Antagonism of histamine and leukotrienes by azelastine in isolated guinea pig ileum

The effects of azelastine on histamine- and leukotriene C4 and D4 (LTC4, LTD4)-induced contractile responses in isolated guinea pig ileum were investigated. Following a 2-min contact with the ileum, azelastine produced competitive antagonism of histamine (pA2 = 8.24). Following a 15-min contact, azelastine at 2.5 X 10(-9) M exerted competitive antagonism, but at higher concentrations (10, 40 and 160 X 10(-9) M) it not only shifted histamine concentration-effect curves to the right but also suppressed its maximum. Thus, azelastine exerts a dual (competitive/noncompetitive) antagonism of histamine depending upon the concentration and duration of contact. Azelastine and FPL 55712 (a known LT receptor antagonist) produced concentration-dependent antagonism of LTC4 and LTD4. Azelastine and compound FPL 55712 also exerted concentration-dependent reversal (relaxation) of pre-existing LTC4-induced contractions. In conclusion, the potent H1-histamine and leukotriene receptor blocking activities of azelastine may contribute to its antiasthmatic/antiallergic activities.     

Pharmacological effects of 2-aminotetralins, octahydrobenzo[f]quinolines and clonidine on the isolated guinea pig ileum

The ability of derivatives of 2-aminotetralins (2AT), cis- or trans-isomers of octahydrobenzo[f]quinolines (BfQ) and clonidine to modulate acetylcholine release was studied using field-stimulated guinea pig ilea (GPI). Antihistaminic and antiacetylcholine activities were also determined using isolated superfused segments of GPI. Hydroxylated 2AT, BfQ and clonidine inhibited field stimulation-induced contractions through alpha-adrenoceptor mechanisms which were antagonized by phentolamine. In contrast, the inhibition produced by nonhydroxylated 2AT was not attenuated by alpha-adrenoceptor antagonism. 2AT, trans-7,8-dihydro-BfQ and cis-8,9-dihydroxy-BfQ inhibited contractions induced by nicotine bitartrate using superfused GPI. Clonidine was inactive as an antinicotinic agent and there was no correlation between a compound's ability to inhibit contractions induced by field stimulation and its antinicotinic activity. Various 2AT derivatives demonstrated weak antimuscarinic and/or antihistaminic activities on superfused ileal segments. These data demonstrate that these agents possess a spectrum of pharmacological activity.     

Contractile effect of prolactin on guinea pig isolated ileum

Prolactin (PRL) at high concentrations contracted the guinea pig isolated ileum. The maximum response elicited by PRL was 44% of that of histamine-induced responses. There was no significant difference in potency between PRL preparations obtained from two different sources. PRL responses were nullified by denaturation or proteolytic digestion of the hormone. The contractile response was antagonised by atropine and potentiated by neostigmine, but unaffected by the prostaglandin antagonist SC-19220. The pA2 values of atropine against PRL and ACh were similar. Preincubation with morphine, which inhibits ACh release, produced slight inhibition of PRL-evoked contractions. Even high concentrations of PRL failed to produce any response in neostigmine-treated frog rectus muscle preparations. This suggests that PRL may produce contractions through a cholinergic mechanism involving muscarinic receptors. Enhanced gut motility reported earlier for hyperprolactinemic states may be attributed to this cholinomimetic effect of PRL on the intestinal tract.     

Antihistaminic activity of carane derivatives in isolated guinea pig ileum

Local anesthetics (LAs) inhibit membrane depolarization by reducing sodium and potassium conductance, and subsequent displacement of calcium ions from binding sites seems to occur. Histamine release appears to be a secretory process in which calcium couples the stimulus to the exocytosis of histamine-containing granules. Furthermore, LAs are structurally similar to histamine H₁-receptor antagonists. Thus, LAs can be considered antihistaminic drugs.Previous pharmacological investigations have shown strong local anesthetic, anti-inflammatory and analgesic activity of the carane derivative KP-23. As it has previously been demonstrated that KP-23R, S and its R, S-diasteroisomers have an inhibitory effect on guinea pig ileum contractions, the aim of the present study was to determine and compare the antihistaminic effects of KP-23R, S and its individual isomers KP-23R and KP-23S on isolated guinea pig ileum.     

