Loperamide inhibits gallbladder inflammatory fluid secretion in experimental cholecystitis

Summary Fluid secretion by the gallbladder mucosa is suggested to have a key pathophysiological role in acute cholecystitis, since it causes distension of the obstructed gallbladder. The present study investigates the actions of loperamide on the gallbladder function in experimental cholecystitis. Gallbladder fluid transport and motility were studied in vivo with a continuous perfusion technique. A net fluid secretion by the gallbladder mucosa was seen in cats in which cholecystitis was induced whereas there was a net fluid absorption from the gallbladder lumen in the control animals. The net fluid secretion in experimental cholecystitis was inhibited by loperamide (1 mg/kg), an effect that was blocked by naloxone (1 mg/kg), suggesting an involvement of specific opiate receptors. Loperamide (1 mg/kg) relaxed the normal gallbladder but had no significant effects on its fluid absorption. Since loperamide reduces mucosal fluid secretion in experimental cholecystitis without contracting the gallbladder wall, it is suggested that this peripherally acting opiate agonist could be useful in the treatment of patients with acute cholecystitis.     

CFTR pharmacology and its role in intestinal fluid secretion

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-activated Cl(-) channel expressed in epithelial cells in the airways, pancreas, intestine and other fluid-transporting tissues. Cystic fibrosis is caused by mutations in the CFTR, resulting in impaired Cl(-) transport and plasma membrane targeting. CFTR is expressed in the lumenal membrane of enterocytes, where it functions as the principal pathway for secretion of Cl(-) and fluid in enterotoxin-induced secretory diarrheas such as cholera. Small-molecule CFTR inhibitors reduce enterotoxin-induced intestinal fluid secretion in animal models. CFTR inhibition might also reduce intestinal fluid losses in cholera and possibly in other infectious and non-infectious diarrheas.     

Leu-enkephalin modulates gastric secretion activated by various stimulants

The results of chronic experiments on dogs showed that leu-enkephalin in doses 1, 7, and 9 microg/kg produced different effects on the gastric secretion and excretion on the background of various stimulants. The maximum protective effect of opiate was produced in a dose of 7 microg/kg. The peptide effect depended on the gastric secretion stimulator used: on the background of carbachol and pentagastrine, the activity of acidic and peptic factors was decreased and the protective factors of gastric juice were increased. In the case of histamine, leu-enkephalin increased the juice acidity and mucus secretion, but decreased the activity of pepsin and the excretion of ammonia from the stomach.     

A model for agonists acting directly as well as indirectly

A theoretical model is presented to describe the receptor interaction of a drug which possesses indirect as well as direct pharmacological action. Sets of theoretical log concentration-effect curves predicted by this model are presented. The model predicts that the shape of the log concentration-effect curves may be sigmoid (S-shaped), biphasic (bell-shaped) or composed of a combination of two sigmoid curves, joined together by a plateau. The theoretical predictions are comparable with the results obtained from an experimental study.     

Mechanisms underlying the intestinal fluid secretion evoked by nociceptive serosal stimulation of the rat

Summary Intestinal net fluid transport was measured in vivo continuously with a gravimetric method. Chemical stimulation of the jejunal serosa with hydrochloric acid (0.1 M), ethanol (20%), cat bile or 7-deoxycholic acid (10 mM) evoked an intestinal fluid secretion. Hexamethonium (10 mg/kg b. wt. i. v.) or serosal application of lidocaine (1% solution) partially blocked this secretory response. Bradykinin and prostaglandin E₁, two important inflammatory mediators, elicited fluid secretion when applied to the serosal surface at a concentration of 10^–4M. This secretion was also partly inhibited by hexamethonium. Furthermore indomethacin (10 mg/kg b. wt. i. v.) or pyrilamine (10 mg/kg b. wt. i. v.), a H₁-receptor blocker, partly inhibited the secretory response caused by chemical stimulation of the serosa while cimetidine (1 mg/kg b. wt. i. v.), a H₂-receptor blocker, had no effect. Freeze sectioned samples from chemically stimulated intestines were examined by fluorescence microscopy. A leakage of i. v. administrated Evans blue labelled albumin into the interstitial space of the serosa and the outer layer of the muscularis was found.It is concluded: (1) The intestinal fluid secretion studied is mainly elicited by nociceptive stimulation of nerves in the serosa or the outer muscularis. (2) The reflex may be activated by the local release of histamine, kinins and prostaglandins. (3) The reflex studied is part of an inflammatory response.     

