Effects of selective phosphodiesterase inhibitors on platelet-activating factor- and antigen-induced airway hyperreactivity, eosinophil accumulation, and microvascular leakage in guinea pigs

There is currently interest in the potential use of selective inhibitors of cyclic nucleotide phosphodiesterases (PDE) in the treatment of asthma. In this study we examined the effects of three selective PDE inhibitors, milrinone (PDE III), rolipram (PDE IV) and zaprinast (PDE V), on the broncoconstriction produced by antigen and histamine, the airway hyperreactivity and microvascular leakage after aerosol exposure to platelet-activating factor (PAF) and antigen, and the antigen-induced eosinophil infiltration in guinea-pig lung. Inhaled rolipram (0.01–10 mg ml^–1) inhibited dose dependently the bronchospasm produced by aerosol antigen (5 mg ml^–1) an anaesthetised, ventilated guinea-pigs. Rolipram (10 mg ml^–1) produced maximal inhibition of antigen-induced bronchoconstriction but only partial inhibition of the response to aerosol histamine (1 mg ml^–1). Milrinone and zaprinast (each 10 mg ml^–1) showed weak, or no, inhibitory effects against bronchoconstriction produced by aerosol antigen or histamine. Pretreatment with rolipram (10 mg kg^–1, i.p.) prevented airway hyperreactivity to histamine which develops 24 h after exposure of conscious guinea-pigs to aerosol PAF (500 g ml^–1) or antigen (5 mg ml^–1). The pulmonary eosinophil infiltration obtained with 24 h of antigen-exposure was inhibited by rolipram. In contrast, milrinone and zaprinast (each 10 mg kg^–1, i.p.) failed to reduce either the airway hyperreactivity of the eosinophil accumulation in these animals. Rolipram (1–10 mg ml^–1) reduced the extravasation of Evans blue after aerosol PAF (500 g ml^–1) at all airway levels while a lower dose (0.1 mg ml^–1) was only effective at intrapulmonary airways. Rolipram (0.01–1 mg ml^–1) markedly reduced airway extravasation produced by inhaled antigen (5 mg ml^–1). Zaprinast (1–10 mg ml^–1) was also effective against airway microvascular leakage produced by aerosol PAF or antigen while milrinone (10 mg ml^–1) had no antiexudative effect. These data support previous suggestions that pharmacological inhibition of PDE IV results in anti-spasmogenic and anti-inflammatory effects in the airways and may be useful in the treatment of asthma.     

Anti-inflammatory and bronchodilator properties of RP 73401, a novel and selective phosphodiesterase type IV inhibitor

1 We have investigated the effects of RP 73401, a novel, potent and highly selective cyclic nucleotide phosphodiesterase (PDE) type IV inhibitor, in guinea-pig and rat models of bronchoconstriction and allergic inflammation. In some models, the effects of RP 73401 have been compared with those of the standard PDE type IV inhibitor, rolipram.

2 RP 73401 (0.4-400 μg kg^-1, intratracheally (i.t.) on lactose) inhibited antigen-induced bronchospasm in previously sensitized conscious guinea-pigs (ID₅₀: 7±1 μg kg^-1) and in anaesthetized rats (ID₅₀: 100±25 μg kg^-1). Rolipram inhibited the antigen-induced bronchospasm in guinea-pigs with an ID₅₀ of 5±1 μg kg^-1. In guinea-pig bronchoalveolar lavage (BAL) fluid, total inflammatory cell and eosinophil numbers were reduced by RP 73401 (ID₅₀S: 3.9±0.8 μg kg^-1 and 3.2±0.7 μg kg^-1, respectively). In the rat, inflammatory cell numbers are less affected. Only the highest dose of RP 73401 (400 μg kg^-1) significantly inhibited eosinophil influx (41±16% inhibition).

3 RP 73401 (0.02-100 μg kg^-1, i.v.) inhibited PAF-induced bronchial hyperreactivity to bombesin in the anaesthetized guinea-pig (ID₅₀: 0.09±0.03 μg kg^-1) and inhibited (0.4-40 μg kg^-1, i.t.) histamine-induced airway microvascular leakage in the anaesthetized guinea-pig by approximately 60% at all doses.

