The pharmacological actions of nicotine on the gastrointestinal tract

Increasing use of tobacco and its related health problems are a great concern in the world. Recent epidemiological findings have demonstrated the positive association between cigarette smoking and several gastrointestinal (GI) diseases, including peptic ulcer and cancers. Interestingly, smoking also modifies the disease course of ulcerative colitis (UC). Nicotine, a major component of cigarette smoke, seems to mediate some of the actions of cigarette smoking on the pathogenesis of GI disorders. Nicotine worsens the detrimental effects of aggressive factors and attenuates the protective actions of defensive factors in the processes of development and repair of gastric ulceration. Nicotine also takes part in the initiation and promotion of carcinogenesis in the GI tract. In this regard, nicotine and its metabolites are found to be mutagenic and have the ability to modulate cell proliferation, apoptosis, and angiogenesis during tumoriogenesis through specific receptors and signalling pathways. However, to elucidate this complex pathogenic mechanism, further study at the molecular level is warranted. In contrast, findings of clinical trials give promising results on the use of nicotine as an adjuvant therapy for UC. The beneficial effect of nicotine on UC seems to be mediated through multiple mechanisms. More clinical studies are needed to establish the therapeutic value of nicotine in this disease.     

The inhibitory actions of prostaglandins on respiratory smooth muscle

Prostaglandin E₁, in concentrations as low as 1 ng/ml., relaxed isolated tracheal muscle from cat, monkey, rabbit, guinea-pig and ferret. Tracheal muscle from the cat, monkey and rabbit did not exhibit inherent tone and the effect of prostaglandin E₁ on these preparations was seen only after a sustained contraction had been produced by a previous dose of acetylcholine or of another agonist. Prostaglandins E₂, E₃ and F_1α also relaxed isolated cat tracheal muscle which had been stimulated by acetylcholine: their activities relative to that of prostaglandin E₁ were, respectively, 1.0, 0.2 and 0.002. In the anaesthetized cat prostaglandin E₁ increased lung “resistance to inflation” (presumably comparable to bronchial resistance) and the heart rate. In the anaesthetized rabbit and guinea-pig, prostaglandin E₁ antagonized the rise in resistance to inflation of the lungs obtained after vagal stimulation or after the intravenous injection of histamine; it sometimes lowered the resistance to inflation in these species. The possibility that prostaglandin may have a local physiological role in the control of bronchial smooth muscle tone is discussed.     

Responses of guinea-pig gastric, ileal and gall bladder smooth muscle to desamino-cholecystokinin-octapeptide (CCK 7)

Cholecystokinin 7 (CCK 7), a synthetic analogue of cholecystokinin/pancreozymin (CCK 33), increased in a dose-dependent manner the tone of the guinea-pig ileal, gastric and gall bladder smooth muscle preparations. In all these preparations CCK 7 was more potent than CCK 8 and CCK 33 and all three cholecystokinins were more potent than acetylcholine (ACH). Atropine and tetrodotoxin (TTX) did not influence the CCK 7 action in fundus and gall bladder muscle strips but reduced non-competitively its effect in ileal muscle strips. Neither GE 410 nor dbcGMP affected the ACH and histamine (His) response of the muscle strips but both antagonists shifted the dose-response curve of CCK 7 to the right, GE 410 (cholecystokinin antagonist) being a much more potent antagonist of CCK 7 as compared to dbcGMP. In all muscle strips a competitive action on the CCK 7 responses was found for GE 410. In gastric muscle strips a competitive influence on the CCK 7 responses was found for dbcGMP at low concentration (1 x 10(-5)M) and a non-competitive influence at high concentration (5 x 10(-4)M). The results suggest that the contractile effects of CCK 7 in the isolated ileal smooth muscle are realized by cholinergic and direct myogenic mechanisms, whereas in the isolated gall bladder and gastric smooth muscles, by a direct myogenic mechanism only.     

Relaxant actions of khellin on vascular smooth muscle

To clarify the mechanism of the vasodilatory action of khellin on calcium, we have investigated its relaxant action on base line and on K+ and noradrenaline-induced contractile tensions in rat aorta smooth muscle and on spontaneous contractile activity of rat portal vein. Khellin relaxed both of these preparations with a similar potency, which suggests a non-specific inhibition of calcium flux, without any difference related to the specific calcium channels. We have also studied the capacity of khellin to interfere with the loading and release mechanisms of caffeine and noradrenaline-sensitive calcium stores in Ca-free medium. Khellin's Ca2+ loading reduction may be related with its capacity to inhibit calcium influx. Khellin applied during Ca2+ release also caused relaxation. We propose that this drug may enhance calcium extrusion or sequestration rather than the calcium release mechanism. These actions on calcium influx and intracellular mobilization can contribute to its vasorelaxant action.     

