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PubMed1992

Effects of capsaicin, bradykinin and prostaglandin E2 in the human skin.

The actions and interactions of putative mediators of inflammation, such as substance P (SP), histamine, bradykinin and prostaglandins (PGE2) were studied in human skin. In addition, the effects of capsaicin were examined as it is known to release (and to deplete) SP and calcitonin gene-related peptide from C-fibres. The flare evoked by bradykinin was abolished by pretreatment with lignocaine (local anesthetic), compound 48/80 (mast-cell histamine liberator), mepyramine (H1-receptor antagonist) and indomethacin (cyclo-oxygenase inhibitor) but was unaffected by atropine and ketanserin (serotonin antagonist). The weal response was not reduced by any of the drugs. The flare evoked by capsaicin was abolished by lignocaine and indomethacin but was unaffected by compound 48/80, mepyramine, atropine and ketanserin. The weal response was reduced by indomethacin. The flare response to bradykinin seems to reflect the activation of C-fibres and associated mast cells, while the flare response to capsaicin seems to reflect the activation of C-fibres only. Repeated injections of capsaicin and bradykinin produced tachyphylaxis (and cross-tachyphylaxis) and greatly reduced the SP-evoked flare. Capsaicin produced tachyphylaxis also after treatment of the skin with a local anaesthetic, suggesting that it develops independently of C-fibre impulse flow. The tachyphylaxis produced by bradykinin and capsaicin seems to reflect the depletion of messenger peptides from the C-fibres. The flare response to SP following capsaicin- or bradykinin-induced desensitization gradually returned to normal after 5-8 weeks. The erythema evoked by PGE2 was reduced by 30% following pretreatment with lignocaine, mepyramine or compound 48/80.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1970

The action of ranatensin, a new polypeptide from amphibian skin, on the blood pressure of experimental animals.

1. The blood pressure response to ranatensin, an undecapeptide from the skin of the frog, Rana pipiens, has been studied in various experimental animals.2. Ranatensin raised blood pressure in the dog and rabbit. The response was not altered by atropine, phentolamine, propranolol or hexamethonium, suggesting a direct peripheral vasoconstrictor action. In both animals ranatensin was about one-tenth as potent as angiotensin. Tachyphylaxis to ranatensin did occur, but there was no cross-tachyphylaxis with angiotensin, bradykinin, or noradrenaline.3. The peptide lowered blood pressure in the monkey, being as potent as eledoisin. The response was not altered by atropine, phentolamine, propranolol, tripelennamine, tetraethylammonium, bretylium, or methysergide. This again suggests a direct peripheral action on vascular smooth muscle. There was no tachyphylaxis to the depressor action, nor was there cross-tachyphylaxis with angiotensin, eledoisin, bradykinin, or noradrenaline.4. Ranatensin did not alter the blood pressure in cats and had a variable action in the guinea-pig with a rapid onset of tachyphylaxis.5. Ranatensin has a variable effect on the blood pressure in the rat that is related to the basal level of blood pressure. When the blood pressure is high, the response to the peptide is hypotension. Ranatensin raises blood pressure in the rat when the basal blood pressure is low. The pressor response to ranatensin appears to be due, in part, to the release of noradrenaline from peripheral sympathetic nerve endings.6. The composite action of ranatensin on blood pressure of various experimental animals is unlike that of any other peptide. Its hypertensive action in the dog or rabbit, together with a potent hypotensive action in the monkey, readily distinguishes it from all other vasoactive peptides.

Angiotensin II↗
PubMed1972

The action of bombesin on the systemic arterial blood pressure of some experimental animals.