4 RP 73401 relaxed guinea-pig isolated trachea under basal tone (EC₅₀: 9 nM) and when precontracted with histamine (IC₅₀: 2 nM), methacholine (IC₅₀: 29 nM) or leukotriene D₄ (LTD₄, IC₅₀: 4 nM).

5 RP 73401 (0.4-100 μg kg^-1, i.t.) inhibited bronchospasm induced by histamine (ID₅₀: 34±6 μg kg^-1), methacholine (ID₅₀: 66±12 μg kg^-1) and LTD₄ (ID₅₀: <4 μg kg^-1) in the anaesthetized guinea-pig. Against these same bronchoconstrictors, rolipram (i.t.) had ID₅₀ values of 44±4, 72±18 and <4 μg kg^-1 respectively. RP 73401 (4 and 40 μg kg^-1, i.t.) increased the magnitude and duration of bronchodilatation produced by salbutamol in the anaesthetized guinea-pig. At doses producing significant bronchodilatation, RP 73401 was without effect on heart rate or blood pressure in the anaesthetized guinea-pig. RP 73401 (0.01-0.25 mg kg^-1, i.v.) did not affect heart rate and produced only a small fall in blood pressure in the anaesthetized rat.

6 These data demonstrate that RP 73401 and rolipram inhibit antigen- and mediator-induced bronchospasm in guinea-pigs with the same potency. Furthermore, RP 73401 administered directly into the airways, protects against allergic airway inflammation. These results indicate the importance of PDE IV in regulating smooth muscle and inflammatory cell activity. At doses suppressing the inflammatory response in the lung, RP 73401 had little effect in the cardiovascular system. RP 73401 may have a role as a bronchodilator and, more importantly, as a prophylactic anti-inflammatory agent in the treatment of asthma.

     

Effects of Endotoxin on Neurally-mediated Gastric Acid Secretion in the Rat

The effects of a peripheral administration of E. coli endotoxin on neurally-mediated gastric acid secretion and the role of endogenous opioids or PAF receptors in endotoxin effects have been evaluated in the continuously perfused stomach of the anaesthetized rat. Gastric acid secretion stimulated by distension (20 cm H₂O) was reduced dose-dependently by single intravenous bolus injection of endotoxin (0.1–10 μg kg^?1). Doses of 5 μg kg^?1 induced a peak reduction of distension-stimulated acid output and significantly reduced the secretory response induced by an intravenous bolus of 2-deoxy-d -glucose (150 mg kg^?1). This dose of endotoxin did not significantly modify mean systemic arterial blood pressure throughout the experimental period. Pretreatment with the opioid receptor antagonist naloxone (1 mg kg^?1, i.v.) or the platelet-activating factor (PAF) receptor antagonist WEB 2086 (2 mg kg^?1, i.v.) did not reverse the inhibitory effects of endotoxin (5 μg kg^?1, i.v.) on acid secretion stimulated by both distension and 2-deoxy-d -glucose. These findings suggest that endotoxin-induced acute inhibition of neurally-mediated acid responses, stimulated by gastric distension or administration of 2-deoxy-d -glucose, do not involve the activation of endogenous opioids or PAF receptors.     

Antagonism by SB 204070 of 5-HT-evoked Contractions in the Dog Stomach: an In-vivo Model of 5-HT4 Receptor Function

