Different mechanisms are responsible for the contractile effects of histaminergic compounds on isolated intestinal smooth muscle cells

The effects of histamine and dimaprit on intestinal smooth muscle contractility were investigated on isolated cells from longitudinal muscle of the guinea pig ileum. Both histamine (10⁻¹⁴–10⁻¹⁰ M) and dimaprit (10⁻¹³–10⁻¹⁰ M) exerted a concentration-dependent contraction of intestinal cells, causing a maximum decrease in cell length of about 20%. This effect was not significantly different from that induced by cholecystokinin-octapeptide (CCK-8) 10⁻⁹ M. The concentration-response curves to histamine and dimaprit were shifted to the left in the presence of the histamine H₂-receptor antagonist famotidine (10⁻⁷ M) indicating the occurrence in the smooth muscle of H₂ receptors mediating relaxation. Whereas the contraction produced by histamine was competitively antagonized by the H₁ receptor antagonist mepyramine (10⁻⁸ M), neither mepyramine (10⁻⁷ M) nor temelastine (10⁻⁷ M) did modify the contractile effect of dimaprit. In contrast, atropine (10⁻⁸ M) significantly depressed the maximum response to dimaprit without affecting that exerted by histamine. These data indicate that histamine and dimaprit can modify intestinal contractility, by acting via different mechanisms; while the contractile action of histamine is related to H₁ receptor activation, that produced by dimaprit involves cholinergic pathways.     

Histamine H2-receptors in guinea pig peripheral airway smooth muscle.

The presence and function of histamine H₂-receptors in guinea pig lung was studied using lung strips as an in vitro model of peripheral airway smooth muscle. The lung strips were incubated in Krebs-Henseleit solution in the absence or presence of specific antagonists for 20 min prior to the addition of either histamine or dimaprit added in a half-log cumulative fashion. Changes in isometric tension were recorded. Histamine at low concentrations (10^?7?10^?6M) caused a slight relaxation which was potentiated by the histamine H₁-antagonist chlorpheniramine (10^?7 or 10^?6M) and abolished by the histamine H₂-antagonist metiamide (10^?4M). Higher concentrations of histamine produced a dose-related contraction which was antagonized competitively by chlorpheniramine or potentiated by metiamide. Dimaprit, a histamine H₂-agonist, produced only a relaxant response over the concentration range of 10^?7 ? 10^?3M. This relaxation was reduced by metiamide but not by the beta adrenergic antagonist propranolol. These results indicate the presence of both histamine H₂ and H₁-receptors in guinea pig peripheral airway smooth muscle which mediate the relaxant and contractile effects of histamine respectively.     

Histamine H3 receptors in the guinea pig ileum: evidence for a postjunctional location.

The effect of the selective histamine H3 receptor agonists (R)alpha-methylhistamine, (R)MHA and immepip (IMM) on intestinal smooth muscle contractility was investigated on isolated cells from the longitudinal muscle of the guinea pig ileum. (R)MHA (10(-13)-10(-8) M) and IMM (10(-13)-10(-8) M) did not significantly modify the basal length of intestinal cells; in contrast both agonists (10(-15)-10(-11) M) prevented the contraction produced by acetylcholine (10(-7) M). The (S)-isomer of alpha-methylhistamine, (S)MHA, was inactive both on basal contractility and on acetylcholine-induced contractions. The relaxant effect of (R)MHA was not modified by famotidine (10(-7) M), but totally prevented by the selective H3 receptor antagonist clobenpropit (10(-8) M), which per se did not modify either basal contractility or the contractile response to acetylcholine. These data indicate that inhibitory histamine H3 receptors are present on smooth muscle cells of the guinea pig ileum and can be activated by very low concentrations of selective agonists. It is not clear, however, whether they can have a functional importance in the regulation of intestinal contractility in an intact system.     

Accelerated communication H1 contractile and H2 relaxant receptors in canine gastric muscularis mucosae

Histamine had two effects on the contractility of canine gastric muscularis mucosae in vitro: relaxation at or below 10 μM and contraction at higher concentrations. Selective agonists and antagonists were used to test the possibility that these effects were mediated by different receptor subtypes. The H₁-selective agonist 2-pyridylethylamine (2-PEA) and the H₂-selective agonist dimaprit contracted and relaxed this muscle, respectively, while the H₃-selective agonist R-α-methylhistamine had no effect. The H₁- and H₂-selective antagonists mepyramine and ranitidine selectively blocked 2-PEA-mediated contractions and dimaprit-mediated relaxations, respectively. Agonist responses, were unaltered by tetrodotoxin, suggesting a site of action other than nerves. Our results indicate that canine gastric corpus muscularis mucosae possesses both contractile H₁ and relaxant H₂ receptors.     

