The reassertion profiles of long acting ß2-adrenoceptor agonists in the guinea pig isolated trachea and human recombinant ß2-adrenoceptor.

Long acting ß(2)-adrenoceptor agonists as exemplified by salmeterol and formoterol, exhibit reassertion behaviour in isolated airway preparations. This phenomenon is the inhibition of relaxation by a ß(2)-antagonist (e.g. sotalol), followed by the re-establishment of the relaxation when all drugs have been washed out and in the absence of any further agonist addition to the bathing solution. In this study we have compared the reassertion behaviour of salmeterol and formoterol with the new long acting ß(2)-adrenoceptor agonists indacaterol, carmoterol and three Pfizer agonists (PF610,355, PF613,322, UK503590) in the guinea pig isolated trachea and in a novel assay developed in CHO cells expressing the recombinant human ß(2)-adrenoceptor. The results obtained can be divided into two groups: salmeterol-like (persistent duration of action following agonist removal--coupled with reassertion behaviour), as exemplified by indacaterol, PF610,355, PF613,322 and UK503,590 and, formoterol-like (short duration of agonist action and little reassertion behaviour unless supramaximal concentrations are used), as exemplified by carmoterol. Results are discussed in the context of the two theories proposed to explain the long duration of action of salmeterol (binding to a specific 'exosite' of the ß(2)-adrenoceptor) and formoterol (membrane deposition: micro-kinetic theory). Our data suggest that the micro-kinetic theory is an adequate explanation to explain the long duration of action of the ß(2)-adrenoceptor agonists studied in these two assays, although with the current data set we cannot definitively exclude the 'exosite' theory.

Treating lung inflammation with agonists of the adenosine A2A receptor: promises, problems and potential solutions.

Adenosine A(2A) receptor agonists may be important regulators of inflammation. Such conclusions have come from studies demonstrating that, (i) adenosine A(2A) agonists exhibit anti-inflammatory properties in vitro and in vivo, (ii) selective A(2A) antagonists enhance inflammation in vivo and, (iii) knock outs of this receptor aggravate inflammation in a wide variety of in vivo models. Inflammation is a hallmark of asthma and COPD and adenosine has long been suggested to be involved in disease pathology. Two recent publications, however, suggested that an inhaled adenosine A(2A) receptor agonist (GW328267X) did not affect either the early and late asthmatic response or symptoms associated with allergic rhinitis suggesting that the rationale for treating inflammation with an adenosine A(2A) receptor agonist may be incorrect. A barrier to fully investigating the role of adenosine A(2A) receptor agonists as anti-inflammatory agents in the lung is the side effect profile due to systemic exposure, even with inhalation. Unless strategies can be evolved to limit the systemic exposure of inhaled adenosine A(2A) receptor agonists, the promise of treating lung inflammation with such agents may never be fully explored. Using strategies similar to that devised to improve the therapeutic index of inhaled corticosteroids, UK371,104 was identified as a selective agonist of the adenosine A(2A) receptor that has a lung focus of pharmacological activity following delivery to the lung in a pre clinical in vivo model of lung function. Lung-focussed agents such as UK371,104 may be suitable for assessing the anti-inflammatory potential of inhaled adenosine A(2A) receptor agonists.

Suppression of inflammatory and immune responses by the A(2A) adenosine receptor: an introduction.

The purine nucleoside adenosine has been described as a 'retaliatory metabolite' by virtue of its ability to function in an autocrine manner to modify the activity of a range of cell types following its extracellular accumulation during cell stress or injury. These effects are largely protective and are triggered by the binding of adenosine to any of four G-protein-coupled adenosine receptors. Most of the anti-inflammatory effects of adenosine have been assigned to the adenosine A(2A) receptor subtype, which is expressed in many immune and inflammatory cells. In this brief article, we will outline the growing evidence to support the hypothesis that the development of agonists selective for the A(2A) receptor is an effective strategy for suppressing the exaggerated inflammatory responses associated with many diseases by virtue of the receptor's ability to inhibit multiple pro-inflammatory signalling cascades.