1. The changes in blood pressure in response to parenteral administration of bombesin, the active tetradecapeptide of the skin of the European discoglossid frogs Bombina bombina and Bombina variegata variegata have been investigated in some experimental animals.2. In most species, the polypeptide elicited hypertension which was usually gradual in onset and slow to disappear. Blood pressure increases rarely exceeded 40-50 mmHg. At the beginning of an experiment some dose-response relationship could often be observed, but later tachyphylaxis developed. During an intravenous infusion of bombesin the rise in blood pressure could sometimes be maintained at a steady level as long as the infusion was continued, but at other times, the rise of pressure slowly subsided with continued administration of the polypeptide. In the rat and the chicken hypertension elicited by high doses of bombesin was often followed by secondary hypotension.3. Bombesin-induced hypertension was apparently not affected by pretreatment with either alpha- or beta-adrenergic blocking agents. Similarly secondary hypotension was not abolished by atropine. Thus, the effect of bombesin on vascular smooth muscle seems to be predominantly a direct one.4. Angiotensin was usually more potent than bombesin, and its effect on blood pressure was more rapid and of shorter duration. Tachyphylaxis to angiotensin was lacking or moderate.5. In sharp contrast to the other species, the monkey responded to bombesin with frank hypotension, which was usually proportional to the dose. In the monkey the hypotensive effect of bombesin was equal to, or greater than that of eledoisin or physalaemin and bombesin-induced hypotension was of longer duration than that of the other polypeptides. Tachyphylaxis was moderate for low and adequately spaced doses of the polypeptide, but prompt and intense for high doses. Long-lasting hypotension was obtained by intravenous infusion of bombesin, but repeated infusions caused tachyphylaxis. Bombesin-induced hypotension was not affected by pretreatment with atropine.6. Bombesin may be easily distinguished from all other known peptides active on vascular and extravascular smooth muscle by its effects on blood pressure. This does not apply to bombesin-like peptides, such as alytesin and ranatensin.

Angiotensin II↗
PubMed1995

Comparative effects of angiotensin II and its degradation products angiotensin III and angiotensin IV in rat aorta.

1. In the present study, the contractile effects of angiotensin III (AIII) and angiotensin IV (AIV) compared with those of angiotensin II (AII) were determined in rat aortic ring preparations. 2. All three peptides caused concentration-dependent contractions with similar maximal responses. AIII proved approximately 4 times less potent than AII, whereas AIV was about 1000 times less active than AII. 3. The selective AT1-receptor antagonist, losartan (10-300 nM) caused parallel rightward shifts of the concentration-response curves (CRC) for all three peptides. The Schild plot slopes for the effect of losartan on AIII curves were significantly lower than unity (P < 0.05). The selective AT2-receptor antagonist, PD123177 did not influence the CRCs for AII and AIV. However, the AIII curves were moderately shifted leftward in the presence of PD123177 (0.1 and 1 microM). 4. Destruction of the endothelium or incubation with the NO-synthesis inhibitor NG-monomethyl-L-arginine acetate (L-NMMA) (0.1 mM) significantly enhanced the contractile responses to all three peptides. 5. Tachyphylaxis was investigated by constructing a second CRC for all three peptides, after an interval of 1 h. The presence of endothelium significantly enhanced the development of tachyphylaxis to all three peptides. However, in endothelium-denuded preparations, the Emax value of the second curve elicited by AII was about 50%, compared with the first one, whereas for AIII and AIV Emax values were as high as 90% and 100%, respectively. 6. Our results indicate that both AIII and AIV are less potent but similarly efficacious vasoconstrictor agents compared with AII. Their contractile effects are also mediated by AT1-receptors and probably modulated by endothelium. Tachyphylaxis induced by AIII and AIV proved weaker than that for AII. Tachyphylaxis appears to be enhanced by the presence of an intact endothelium.

Angiotensin II↗
PubMed1986

Choline evokes fluid secretion by perfused rat mandibular gland without desensitization.