Pharmacological actions of eledoisin on extravascular smooth muscle

Some general effects and the action of eledoisin on a number of isolated smooth muscle preparations have been studied. It has been found that eledoisin possesses a potent stimulating action on all preparations of gastro-intestinal smooth muscle examined and also on the bronchial muscle of the guinea-pig in situ. Preparations of other smooth muscles were less sensitive. The rabbit colon, the guinea-pig ileum and, subordinately, the rabbit uterus and the frog stomach may be profitably used, owing to their sensitivity and the satisfactory dose/response relationship, for the quantitative bioassay of eledoisin in crude or pure preparations of the polypeptide. In parallel assays eledoisin could be easily distinguished from the biogenic amines and from all other known naturally occurring hypotensive polypeptides (bradykinins, wasp kinin, bradykinin-like polypeptides of the amphibian skin, physalaemin, substance P). In the unanaesthetized dog, subcutaneous doses of 25 to 100 μg/kg eledoisin caused a powerful stimulation of the motility and some secretions of the alimentary canal. This effect was much less pronounced in the rat and the rabbit.     

Stimulant actions of volatile anaesthetics on smooth muscle

A number of volatile anaesthetics, and some compounds synthesized in the search for new anaesthetics, have been tested on guinea-pig intestinal smooth muscle in vitro. All the compounds produced a contractile response. This effect did not correlate well with convulsant activity in vivo among the compounds tested. Two kinds of stimulant effect were distinguishable: (1) Rapid, transient contractions, abolished by cocaine or lachesine; most of the anaesthetics in clinical use had this action. (2) Slow, sustained contractions, unaffected by cocaine or lachesine; this effect predominated among the fluorinated ring compounds. Hexamethonium and mepyramine did not affect the contractile response to any of the compounds. The first type of effect presumably represents excitation of postganglionic nerve cells, while the second type is a direct action on the muscle cell. The action of perfluorobenzene, which is of the latter kind, was studied further. Adrenaline and lack of calcium diminished the contraction in parallel with the contraction to histamine, which suggests that the cell membrane was the site of action; in contrast to the stimulant action of histamine or acetylcholine, the effect was highly temperature-sensitive, being almost abolished by cooling to 32° C, and enhanced at 40° C. The depressant action of anaesthetics on smooth muscle is affected very little by temperature changes. These findings are discussed in relation to other observations which suggest a stimulant action of volatile anaesthetics on excitable tissues. Protein denaturation is tentatively suggested as a mechanism of action.     

The actions of caerulein on gastric secretion of the dog and the rat

1. Caerulein, as expected from its amino-acid composition and sequence, has a potent stimulant action on gastric secretion in the dog, the rat and the frog.2. In the denervated fundic pouch of the dog, caerulein increases the rate of flow of gastric juice and the outputs of acid and pepsin. Acid concentration and pepsin concentration in caerulein-produced juice are generally greater than in control juice. The threshold subcutaneous dose of caerulein is 0.15-0.5 mug/kg and the threshold rate of intravenous infusion 0.25-0.5 mug/kg per hr. Rapid intravenous injection is ineffective. On a molar basis, caerulein is approximately twice as active as human gastrin I on volume and acid output of the gastric pouch and 4 times as active on pepsin output.3. Sustained acid secretion of the fundic pouch produced by histamine infusion is inhibited by caerulein, administered either intravenously or subcutaneously. In turn, acid secretion elicited by caerulein is inhibited by atropine.4. In the rat, the activity ratio of caerulein to human gastrin I is 7-30, calculated on a molar basis, and is thus considerably greater than in the dog. Further, caerulein is 3 times more active than cholecystokinin-pancreozymin. Tested on the perfused stomach preparation of the rat, the threshold dose of caerulein by rapid intravenous injection is 25 ng/kg, by intravenous infusion 0.25 mug/kg per hr, and by subcutaneous injection 0.25 to 0.5 mug/kg.5. The activity of caerulein is sharply reduced by pretreatment of the rats with the histamine liberator 48/80 and potentiated by pretreatment with the diamine oxidase inhibitor aminoguanidine. When caerulein is given by rapid intravenous injection during a priming infusion of histamine its effect is enhanced and considerably prolonged.6. The isolated mucosa of the frog stomach is extremely sensitive to caerulein which, in a concentration of a few pg/ml., stimulates active transport of chloride.7. Qualitative and quantitative differences in the action of gastrin and caerulein are pointed out, and particular emphasis is laid on the importance of esterification of the tyrosyl residue for the biological activity of caerulein.     