Vasoactive intestinal polypeptide: increased tone, enhancement of acetylcholine release, and stimulation of adenylate cyclase in intestinal smooth muscle

Vasoactive intestinal polypeptide (VIP) was examined $\text{in vitro}$ for effects on tone and neuronal release mechanisms in intestinal smooth muscle since this is a site of high peptide concentration. VIP contracted the guinea pig ileum and rabbit jejunum in concentrations ranging from 10^?9 to 10^?7 M. Increased tone in the guinea pig ileum was partially antagonized by the anticholinergic agent, atropine (4.38 × 10^?6 M) suggesting that one component of the contractile response was due to the indirect release of acetylcholine. The H₁ receptor antagonist, pyrilamine, did not alter the increased tone produced by VIP indicating that histamine release did not contribute to the ileal contractile response and that VIP exerted a selective effect to enhance neuronal release of acetylcholine. The ability of VIP to modulate acetylcholine release was confirmed in field stimulated ileal preparations where VIP increased the force developed to endogenously released acetylcholine without altering the direct response to acetylcholine. In rabbit jejunum and ileal smooth muscle, VIP related cyclic AMP levels. However, inhibition of phosphodiesterase with papaverine did not potentiate either the VIP-induced ileal contraction or enhancement of the field stimulated response. This raises the possibility that increases in intestinal cyclic AMP may be involved more in VIP-induced alterations in ion transport or secretory phenomenon than in intestinal motility. These studies describing the ability of VIP to modulate acetylcholine release and to increase ileal tone are consistent with the proposed role of VIP in intestinal patholgies involving excessive mucous secretion and motility.     

Studies on histamine H2 receptors coupled to cardiac adenylate cyclase Effects of guanylnucleotides and structural requirements for agonist activity

In particular preparations from guinea-pig ventricle, histamine in the concentration range 10^?6–10^?3 M caused a 3–5-fold stimulation of adenylate cyclase activity which was dependent on the presence of GTP. The effects of fourteen analogs of histamine were examined on this cyclase preparation. Five of the compounds studied proved to be partial agonists relative to histamine while nine others had essentially the same intrinsic activity as histamine. The intrinsic activities of the partial agonists were increased by GppNHP to the extent that dimaprit, which was a partial agonist in the presence of GTP, became a full agonist in the presence of GppNHp. The relative potencies of the full agonists as activators of the cyclase were found to correlate with the relative potencies on physiologically defined H₂ receptor systems. Activation of the cyclase by histamine, as well as by several of the agonist analogs, including dimaprit and tolazoline, was completely blocked by the H₂ antagonist cimetidine, but was not affected by pharmacologically relevant concentrations of the H₁ antagonist mepyramine, the β-blocker alprenolol, or the α-blocker phentolamine. The results suggest that all the agonists studied probably interact with a common H₂ receptor site on the cardiac muscle cell leading to activation of adenylate cyclase. The accompanying increase in cyclic AMP is presumably responsible for the chronotropic and inotropic effects of histamine and related compounds on cardiac muscle.     

Functional role of M2 muscarinic receptors in the guinea pig ileum

Muscarinic agonists elicit contraction in the standard guinea pig ileum bioassay through activation of M3 muscarinic receptors that are also linked to phosphoinositide hydrolysis. Surprisingly, the most abundant muscarinic receptor in the ileum is the M2 which causes a specific inhibition of cyclic AMP accumulation elicited by the beta-adrenergic receptor. After most of the M3 receptors are inactivated, the ileum still retains high sensitivity to muscarinic agonists provided that the contractile responses are measured in the presence of histamine and forskolin, which together, have no effect on contraction. Under these conditions, the potencies of antagonists for blocking the contractile response are consistent with those expected for an M2 response. Moreover, the muscarinic contractile response measured in the presence of histamine and forskolin after inactivation of M3 receptors is pertussis toxin sensitive. In contrast, muscarinic contractions in the standard bioassay are pertussis toxin insensitive. These results demonstrate that the M2 muscarinic receptor can cause an indirect contraction of the guinea pig ileum by preventing the relaxing effect of agents that increase cAMP.     