Fibrin formation by wounded bronchial epithelial cell layers in vitro is essential for normal epithelial repair and independent of plasma proteins.

BACKGROUND: The bronchial epithelium is in contact with, and continually damaged by, the environment. Animal models have indicated that normal epithelial repair is rapid and supported by the formation of a provisional fibrin matrix that is exclusively plasma-derived. OBJECTIVES: Our objectives were to demonstrate the ability of normal human bronchial epithelial (NHBE) cells to produce coagulation cascade proteins and form fibrin in response to damage, independently of plasma proteins, and to show that formation of a cross-linked fibrin matrix is essential for normal epithelial repair in vitro. METHODS: Primary NHBE cells and cells of the 16HBE 14o- bronchial epithelial cell line were grown and maintained in vitro prior to mechanical wounding of confluent monolayers in serum-free media. Tissue factor (TF) and factor XIII (FXIII) were visualized on 16HBE 14o- monolayers using immunohistochemistry. The time-dependent expression of TF, factor VII (FVII), factor X (FX), fibrinogen, soluble fibrin, FXIII subunit A (FXIIIA) and D-dimers following wounding of confluent 16HBE 14o- monolayers was investigated using immunoassays. TF and FVII expression at the mRNA level was investigated by RT-PCR. The role of coagulation cascade proteins in the repair response of NHBE and 16HBE 14o- monolayers was investigated using neutralizing antibodies. RESULTS: Active TF was constitutively expressed in 16HBE 14o- cells. Levels of FVII, FX, fibrinogen, soluble fibrin, FXIIIA and D-dimers in culture supernatants increased rapidly and were maximal 20 min after wounding the monolayers. Expression of TF and FVII mRNA was significantly increased 10 and 4 h, respectively, after wounding. Neutralizing antibodies to TF, fibrinogen and FXIIIA significantly inhibited repair of NHBE and 16HBE 14o- cell layers. CONCLUSIONS: The bronchial epithelium has the potential to respond rapidly to mechanical damage by forming a cross-linked fibrin matrix that is essential for normal epithelial repair, independently of plasma proteins.

The potential role of spinal cord cyclooxygenase-2 in the development of Freund's complete adjuvant-induced changes in hyperalgesia and allodynia.

Chronic inflammatory conditions produce a state of hyperalgesia which is evident from a few hours to days after administration of an inflammatory stimulus. The molecular mechanisms involved in the initiation of hyperalgesia are not well understood and in this study we have investigated the role of prostaglandins in this process in the rat. Unilateral intraplantar injection of Freund's complete adjuvant produces an immediate localized swelling (oedema) with the development of altered pain responses in the ipsilateral paw such as a reduced threshold to noxious stimuli (hyperalgesia) and lowered thresholds such that normally innocuous stimuli produce a pain response (allodynia). We have monitored levels of cyclooxygenase messenger RNA and prostaglandins in lumbar spinal cord in parallel with these behavioural responses (oedema, hyperalgesia and allodynia) and identified a marked increase in cyclooxygenase-2 messenger RNA (3-fold), maximal at 2-4 h after Freund's complete adjuvant, followed by a significant increase in 6-keto prostaglandin F1alpha and prostaglandin E2 which is maximal by 8 h. Pretreatment of animals with the unselective cyclooxygenase inhibitor indomethacin attenuated oedema (approximately 40%) and allodynia (80-100%), but had no effect on the development of mechanical hyperalgesia. Pretreatment with the cyclooxygenase-2 selective inhibitors DuP 697, flosulide and SC58125 also attenuated allodynia (by 80-100%) but had no effect on the development of oedema or mechanical hyperalgesia. The marked increase in cyclooxygenase-2 messenger RNA in the lumbar spinal cord following intraplantar Freund's complete adjuvant suggests that the cyclooxygenase enzyme and its product may have a role in the adaptive response that occurs in the lumbar spinal cord during a peripheral inflammatory reaction. Pharmacological analysis reveals that prostaglandins are directly involved in the development of allodynia. However, these studies show that the development of mechanical hyperalgesia does not require the production of prostaglandins indicating that more than one pathway mediates the altered pain responses associated with a peripheral inflammatory lesion.