Involvement of cholinergic neurons in orexin-induced contraction of guinea pig ileum

The mechanism underlying orexin-induced contraction was examined in isolated preparations of guinea pig ileum, in relation to cholinergic transmission. Orexin-A caused contraction of ileal strips in a concentration-dependent manner. 1-(2-Methylbenzoxazol-6-yl)-3-[1,5]napthyridin-4-yl-urea hydrochloride (SB-334867-A) antagonized the orexin-A-induced contraction, with no effects on the acetylcholine-induced contraction and twitch contractions. The orexin-A-induced contraction was inhibited by tetrodotoxin and atropine, but not by hexamethonium, an antagonist of vasoactive intestinal peptide and a mixture of 5-hydroxytryptamine receptor antagonists. Orexin-A evoked an outflow of [3H]acetylcholine from the ileal strips preincubated with [3H]choline, in a concentration-dependent manner, and the orexin-A-evoked outflow was inhibited by tetrodotoxin, indicating that the outflow of [3H]acetylcholine originates from the nerve terminals. The orexin-A-evoked outflow of [3H]acetylcholine was antagonized by SB-334867-A. Thus, orexin-A evokes the release of acetylcholine from the enteric cholinergic neurons due to stimulation of the orexin-1 receptors and then causes contractions of guinea pig ileum.     

Desensitization of the isolated guinea pig ileum to antihistaminic agents

Guinea pig ileum developed in vitro a progressive desensitization to the antihistaminic agents mepyramine and benadryl. This desensitization had uncommon characteristics: (1) at the 6.5-9 h period of the experiments, it consisted only of a decreased rate of action of the drugs (1.66 fold and 2 fold increases in the 2 min Kb value of mepyramine and benadryl respectively), without variation in the equilibrium Kb values; (2) it was not a drug effect since control strips (strips exposed to the first dose of antihistaminic agent after 5.5 h in vitro) also showed a decreased rate of action of the drugs (1.58 fold and 1.6 fold increases in the 2 min Kb value of mepyramine and benadryl respectively), without variation in the Kbe values. The desensitization also did not depend on the bathing medium or on the amount of available histamine receptors. The only explanation of the desensitization is a slowing in the antihistaminic agent-receptor reaction either in its access stage or less probably in its interaction stage.     

粉防己碱对吗啡在离体豚鼠回肠中依赖性的作用(英文)

目的:研究粉防己碱(Tet)和尼莫地平(Nim)对吗啡在离体豚鼠回肠中戒断性反应的影响。方法:戒断性收缩由纳洛酮(1μmol·L~(-1))加入已在含吗啡(3μmol·L~(-1))的37.5℃ Krebs液中孵育4h的离体豚鼠回肠或加入从吗啡依赖豚鼠中取得的回肠引起。结果:离体豚鼠回肠在含吗啡的Krebs液中孵育4h,给Nim(0.01、0.05和0.1μmol·L~(-1))或Tet(1、10和50μmol·L~(-1))抑制其戒断性收缩。Nim和Tet体内或体外给药都能抑制吗啡依赖豚鼠离体回肠的戒断性收缩。结论:钙拮抗剂Nim和Tet抑制吗啡在离体豚鼠回肠的戒断性收缩。     

Acute effects of aflatoxins on guinea pig isolated ileum.

Previous studies on the aflatoxins have focused mainly on their chronic toxic effects. In this study we investigated the acute gastrointestinal effects of four common aflatoxins on isolated guinea pig ileum. AFB(1) (EC(50) 4.6+/-0.4 microM) and AFB(2) (EC(50)17+/-4.4 microM) contracted isolated guinea pig ileum in a dose-dependent manner, whereas AFG(1) and AFG(2) evoked no contractions. Atropine (5.9 nM 11.8 and 23.6 nM) antagonized AFB(1)-induced contractions in a dose-dependent manner. Pretreatment with the nicotinic ganglionic blocker, hexamethonium (up to 55 microM), left AFB(1)-induced contractions unchanged. In contrast, tetrodotoxin (0.3 microM), blocked AFB(1) contractile activity. The two inhibitors of ACh release, morphine (0.3 microM) and clonidine (0.4 microM), antagonized EC(50) AFB(1)-induced contractions, and apamin, a drug that increases neuronal excitability, facilitated the EC(50) AFB(1)-induced contractile effect. The choline uptake blocker, hemicholinium (17.4 microM) markedly reduced AFB(1)-induced contractions. These results suggest that aflatoxins induce their contractile effect indirectly through the cholinergic system by stimulating acetylcholine release from the postganglionic parasympathetic nerve endings. The acute actions of aflatoxins on isolated guinea pig ileum could explain their acute gastrointestinal effects in humans and animals.     