The secretomotor action of choline on salivary secretion has been studied in the isolated perfused mandibular gland of the rat. Choline made up in substituted Ringer solutions (Na concentrations of 40, 70, or 100 mM) was an effective secretomotor agonist in the concentration range of 1-100 mM and evoked secretory responses comparable with those of acetylcholine (0.05-1.0 microM) administered at similar Na concentrations. Continuous infusion of choline, in contrast to acetylcholine, did not lead to a fall off in the secretory response (desensitization or tachyphylaxis) until the choline concentration used exceeded approximately 80 mM. The secretomotor action of choline (46 mM) was blocked completely and reversibly by atropine (5 microM) but not by propranolol (2.5 microM) and phentolamine (2.5 microM) administered together. When acetylcholine (1.0 or 0.05 microM) was infused on a background of choline stimulation, a small additional secretory response was elicited whenever the choline stimulus was submaximal, and, regardless of the choline concentration employed, addition of acetylcholine always induced tachyphylaxis. The results suggest that choline and acetylcholine act on the same population of muscarinic receptors, but it is unclear why choline does not evoke tachyphylaxis. The response to choline allows us to exclude a number of the possible causes of tachyphylaxis that have previously been considered, so that an excessive buildup of cytosolic free Ca now remains as the most likely cause of the phenomenon.

Acetylcholine↗
PubMed1993

Functional evidence for different endothelin receptors in the lung.

The present study was undertaken to compare and contrast the characteristics of the pulmonary and systemic vascular responses to endothelin (ET) isoforms in the intact spontaneously breathing cat under conditions of constant pulmonary blood flow and left atrial pressure. When pulmonary vasomotor tone (PVT) was actively increased by intralobar infusion of U-46619, intralobar arterial bolus injections of 1 microgram ET-1, 1 microgram ET-2, or 3 micrograms ET-3 markedly decreased lobar arterial pressure, systemic arterial pressure, and systemic vascular resistance. After seven repeated injections of ET-1 or ET-2 to separate groups of cats, pulmonary and systemic responses were largely reversed from vasodilation to vasoconstriction. In contrast, the pulmonary vasodilator response to ET-3 remained intact after multiple ET-3 injections, whereas its systemic vasodilator response was lost. Repeated intralobar arterial bolus injections of ET-1, ET-2, or ET-3 also caused the loss of pulmonary vasodilation to subsequent doses of ET-1, ET-2, or sarafotoxin 6b but not to ET-3. The present data suggest that the pulmonary and systemic vasodilator responses to ET-1 and ET-2 undergo tachyphylaxis and cross-tachyphylaxis. In contrast, the pulmonary vasodilator response to ET-3, unlike its systemic vasodilator response, is resistant to tachyphylaxis and cross-tachyphylaxis. The present data provide a functional correlate for the existence of at least two ET receptor subtypes, ETA-like and ETC-like receptors, in the adult pulmonary vascular bed.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

Capsaicin-induced currents with distinct desensitization and Ca2+ dependence in rat trigeminal ganglion cells.

1. Whole cell patch-clamp records from cultured rat trigeminal ganglion cells having soma diameters ranging from 20 to 50 microM revealed that capsaicin activated two inward currents and an outward current. At -60 mV, the inward currents could be distinguished by their different peak times, which were 4.2 +/- 3.1 and 41.4 +/- 16.4 (SD) s. 2. Cells with the smallest soma diameters had the largest current densities. 3. The more rapidly activating current had a linear current-voltage relation and a reversal potential near 0 mV. 4. The more slowly activating current is not a Ca(2+)-activated Cl- current. 5. The peak of the rapid current (Ip)-capsaicin concentration (C) relationship was characterized by Ip/Ipmax = [1 + (C/Kd)n]-1, where n = 1.2 and the dissociation constant (Kd) = 0.68 microM. 6. The rapidly activating current was heterogeneous in regards to both its rate of activation and extent of desensitization. In cells bathed in buffer containing calcium and held at -60 mV, most of the capsaicin-activated currents desensitized. Removal of extracellular Ca2+ could reduce, eliminate, or have no effect on desensitization. 7. At positive holding potentials the currents very slowly desensitized, even in the presence of Ca2+. 8. Repeated 30-s applications of 1 microM capsaicin separated by 0.5, 2.5, and 5.5 min all induced tachyphylaxis. Tachyphylaxis decreased exponentially until the current remained approximately constant. Decreasing the time between capsaicin applications increased the extent of tachyphylaxis, whereas elimination of extracellular Ca2+ markedly reduced tachyphylaxis.