The beta 3-adrenoceptor agonist CL316243 prevents indomethacin-induced jejunal ulceration in the rat by reversing early villous shortening.

Jejunal villi undergo early histological shortening and vascular injury in indomethacin-induced ulcerative enteropathy in the rat. The protective effects of the beta 3-adrenoceptor agonist CL316243 on this rat model and the mechanism of action were examined using histological techniques. Groups of rats received oral indomethacin (15 mg/kg) and oral CL316243 (0, 0.01-10 mg/kg) 0.5 h beforehand. Jejunal ulceration was assessed 48 h after indomethacin. Other groups received CL316243 either 6 h before or 3 or 6 h after indomethacin. Plasma indomethacin and jejunal prostaglandin E2 levels were determined in groups of rats with and without prior CL316243. CL316243 was a potent dose-dependent inhibitor of jejunal ulceration (> 98 percent inhibition at doses > or = 0.1 mg/kg; ED50 = 0.025 mg/kg) but was not protective when given 6 h after indomethacin. CL316243, 1 mg/kg, reversed early villous shortening and vascular injury. CL316243 did not affect either indomethacin bioavailability or the inhibition of prostaglandin E2. To conclude, the beta 3-adrenoceptor agonist CL316243 is a potent inhibitor of indomethacin-induced jejunal ulceration and the mechanism of protection involves reversal of both villous shortening and vascular injury, which are usefully assessed by histomorphological techniques.

The role of acid in the pathogenesis of indomethacin-induced gastric antral ulcers in the rat.

BACKGROUND: The role of acid in the pathogenesis of indomethacin-induced ulcers of the rat gastric antrum was studied by comparing the effects of pretreating animals with both long-acting (loxtidine, AH22216) and short-acting (ranitidine and cimetidine) inhibitors of acid secretion. RESULTS: Ranitidine and cimetidine were much weaker at inhibiting antral damage when compared to their reported potencies as antisecretory agents. In marked contrast, loxtidine and AH22216 inhibited indomethacin-induced antral ulcers at doses similar to their reported potencies as inhibitors of acid secretion. Histological analysis at doses causing near maximal inhibition of macroscopic damage revealed an almost complete absence of ulcers but a large and significant increase in mucosal damage due to superficial erosions. Hourly dosing with hydrochloric acid reversed the protective effect of ranitidine, cimetidine and loxtidine on macroscopic damage and, histologically, this was associated with the widespread appearance of antral ulcers and a reduction in the proportion of mucosal damage caused by superficial erosions. CONCLUSIONS: The results of this study suggest that the pathogenesis of nonsteroidal anti-inflammatory drug (NSAID)-induced antral ulcers involves at least two stages: (1) an initial acid-independent formation of mucosal erosions followed by (2) an acid-dependent conversion of erosions to frank ulcers. Clinically, drugs that suppress acid completely for long periods may be very effective in preventing NSAID-induced gastric antral ulcers.

Comparison of the profiles of agonists as stimulants of the beta 3-adrenoceptor in vitro with their gastroprotective effects in the conscious rat.