The ability of 5-hydroxytryptamine (5-HT) to evoke contractile activity in the gastric Heidenhain pouch was measured in conscious dogs using a method in which 5-HT₄ receptor-antagonist activity can be measured in-vivo. At doses of 5-HT which evoked short-lived measurable responses (5 or 10 μg kg^?1, i.v.), it was found that this activity was greatly reduced by atropine (100 μg kg^?1, i.v.), but was unaffected by methysergide, methiothepin, ketanserin (each at 100 μg kg^?1, i.v.) or granisetron (10 or 100 μg kg^?1, i.v.). At best SDZ 205–557 2-diethylaminoethyl-[2-methoxy-4-amino-5-chloro] benzoate; 100 μg kg^?1, i.v.) reduced the action of 5-HT in 4/5 animals and increased it in the other but its effects were variable in magnitude and not consistently maintained. However, the more potent and selective 5-HT₄-receptor antagonist SB 204070 (1-butyl-4-piperidinylmethyl 8-amino-7-chloro-1,4-benzodioxan-5-carboxylate hydrochloride) dose-dependently antagonized the 5-HT-evoked contractions in all dogs tested. This action was reversible, but long-lasting with an effective half-life of 18·0 h when administered at 1 μg kg^?1. The estimated ID50 value was 0·55 μg kg^?1.     

Pharmacological characterization of the inhibitory effect of (R)-α-methylhistamine on sympathetic cardiopressor responses in the pithed guinea-pig

1 The effect of (R)-α-methylhistamine (R-α-mHA), a selective histamine H₃-receptor agonist, on increases in blood pressure and heart rate mediated by activation of the sympathetic nervous system induced by electrical stimulation of the spinal cord, was characterized in the vagotomized, pithed guinea-pig. 2 The frequency-dependent nature of (R)-α-mHA's effect on sympathetic cardiopressor responses was studied at frequencies between 1 and 20 Hz. (R)-α-mHA (10–100 μg kg^?1, i.v.) produced a dose-dependent inhibition of the stimulated increase in both blood pressure (BP) and heart rate (HR). The inhibition was inversely related to frequency and maximum inhibition (BP, 61% at 1 Hz; HR, 50% at 1 Hz) was seen with 100 μg kg^?1 of (R)-α-mHA. Treatment with the H₃ receptor inactive stereoisomer, (S)-α-methylhistamine (300 αg kg^?1, i.v.) did not inhibit the neurogenic sympathetic cardiopressor responses. 3 Pretreatment with thioperamide (1 mg kg^?1, i.v.), a histamine H₃ receptor antagonist, blocked (R) -α-mHA's inhibitory effect on stimulation-induced sympathetic cardiopressor responses. 4 Combined pretreatment with the H₃-receptor antagonist cimetidine (3 mg kg^?1, i.v.) and the H₁-receptor antagonist chlorpheniramine (0.3 mg kg^?1, i.v.) did not attenuate (R) -α-mHA's inhibitory effects. 5 (R) -α-mHA (100 μg kg^?1) had no effect on the hypertensive or tachycardia effects induced by adrenaline (1 and 3 μg kg^?1, i.v.). 6 Treatment with a combination of prazosin (1 mgkg^?1, i.v.) and yohimbine (1.5 mg kg^?1, i.v.) to block α₁ and α₂-adrenoceptors, abolished the sympathetic hypertension without affecting the inhibition of sympathetic tachycardia induced by (R) -α-mHA. Conversely, pretreatment with the β-adrenoceptor antagonist propranolol (1 mg kg^?1, i.v.), which blocked the sympathetic tachycardia, did not block (R)-α-mHA's inhibition of sympathetic hypertensive responses. 7 In adrenalectomized guinea-pigs, (R) -α-mHA (100μg kg^?1, i.v.) also produced a frequency-dependent inhibition of sympathetic hypertensive cardiopressor responses that was not significantly different from intact animals. 8 These results demonstrate that (R) -α-mHA produces a frequency-dependent inhibition of the cardiopressor responses due to activation of the sympathetic innervation to the resistance vessels and the heart. These effects of (R)-α-mHA are mediated by a prejunctional inhibitory H₃-receptor mechanism, and an intact CNS is not needed to elicit these effects. The most likely site of action is on the postganglionic sympathetic neuroeffector junction whereas a site in the adrenal medulla, unlike the sympathetic ganglia can be excluded. Furthermore, the inhibitory modulation of the sympathetic tachycardia responses with (R)-α-mHA is not affected by α₁- and α₂-adrenoceptor blockade.     