Direct actions of prostaglandins E1, A1, and F2α on myocardial contraction

The inotropic and chronotropic actions of prostaglandin (PG) types PGE₁, PGA₁, and PGF_2α were studied in isolated guinea pig right and left atria, and papillary muscles; rabbit atria; and toad ventricular strips in order to more completely define the cardiac contractile properties of PG. All three prostaglandins, in muscle bath concentrations of 10μg/ml, exerted positive inotropic and chronotropic actions on guinea pig atrium. These contractile effects were persistent after removal of PG from the muscle bath and appeared to limit the relative response to a subsequent dose of PG. The inotropic action of PGE₁ was present over a wide range of bath calcium concentrations (1.1 to 4.4 mM/L). Beta adrenergic receptor blockade, histamine blockade, and pretreatment with reserpine failed to significantly affect the inotropic actions of PG. Norepinephrine and histamine produced more potent inotropic and chronotropic effects on guinea pig atria than did PG and these contractile effects did not exhibit persistence or tachyphylaxis. The prostaglandins did not significantly affect dose response curves for norepinephrine inotropic and chronotropic actions. The prostaglandins had no effect on the force or frequency of contraction in rabbit atria. PGE₁ exerted a positive inotropic effect on toad ventricular myocardium whereas PGA₁ had no effect and PGF_2α had a negative inotropic action.     

Inhibition of cyclooxygenase-2 and EP1 receptor antagonism reduces human colonic longitudinal muscle contractility in vitro

We investigated the contribution of cyclo-oxygenase enzyme inhibition and prostamide agonism on human colonic contractility in vitro. The effects of the non-specific COX inhibitor diclofenac were compared against selective COX-2 inhibition via nimesulide, the prostanoid EP₁ receptor antagonist SC19220 or the prostaglandin prodrug/prostamide receptor agonist bimatoprost, on potency of contraction to acetylcholine in human colonic circular and longitudinal muscle strips. Pre-treatment with either nimesulide (10^?5 M) or diclofenac (10^?6 M) caused a significant decrease in the potency of acetylcholine-evoked longitudinal muscle contraction, but did not inhibit acetylcholine-evoked circular muscle contraction. Pre-treatment with the EP₁ receptor antagonist SC19220 (10^?5 M) similarly decreased cholinergic potency in longitudinal muscle, without influence on circular muscle contraction. The prostamide agonist bimatoprost (10^?6 M) increased basal circular and longitudinal muscle tone, but did not alter cholinergic potency in either muscle layer. In conclusion, colonic longitudinal muscle contraction is augmented by COX-2 activity, most likely via PGE₂ acting at EP₁ receptors. While colonic contraction is tonically modulated by bimatoprost, it does not share the same functional properties attributed to other endogenous COX-2 metabolites on colonic contractile function.     

Effect of vanadate on cardiac contraction and adenylate cyclase.

Vanadate produces a positive inotropic effect on ventricular muscle from rat, rabbit, guinea pig and cat; a positive inotropic effect on the atria of rat and rabbit, but a negative inotropic effect on the atria of guinea pig and cat. The effects of vanadate are completely reversible and occur in a concentration range of 10^?5M to 10^?3M. In this same concentration range, vanadate also causes a marked activation of cardiac adenylate cyclase suggesting that the positive inotropic action might be due in part to an elevation of cyclic AMP levels. The effects of vanadate are not influenced by alprenolol, cimetidine, or mepyramine, indicating a lack of involvement of β-adrenergic or histamine H₂ and H₁ receptors.     

The effect of calcium antagonists on contractions of the sensitized and normal guinea pig ileum

The purpose of this study was to learn wether a number of Ca²⁺ antagonists were effective in reducing contractile response of the isolated ileum of the sensitized and normal guinea pig. Contractions of the normal ileum in response to LTD₄, acetylcholine, histamine, and potassium chloride were obtained before and after verapamil, diltiazen and papaverine. Ovalbumin-induced contractions of the ovalbumin-sensitized ileum were obtained in the presence of the three Ca²⁺ antagonists. In the normal ileum, all the Ca²⁺ antagonists were highly effective in diminishing the contractile responses to LTD₄, acetylcholine, histamine and potassium chloride. In the sensitized ileum, ovalbumin-evoked contractions, with subsequent release of a potent contractile mediator (presumably SRS-A), were Ca²⁺-dependent since verapamil, diltiazem and papaverine caused a concentration-related reduction of contractions. Thus, the influx of extracellular Ca²⁺ plays a key role in the contractile responses of the normal and sensitized guinea pig ileum when stimulated by various potent agonists acting on specific receptors or on the cell membrane.     