1. This paper compares the activity of a range of agonists as stimulants of the beta 3-adrenoceptor in rat isolated oesophagus with their ability to afford protection against indomethacin-induced gastric damage in the conscious rat. 2. The beta 3-adrenoceptor agonists, CL 316243 and BRL 37344, the non-selective beta-adrenoceptor agonist, isoprenaline and the selective beta 2-adrenoceptor agonist, salmeterol, all evoked concentration-dependent relaxation of precontracted muscularis mucosa from rat oesophagus. The rank order of agonist potency was BRL 37344 > CL 316243 > isoprenaline >> salmeterol. The selective beta 1-adrenoceptor agonist, denopamine, did not relax the preparation. 3. The relaxant responses to all agonists were resistant to blockade by atenolol (10 microM), and ICI 118551 (1 microM) thus suggesting that they were not mediated by either beta 1- or beta 2-adrenoceptor stimulation. In contrast, cyanopindolol and propranolol did inhibit responses to BRL 37344, CL 316243 and isoprenaline, giving pA2 values or pKB estimates which were consistent with an interaction at beta 3-adrenoceptors (i.e. approximately 8.0 and 6.5 respectively). However, responses to salmeterol were resistant to blockade by all the antagonists tested, which suggests that the high (> 1 microM) concentrations of salmeterol used exerted non-specific relaxant effects. 4. The agonist effects of CL 316243 and BRL 37344 on beta 1- and beta 2-adrenoceptors were assessed on guinea-pig right atrium and precontracted trachea respectively. Both agonists had minimal activity as stimulants of heart rate, but did relax trachea, being 380 (CL 316243) and 21 (BRL 37344) fold less potent than isoprenaline. 5. CL 316243 and BRL 37344 were potent inhibitors of indomethacin-induced gastric antral ulceration in the conscious rat (ED50 values = 0.24 and 0.09 mumol kg-1, p.o.) Salmeterol was approximately 100 times less potent than BRL 37344 as a gastroprotective agent and denopamine was without effect. 6. The gastroprotective effects of CL 316243 and BRL 37344 were resistant to blockade by ICI 118551 (10 mg kg-1, p.o.) and propranolol (10 mg kg-1, p.o.). In contrast, both antagonists caused dose-related inhibition of the protective action of salmeterol (10 mg kg-1, p.o.). Cyanopindolol was not assessed as an antagonist in vivo because preliminary experiments revealed that it exacerbated indomethacin-induced gastric damage in its own right. 7. In conclusion, the beta 3-adrenoceptor agonists CL 316243 and BRL 37344 were potent inhibitors of indomethacin-induced gastric antral ulceration in the rat. These data suggest that an agonist which is potent and selective for the human beta 3-adrenoceptor may confer mucosal protection in man.

Non-steroidal anti-inflammatory drug-induced gastric damage in experimental animals: underlying pathological mechanisms.

A major impetus to experimental studies examining the pathogenesis of NSAID-induced gastric damage is the hope that key mechanisms can be identified that may lead to the design of "safer" NSAIDs or to the development of novel cytoprotectives to co-administer with current NSAIDs. Virtually every hypothesis proposed to explain the pathogenesis of NSAID-induced gastric damage has arisen from studies examining fundic lesions. Our results suggest that not only is the pathogenesis of gastric damage in the fundus and antrum of the rat potentially very different but that it is NSAID-induced damage to the rat gastric antrum (and not the fundus) that more closely resembles that of humans. Thus, hypotheses constructed from experimental studies examining fundic damage may not be predictive of the clinical setting. We would suggest, therefore, that future studies should concentrate on studying the pathogenesis of antral ulceration induced by NSAIDs. In particular, we believe that future research should assess whether NSAIDs do indeed reduce blood flow in the gastric antrum and define the mechanism(s) involved. Identification of these processes should significantly advance our understanding of antral ulceration and may suggest novel approaches in the design of cytoprotective agents. Recent work has established that two distinct forms of the enzyme cyclooxygenase (COX) can catalyse the metabolism of arachidonic acid and initiate prostaglandin synthesis. It is hypothesised (De Witt et al., 1993) that the analgesic/anti-inflammatory effect of current NSAIDs is achieved through inhibition of COX 2, whereas their side effects (such as antral ulceration) result as a consequence of inhibition of gastric COX 1. The recently described selective inhibitor of COX 2, NS398, has been shown to be analgesic and anti-inflammatory without causing gastric ulceration (Futaki et al., 1993; Masferrer et al., 1994). If key mechanisms (such as alterations in blood flow) of NSAID-induced antral damage can be identified, then it would be hypothesised that selective inhibitors of COX 1 would be ulcerogenic and reduce antral blood flow, whereas inhibitors of COX 2 would not share either of these properties. If this hypothesis can be substantiated, then inhibitors of COX 2 may be the next generation of "gastric safe" NSAIDs.