Animals↗
PubMed1996

Similarities and differences in the currents activated by capsaicin, piperine, and zingerone in rat trigeminal ganglion cells.

1. Capsaicin, piperine, and zingerone are natural pungent-tasting compounds found in chili pepper, black pepper, and ginger, respectively. These structurally related compounds evoke many of the same physiological responses, but at comparable concentrations capsaicin produces complete tachyphylaxis, piperine produces partial tachyphylaxis, and zingerone can either induce or not induce tachyphylaxis. Whole cell patch-clamp studies were performed on rat trigeminal ganglion cells to determine the similarities and differences between these three pungent compounds. 2. Capsaicin (1 microM) activated a variety of inward currents having peak times ranging from 2 to 46 s that desensitized to various extents ranging from 0 to 100%. The inward currents activated by zingerone (30 mM) had peak times of approximately 2 s and all currents exhibited marked desensitization. The inward currents activated by piperine (100 microM) had peak times of approximately 25 s and all exhibited a small desensitization. 3. Piperine- and zingerone-induced currents were found only in cells that could be activated by capsaicin. 4. Capsazepine (10 microM), an established antagonist of capsaicin-induced currents, inhibited the currents evoked by piperine and zingerone, suggesting that all three compounds activate vanilloid receptors. 5. Dose-response relationships for capsaicin, piperine, and zingerone obtained at a holding potential of -60 mV had threshold and apparent dissociation constants of 0.1 and 0.68 microM, 3 and 35 microM, and 1 and 15 mM, respectively. These values were consistent with those previously obtained in behavioral studies. 6. After seven 30-s applications of 1 microM capsaicin or 100 microM piperine (in a buffer with 2 mM Ca2+), each interspersed with 2-min, 50-s washes, the peak currents were inhibited by approximately 60 and 40%, respectively. In contrast, 30 mM zingerone failed to evoke a current after six applications. After complete tachyphylaxis produced by 30 mM zingerone, 1 microM capsaicin failed to evoke a current, suggesting that these two compounds cross desensitize. 7. The similar physiological responses produced by these three compounds can be rationalized by their binding to receptors and activating currents that can all be inhibited by capsazepine. Their different physiological responses evoked by these compounds can be rationalized, in part, by their very different activation and desensitization kinetics, and perhaps by the existence of different subtypes of vanilloid receptors.

Alkaloids↗
PubMed1985

Margination and emigration of leucocytes.

