Delayed evacuatory function due to specific smooth muscle reactivity in the gastrointestinal tracts of tacrine-treated rats.

Most of the side effects induced by tacrine are associated with the gastrointestinal (GI) tract. The aim of the study was to analyze the nature of radiographically registered, tacrine-induced changes in evacuatory function, as well as to find a possible correlation with the immediate in vitro action of the drug on smooth muscles from the GI tracts of rats. The tacrine dose we used reliably delayed GI passage: contrast matter was not fully evacuated, predominantly from the stomach and cecum. The delay resulted from changes in tone and peristaltic activity, specific for the various regions of the tract. These changes were associated with a superposing of the responses due to the anticholinesterase and noncholinergic action of tacrine.

Neostigmine, but not metoclopramide, abolishes ethosuximide-induced functional gastrointestinal disturbances.

Ethosuximide is a drug used for the treatment of absence seizures. Its prolonged application leads to gastrointestinal (GI) disturbances. The purpose of the present study was to determine the severity and nature of the disturbances, as well as the influence exerted upon them by neostigmine methylsulfate and metoclopramide. The drug-induced alterations, occurring in the rat GI tract, were registered by X-ray contrast examination. In vitro experiments were carried out on isolated GI smooth muscle (SM) preparations. The latter revealed that the drug hyperpolarized the SM tissues and inhibited their contractile activity. X-rays of ethosuximide-treated rats showed GI hypotonia, disturbed peristalsis and decreased evacuation activity. The inhibition of the GI functions was associated with hyperpolarization of SM and a reduction in Ca(2+) influx, ensuring spontaneous contractile activity. The application of neostigmine methylsulfate significantly removed ethosuximide-induced functional GI disturbances in rats treated for 15 days with ethosuximide.

Effects of GABA(B) receptor antagonists on spontaneous and on GABA-induced mechanical activity of guinea-pig smooth muscle preparations.

The majority of GABA(B) receptor antagonists have been based on alterations of the acidic moiety of gamma-aminobutyric acid (GABA) or baclofen, such as the first selective antagonist phaclofen. More recently, a new structural class of compounds derived by p-alkyl substitution in the phosphinic analog of GABA, such as CGP35348 (3-amino-propyl-(diethoxymethyl)-phosphinic acid), have been introduced as GABA(B) receptor antagonists. The present study examine the influence of a series of structurally related phosphinic acid analogues on mechanical activity and their effect on GABA-induced reactions in ileal smooth muscle. In our experiments, GABA exerted a biphasic contractile-relaxation effect with pronounced dose-dependent characteristics. 3-[[1-(S)-(3,4-Dihydrophenyl) ethyl]amino]-2-(S)-hydroxy-propyl]-(phenylmethyl)-phosphinic acid hydrochloride (CGP55845A) induced prolonged relaxation without changing the phasic activity of the ileum preparations. [3-[1-R-[[2-(S)-hydroxy-3-[hydroxy-4-methoxyphenyl]-methyl]-phosphinyl]-propyl]-aminoethyl]-benzoic acid (CGP62349) did not change the mechanical activity of smooth muscle preparation. Trans 3-[6-[[Cyclo hexylmethyl-hydroxy-phosphinyl]-methyl]-3-morpholinyl]-benzoic acid (CGP71982) itself induced smooth muscle contractions. GABA(B) receptor antagonists decreased concentration-dependently the relaxation phase of the action of GABA from 50% to 90%. Their effect on the contractile phase of the action of GABA was quite different-CGP55845A decreased it dose-dependently, whereas CGP62349 and CGP71982 did not change it significantly. These findings prompted us to assume that the GABA(B) receptor antagonists studied, being phosphinic analogues, probably act on GABA(B) receptors in guinea-pig ileum smooth muscles.