Direct and indirect actions of dopamine on tracheal smooth muscle

Summary The effects of dopamine (DA) were studied on guinea-pig isolated tracheal chains. At a low concentration (10^–6M) DA occasionally produced a small contraction; this was followed by a dose-dependent relaxation 3×10^–6–3×10^–3 M).On a molar basis, DA was about 40 times less potent than noradrenaline (NA) in relaxing tracheal chains, and about 2700 times less potent than isoprenaline (ISO). The maximum degree of relaxation obtained with each drug was the same.Pretreatment of the guinea-pig with reserpine (5 mg/kg) resulted in a 3-fold shift of the DA curve to the right without concomitantly affecting the ISO doseresponse curve. Reserpine completely abolished the relaxant effects of tyramine, but a small contractile response remained.Desipramine (DMI), at a concentration of 10^–5 M, caused a 4-fold shift of the DA curve to th right. The same concentration of DMI resulted in a shift to the left of the NA dose-response curve by about 8-fold. Benztropine (10^–5 M) and haloperidol (10^–5 M and 3×10^–5 M) did not affect the DA dose-response curve.The DA-induced relaxation was inhibited by propranolol (10^–8–10^–6 M) in a dose-dependent manner. The higher concentrations of propranolol (10^–7 and 10^–6 M) unmasked the contractile effect of DA. In the presence of propranolol, phentolamine (10^–5 M) abolished the contractile effect of DA.It is concluded that DA has both direct and indirect actions on guinea-pig isolated tracheal smooth muscle. The relaxant effects of DA are predominantly due to a direct action on smooth muscle -adrenoceptors, with a component due to release of NA from adrenergic nerves. The contractile effects, which under normal conditions are masked by the relaxant effect of DA, are mediated by functional -adrenoceptors. There is no evidence for either specific dopaminergic nerves, uptake mechanisms or receptors in guinea-pig trachealis muscle.     

Potassium channels in gastrointestinal smooth muscle

1. Electromechanical coupling in smooth muscle serves to coordinate the contractile activity of the syncytium. Electrical activity of smooth muscle of the gut is generated by ionic conductances that regulate and in turn are regulated by the membrane potential of smooth muscle cells. This activity determines the extent of Ca2+ entry into smooth muscle cells, and thus, the timing and intensity of contractions. 2. Potassium channels play an important role in regulating the excitability of the syncytium. The different types of K+ channel are characterized by different sensitivities to membrane potential, to intracellular Ca2+ levels and to modulation by agonists. 3. This review highlights the different types of K+ channels found in gut smooth muscle and describes their possible roles in regulating the electrical activity of the muscle.     

The effect of cromakalim on the smooth muscle of the guinea-pig urinary bladder.

1. The actions of cromakalim were studied on the detrusor muscle from guinea-pig urinary bladder. Cromakalim reduced the frequency and amplitude of spontaneous contractile activity of the smooth muscle of the guinea-pig urinary bladder at 5 x 10(-8)M and abolished the activity at concentrations above 5 x 10(-7)M. 2. Electrophysiological experiments demonstrated that cromakalim increased membrane conductance, caused a dose-dependent hyperpolarization of the cell membrane and loss of spike activity. These events are consistent with the opening of K+ channels. 3. The effects of 10(-6)M and 10(-5)M cromakalim on the contractile responses to carbachol, potassium and transmural nerve stimulation were studied. Cromakalim did not prevent the detrusor from responding to these agents, although it significantly reduced the contractile response to K+ at concentrations below 70 mM. 4. Uptake and efflux experiments using 86Rb+ were unable to demonstrate any significant effect on transmembrane movement produced by cromakalim (10(-5)M). 5. 43K+ efflux showed a dose-dependent increase in the rate constant on addition of cromakalim. The difference in the selectivity for K+ over Rb+ was confirmed in dual label uptake experiments. 6. Substitution experiments in which the K+ ions in the tissue were gradually replaced by Rb+ demonstrated that cromakalim had a progressively decreasing effect on spontaneous activity as internal K+ was lowered. When all the K+ was replaced by Rb+, cromakalim no longer inhibited spontaneous activity, confirming that the channel opened by cromakalim appears relatively impermeant to Rb+.     

