Rat Stomach Strip Research Articles

Role of intrinsic arachidonate metabolites in the vascular action of erythrocyte breakdown products.

In helically-cut strips of dog basilar and mesenteric arteries, the isometric tension developed by application of ghost-free hemolysate from dog erythrocytes was recorded. The hemolysate contracted basilar arteries in a concentration-dependent fashion, the response being attenuated by treatment with either aspirin or polyphloretin phosphate, a prostaglandin antagonist. Mesenteric arteries were contracted only slightly by high concentrations of hemolysate. When the mesenteric arteries had partially been contracted with prostaglandin F2 alpha or norepinephrine, the hemolysate induced relaxations, which were abolished by aspirin in approximately half the preparations used. Studies on rat stomach strips exposed to superfusate of dog cerebral arteries showed a release of prostaglandin-like substance by the hemolysate application. It may be concluded that the hemolysate contracts basilar arteries and relaxes mesenteric arteries, mainly through prostaglandins synthesized in and released from the vascular wall. Such a mechanism may be involved in the pathogenesis of cerebral vasospasm following a subarachnoid hemorrhage.

Extremely decreased release of prostaglandin E2-like activity from chopped lung of ethyl linolenate-supplemented rats.

Three groups of weanling male rats were reared on a fat-free diet for 13 weeks. One group received only the fat-free diet (FF rats), the other 2 groups received the fat-free diet and a daily supplement of 2 energy% ethyl linoleate ([n-6] rats), or 2 energy% ethyl linolenate ([n-3] rats). The chopped lung preparation was used to illustrate an in vitro prostaglandin formation. PGE2-like activity was quantified on rat stomach strip. The release of PGE2-like activity expressed as ng PGE2-equivalent per g lung tissue (mean +/- SD) was 23 +/- 7, less than 6, and 65 +/- 20 for the FF rats, the (n-3) rats, and the (n-6) rats, respectively. PGE2 quantification by radioimmunoassay of the chopped lung effluent collected after passing over the rat stomach strip revealed the same release pattern as the bioassay. Fractionation of chopped lung effluent on HPLC with radioimmunoassay detection indicated that the lung tissue from (n-3) rats released very little PGE3, if any, in spite of a 20:5(n-3)/20:4(n-6) ratio of 5.2 in the lipids of the lung. It is suggested that the pool of arachidonic acid for prostaglandin production in vitro is different from the one which functions in vivo, and the these pools are differently affected by dietary EFA.

The effect of some flavone drugs on the conversion of prostacyclin to 6-oxoprostaglandin E 1

Flavonoid drugs (rutin, naringenin and quercetin) were compared with indomethacin and sulphasalazine as inhibitors of rat and rabbit renal 9-hydroxyprostaglandin dehydrogenase, prostaglandin synthesis (bovine seminal vesicle microsomes) and inactivation (rabbit colon 100,000 g supernatant), vascular PGI 2 formation (rat aortic rings) and for effects on platelet aggregation and on the isolated rat stomach strip. Rutin and naringenin potently inhibited rabbit renal conversion of PGI 2 and PGF 2α to 6-oxoPGE 1 and PGE 2, respectively, but had no effect on rat renal 9-hydroxyprostaglandin dehydrogenase activity, prostaglandin breakdown, vascular PGI 2 synthesis, platelet aggregation or the antiaggregatory effect of PGI 2 and 6-oxoPGE 1. High concentrations (100 μM) of both drugs inhibited the spasmogenic effect of PGI 2on the rat stomach strip. Naringenin and quercetin (1 mM) inhibited whilst rutin (1 mM) stimulated microsomal prostaglandin synthesis. These results suggest that rutin and naringenin may be useful experimental tools to study the biological roles of 6-oxoPGE 1.

Potent vasoconstriction of the isolated perfused rat kidney by leukotrienes C4 and D4.

Chemically synthesized leukotriene C4, D4, and E4 have been compared for their effects on the isolated Krebs-perfused rat kidney, rat stomach strip, and guinea pig ileum. C4 was more potent than D4 or E4 at all concentrations tested in contracting the rat stomach strip and in constricting the isolated rat kidney, while D4 was more potent than C4 or E4 in contracting the guinea pig ileum. While the effect of leukotrienes on the isolated kidney was blocked dose dependantly by FPL 55712, a blocker of leukotriene action, it was not blocked by the presence of either indomethacin, a cyclooxygenase blocker, or OKY-1581, a blocker of thromboxane synthesis. These results indicate that leukotriene action in the kidney is of a direct nature and is not mediated via activation of the prostaglandin pathway, especially thromboxane A2 synthesis.