Effects of atropine on responses to directly and indirectly acting cholinomimetics

In the isolated guinea-pig ileum atropine delayed the onset and slowed the rate of contraction of responses to indirectly acting cholinomimetics (nicotine, dimethylphenylpipezinium, dimethlaminoethanol, dimethylaminopropanol and supinidine), while response heights were little affected. In contrast, atropine had little effect on the time taken for acetylcholine to produce its peak response, while contraction height was reduced.The competitive action of atropine on concentration-effect curves to acetycholine was not apparent with indirectly acting cholinomimetics. Nevertheless analysis of time-effect rather than concentration-effect curves showed that atropine competitively antagonized responses to acetylcholine released by the latter agonists. Atropine antagonism of exogenously administered and endogenously released acetylcholine was similar. The extent and offset of acetylcholine antagonism by atropine was unaffected by indirectly acting compounds.With indirectly acting cholinomimetics, the atropine resistance may be explained on the basis of the differing mechanisms by which exogenous and endogenous acetylcholine elicit responses, rather than a difference in the receptors involved or limited access of atropine to endogenous sites.     

Thiophenecarboxylate suppressor of cyclic nucleotides discovered in a small-molecule screen blocks toxin-induced intestinal fluid secretion

We carried out a "pathway" screen of 50,000 small molecules to identify novel modulators of cAMP signaling. One class of compounds, the 2-(acylamino)-3-thiophenecarboxylates, strongly suppressed cAMP and cGMP in multiple cell lines in response to different agonists acting on G-protein-coupled receptors, adenylyl cyclase, and guanylyl cyclase. The best compounds from structure-activity analysis of 124 analogs, including several synthesized chiral analogs, had and IC(50) of <5 microM for suppression of agonist-induced cAMP and cGMP elevation. Measurements of cAMP, cGMP, and downstream signaling in response to various activators/inhibitors suggested that the 2-(acylamino)-3-thiophenecarboxylates function as nonselective phosphodiesterase activators, although it was not determined whether their action on phosphodiesterases is direct or indirect. The 2-(acylamino)-3-thiophenecarboxylates suppressed CFTR-mediated Cl(-) current in T84 colonic cells in response to cholera and Escherichia coli (STa) toxins, and prevented intestinal fluid accumulation in a closed-loop mouse model of secretory diarrhea. They also prevented cyst growth in an in vitro renal epithelial cell model of polycystic kidney disease. The 2-(acylamino)-3-thiophenecarboxylates represent the first small-molecule cyclic nucleotide suppressors, whose potential therapeutic indications include secretory diarrheas, polycystic kidney disease, and growth inhibition of cAMP-dependent tumors.     

Genistein directly inhibits native and recombinant NMDA receptors

The protein tyrosine kinase (PTK) inhibitor genistein has been widely used to examine potential effects of tyrosine phosphorylation on neurotransmitter function. We report here that genistein inhibits N-methyl-d-aspartate (NMDA) receptors through a direct effect. Whole-cell NMDA-activated current was recorded in native receptors from mouse hippocampal slice culture and rat recombinant NR1aNR2A and NR1aNR2B receptors transiently expressed in HEK293 cells. Extracellular application of genistein and NMDA reversibly inhibited NMDA-activated current. The inhibition of NMDA-activated current by genistein applied externally was not affected when genistein was also pre-equilibrated in the intracellular solution. Daidzein, an analog of genistein that does not block PTK, also inhibited NMDA-activated current. Coapplication of lavendustin A, a specific inhibitor of PTK, had no effect on the NMDA response. Moreover, genistein-induced inhibition of NMDA-activated current displayed concentration- and voltage-dependence. Our results demonstrate that genistein has a direct inhibitory effect on NMDA receptors that is not mediated via inhibition of tyrosine kinase. Thus, other PTK inhibitors may be more suitable for studying involvement of PTKs in NMDA receptor-mediated events.     

Progesterone inhibits mast cell secretion

Mast cells are involved in allergic reactions, where they secrete numerous vasoactive, inflammatory and nociceptive mediators in response to immunoglobulin E (IgE) and antigen. However, they have also been implicated in inflammatory conditions, such as painful bladder syndrome/interstitial cystitis (PBS/IC), irritable bowel syndrome (IBS) and migraines, all of which occur more often in women and are exacerbated during ovulation, but are suppressed during pregnancy. Mast cells express high affinity estrogen receptors and estradiol augments their secretion, while tamoxifen inhibits it. Here we report that progesterone (100 nM), but not the structurally related cholesterol, inhibits histamine secretion from purified rat peritoneal mast cells stimulated immunologically or by substance P (SP), an effect also documented by electron microscopy. These results suggest that mast cell secretion may be regulated by progesterone and may explain the reduced symptoms of certain inflammatory conditions during pregnancy.     