A recurrent conclusion of studies on margination and emigration of leucocytes into acute inflammatory lesions has been that these two processes are the result of different stimuli. The recent description of tachyphylaxis of skin lesions to neutrophil chemotaxins is compared with the purported regulation of acute inflammation by deactivation of neutrophils, inactivation of chemotaxins and inhibition of cell migration. It is concluded that tachyphylaxis might regulate the intensity of the peak neutrophil influx whereas chemotaxin inactivators and migration inhibition factors might regulate the subsequent low grade neutrophil influx into lesions. It is suggested that the chemotaxin receptors which manifest tachyphylaxis may be located on endothelial cells of post-capillary venules. The literature indicates that an alteration in endothelium provides a sufficient stimulus for margination to occur. It is emphasised that attention should be directed towards determining the minimal changes in endothelium necessary to permit or induce margination to proceed. Emigration of marginated neutrophils might then occur in response to chemotaxin diffusing to the vessel wall or by locomotion along a gradient of substratum-bound chemotaxin. The selectivity of the leucocyte infiltration of tissues that occurs in some types of inflammation could be exerted by the stimulus for margination or the stimulus for emigration. It is noted that selective margination of lymphocytes occurs in post-capillary venules of lymphoid tissues. The role of a lymphocyte chemotaxin as the stimulus for emigration in this location is unknown. To encompass the known phenomena, a general theory of leucocyte margination and emigration would predict that leucocytes selectively marginate onto acceptor molecules expressed by endothelium and extravasate in response to a chemotactic stimulus. Endothelium-bound chemotaxins may function as acceptor molecules. A bipartisan model of leucocyte migration to extravascular locations is proposed which contends that leucocyte can be recruited non-specifically as inflammatory cells or they can be recruited specifically as effector cells of immune reactions. It is suggested that tachyphylaxis is a characteristic of inflammatory cell recruitment but not of immunologically driven cell recruitment. The binding of chemotaxins to endothelial cells in vivo, the selectivity of margination, the status of margination in desensitised tissues and the role of chemotaxins in lymphocyte recirculation through lymph nodes are identified as critical questions to resolve the mechanisms of leucocyte margination and emigration.

Capillary Permeability↗
PubMed1987

Adverse effects of acetylcysteine on human and guinea pig bronchial asthma in vivo and on human fibroblasts and leukocytes in vitro.

The term 'allergen tachyphylaxis' denotes decreasing bronchial reactivity to allergen after repeated allergen inhalation challenges. In guinea pig bronchial asthma this self-protecting mechanism depends on endogenous prostaglandin E biosynthesis and can be inhibited by certain thiols. Therefore, we tested the effect of acetylcysteine (AC), a secretolytic thiol, on allergen tachyphylaxis in 25 guinea pigs. We observed inhibition of allergen tachyphylaxis and prolongation of each single asthmatic reaction. A possible clinical relevance of this observation was tested by the following experiments: Human lung fibroblasts (Wi-38) were stimulated with arachidonic acid and calcium ionophore and exposed to increasing amounts of AC. PgE biosynthesis was reduced from 2,408 pg/ml (control) to 84.2 pg/ml (0.6% AC) and 18.6 pg/ml (6% AC). Histamine release (HR) from human peripheral leukocytes was induced by anti-IgE. AC (0.016, 0.16, 1.6%) augmented both spontaneous HR (0-51.8%) and anti IgE induced HR (23.5-57.9%, p less than 0.001). Patients with isolated immediate bronchial reactions after allergen challenge inhaled 3 times a constant allergen dose. In few cases the reaction decreased from one test to another. This 'allergen tachyphylaxis' was inhibited by AC. We conclude that AC should be used with caution in patients suffering from bronchial asthma.

Acetylcysteine↗
PubMed1995

Repeated inhalation challenge with exogenous and endogenous histamine released by acetaldehyde inhalation in asthmatic patients.

We previously reported that inhaled acetaldehyde, a metabolite of ethanol and a main factor in alcohol-induced asthma, causes bronchoconstriction indirectly through endogenously released histamine in asthmatic subjects. No study has examined the difference between tachyphylaxis in response to endogenous as opposed to exogenous histamine. Therefore, we examined tachyphylaxis occurring in response to repeated inhalation of histamine or acetaldehyde in nine asthmatic subjects. The mean acetaldehyde concentration causing a 20% decrease in FEV1 increased significantly from 18.4 (geometric standard error of the mean (GSEM = 0.14) to 45.2 (GSEM = 0.14) mg/ml over a period of 1 h (p < 0.002), whereas the mean histamine concentrations causing a 20% decrease in FEV1 were identical. No correlations were observed between the change in bronchial responsiveness to each solution and the change in baseline FEV1. These results suggest that tachyphylaxis in response to histamine is observed only when the latter is released endogenously. We believe that this is the first report suggesting tachyphylaxis caused by endogenous histamine.