Inhibition of constitutive and inducible cyclooxygenase activity in human platelets and mononuclear cells by NSAIDs and Cox 2 inhibitors.

A range of NSAIDs and reported Cox 2 selective compounds were tested in human freshly isolated platelets and LPS-stimulated mononuclear cells to determine their potency and selectivity as inhibitors of constitutive (presumably Cox 1) and inducible (presumably Cox 2) cyclooxygenase respectively. All compounds tested were either equipotent at inhibiting constitutive and inducible cyclooxygenase or were selective for the inducible form. The most selective compound was Dup697 and the least selective, ketoprofen. Several compounds only produced a partial inhibition of constitutive cyclooxygenase as the maximum inhibitor concentration achievable in the assay was limited to 1 mM. With the exception of paracetamol, all compounds were able to produce full inhibition curves against the inducible form. Potency estimates against constitutive Cox compare closely with published data but most compounds were consistently more potent against the inducible isoform than in published data for human cloned, microsomal Cox 2. These data suggest that human mononuclear cells are either exquisitely sensitive to some NSAIDs or they may contain another Cox isoform as yet indistinguishable from Cox 2.

Neutrophil infiltration does not contribute to the ulcerogenic effects of indomethacin in the rat gastric antrum.

We have previously suggested (Trevethick et al., Gut 34, 156-160) that indomethacin-induced ulceration of the rat gastric antrum may be a neutrophil-dependent process. Accordingly, in this study we have used an anti-neutrophil serum (ANS) to investigate the effects of neutrophil depletion on this pathology. In animals pretreated with the ANS to induce a nearly total neutropaenia, indomethacin-induced increases in blood neutrophilia and cell infiltration into the gastric antrum (assessed as LTB4 release ex vivo) were eliminated. In marked contrast, however, ANS pretreatment affected neither the area of mucosa damaged nor the microscopic characteristics or distribution of the lesions. These results suggest that, in contrast to the published reports examining indomethacin-induced ulceration of the gastric fundus, neutrophil infiltration is not involved in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum.

Leukotrienes do not contribute to the pathogenesis of indomethacin-induced ulceration of the gastric antrum in the re-fed rat.

The potential involvement of leukotrienes in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum has been studied. Pretreatment with the leukotriene biosynthesis inhibitor, MK886 (30 mg/kg p.o.), inhibited the increases in blood and antral leukotriene B4 release ex vivo associated with the evolution of antral ulceration. Despite this, however, there was no significant reduction in either the area of antral ulceration, or in the associated blood neutrophilia and neutrophil infiltration into the gastric antrum. Similarly, pretreatment with the leukotriene B4 antagonist, SC41930 (50 mg/kg p.o.) or the peptidyl leukotriene antagonist ICI198,615 (50 mg/kg p.o.) did not inhibit the area of antral ulceration induced by indomethacin. Thus, in contrast to published reports studying fundic ulceration, our results suggest that leukotrienes do not play a major role either in the pathogenesis of indomethacin-induced ulceration of the rat gastric antrum or neutrophil infiltration into the damaged antrum.

Acute indomethacin-induced jejunal injury in the rat: early morphological and biochemical changes.