Inhibition of Escherichia coli heat-stable enterotoxin effects on intestinal guanylate cyclase and fluid secretion by quinacrine

Enterotoxigenic Escherichia coli may produce a heat-stable enterotoxin (ST) that causes diarrheal disease in humans and in animals ST activates particulate guanylate cyclase in intestinal mucosal cells and causes intestinal fluid secretion. In this study, we examined the effects of quinacrine on ST activation of guanylate cyclase and ST-mediated intestinal fluid secretion. Quinacrine significantly reduced ST activation of particulate guanylate cyclase in rat intestinal tissue. Additionally, quinacrine reduced ST-mediated fluid secretion in a rat intestinal loop assay (P less than 0.05). In the suckling mouse model, subcutaneous quinacrine (0.1 mumole/mouse) reduced ST-induced fluid secretion at a submaximally effective dose of the toxin, but it did not reduce ST-mediated fluid secretion at a near maximally effective dose. Quinacrine (0.1 mumole/mouse) did not significantly reduce intestinal fluid secretion induced by the analog of cyclic GMP, 8-bromo cyclic GMP. However, at a higher concentration of quinacrine (1 mumole/mouse), significant inhibition of 8-bromo cyclic GMP-induced secretion was observed. Inhibition by the antimalarial agent quinacrine of ST-induced fluid secretion, by a block prior to guanylate cyclase activation, suggests a possible role for a phospholipase early in the sequence of events of ST activation of guanylate cyclase. The results suggest that ST may activate membrane phospholipases prior to ST activation of guanylate cyclase.     

Comparison of alkylation rates and mutagenicity of directly acting industrial and laboratory chemicals

Groups of industrial and laboratory chemicals were tested for their alkylation activity using 4-(p-nitrobenzyl)-pyridine and deoxyguanosine as nucleophiles. The alkylation activity was compared with mutagenicity of the chemicals to E. coli WP2 uvrA without metabolic activation. All the epoxide-containing compounds including simple epoxides and glycidyl ethers elicited alkylation activity and mutagenicity. Furthermore there was a reasonable correlation between the rate of alkylation and the mutagenic potency. All the methylating and ethylating compounds tested were active but no correlation was observed between the rate of alkylation and the mutagenic potency, apparently due to the different types of alkylation products formed. The other compounds tested including halogenated hydrocarbons, hydrazine derivatives, aldehydes, thiuram and dithiocarbamate derivatives elicited a slow or no alkylation activity while many of the compounds were mutagenic. There was no evidence among the chemicals tested of an alkylating non-mutagen. Thus evidence of alkylation activity appears to indicate mutagenic risk.     

Red blood cells generate nitric oxide from directly acting, nitrogenous vasodilators

Human red blood cells (RBC) incubated under nitrogen with methylene blue and glucose at physiological temperature and pH can be used to test for the biotransformation of nitrogenous vasodilators to nitric oxide (NO). The NO generated was trapped as nitrosylated heme by reduced subunits (hemeII) on various hemoglobin valency species and quantified by electron paramagnetic resonance spectroscopy. It was possible to separate the various valency species of hemoglobin present in the mixture as (alpha 2 + beta 2)2, (alpha 2 + beta 3+)2, (alpha 3 + beta 2+)2, or (alpha 3 + beta 3+)2 by isoelectric focusing (IEF) unless cyanide (from nitroprusside) or azide was present in the mixture. These anions bind tenaciously to oxidized subunits (hemeIII) and prevent the separation of the various species by IEF. The fully oxidized tetramer, (alpha 3 + beta 3+)2, does not bind NO, but the other three species have hemeII units which can be nitrosylated. In the absence of cyanide or azide the valency species could be separated by IEF, and it was possible to quantify the degree of nitrosylation on each individual species. The various agents tested (nitrite, glyceryl trinitrate, hydroxylamine, hydralazine, nitroprusside, and azide) produced different patterns of valency species and degrees of nitrosylation of hemeII. When hemeIII ligands were present or in cases of very low yields, it was still possible to quantify the total concentration of NO-hemeII in the mixture. Thus, the method could still be used to test for NO formation. All of the so-called NO vasodilators tested yielded detectable amounts of NO in the system.     