Stability of [6]-gingerol and [6]-shogaol in simulated gastric and intestinal fluids

The degradation kinetics of [6]-gingerol and [6]-shogaol were investigated in simulated gastric (pH 1) and intestinal (pH 7.4) fluids at 37 degrees C. Degradation products were quantitatively determined by HPLC (Lichrospher 60 RP select B column, 5 microm, 125 mm x 4 mm; mobile phase: methanol-water-acetic acid (60:39:1 v/v); flow rate: 0.6 ml/min; detection UV: 280 nm). In simulated gastric fluid (SGF) [6]-gingerol and [6]-shogaol underwent first-order reversible dehydration and hydration reactions to form [6]-shogaol and [6]-gingerol, respectively. The degradation was catalyzed by hydrogen ions and reached equilibrium at approximately 200 h. In simulated intestinal fluid (SIF) both [6]-gingerol and [6]-shogaol showed insignificant interconversion between one another. Addition of amino acids glycine, 3-amino propionic acid (beta-alanine) and gamma-amino butyric acid (GABA), and ammonium acetate at a range of concentrations of 0.05-0.5mM had no effect on the rate of degradation of [6]-shogaol in SGF and 0.1M HCl solution. However, at exceedingly high concentration (0.5M) of ammonium acetate and glycine, significant amounts of [6]-shogaol ammonia and glycine adducts were detected. The degradation profile of [6]-gingerol and [6]-shogaol under simulated physiological conditions reported in this study will provide insight into the stability of these compounds when administered orally.     

Effects of dapiprazole on contractile responses of guinea pig isolated ileum

The effects of dapiprazole, a relatively new alpha 1-adrenolytic agent, on contractile responses and on spontaneous mechanical activity were studied in guinea pig isolated ileum. Dapiprazole (10(-10) to 10(-4) M) produced a concentration-dependent inhibition of high K+ (80 mM) -induced contractions. These inhibitory effects were observed with dapiprazole added either before or after the induced contractions. The Ca2+-induced contractions of K+-depolarized ileum were also inhibited by dapiprazole. Dapiprazole inhibited in a non competitive manner the responses of the ileum to: carbachol, histamine, 5-hydroxytryptamine, pentagastrin, angiotensin II and cholecystokinin. In order to analize whether dapiprazole exerts an intracellular effect on Ca2+-store, skinned preparations were used. The results suggest that dapiprazole might inhibit Ca2+ entry through both voltage-and receptor-operated channels of the smooth muscle membrane.     

粉防己碱对吗啡在离体豚鼠回肠中依赖性的作用

AIM: To evaluate the effects of tetrandrine (Tet) and nimodipine (Nim) on the morphine (Mor) withdrawal response in the isolated guinea pig ileum. METHODS: The withdrawal contracture was elicited by addition of naloxone (Nal) (1 mumol.L-1) to the isolated naive ileum incubated with Mor (3 mumol.L-1) at 37.5 degrees C for 4 h or to the ileum obtained from Mor-dependent guinea pig. RESULTS: When Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) was added 1 min before Nal in the naive ilea bathed in Krebs solution containing Mor, or when the ilea from Mor-dependent guinea pigs were incubated with Nim (0.01, 0.05, and 0.1 mumol.L-1) or Tet (1, 10, and 50 mumol.L-1) for 15 min, or when Nim (5 and 10 mg.kg-1, i.p.) or Tet (15 and 30 mg.kg-1, i.p.) was administered in vivo to Mor-dependent guinea pigs, the Nal-precipitated withdrawal contracture was significantly decreased in a dose-dependent manner. CONCLUSION: Tet and Nim, Ca2+ channel blockers, could inhibit the Nal-precipitated Mor withdrawal response in the isolated guinea pig ileum.     

Contractile properties of various histaprodifen derivatives in guinea pig isolated ileum and trachea

We characterized the histamine H(1) receptor agonism of various histaprodifen derivatives in guinea pig isolated ileum and trachea in comparison with histamine. Based on their affinity (calculated pK(A) values for ileum and trachea, respectively), the compounds were ranked as follows: suprahistaprodifen (8.31/8.08) > N(alpha)-(4-phenylbutyl)histaprodifen (7.22/5.93) >or= histamine (5.79/5.19) approximately methylhistaprodifen (5.57/6.07). Based on their efficacy (calculated tau values for ileum and trachea, respectively), the compounds were ranked as follows: methylhistaprodifen (37.67/2.50) > histamine (5.64/1.80) > suprahistaprodifen (1.63/1.42) >or= N(alpha)-(4-phenylbutyl)histaprodifen (0.083/1.54). In the ileum, histamine and methylhistaprodifen showed a high histamine H(1) receptor reserve while suprahistaprodifen and N(alpha)-(4-phenylbutyl)histaprodifen are devoid of any histamine H(1 )receptor reserve. On the trachea, no histamine H(1 )receptor reserve was demonstrable with the four tested agonists. The kinetic of contraction/relaxation of the ileum was faster with histamine and methylhistaprodifen than with suprahistaprodifen and N(alpha)-(4-phenylbutyl)histaprodifen. Histamine contracted the trachea faster than histaprodifen derivatives. Levocetirizine antagonized contractions induced by histamine and histaprodifen derivatives in both tissues. The differences observed in the calculated pA(2) (7.60-8.29) and/or pD'(2) values (6.28-7.90) depending on the tissue and/or the agonist are discussed.     