BACKGROUND/AIMS: Gastrointestinal injury induced by nonsteroidal anti-inflammatory drugs includes smooth muscle contraction, endothelial cell injury, and neutrophil infiltration. The aim of this study was to correlate early morphological changes with those in the metabolism of arachidonic acid. METHODS: Rats administered a single oral dose of indomethacin (15 mg/kg) or vehicle were killed and their intestines perfusion-fixed at 1, 2, 3, 6, and 48 hours after dosage. Serial sections of affected small intestine were immunostained for neutrophils, macrophages, actin, and fibrinogen. In addition, rats receiving either indomethacin (15 mg/kg) or vehicle were killed at 1 and 6 hours after dosage; blood and small intestinal tissue were assayed for blood thromboxane B2, intestinal tissue prostaglandin E2, and the intestinal production of leukotriene B4. RESULTS: At 2-6 hours, both intravascular and extravascular fibrin deposition were evident at the villus tip, and vertical alignment of villus smooth muscle cells was prominent. Significant neutrophil infiltration associated with a significant increase in leukotriene production was observed 6 hours after dosage. The extracted prostaglandin E2 content that was suppressed at 1 hour had recovered by 6 hours, whereas the blood thromboxane B2 levels were suppressed throughout the experiment. CONCLUSIONS: This study identifies an early neutrophil-independent phase of indomethacin-induced enteropathy that involves rapid cyclooxygenase inhibition and both microvascular and smooth muscle changes.

Gastric anti-secretory, mucosal protective, anti-pepsin and anti-Helicobacter properties of ranitidine bismuth citrate.

Ranitidine bismuth citrate is a novel compound formed from ranitidine and a bismuth citrate complex. In conscious dogs, ranitidine bismuth citrate had similar activity to ranitidine hydrochloride as an inhibitor of histamine-induced gastric acid secretion when oral doses containing equivalent amounts of ranitidine base (0.1 or 0.3 mg/kg) were compared. In the rat, ranitidine bismuth citrate (3-30 mg/kg p.o.) prevented gastric mucosal damage induced by ethanol (fundic damage) and indomethacin (antral damage). Ranitidine hydrochloride and tripotassium dicitrato bismuthate were also effective against indomethacin-induced damage, but were both significantly less potent than ranitidine bismuth citrate in this model. Ranitidine hydrochloride was inactive against ethanol-induced damage. In vitro, ranitidine bismuth citrate (1 mmol/L) inhibited human pepsin isoenzymes 1, 2, 3 and 5. Pepsin 1 was inhibited to a similar extent by ranitidine bismuth citrate, bismuth citrate and tripotassium dicitrato bismuthate at concentrations equivalent to 1 mmol/L bismuth, but ranitidine (1 mmol/L) was inactive. Ranitidine bismuth citrate was more potent than tripotassium dicitrato bismuthate as an inhibitor of pepsins 2, 3 and 5. Ranitidine bismuth citrate inhibited both Helicobacter pylori (effective concentration 4-32 micrograms bismuth/ml) and H. mustelae (1-4 micrograms bismuth/ml); similar results were obtained with tripotassium dicitrato bismuthate. Bismuth citrate was slightly less effective, and ranitidine hydrochloride was inactive (> 125 micrograms/ml). In ferrets naturally colonized with H. mustelae, oral treatment with ranitidine bismuth citrate, 12 or 24 mg/kg twice daily for 4 weeks, caused a dose related clearance of H. mustelae. Qualitatively similar results were obtained in a small study with tripotassium dicitrato bismuthate and bismuth citrate.

Do infiltrating neutrophils contribute to the pathogenesis of indomethacin induced ulceration of the rat gastric antrum?

The potential involvement of neutrophils in the pathogenesis of indomethacin induced ulceration of the gastric antrum in the re-fed rat was studied. Indomethacin was associated with a time dependent increase in the extent and severity of ulceration, blood neutrophilia, neutrophil infiltration into the gastric antrum, and calcium ionophore induced immunoreactive leukotriene B4 (LTB4) release from the antrum ex vivo. Neutrophil infiltration into the antrum was detectable 1 hour after dosing with indomethacin, at which time damage was apparent microscopically but not macroscopically. Thus, cell infiltration may contribute to the development, if not the initiation, of ulceration. Consistent with this suggestion, oral dexamethasone (5 mg/kg) significantly attenuated indomethacin induced ulceration, the associated neutrophil infiltration, and calcium ionophore induced immunoreactive leukotriene B4 release from the gastric antrum and whole blood ex vivo, although the blood neutrophilia was unaffected. These results suggest that indomethacin induced ulceration of the rat gastric antrum may have a dependence on neutrophil infiltration for its pathogenesis.