Mode of action of cholecystokinin octapeptide on smooth muscles of stomach, ileum and gall bladder

Mechanical activity of preparations isolated from canine and guinea-pig stomach, ileum and gall bladder was recorded. At least 2 strips were cut out from each organ and investigated simultaneously in thermostatically controlled organ baths. Responses to acetylcholine (ACH) were used for comparison. Octapeptide of cholecystokinin (CCK-OP) at concentrations of 5 X 10(-11) M to 10(-8) M produced dose-dependent tonic concentrations in all muscle strips and showed a higher affinity but lower efficacy as compared to ACH. Atropine (10(-7) M 10(-5) M) had no effect on the CCK-OP responses in stomach and gall bladder muscle strips but it significantly decreased the CCK-OP responses in ileum muscle strips. Dibutyryl cyclic GMP (dbc GMP) at concentrations of 10(-5) M-5 X 10(-4) M did not change the ACH dose-response curves but shifted to the right in parallel to the control the dose-response curves for CCK-OP in all muscle preparations with pA2 values 5, 5.3, 7.2, and 6 for canine stomach and guinea-pig stomach, ileum and gall bladder, respectively. Michaelis-Menten's analysis suggested a competitive type of interaction of dbc GMP on CCK-OP contractile responses of guinea-pig ileum and gall bladder; at a higher concentration (5 X 10(-4) M) the antagonistic effect of dbc GMP in canine and guinea-pig stomach appeared to be a mixed or uncompetitive type. The data suggest that the contractile effects of CCK-OP in the iliac smooth muscle are caused by cholinergic and direct mechanisms whereas on the gall bladder and gastric smooth muscles by direct myogenic mechanisms only.     

葛根素对腹泻型肠易激综合征肠道平滑肌神经递质调节机制的影响研究

目的　观察葛根素对腹泻型肠易激综合征（IBS-D）大鼠的治疗作用并探讨其对肠道平滑肌的神经调节机制。方法　2021年11月至2022年5月将24只SPF级4周龄雄性SD大鼠随机分为对照组,模型组,葛根素低、高剂量组。采用慢性束缚应激诱导建立IBS-D模型。造模完成后葛根素低、高剂量灌胃给药,剂量分别为22、44 mg/（kg·d）,每日1次,持续14 d;对照组与模型组以等量生理盐水灌胃,持续14 d。定期测定各组大鼠内脏敏感性、排便情况,采用苏木精-伊红（HE）染色法观察大鼠结肠组织病理改变,末次给药后测定结肠匀浆乙酰胆碱（Ach）、一氧化氮（NO）、五羟色胺（5-HT）的含量。统计学方法采用独立样本t检验。结果　光学显微镜观察示模型组大鼠无明显病理改变,符合IBS-D定义与组织学表现。与对照组比较,模型组大鼠腹壁回缩反射评分显著升高,第21、28天排便面积均显著增加,结肠组织Ach、5-HT表达均显著升高,NO表达显著降低,差异均有统计学意义（均P<0.05）。各项数据变化均符合IBS-D模型相关改变。与模型组比较,葛根素低、高剂量组的腹壁回缩反射评分均显著降低［（0.48±0.06）分、（0.54±0.06）分比（0.84±0.03）分］,差异均有统计学意义（均P<0.05）;与模型组比较,葛根素低、高剂量均使第21、28天排便面积显著减少（均P<0.05）;模型组的Ach、5-HT表达为（3.67±0.87）μg/mgprot、（131.97±16.64）μg/L,葛根素低剂量组的Ach、5-HT表达为（2.65±0.87）μg/mgprot、（115.01±12.07）μg/L、葛根素高剂量组的Ach、5-HT表达为（2.26±1.05）μg/mgprot、（109.01±6.59）μg/L,葛根素低、高剂量组的Ach、5-HT表达均显著降低（均P<0.05）;模型组NO表达为（9.61±1.50）μg/mgprot、葛根素低剂量组NO表达为（16.32±4.15）μg/mgprot、葛根素高剂量组NO表达为（9.34±5.80）μg/mgprot（P<0.05）。结论　葛根素对慢性束缚应激诱导的IBS-D大鼠模型具有一定的治疗作用,其作用机制或与上调结肠NO表达水平,下调结肠Ach、5-HT表达水平有关。     

Interactions of caerulein and morphine on gastrointestinal propulsion in the mouse

Summary The effects of subcutaneously administered caerulein (ceruletide) and morphine hydrochloride on gastric emptying and gastrointestinal propulsion were studied in male mice. Drug effects were evaluated by the movement of Indian ink administered directly into the stomach after drug injection. Morphine inhibited both gastrointestinal propulsion (ED₅₀=2.1 mol/kg) and gastric emptying (ED₅₀=43 mol/kg). Caerulein enhanced gastrointestinal propulsion (ED₅₀=0.93 nmol/kg) but inhibited gastric emptying (ED₅₀=17 nmol/kg). Inhibition of gastric emptying was further potentiated by the combined administration of caerulein and morphine. Naloxone reversed both effects of morphine but not those of caerulein. Morphine antagonized the propulsion-enhancing effect of caerulein.     