Biological activities of a chemically synthesized form of leukotriene E4

A chemically synthesized form of leukotriene E₄ (LTE₄) has been studied for its ability to induce contractions in isolated guinea pig ilea, to induce vascular permeability changes in rat skin when injected intradermally, and to induce bronchoconstriction in guinea pigs after intravenous injection. The synthetic compound induced a contraction in the guinea pig ileum which was slower in developing than that induced by histamine but faster in developing than that induced by a crude preparation of SRS-A isolated from guinea pig lung. The compound was 70-fold more active than histamine on the guinea pig ileum (EC₅₀ of 5 × 10^?9 and 3.5 × 10^?7 M, respectively). FPL 55712, a known SRS-A antagonist, exhibited the same potency in blocking the contractions elicited by the synthetic material as it did in blocking contractions produced by guinea pig SRS-A generated biologically (IC₅₀ of 3.5 × 10^?8 M). The synthetic LTE₄ induced a dose dependent increase in vascular permeability in the rat skin which was antagonized by the intravenous injection of FPL 55712 (ID₅₀ of 1.2 mg/kg). The synthetic material was also a potent bronchoconstrictor in the guinea pig when injected intravenously. The bronchoconstriction, too, was antagonized by FPL 55712 when injected intravenously (ID₅₀ of 0.2 mg/kg). In both the rat and guinea pig, FPL 55712 exhibited a short duration of action $\text{in vivo}$. The $\text{in vivo}$ model systems discussed in this study, utilizing the synthetic form of LTE₄ should be useful in the future evaluation of other SRS-A antagonists.     

Histaminergic effect of crude papaya latex on isolated guinea pig ileal strips.

In the present study, we investigated the effect of the crude latex of Carica papaya L. (CPX) on isolated guinea pig ileal strips. CPX (0.5-512 microg/ml) caused concentration-dependent contraction of ileal strips suspended in Tyrode solution. The concentration of atropine (0.69 microM) that significantly blocked the contractile effect of acetylcholine on the isolated guinea pig ileum showed no significant effect on CPX- and histamine-induced contractions of the ileal strips. Mepyramine (87.6 nM) significantly blocked the contractile effect of histamine and CPX on the ileum. The same concentration of mepyramine, however, had no significant effect on acetylcholine-induced contraction of the isolated ileal strips. Removal of Ca2+ from the bathing medium abolished ileal contractions induced by acetylcholine, histamine and CPX. All the test substances were able to provoke ileal contractions after replacement of the Ca(2+)-free solution with Tyrode solution. Furthermore, 10(-5) M of nifedipine, a Ca(2+)-entry antagonist, reversibly inhibited the contractile effect of all the test substances on the ileal strips. Results of this study together appear to show that CPX-induced contraction of the isolated guinea pig ileum is mediated via H1-receptors and dependent on extracellular Ca2+ influx.     

Isolation and characterization of smooth muscle cell membranes

A method for the isolation of guinea pig ileum smooth muscle cell membranes is described. The plasma membrane fraction possessed a (Na⁺, K⁺)-ATPase which was inhibitied by ouabain. The Mg²⁺-dependent ATPase of the membrane fraction was stimulated by 1 μM Ca²⁺. A basal ATPase, not dependent on Mg²⁺, was directly stimulated by Ca²⁺ in the range of 1 μM to 1 mM.The isolated membranes contracted in response to the following substances: ATP, angiotensin II and some of its analogs, bradykinin, acetylcholine and histamine. The contractility was inhibited by ouabain and chlorambucil-angiotensin II, but not by cytochalasin B. No contraction was produced by AMP, angiotensin I and adrenaline.     

PAF antagonists: different effects on platelets, neutrophils, guinea pig ileum and PAF-induced vasolidation in isolated rat lung

The effects of structurally different PAF receptor blockers were investigated in platelets, neutrophils, guinea pig ileum, rat isolated lung and rat isolated pulmonary artery. PAF caused serotonin release from platelets and a characteristic shape change and adhesion of neutrophils. The antagonists (CV 3988, alprazolam, 48740 RP and Merck-Sharp and Dohme L-652, 731) inhibited platelet serotonin release but not neutrophil shape change adhesion or lysosomal enzyme release. The antagonists in high concentrations (10⁻⁵ −10⁻⁴M) inhibited nonspecifically the PAF-induced (10⁻⁸M) guinea pig ileum contraction, but were ineffective at concentrations which inhibited platelet responses. In the rat lung the compounds, in high concentrations, partially inhibited the low dose PAF-induced pulmonary vasodilation and the high dose PAF induced pulmonary vasoconstriction and edema. Our data indicate that some platelet PAF antagonists may be ineffective in blocking the action of PAF on neutrophils and smooth muscle preparations and suggest either PAF-receptor independent actions of PAF or different classes of PAF receptors.     