Autoradiographic distribution of [ 3H]neurotensin receptors in rat brain: Visualization by tritium-sensitive film

[ 3H]Neurotensin ([ 3H]NT) binds specifically to a single class of binding sites on slides-mounted sections of rat brain (K D=5.1 nM; B max=16.2 fmol/mg tissue). Bound [ 3H]NT can be displaced by nonradioactive NT and a series of its fragments and analogues with relative potencies that correlate closely (r=0.89; p<0.01) to their potencies in the rat stomach strip bioassay. These results suggest that NT receptors are similar in both systems. [ 3H]NT binding sites were visualized by using tritium-sensitive LKB film analysed by computerized densitometry. [ 3H]NT receptors are highly concentrated in the external layer of the olfactory bulb, in the rhinal sulcus, in certain nuclei of the amygdala, in the substantia nigra, zona compacta and in the ventral tegmental area. The high density of [ 3H]NT receptors in the last two areas suggest an interaction between NT and brain dopaminergic systems such as the nigrostriatal and the mesolimbic pathways.

Localization of neurotensin binding sites in rat kidney

[ 3H]Neurotensin ([ 3H]NT) appears to bind specifically to a single class of sites in slidemounted rat kidney sections (K D=8.3 nM; B max=31.6 fmol/mg tissue). Bound [ 3H]NT can be displaced by nonradioactive NT and a series of its fragments and analogues with relative potencies that correlate well (r=0.91; p<0.005) to their potencies in the rat stomach strip bioassay. These results suggest that NT receptors are similar in both systems. However, they are probably slightly different from those present in the guinea pig atria (r=0.78; p<0.1). We visualized these sites by using the tritium-sensitive LKB film technique analysed by computerized densitometry. [ 3H]NT binding sites are highly concentrated in the renal cortex while low levels are observed in the renal medulla. The possible physiological and/or pathophysiological significances of the presence of [ 3H]NT binding sites in the kidney are discussed.

Effect of various drugs and extrinsic denervation on the non-adrenergic inhibitory neurons in the rat stomach.

The effects of various drugs and extrinsic denervation on the non-adrenergic inhibitory nerves in the rat stomach were examined. Stimulation of the intramural nerves supplying the longitudinal smooth muscle strips taken from the rat stomach produced responses consisting initial contractions followed by relaxations in the presence of guanethidine in case of the tone of the preparation maintained with serotonin. After scopolamine treatment, transmural nerve stimulation (TMS) caused a relaxation or a relaxation followed by a transient after-contraction. All of these responses were abolished reversibly with tetrodotoxin. After cold storage of rat stomach strips for 5 d at 4 degrees C, the TMS-induced response was not observed, but noradrenaline still relaxed these strips. The TMS-induced relaxation reached a maximum amplitude at 2-5 Hz, and was entirely independent of alpha- and beta-blockers, or a combination of them. It was not affected by treatment of 6-hydroxydopamine and reserpine. These results strongly suggested that the relaxation was not myogenic, but neurogenic, and was not elicited by stimulation of adrenergic neurons. Strychnine and poly-L-lysine inhibited the relaxation elicited by TMS even in normal and transection-treated rats. Histochemical studies showed degenerative changes due to the dissection at the axons of a ganglion in the Auerbach's plexuses by transection. The effect of various drugs and extrinsic denervation on the response to TMS in relation to non-adrenergic inhibitory nerves in the rat stomach is discussed.

Evidence for the inactivation of neurotensin by guinea pig lungs

Intrajugular injections of low doses (46 – 370 ng kg −1) of neurotensin (NT) evoked dose-dependent pressor effects in pentobarbital-anesthetized guinea pigs. When injected intraarterially (i.a) (in the aorta) the same doses of NT produced much larger increases of arterial blood pressure than when given intravenously (i.v). Similar differences of potency were observed when the peptide was given by infusion (96 ng kg −1min −1). To explain these differences, we hypothesized that NT could be inactivated partially after one passage through the pulmonary circulation. To verify this hypothesis, known amounts (50 – 100 ng) of NT were injected via the pulmonary artery cannula into isolated guinea pig lungs perfused with Krebs' solution and the effluent superfused over rat stomach strips. The results clearly indicate that at least 50% of the biological activity of NT was removed by one single passage through the circulation of guinea-pig lungs. Studies with compound SQ 14225 also known as captopril, a potent angiotensin-converting enzyme inhibitor, showed that this compound neither interferes with the pulmonary inactivation of NT in guinea pig isolated lungs nor potentiates its pressor effect. These results suggest that the mecanism through which guinea pig lungs inactivate NT does not involve the enzyme which normally activates angiotensin I and inactivates bradykinin.