Cytotoxic actions of palytoxin on aortic smooth muscle cells in culture

Palytoxin (PTX), isolated from a zoanthid of the genus Palythoa, is the most potent marine toxin known. Intoxication by PTX leads to vasoconstriction, hemorrhage, ataxia, muscle weakness, ventricular fibrillation, pulmonary hypertension, ischemia and death. In this study, clonal A7r5 rat aortic smooth muscle cells were used to study the mechanism of PTX-mediated cytotoxicity. A7r5 cells exposed to PTX for > or = 15 min exhibited surface granularities, vacuoles and rounding. These alterations culminated in a loss of viability as indicated by marked increases in the release of lactate dehydrogenase. Electrophysiological recording from A7r5 cells disclosed a profound membrane depolarization and an increase in conductance to Na+ and K+. PTX-mediated cytotoxicity could not be reversed by washout or by the addition of 10 microM verapamil but was antagonized by 100 microM ouabain or by removal of extracellular Na+ or Ca2+. In light of the involvement of vascular smooth muscle in PTX poisoning, A7r5 cells could serve as a useful model to test specific drugs for treatment of PTX intoxication.     

Relaxant actions of isoprenaline on guinea-pig isolated tracheal smooth muscle.

1. The effects of isoprenaline on membrane potential and intracellular Ca2+ concentration ([Ca2+]i) in guinea-pig isolated tracheal muscle were studied by use of intracellular micro-electrodes and fura-2 signals respectively. Measurements of membrane potential were carried out in the presence of spontaneously-generated muscle tone, whereas fura-2 signals were measured during contraction produced by exogenous prostaglandin E2 (100 nM). The potency of isoprenaline in causing relaxation was the same in these two different situations. 2. Isoprenaline (0.01 microM) produced relaxation accompanied by 5 mV hyperpolarization. A combination of tetraethylammonium (TEA, 10 mM) and verapamil (3 microM) did not alter the effects of isoprenaline. Removal of external K+ did not increase the degree of hyperpolarization produced by isoprenaline. 3. In the presence of TEA (10 mM) and verapamil (3 microM), isoprenaline (0.03-1 microM) reduced [Ca2+]i concentration-dependently. A similar degree of inhibition was observed when isoprenaline was applied during the maintained contraction induced by prostaglandin E2 and against the contraction evoked by the addition of Ca2+ to tissues bathed in a Ca(2+)-free medium and pretreated with both isoprenaline and prostaglandin E2. 4. It is concluded that activation of TEA-sensitive Ca(2+)-dependent K+ channels does not play a significant role in isoprenaline-induced relaxation. We propose that, in the guinea-pig tracheal muscle, isoprenaline may produce relaxation mainly by inhibiting a receptor-operated pathway for Ca2+ influx across the plasma membrane which is normally activated by prostaglandins.     

The actions of bradykinin and lys-bradykinin on tracheal blood flow and smooth muscle in anaesthetized sheep

The actions of bradykinin and the related compound lys-bradykinin have been studied on the tracheal circulation and tracheal smooth muscle of the sheep. Cranial tracheal arteries of ten anaesthetised and paralysed sheep were isolated and perfused at systemic arterial pressure; arterial inflow was measured with an electromagnetic flow probe. Tracheal smooth muscle tone was assessed by measuring the external diameter of the cranial trachea. Close arterial injection of bradykinin and lys-bradykinin (0.1 to 1000 pmoles) produced potent dose-dependent falls in tracheal vascular resistance: for bradykinin a maximum fall of −56.4% (52.3–60.5%, 95% confidence interval) and for lys-bradykinin −52.8% (46.5–59.1%). The ED50 values were 0.69 (0.51–1.32) and 1.46 (1.19–2.28) pmoles respectively. Small and inconsistent relaxation of tracheal smooth muscle was seen with the higher doses (> 1.9 pmoles) of both kinins. Intravenous indomethacin (5mg.kg⁻¹) increased the vasodilation produced by bradykinin and lys-bradykinin. Oxyhaemoglobin (4 μm at 0.35ml.min⁻¹) infused into the tracheal circulation almost abolished the responses to bradykinin and methacholine. The results indicate that in the sheep trachea bradykinin has little action on airway smooth muscle but is a potent dilator of the vasculature; bradykinin and lys-bradykinin are of similar potency suggesting the action may be via B₂ receptors. While the vascular responses may be modulated by vasoconstrictor cyclo-oxygenase products the vasodilation is likely to be endothelium-dependent and not prostanoid-mediated.