Tetrodotoxin secretion from the lined moon shell Natica lineata in response to external stimulation

The lined moon shell Natica lineata secretes tetrodotoxin (TTX) in response to an external stimulation such as removal from the seawater. The toxin released from the shellfish contained 14-361 mouse units of TTX per specimen. The shellfish did not secrete any further toxin when seawater removal was repeated over four times at about 1 hr intervals. All specimens recovered TTX secreting ability when they were kept in an aquarium for 5 days.     

(+)-AJ 76 and (+)-UH 232: Central stimulants acting as preferential dopamine autoreceptor antagonists

Summary The biochemical and behavioral effects of the putative dopamine autoreceptor antagonists cis-(+)-5-methoxy-1-methyl-2-(n-propylamino)tetralin, (+)-AJ 76 and cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin, (+)-UH 232, were evaluated in various in vivo models in rats. Both compounds produced a marked elevation in brain dopamine synthesis and turnover with only slight effects on the synthesis and turnover of serotonin (5-HT) and noradrenaline being noted. (+)-AJ 76 and (+)-UH 232 also failed to antagonize the decrease in cortical noradrenaline synthesis rate caused by the alpha₂ agonist clonidine. The apomorphine-induced decrease in dopamine synthesis rate in gamma-butyrolactone (GBL) treated animals was completely blocked by (+)-AJ 76 and (+)-UH 232 but not by d-amphetamine or methylphenidate. In activity experiments using habituated animals, (+)-AJ 76 and (+)-UH 232 produced locomotor stimulation and weak stereotypies and antagonized the sedative effects of low doses of apomorphine. Locomotor hyperactivity induced by apomorphine or the dopamine agonist DiPr-5,6-ADTN was antagonized by (+)-UH 232 and to a lesser degree by (+)-AJ 76. The locomotor hyperactivity produced by (+)-AJ 76, (+)-UH 232 and methylphenidate was completely prevented by reserpine pretreatment and partially blocked by the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (alpha-MT), whereas d-amphetamine-induced hyperactivity was only antagonized by alpha-MT pretreatment. It is concluded that (+)-AJ 76 and (+)-UH 232 produce behavioral stimulation via a preferential antagonism on central dopamine autoreceptors, an action different from that of all known stimulants including apomorphine, d-amphetamine and methylphenidate. (+)-AJ 76 and (+)-UH 232 possess but weak antagonistic effects on postsynaptic dopamine receptors and only the latter compound is able to induce sedation in rats.     

依他尼酸抑制胰腺外分泌

AIM: The effect of ethacrynic acid on pancreaticexocrine secretion function and potential mechanisms ofinterference with the secreory process in pancreatic acinarcells were investigated. METHODS: After incubationwith ethacrynic acid for 30 min, caerulein-stimulatedamylase release and cholecystokinin (CCK) receptorbinding characteristics were assessed in isolated ratpancreatic acini. The level of thiol groups (glutathioneand protein thiols) and cytosolic free calcium weremeasured in pancreatic acinar cells. RESULTS:Ethacynic acid decreased caerulein (0. 1 nmol/L)-stimulated amylase release and the level of pancreaticacinar glutathione in a concentration-dependent fashionwithout a marked increase in cell damage. Ethacrynicacid also inhibited the caerulein (1 nmol/L)-inducedCa~(2 ) mobilization in pancreatic acinar cells. But neitherprotein thiol nor CCK-receptor binding characteristics wasaltered by ethacrynic acid. CONCLUSION: Ethacrynicacid inhibit pancreatic exocrine secretion by depletion ofglutathion     

Protein kinase C and intestinal fluid secretion: involvement of prostaglandin E2 but not of 5-hydroxytryptamine

To determine the role of protein kinase C in the regulation of intestinal fluid transport, experiments were performed with the rat jejunum in vivo, using the active phorbol ester, 4-beta-phorbol 12-myristate 13-acetate (PMA), as stimulator of protein kinase C. Intraluminally administered PMA dose dependently reversed the net fluid absorption to net fluid secretion and significantly increased prostaglandin E2 (PGE2) but not 5-hydroxytryptamine (5-HT) output into the lumen. Mucosal cyclic AMP levels remained unchanged by PMA. Indomethacin inhibited the increase in PGE2 output and partially reduced the secretory response to PMA. Ketanserin was without effect whereas verapamil totally blocked the secretory response to PMA. It is concluded that intestinal fluid secretion, stimulated by activation of protein kinase C is partly mediated by PGE2 release. PGE2 may facilitate calcium entry rather than increase intracellular calcium through activation of cyclic AMP. Protein kinase C appears to play an important role as an intermediate in phosphoinositol hydrolysis, which is initiated by 5-HT, and finally induces fluid secretion via PGE2.