Mucoadhesive effect of Curcuma longa extract and curcumin decreases the ranitidine effect, but not bismuth subsalicylate on ethanol-induced ulcer model.

The study of pharmacological interactions between herbal remedies and conventional drugs is important because consuming traditional herbal remedies as supplements or alternative medicine is fairly common and their concomitant administration with prescribed drugs could either have a favorable or unfavorable effect. Therefore, this work aims to determine the pharmacological interactions of a turmeric acetone extract (TAE) and its main metabolite (curcumin) with common anti-ulcer drugs (ranitidine and bismuth subsalicylate), using an ethanol-induced ulcer model in Wistar rats. The analysis of the interactions was carried out via the Combination Index-Isobologram Equation method. The combination index (CI) calculated at 0.5 of the affected fraction (fa) indicated that the TAE or curcumin in combination with ranitidine had a subadditive interaction. The results suggest that this antagonistic mechanism is associated to the mucoadhesion of curcumin and the TAE, determined by rheological measurements. Contrastingly, both the TAE and curcumin combined with bismuth subsalicylate had an additive relationship, which means that there is no pharmacological interaction. This agrees with the normalized isobolograms obtained for each combination. The results of this study suggest that mucoadhesion of curcumin and the TAE could interfere in the effectiveness of ranitidine, and even other drugs.

Carrier-mediated uptake of H2-receptor antagonists by the rat choroid plexus: involvement of rat organic anion transporter 3.

The choroid plexus (CP) acts as a site for the elimination of xenobiotic organic compounds from the cerebrospinal fluid (CSF). The purpose of the present study is to investigate the role of rat organic anion transporter 3 (rOat3; Slc22a8) in the uptake of H(2)-receptor antagonists (cimetidine, ranitidine, and famotidine) by the isolated rat CP. Saturable uptake of cimetidine and ranitidine was observed in rOat3-LLC with K(m) values of 80 and 120 microM, respectively, whereas famotidine was found to be a poor substrate. The steady-state concentration of the H(2)-receptor antagonists in the CSF was significantly increased by simultaneously administered probenecid, although it did not affect their brain and plasma concentrations. Saturable uptake of cimetidine and ranitidine was observed in the isolated rat CP with K(m) values of 93 and 170 microM, respectively, whereas 50% of the uptake of famotidine remained at the highest concentration examined (1 mM). The K(i) value of ranitidine for the uptake of cimetidine by the isolated CP (50 microM) was similar to its own K(m) value, suggesting that they share the same transporter for their uptake. The inhibition potency of organic anions such as benzylpenicillin, estradiol 17beta-glucuronide, p-aminohippurate, and estrone sulfate for the uptake of cimetidine by the isolated rat CP was similar to that for benzylpenicillin, the uptake of which has been hypothesized to be mediated by rOat3, whereas a minimal effect by tetraethylammonium excludes involvement of organic cation transporter(s). These results suggest that rOat3 is the most likely candidate transporter involved in regulating the CSF concentration of H(2)-receptor antagonists at the CP.

Ketamine inhibits the anticholinesterase activity of ranitidine and physostigmine.

1. The present study was performed to investigate the effect of ketamine on the contractile responses induced by the H2-receptor antagonist ranitidine and the anticholinesterase agent physostigmine on the isolated guinea pig ileum. 2. The contractile responses induced by ranitidine and physostigmine on the guinea pig ileum were significantly prevented, in a concentration-dependent manner, by ketamine, while the ones induced by acetylcholine were not modified. The contractile responses induced by acetylcholine were inhibited by exogenous acetylcholinesterase. Ranitidine and physostigmine inhibited the above reduction, and this effect was significantly prevented by ketamine in a concentration-dependent manner. 3. These findings show that ketamine inhibits the contractile effect of ranitidine and physostigmine on the guinea pig ileum. This inhibition caused by ketamine seems to be associated with the protection of acetylcholinesterase against the inhibition by ranitidine and physostigmine.

Ranitidine but not famotidine releases acetylcholine from the guinea pig myenteric plexus.

The effects of the histamine H2-receptor antagonists ranitidine and famotidine on acetylcholine release have been studied in the guinea pig myenteric plexus longitudinal muscle preparation incubated with [3H]-choline. Ranitidine (3 x 10(-5)-3 x 10(-4) M) dose-dependently increased the resting release of acetylcholine and that evoked by electrical stimulation. The effect was present only in strips perfused with 10(-5) M physostigmine. The effect of ranitidine was inhibited by tetrodotoxin and hexamethonium. Famotidine (10(-5)-3 x 10(-4) M) was totally ineffective in modifying both the resting release and that evoked by field stimulation. Ranitidine did not antagonize the inhibitory effect of oxotremorine, which specifically activates negative feedback mechanisms via presynaptic muscarinic receptors.

Mechanism of ranitidine associated anemia.

Ranitidine, an H2 receptor antagonist, has been associated with hematotoxicity. The mechanism(s) underlying the toxicity is not well understood. The authors studied the mechanism of anemia in a patient with ranitidine associated anemia and thrombocytopenia. Clinical evaluation suggested drug-induced Coombs' positive reticulocytopenic hemolysis. In vitro, with the patient off ranitidine, the authors were able to induce Coombs' positivity by incubating patient's red cells with ranitidine and his serum. This process was inhibited by prior exposure of his red cells to histamine. In vitro studies using clonal assays for hematopoietic progenitors revealed that while the patient's serum or ranitidine alone did not affect the patient's or normal bone marrow hematopoiesis, the simultaneous presence of both agents significantly suppressed both patient's and normal erythroid progenitor (BFU-E) colony development. This suppressive effect was prevented by the prior exposure of marrow to histamine and was not observed when the patient's serum was heat inactivated. These studies suggest that the anemia may have resulted from complement-dependent autoimmune destruction/inhibition of progenitor/mature erythroid cells by a process critically dependent on the presence of ranitidine and possibly acting at or near the histamine receptor.

The inhibition of acetylcholinesterase by ranitidine: a study on the guinea pig ileum.

The present work was performed to investigate if the stimulating effect of ranitidine on the intestinal smooth muscle is connected with a possible inhibition of the acetylcholinesterase. Isolated segments of guinea pig ileum were used in Tyrode solution at 37 degrees C. The maximum activity of ranitidine on the ileum was about 79% of the maximum activity of acetylcholine and about 90% of the maximum activity of physostigmine. The contractile responses induced by ranitidine were prevented by atropine and this prevention was stronger against physostigmine. Ranitidine produced an augmentation of the acetylcholine induced contractions which was less against physostigmine. The contractile responses induced by acetylcholine were prevented by acetylcholinesterase. This acetylcholinesterase activity was inhibited by ranitidine and this inhibition was weaker than that caused by physostigmine. These findings suggest that ranitidine exerts at least an anticholinesterase activity which is weaker against physostigmine.