Acetaldehyde↗
PubMed1993

Exercise-induced refractoriness in asthmatic subjects involves leukotriene and prostaglandin interdependent mechanisms.

Exercise-induced bronchoconstriction is caused, in part, by leukotriene (LT)D4 release in asthmatic airways. Asthmatics become refractory to exercise bronchoconstriction with repeated challenges, due to inhibitory prostaglandin release. The purpose of this study was to test the hypothesis that exercise refractoriness is caused by LTD4-induced inhibitory prostaglandin release. Fourteen stable asthmatic subjects with exercise-induced bronchoconstriction were studied. On the first 2 days, subjects underwent two challenges, 1 h apart, with either exercise or inhaled LTD4. Eight subjects then took part in three double-blind, randomized, placebo-controlled, crossover studies with flurbiprofen, a prostaglandin synthetase inhibitor, to determine whether cross refractoriness occurs between exercise and LTD4, whether flurbiprofen attenuates this effect, and whether flurbiprofen attenuates LTD4 tachyphylaxis. There was a reduction in the intensity of bronchoconstriction to the second challenge both with exercise (refractoriness) and with LTD4 (tachyphylaxis). The degrees of refractoriness and tachyphylaxis were correlated (r = 0.72, p = 0.005). Flurbiprofen attenuated LTD4 tachyphylaxis. Cross refractoriness occurred between exercise and LTD4, and flurbiprofen treatment also attenuated this effect. One hour after LTD4 challenge, the mean fall in FEV1 after exercise was 12.3% (%SEM 2.3) on placebo and 17.1% (%SEM 3.8) on flurbiprofen (p = 0.027). Similarly, 1 h after exercise, the LTD4 PC20 increased to 0.73 (%SEM 1.4) microgram/ml on placebo and 0.30 (%SEM 1.8) microgram/ml on flurbiprofen (p = 0.026). These results suggest that LTD4 released in asthmatic airways as a result of exercise stimulates inhibitory prostaglandin release, resulting in exercise refractoriness.

Adult↗
PubMed1986

Interactions of bombesin and substance P at the feline lower esophageal sphincter.

The purpose of this study was to determine the interactions between bombesin and substance P at the feline lower esophageal sphincter (LES). Intraluminal pressures were recorded using a fixed, perfused catheter assembly. Myoelectrical activity was recorded using bipolar Ag-AgCl serosal electrodes. Bombesin, i.v., gave a dose-dependent increase in LES pressure and electronically counted spike activity. The threshold dose was 10(-7) g/kg, while the maximal dose, 10(-5) g/kg, increased LES pressure by 65.5 +/- 14.8 mmHg. The neuroantagonist, tetrodotoxin, decreased the LES response to bombesin by 74.1% +/- 7.9% (P less than 0.05), but had no significant effect on the LES response to substance P. The sphincteric response to bombesin was not inhibited by bilateral cervical vagotomy, atropine, propranolol, or phentolamine (P less than 0.10). Bombesin tachyphylaxis abolished the LES response to bombesin but had no effect on the response to substance P. Conversely, substance P tachyphylaxis completely abolished the LES response to bombesin (P less than 0.001). The substance P antagonist [D-Pro2, D-Trp7,9]substance P also significantly inhibited the LES response to bombesin (P less than 0.05). Acidification of the distal esophagus with 2.0 ml of 0.1 N HCl increased LES pressure by 32.5 +/- 5.2 mmHg (P less than 0.02). The LES response to acid was inhibited by bombesin tachyphylaxis (maximal pressure response, 4.7 +/- 2.1 mmHg, P less than 0.01 compared with control acid response). The tachyphylaxis techniques were specific for the peptides giving no effect on the LES responses to phenylephrine, bethanechol, or pentagastrin. We drew the following conclusions: (a) bombesin increased feline LES pressure via nonvagal neural pathways that were insensitive to adrenergic or cholinergic antagonists; (b) bombesin may be involved in the enteric pathways that mediate the feline LES response to distal esophageal acidification; and (c) substance P mediates the effect of bombesin at the LES and is a neurotransmitter in the LES response to acidification.