ChemInform Abstract: SYNTHESIS OF PEPTIDES BY THE SOLID‐PHASE METHOD. 6. NEUROTENSIN, FRAGMENTS, AND ANALOGS

AbstractNach der Festphasenmethode werden Neurotensin und 24 ähnliche Verbindungen dargestellt und durch Kationenaustauscher‐Chromatographie gereinigt.

Contractile characteristics of the rat stomach strip and the rabbit aorta and mesenteric artery

A comparison was made of the dose-response curves obtained in the measurement of the prostaglandin E- and thromboxane A 2-like activities using a cascade system consisting of a rabbit aorta strip and mesenteric artery and a rat fundus strip. The results indicate that the contractile properties of these tissues are different. In platelets during aggregation, the TxA 2-like activity was measured by bioassay; the amount of TxB 2 by a radioimmunological method.

Sensitization by (+) inpea of rat stomach strip contraction induced by PGE 2 or pleural exudates

The effects of (+) Inpea on the contractions of isolated rat stomach strip elicited by stimulating substances (synthetic PGE 2 and pleural exudates induced by carrageenin or by dextran) has been examined. (+) Inpea sensitized the rat isolated smooth muscle preparation to synthetic PGE 2 and also to pleural exudates induced by carrageenin. The sensitizing effect of (+) Inpea was specific since there was no increase in sensitivity toward exudates induced by dextran.

Importance of circulating angiotensin II for elevation of arterial pressure during acute hypercapnia in anaesthetized dogs.

SUMMARY1. In anaesthetized dogs acute hypercapnia produced by ventilation with 10% CO2 in air caused release of vasoactive substances and changes of arterial pressure. Catecholamines, angiotensin II, bradykinin and prostaglandin‐like substances were bioassayed continuously in arterial blood using the blood‐bathed organ technique of Vane.2. Acute hypercapnia in control dogs causes responses of rat stomach strip, chick rectum and rat colon indicating initial release of noradrenaline, followed by angiotensin II, and occasionally release of prostaglandin‐like substances into the circulation.3. The initial transient, pressor response to hypercapnia coincided with the appearance of noradrenaline, and the secondary progressive rise in arterial pressure was accompanied by increased circulating angiotensin II.4. In dogs treated with the angiotensin converting enzyme inhibitor SQ 20881 (1–2 mg/kg, i.v.), hypercapnia did not cause the secondary elevation of arterial pressure despite pronounced elevation of noradrenaline levels in the circulation. Increased arterial concentrations of bradykinin of less than 1 ng/ml, assayed by a strip of cat jejunum, were detected during hypercapnia in four out of six dogs treated with SQ 20881, but not in untreated dogs.5. Intravenous infusion of the angiotensin antagonist [Sar1‐Ile8]‐angiotensin II (0.5–1.0 μg/kg per min) attenuated the secondary pressor response to hypercapnia and abolished the contractions of rat colon produced by hypercapnia and angiotensin II.6. The results indicate that adrenergic stimulation may be responsible for the transient pressor response on induction of hypercapnia, but elevation of angiotensin II activity in the circulation is of major importance for mediating the secondary progressive rise in arterial pressure during the later stage of acute respiratory acidosis.7. After inhibition of angiotensin converting enzyme, hypercapnia reduces arterial pressure, not only because the vasoconstrictor effect of angiotensin has been removed, but also because inhibition of pulmonary kininase may allow vasodilator kinins to reach the arterial circulation.

The effect of cigarette smoke on the metabolism of arachidonic acid to myotropic compounds in rat and hamster isolated lungs