Effect of l-ephedrine on cholinergic neurotransmission in the isolated guinea pig ileum

In the isolated guinea pig ileum, the effects of I-ephedrine on the twitch response to field stimulation were investigated in the presence of propranolol. Ephedrine and clonidine inhibited the twitch response but not the contraction to exogenous acetylcholine. The inhibitory effect of clonidine was significantly diminished by yohimbine pretreatment. However, the inhibitory effect of ephedrine was not influenced by yohimbine, sulpiride or 6-hydroxydopamine (6-OHDA) pretreatment. Most of this action of ephedrine appeared to be cholinergic prejunctional in nature, but unrelated to activation of prejunctional alpha 2-adrenoceptors and dopamine sensitive receptors on the cholinergic nerves in this preparation.     

Mechanism of inhibition of peroxynitrite-induced oxidation and nitration by [6]-gingerol

[6]-Gingerol potently inhibits peroxynitrite-induced oxidation and nitration reactions, but its mechanism of action is unclear. In order to discover the mechanism of inhibition, [6]-gingerol was reacted with peroxynitrite and the reaction mixture was analyzed using HPLC. The HPLC chromatogram showed one novel peak, indicative of the formation of a reaction product between [6]-gingerol and peroxynitrite. This compound was purified and identified as a symmetrical dimer of [6]-gingerol covalently linked at the aromatic ring. It has been assumed that this dimer is generated from a phenoxyl radical intermediate produced from [6]-gingerol via one-electron oxidation by peroxynitrite-derived radicals. We propose a mechanism in which [6]-gingerol scavenges peroxynitrite-derived radicals and consequently inhibits peroxynitrite-induced oxidation and nitration reactions.     

Reflex peristalsis in the guinea pig isolated ileum is endogenously controlled by kappa opioid receptors

Summary (1) Reflex peristalsis in the circular muscle of the guinea pig ileum was elicited in vitro by sustained luminal distension of the intestinal wall according to 2 cm H₂O and evaluated in terms of the number of peristaltic waves within 15 min intervals. (2) The poorly -selective opioid antagonist naloxone at concentrations of 10^–7 and 10^–6 mol/l increased the frequency of peristaltic contractions within the first 15 min interval, and thereafter in a declining fashion, by 68 and 88%, respectively. The highly -selective opioid antagonist nor-binaltorphimine behaved similarly. It was, by one order of magnitude, more potent but a little less effective than naloxone, i.e., the maximum effect was 57% increase in peristaltic frequency at 10^–8 mol/l. Concentrations of 10^–7 and 10^–6 mol/l had the same effect as 10^–8 mol/l, and 10^–9 mol/l were ineffective. The highly -selective antagonist CTOP-NH₂ and the highly -selective antagonist ICI 174,864 were ineffective up to 10^–6 mol/l. (3) It is concluded that predominantly opioid receptors are used by endogenous opioids under the present conditions to inhibit reflex peristalsis.     

Calcium antagonism of enpiperate on isolated rabbit aorta strips and guinea pig ileum

Enpiperate, 4-(3, 5)-exocydopropyl-N-methylpiperidyl diphenyl hydroxy acetate, was synthesized in China. It has been shown to have no effect on the normal tension of rabbit aorta strips or contractions induced by NE. It inhibited the contraction of high K+-depolarized rabbit aorta strips at concentrations of 3.8 and 10.9 mumol/L. The same effect was seen on isolated guinea pig ileum, at a concentration of 10.9 mumol/L, which was depolarized by Ca2+ free high K+ Locke-Ringer's solution and the contraction was extragenous Ca2+ dependent. The inhibition was overcome by increasing the extracellular Ca2+ concentration. In the presence of EDTA (0.1 mmol/L), the NE induced intracellular Ca2+ dependent contraction was inhibited by enpiperate (3.8, 10.9 mumol/L), although no significant difference was found between enpiperate and papaverine. It is suggested that enpiperate is a calcium antagonist and that the antagonism is carried out by blocking the potential dependent calcium channel (PDC) in the membrane of vascular smooth muscles. A intracellular calcium antagonistic action may also be involved.