Early histological features of small intestinal injury induced by indomethacin.

The early histological features of indomethacin-induced jejunal injury in the rat are described in tissues preserved by perfusion-fixation with 10% formol-saline. After an oral dose of indomethacin (15 mg/kg, known to cause severe multifocal ulceration of the rat jejunum), groups of rats were anaesthetized with subsequent perfusion-fixation of the gastrointestinal tract at 1, 2, 3, 6 and 48 h after dosing. Using routine light microscopic techniques, we have observed a sequence of four distinct stages, in time, of small intestinal injury. The earliest histological features were shortening of the villi, epithelial stratification, basal lamina degeneration, eosinophil degranulation and infiltration of the epithelium prior to infiltration of the mucosa by neutrophils. We consider that these earliest changes, seen at 1, 2 and 3 h, represent a distinct histological entity termed Type 1 change or villous 'tufting'. Type 2 change includes all of the features of Type 1 change plus the subsequent infiltration of the mucosa by neutrophils at 2, 3 and 6 h. Type 3 change includes necrosis of the upper-third of the villi and was mainly seen at 3 and 6 h. Type 4 change describes extreme injury to more than one-third of the mucosa with severe, acute inflammation and perforation of the bowel wall by 48 h. Although a small number of neutrophils had appeared to infiltrate the mucosa as early as 2 h after dosing, they were only significantly increased at 3, 6 and 48 h. Possible pathogenic mechanisms involved in shortening of villi as a result of smooth muscle contraction and the role of mucosal eosinophils in NSAID-induced jejunal injury in the rat are discussed.

5-Carboxamidotryptamine: a potent agonist mediating relaxation and elevation of cyclic AMP in the isolated neonatal porcine vena cava.

5-Carboxamidotryptamine (5-CT) caused concentration dependent relaxation of isolated rings from the porcine vena cava contracted with either prostaglandin F2 alpha, histamine or alpha-methyl 5-hydroxytryptamine. Relaxation was not inhibited by propranolol (l microM), atropine (1 microM), indomethacin (3 microM), mepyramine (1 microM), cimetidine (1 microM), or cocaine (10 microM). Methysergide, but not cyproheptadine, was a competitive antagonist of the relaxant effect of 5-CT with a pA2 value of 7.88. 5-Carboxamidotryptamine also increased the intracellular levels of cyclic AMP, an effect which was antagonised by methysergide (apparent pA2: 7.95) but not cyproheptadine. The alpha-methyl analogue of 5-hydroxytryptamine did not cause relaxation or elevate cyclic AMP. These results suggest that 5-CT causes relaxation and elevation of cyclic AMP by interaction with a specific 5-hydroxytryptamine receptor which is '5-HT1-like'.

5-hydroxytryptamine-induced relaxation of neonatal porcine vena cava in vitro.

5-hydroxytryptamine (5-HT) caused concentration-dependent relaxation of isolated rings from porcine vena cava contracted with alpha-methyl 5-HT or prostaglandin F2 alpha. Relaxation was not blocked by propranolol (1 micron), atropine (1 micron), indomethacin (3 microns), mepyramine (1 micron), cimetidine (1 micron), or cocaine (10 microns). Further receptor analysis could not be performed by antagonism of the relaxant response but was possible using 5-HT induced increases in cyclic AMP. Methysergide (1 micron) but not cyproheptadine (0.1 micron), specifically antagonised the 5-HT induced increase in cyclic AMP with an estimated pA2 of 7.19. The alpha-methyl analogue of 5-HT, a potent agonist at M and D receptors, did not cause relaxation or elevate cyclic AMP. These results suggest that the 5-HT receptor described here is not of the classical M or D type and unlike that described thus far in the vasculature. This receptor shares some similarities with brain 5-HT1 receptors since both may be linked with adenylate cyclase.