Action Potentials↗
PubMed1991

Effect of pH of bupivacaine on duration of repeated sciatic nerve blocks in the albino rat. Local Anesthetics for Neuralgia Study Group.

Tachyphylaxis has been ascribed to tissue acidification after repeated injections of acidic local anesthetic solutions. We studied the effect of pH on the duration of action of bupivacaine to determine the validity of this proposed mechanism of tachyphylaxis by injecting bupivacaine solutions adjusted to pH 4.2 or 6.8 into a surgically implanted system created to permit in vivo irrigation of rat sciatic nerves with local anesthetic. Tachyphylaxis developed at both pH values. The results fail to support the acidification hypothesis as there was no statistically significant effect of a 400-fold difference in hydrogen ion concentration on the development of tachyphylaxis or the duration of motor dysfunction.

Anesthesia, Local↗
PubMedDate not supplied

Pharmacodynamic effects of 3-day intravenous treatment with pantoprazole or ranitidine after 10 days of oral ranitidine.

Tachyphylaxis (drug tolerance) is an undesirable condition in drug therapy with histamine-2-receptor antagonists (H2RAs). The concept of overcoming tachyphylaxsis via intravenous (i.v.) administration of proton-pump inhibitors (PPIs) or H2RAs is of significant interest to physicians. In the present study, 32 healthy Helicobacter pylori negative male volunteers were evaluated for the ability of i.v. pantoprazole or i.v. ranitidine to overcome oral ranitidine tachyphylaxis. After 10 days of oral treatment with enteric-coated 300-mg ranitidine tablets once daily in the evening, two groups of 16 volunteers each were randomized to receive either i.v. pantoprazole or i.v. ranitidine for up to 72 h. The primary variable was defined as the increase in 24-h gastric pH median after 1 day of i.v. treatment; the secondary variable was median percentage of time that 24-h gastric pH was <4, as calculated by Hodges-Lehman shift estimators. After 10 days of oral ranitidine treatment, tachyphylaxis was present in all volunteers. Within 1 day of continuous i.v. pantoprazole or i.v. ranitidine administration, 24-h median gastric pH increased from pH 1.45 to pH 3.50 (241%) and from pH 1.50 to pH 2.35 (157%), respectively. I.v. pantoprazole was found to be significantly more effective (p<0.05) than i.v. ranitidine in increasing the 24-h gastric pH after oral ranitidine tachyphylaxis.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed1976

Innate and drug-induced resistance to acute lung damage caused in rats by alpha-naphthyl thiourea (ANTU) and related compounds.

During the 3rd and 4th weeks of life rats were highly resistant to the toxic effects of alpha-naphthyl thiourea (ANTU) and of thiourea and its derivatives but toxicity developed rapidly during the following 2 weeks. Marked resistance to lung damage by toxic thioureas could be induced in older, mature rats by pretreatment with the toxic agent itself (tachyphylaxis), with other toxic and non-toxic antithyroid drugs or with iodine or iodide--even if the rats were pretreated at an early age before susceptibility to the agent developed. ANTU-tachyphylaxis was dose-dependent. Total thyroidectomy did not affect either lung damage induced by ANTU or the resistance due to tachyphylaxis or to pretreatment with iodide or the antithyroid drugs thiourea, 1-ethyl-1-phenyl thiourea or propyl thiouracil. Neither total nor medullary adrenalectomy affected ANTU toxicity. Marked resistance to ANTU-induced lung damage was induced in rats by pretreatment with either an activator (3-4 benzypyrene) or an inhibitor (SKF 525-A) of drug-metabolizine mixed-function microsomal enzyme systems; the inhibitor, sodium phenobarbitone, had no significant effect on toxicity. The sulphydryl compound, AET, induced marked resistance to ANTU; cysteine was less effective. Neither autonomic blockade with nicotine and atropine nor actinomycin D had significant effects on toxicity to ANTU. The acute pulmonary oedema induced in rats by high pressure oxygen, chemical convulsants, pressor agents and ammonium sulphate differed in many respects from that induced by toxic thioureas; it was typically haemorrhagic in nature, did not result in significant pleural effusion, did not exhibit tachyphylaxis, and was not influenced by pretreatment with iodide or derivatives of thiourea.

