-PSE], as determined by their ability to inhibit gastric transit in the rat. (-)-Norephedrine was approximately three times more potent in inhibiting gastric transit than (+)-NOR (p < 0.01). As anticipated, the racemic mixture, PPA, demonstrated an ED50 (25.1 mg/kg) of approximately the mean of the ED50s from the component enantiomers (14.7 and 47.0 mg/kg, respectively). Similarly, administration of 20 mg/kg of either (-)-EPH, (+)-EPH, (-)-PSE, or (+)-PSE significantly decreased gastric transit by 26% (p < 0.001), 12% (p < 0.01), 10% (p < 0.01), and 11% (p < 0.01), respectively. Administration of (-)-NORP and (+)-NORP were without effect. These data confirm and extend previous findings demonstrating pharmacological differences between PPA and its structurally related compounds.

L-tyrosine fails to potentiate several peripheral actions of the sympathomimetics

We have recently reported the ability of L-tyrosine (L-TYR) to potentiate the anorectic activity of various mixed-acting sympathomimetics including phenylpropanolamine (PPA), l-ephedrine (EPH) and d-amphetamine (AMP). Included in those studies was the attenuation of L-TYR's effect when coadministered with L-valine, a large neutral amino acid which competes with L-TYR for uptake into the brain, suggesting a central locus for the action of L-TYR. To determine to what extent L-TYR can potentiate peripheral actions, we investigated the effects of L-TYR with either PPA (20 mg/kg), EPH (20 mg/kg) or AMP (1.75 mg/kg) on gastric transit, gastric retention and intrascapular brown adipose tissue thermogenesis. In each of the paradigms studied, PPA, EPH and AMP significantly increased the expected sympathomimetic-mediated response, but no potentiation of L-TYR was observed. These results are consistent with the hypothesis that L-TYR potentiates the anorectic activity of the mixed-acting sympathomimetics largely via an action at a central locus.