Perfusion effluent from isolated rat and hamster lungs caused a relaxation of superfused strip of bovine coronary artery (BCA). This relaxation was abolished by pulmonary infusion of indomethacin. Pre-exposure of rats and hamsters to cigarette smoke during half an hour before the lung perfusion did not change the degree of this initial relaxation of BCA. Injection of 10 μg of sodium arachidonate (AA) into the pulmonary circulation of isolated hamster lungs caused a contraction of BCA, which was not changed by cigarette smoke pre-exposure. When AA (10 μg) was injected into the pulmonary circulation of isolated hamster lungs during cigarette smoke ventilation the contractions of superfused BCA and rat stomach strip (RSS) were not significantly different from those during the preceding and following air ventilation. In experiments with isolated rat lungs the initial relaxation of superfused BCA was accompanied by a contraction of superfused RSS. AA injection (10 μg) into rat lungs caused a further relaxation of BCA and contraction of RSS, which were abolished by pulmonary infusion of indomethacin. Cigarette smoke ventilation of isolated rat lungs caused a relaxation of superfused BCA, which was not abolished by indomethacin. During cigarette smoke ventilation injection of AA (10 μg) into the pulmonary circulation of rat lungs caused a relaxation of BCA and a contraction of RSS. The present study indicates that neither cigarette smoke ventilation nor pre-exposure to cigarette smoke has a drastic effect on the metabolism of arachidonic acid to myotropic compounds in isolated hamster and rat lungs.

Synthesis of peptides by the solid-phase method. 6. Neurotensin, fragments, and analogues.

Neurotensin (NT) and 24 related compounds, including fragments or analogues modified at the C-terminal end of the parent molecule, have been prepared by the solid-phase method. After purification by cation-exchange chromatography, the compounds were characterized by thin-layer chromatography, amino acid analysis, elemental analysis, and high-pressure liquid chromatography. The stimulating effects of the peptides were evaluated in rat stomach strips, in isolated spontaneously beating atria of guinea pigs, and in the coronaries of perfused rat hearts. The differences between the biological activities of these compounds are discussed.

Prostacyclin (PGI 2) release accompanying angiotensin conversion in rat mesenteric vasculature

The relationship between angiotensin conversion and release of prostaglandins (PGs) was studies in isolated, perfused, mesenteric vasculature of rats. PGs in the mesenteric effluent were detected by bovine coronary artery and rat stomach strip, and by radioimmunoassay of 6-oxo-PGF 1α and PGE 2. Angiotensin II (AII) was assayed simultaneously using rabbit aorta. Both angiotensin I (AI) and AII released a prostacyclin (PGI 2)-like substance, but little PGE 2 from the mesentery, AII being 5 times more potent. Indomethacin (2.8 μM) abolished angiotensin-induced release of PGI 2. Of the AI (0.2–1.5 nmol) injected into the perfusion medium, 3–8% was converted to AII in passage through the mesentery. Captopril (4 μM), infused through the mesentery, inhibited AI-induced PGI 2 release, but did not affect release induced by AII. Release of the PGI 2-like substance by higher doses of AI (2–20 nmol) in the presence of captopril was always accompanied by concomitant contraction of rabbit aorta, indicating residual conversion of AI. Infusion of (Sar 1, Ala 8)AII (3–30 nM) through the mesentery abolished PGI 2 release by both peptides. By choosing doses of AI and AII which produced equivalent amounts of AII in the mesenteric effluent, it appeared that AII generated locally in the mesenteric vasculature was a more effective stimulus for PGI 2 generation than AII in the perfusion fluid. There is no evidence for intrinsic activity of AI, and release of the PGI 2-like substance appears to be mediated through an AII receptor.

Angiotensin-induced relaxation in isolated dog renal and cerebral arteries.

Helically cut strips of dog renal and cerebral (basilar and middle cerebral) arteries contracted with prostaglandin (PG) F2 alpha relaxed in response to angiotensin II (AII; 10(-9) to 10(-7) M) in a dose-dependent manner. In renal arterial strips, the relaxation was preceded by a transient contraction. Both the relaxation and the contraction induced by AII were suppressed by [Sar1,Ala8]AII or [Sar1,Ile8]AII. Treatment with propranolol, atropine, hexamethonium, cocaine, aminophylline, cimetidine, or ouabain failed to alter the relaxing effect of AII. The peptide-induced relaxation was reversed to a contraction by aspirin or indomethacin. Treatment with tranylcypromine or 15-hydroperoxy arachidonic acid suppressed the relaxation induced by AII in renal and cerebral arteries but did not alter relaxations induced by PGI2 or K+ (5 mM). In experiments with superfused dog renal and coronary arteries and rat stomach strips, the renal arteries in response to AII released a prostaglandin like substance; the release was suppressed by [Sar1,Ala8]AII or indomethacin. It appears that the relaxation of isolated dog renal and cerebral arteries induced by AII is mediated by the release of PGI2, which is associated with stimulation of AII receptors.