Mechanism of spasmolytic activity of a fraction of Sarcostemma brevistigma Wight

The effect of chloroform soluble fraction (F-A) of twigs of Sarcostemma brevistigma on contractions induced by KCl, histamine, and acetylcholine in the isolated guinea pig ileum and taenia coli smooth muscles has been evaluated. F-A (19.5 microg/ml) significantly inhibited the contraction induced by 40 mM KCl to the extent of 87.6% in the isolated guinea pig ileum. In the isolated guinea pig ileum, F-A (64.3 and 59.2 microg/ml) significantly inhibited the contractions induced by acetylcholine and histamine to the extent of 85 and 83% respectively. In the isolated guinea pig taenia coli, F-A (65.2 microg/ml) significantly inhibited the contraction induced by 40 mM KCl to the extent of 96.0%. The inhibitory effect of F-A (40 microg/ml) on the isolated guinea pig taenia coli was reduced by Bay K 8644 (10(-6) M) to the extent of 61.6 from 73.6%. These results suggest that the F-A may exhibit smooth muscle relaxant activity by blocking the Ca2+ channels.     

Bornchoconstriction induced by N-formyl-methionyl-leucyl-phenylalanine in t he guinea pig; involvement of arachidonic acid metabolites

The chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (F-met-leu-phe) was shown to be a potent myotropic agent on the guinea-pig parenchymal strip (IC₅₀), 2 × 10⁻⁷ M). The response was unaffected by the histamine (H₁) antagonist, mepyramine, but in the presence of the cyclooxygenease inhibitor, indomethacin, the dose response curve was shifted to the left (IC₅, 4 × qo⁻⁸ M) and the maximal response reduced. Injection of F-met-leu-phe into perfused guinea pig lungs resulted in the release of leukotriene-like activity which was detected by superfusion over guinea-pig ileum preparations in the presence and absence of FPL-55712. Intravenous injection of F-met-leu-phe to spontaneously breathing anaesthetized guinea pigs resulted in transient increases in pulmonary resistance and blood pressure and decreases in dynamic compliance and heart rate. The pulmonary parameters were significantly inhibited by BW 755C, indomethacin, FPL-55712 and a contractile prostanoid antagonist, L-640,305. These results demonstrate that F-met-leu-phe is potent bronchoconstrictor in the guinea pig and that the peptide may induce these changes through the generation of products of the cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism.     

Accelerated communication the direct contractile effect of gastrin releasing peptide on isolated gastric smooth muscle cells of the guinea pig

Smooth muscle cells isolated from the gastric muscle layers of the guinea pig were used to determine whether gastrin releasing peptide (GRP) can cause contraction by exerting a direct action on muscle cells. In addition, the inhibitory effect of 8-( N,N-diethylamino )-octyl-3,4,5-trimethoxybenzoate hydrochloride ( TMB-8 ), an inhibitor of intracellular Ca²⁺ release, and verapamil, a Ca²⁺ channel blocker, on the GRP-induced contraction of gastric smooth muscle cells were examined. GRP elicited a contractile response of gastric muscle cells in a dose-dependent manner. The ED₅₀ was 13 pM. TMB-8 significantly inhibited the contractile effect of GRP in gastric muscle cells. These results demonstrate the direct action of GRP on the gastric smooth muscle cells of the guinea pig, and the importance of Ca²⁺-release from intracellular calcium stores in the contractile response to GRP.     

Isolation, partial purification and pharmacodynamics of a slow contractile substance in the venom sac extract of the wasp Vespa cincta Fabr

The venom of V. cincta contains acetylcholine (ACh), histamine and 5-hydroxytryptamine (5-HT). Blockers of these agonists did not block completely the hypotensive and smooth muscle contractile activity of venom. On smooth muscle, there was a residual slow contraction. The active substance which produced this slow contraction was separated by solvent extraction, gel filtration and TLC. The purified material (which has been provisionally designated "Vecikinin") lowered cat, rat and guinea pig blood pressure, increased amplitude of cardiac contraction, and increased capillary permeability. Vecikinin contracted several smooth muscle preparations (rat uterus, rat ascending colon, guinea pig ileum, guinea pig colon and rat ileum), while relaxing rat duodenum. Its contractile activity was not lost on boiling, but acid or alkali-boiling reduced its contractile activity. It was inactivated on incubation with chymotrypsin and carboxypeptidase but not with trypsin, pepsin or leucine aminopeptidase. It is a peptide, appears to be of low molecular weight, and could be distinguished from substance P, angiotensin, bradykinin and hornet or wasp kinin.