Age Factors↗
PubMed1986

Emigration and accumulation of PMN-leukocytes induced by endotoxin, interleukin 1 and other chemotactic substances.

This publication describes polymorphonuclear leukocyte (PMN) emigration and accumulation, which is prerequisite for their defensive function in infected tissues. The extravasated PMNs can kill microorganisms, but in this process they also release proteolytic enzymes and other cell constituents which can alter and even injure the tissues, primarily the microcirculation. In the first part of the paper in vivo quantitation of the acute inflammatory reaction is described with emphasis on PMN emigration and accumulation. With 51Cr-labeled PMNs the kinetics of their emigration induced by a number of chemotaxins and chemotaxinigens was found to be similar, peaking in 1-4 hour old lesions and returning to baseline values thereafter. The most potent substance tested was endotoxin, which induced a PMN influx at a molar concentration a least 3 orders of magnitude lower than the other substances tested, implying the these substances are not the primary endogenous mediators of endotoxin induced inflammation. Next we describe an observation which shed considerable light on the mechanisms underlying PMN emigration. When a chemotaxin or endotoxin was injected intradermally and after varying periods of time reinjected into the same site, the PMN influx into those sites was diminished, compared to sites not previously injected, i. e. injected for the first time. This tachyphylaxis or diminished responsiveness was attributed to a downregulation of receptors, presumably on endothelial cells, coupled to a facilitatory mechanism. Other mechanism proposed to terminate emigration of PMNs during inflammatory reaction were unlikely, based on our experimental findings. Endotoxin is not chemotactic in vitro but it induces PMN emigration when injected intradermally. Hence the third part of the publication deals with PMN emigration induced by interleukin 1 and its significance for endotoxin-induced inflammation. IL 1 is the only chemotaxin which induces PMN accumulation at a concentration comparable to that of endotoxin and considerably lower than the other chemotaxins. There was cross tachyphylaxis between endotoxin and IL 1 and vice versa. The PMN influx into IL 1 sites injected 6 hours earlier with IL 1 or with endotoxin was diminished compared to IL 1 sites injected into normal skin. Sites injected first with IL 1 and then with a low dose of endotoxin also exhibited cross tachyphylaxis. FMLP or LTB4 injected into sites pretreated with endotoxin did not exhibit cross tachyphylaxis, i. e. the PMN influx was similar to sites injected for the first time with these chemotaxins.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Pharmacological effects and metabolism of neurotensin and bradykinin in the isolated rat uterus.

Neurotensin (NT) and bradykinin (BK) were found to cause contractions of isolated rat uterus preparations. In 97% of the experiments, acute tachyphylaxis followed soon after the initial administration of NT. Interrelation between the oxytocic effects of NT and BK was not observed. Among the NT fragments studied, only NT-(9-13) had an oxytocic effect (less than 1.0%). All NT fragments tested induced tachyphylaxis to NT regardless of their efficacy. Using HPLC analysis, NT but not BK was found to be degraded by the intact rat uterus. A major involvement of a carboxydipeptidase cleaving at Tyr11-Ile12 is suggested. Carboxyl-blocked neurotensinamide (NT-NH2) was found to be resistent to proteolysis and not develop tachyphylaxis. No cross-tachyphylaxis was observed with NT or NT-(1-11). The results suggest the existence of different receptors for NT and BK in the uterus, as well as the existence of different receptors or receptor states that interact with NT or NT-NH2 in the rat uterus.

Animals↗