Effect of indomethacin on electrical field stimulation-induced contractions of isolated transverse and longitudinal rat gastric fundus strips

Doxazosin selectively potentiates contraction to serotonin via 5-HT₂A receptors in longitudinal muscle strips of the rabbit gastric body

The aims of this study were to examine the effects of doxazosin on contractile responses to 5-hydroxytryptamine (5-HT), carbachol, and histamine, and to compare them with those of prazosin, alfuzosin, and terazosin, and then characterize a pharmacological profile of the 5-HT-induced contractile response using preparations of isolated longitudinal muscle strips from the rabbit gastric body. The results from these preparations showed that the contraction response to 5-HT, but not to carbachol or histamine, was found to be dose-dependently potentiated by doxazosin and its enantiomers. The specific potentiation effect on 5-HT was not observed in the preparations that were treated with prazosin, terazosin, or alfuzosin. The contractile response to 5-HT and its potentiation by doxazosin were not affected by treatment with phenoxybenzamine. However, 5-HT-induced contraction was competitively antagonized by nefazodone (with pA₂ value of 8.64 ± 0.17), and was almost completely inhibited by treatment with indomethacin. In conclusion, doxazosin, but not prazosin, alfuzosin, or terazosin, selectively potentiates 5-HT-induced contraction in the rabbit gastric body strips via an α₁-adrenoceptor-independent mechanism, without chiral recognition of its enantiomers. Additionally, the contraction to 5-HT was found to be mediated via 5-HT(₂) receptors, and was similar to PGs synthesis in the preparations.

Effects of washout following indomethacin administration on electrical field stimulation-induced isolated rat gastric fundus strip contractions

BACKGROUND AND AIM

Although gastric hypermotility is one of the mechanisms proposed to explain the ulcerogenic action of indomethacin, the drug has shown relaxatory effects on isolated longitudinal and transverse rat gastric fundus. To explain the above discrepancy, the aim of this study was to investigate the effects of washout following indomethacin administration on the contractile response of isolated rat gastric strips to electrical field stimulation.

METHODS

Transverse and longitudinal strips of stomach were suspended in organ baths containing oxygenated Krebs solution. Contractile responses to electrical field stimulation were recorded on a physiograph before and after administration of a single concentration of indomethacin. Recordings were also taken 15 min after the washout of the drug. To study the part played by K(ATP) channels on post-washout response, the effects of diazoxide as a channel opener and glybenclamide as a channel blocker were also studied.

RESULTS

The amplitude of the contractions was not changed following indomethacin administration but was significantly increased 15 min after washout of the drug. Diazoxide pretreatment inhibited the stimulatory post-washout response of both strips. Glybenclamide pretreatment showed different results depending on the type of strip. In the transverse strips the drug showed no effect while in the longitudinal strips it decreased the post-washout response.

CONCLUSIONS

The present data suggest that indomethacin has a delayed stimulatory effect on gastric smooth muscle, which will appear after the exposure of the strip to the drug followed by its washout. This effect seems to be under the influence of K(ATP) channel modulators.