Prostaglandin-like substances inPropionibacterium acnes. V. Activity profiles using cascade superfusion bioassay and platelet aggregation

The activity spectrum of prostaglandin-like substances (PLS) fromP. acnes was investigated with cascade superfusion technique and by platelet aggregation assay. The biological activity of PLS resembles that of PGI2: both relax bovine coronary artery, rabbit mesentric and coeliac arteries; both contract the rat stomach strip as well as both typically inhibit spontaneous movements of isolated guinea pig ileum. Also, similarly to PGI2, PLS inhibits platelet aggregation regardless the inducer used. However, PLS possesses a specific antiaggregatory pattern on platelet, which indicates that these compounds are not indentical with primary prostaglandins or PGI2.

Angiotensin-induced release of a prostacyclin-like substance from the lungs.

Intravenous infusions of angiotensins I and II into anesthetized dogs caused release of a prostacyclin-like substance into arterial blood: prostacyclin (PGI2) was detected by direct bioassay on bovine coronary artery, rat stomach strip, and rat colon, all of which were treated with phenoxybenzamine, propranolol, and Sar1-Ile8-angiotensin II. This effect of angiotensin I, but not of angiotensin II, was abolished by captopril (1 mg/kg, i.v.), and the effect of angiotensin II was abolished by Sar1-Ala8-angiotensin II (0.5 micrograms/kg/min, i.v.). The PGI2-like substance disappeared during incubation of arterial blood for 6 min, and much less appeared in mixed venous blood withdrawn from the right atrium of pulmonary artery, indicating that it originates from the lungs. Neither arterial nor mixed venous blood contained measurable amounts of prostaglandin E2; infusions of noradrenaline did not release the PGI2-like substance. Release of the PGI2-like substance by angiotensin II was reduced after intravenous administration of indomethacin (2, 5, or 10 mg/kg), aspirin (100 mg/kg), aspirin (100 mg/kg), and meclofenamic acid (2 mg/kg), but was not completely eliminated by any of the above inhibitors. In indomethacin-treated dogs the residual relaxation of the bovine coronary artery induced by intravenous angiotensin II was not further reduced by treating the tissues with hyoscine, mepyramine, cimetidine, and methysergide. Either the pulmonary site of PGI2 biosynthesis, which is stimulated by angiotensin, is partly resistant to inhibition by nonsteroidal anti-inflammatory drugs, or the PGI2-like substance is an unknown substance with similar biological properties.

Intravesical Prostaglandin: Release and Effect of Bladder Instillation on some Micturition Parameters

Bladder washout effluent fluid was examined for prostaglandin-like activity following acidic lipid extraction and bioassay using the rat-stomach strips technique. A low basal level of prostaglandin-like material was detected in washouts collected when the bladder was empty in 4 out of 7 dogs. Increased levels were detected following micturition in 5 of these 7 dogs. A significantly high level of prostaglandin-like material was recovered after pelvic nerve stimulation. The prostaglandin-like material was tentatively identified as PGE based on the bioassay with the addition of specific antibody. Intravesically administered PGE2 or PFG2 alpha significantly reduced, in a dose-dependent response, the threshold micturition volume. All of these findings suggested that prostaglandins may play a role in the micturition process.

The metabolism of arachidonic acid in isolated hamster, rat and guinea pig lungs

The perfusion effluent from isolated rat lungs caused relaxations of superfused strips of bovine (BCA) and pig (PCA) coronary arteries. The effluent from hamster lungs had similar effect on BCA. Bolus injections of arachidonate (AA, 10–20 μg) into rat lungs caused further relaxations of superfused BCA and contractions of rat stomach strip (RSS). AA injections into guinea pig lungs resulted in dose dependent contractions of BCA and PCA. Similar dose dependent contractions of PCA and RSS were seen in hamster experiments, however the responses of BCA varied with the AA dose. Infusion of AA (5–25 μg/min) into guinea pig lungs resulted in dose dependent contractions of superfused PCA and BCA. In hamster experiments AA infusion (5 μg/min) caused a small relaxation of BCA, but had no effect on PCA. When 14 C-AA was injected into the pulmonary circulation, the amounts of metabolites were greater in the perfusion effluent from hamster than from rat lungs. In rat lungs 6-oxo-PGF 1α was one of the main metabolites. In contrast, in hamster lungs this metabolite represented only a small part of the total metabolite formation. Thromboxane B 2 was one of the main metabolites formed in hamster lungs and its rate of formation increased greatly with increasing AA doses. The results indicate that the metabolite pattern of arachidonate in isolated rat lungs is different from that in hamster and guinea pig lungs. The total rate of AA metabolism in rat lungs is smaller than in hamster lungs.