The Adenosine Agonist NECA Inhibits Intestinal Secretion and Peristalsis

Abstract— This study aimed to determine whether the antidiarrhoeal effect of the mixed A₁/A₂ adenosine agonist NECA (5′-N-ethylcarboxamido adenosine) is due to inhibition of intestinal fluid transport or to contractility. Intestinal secretion was stimulated in anaesthetized rats by intra-arterial infusions of PGE₂ (4 μg min^?1) or vasoactive intestinal peptide (0·8 μg min^?1). NECA reversed PGE₂-induced secretion in the jejunum (ED50 16 μg kg^?1) and ileum (ED50 21 μg kg^?1, i.v.) and inhibited VIP-induced secretion in the jejunum (ED50 21·5 μg kg^?1). NECA inhibited twitch responses (0·1 Hz, 1 ms, IC50 11·2Nm ) but not tetanic contractions at 10 Hz of the transmurally stimulated guinea-pig ileum. Likewise, NECA (10 μm ) did not inhibit frequency-related contractions over the range of 2·5 to 40 Hz of rat jejunum or ileum. However, NECA was shown to be a potent inhibitor (30 Nm ) of the peristaltic reflex in the rat ileum. The results indicate that adenosine receptors are involved in modulating peristalsis as well as the secretory activity of the mucosa in the rat small intestine.     

U-46619-induced Ischaemic Electrocardiographic Changes in Rats: Preventive Effects of Prostacyclin and Nitroglycerin

Abstract— The anti-anginal effect of nitroglycerin and prostacyclin was examined using, as an index, the ischaemic electrocardiogram (ECG) change (ST elevation) induced by intracoronary arterial injection of 9,11-dideoxy-11α,9α-epoxymethano-PGF_2α (U-46619), a stable thromboxane A₂ agonist, in anaesthetized rats. The ST elevation induced by U-46619 (5–20 μg kg^?1, i.c.a.) was dose-dependent and reproducible. U-46619-induced ST elevation was markedly prevented by the pretreatment of intravenous administration of prostacyclin (0·01 μg kg^?1), and to a lesser extent by nitroglycerin (0·3 mg kg^?1). Simultaneously, platelet count decreased significantly in the coronary arterial blood which indicated that platelet aggregation was enhanced by U-46619. The decrease of platelet count in coronary arterial blood at the time of ST elevation was significantly suppressed by prostacyclin (0·1 μg kg^?1, i.v.), but not by nitroglycerin (0·3 mg kg^?1, i.v.). These results suggest that the ST elevation induced by intracoronary arterial injection of U-46619 may be derived from spasm of coronary artery and platelet aggregation in the intracoronary artery in rats.     

Effects of Adenosine on NANC Bronchoconstriction in Anaesthetized Guinea-pigs

The present work assesses the effects of the acute administration of adenosine on tachykinergic bronchoconstriction induced in different ways (exogenously administered capsaicin or substance P and vagal electrical stimulation) in anaesthetized and curarized guinea-pigs. Adenosine (30–3000 μg kg^?1, i.v.) enhanced significantly and dose-relatedly the airway narrowing induced by a single dose of capsaicin (0.5-2 μg kg^?1, i.v.), both in normal and in vagotomized animals. A smaller and less dose-dependent enhancement by the nucleoside of the pulmonary resistance increase induced by substance P (5–15 μg kg^?1, i.v.) was observed. This effect was almost completely prevented by the H₁ antagonist diphenhydramine (1 mg kg^?1, i.v.), which also unmasked an inhibitory action of adenosine at the highest doses. Diphenhydramine, on the contrary, did not significantly modify the potentiation by adenosine of capsaicin-mediated bronchoconstriction. Finally, the nucleoside dose-dependently inhibited the atropine-resistant bronchospasm following vagal electrical stimulation. The use of the selective adenosinic agonists R-N⁶-[2-phenylisopropyl]adenosine (1–100 μg kg^?1, i.v.) and 5′-N-methylcarboxamidoadenosine (1–100 μg kg^?1, i.v.) before the administration of capsaicin, revealed the ability of the first to reproduce the enhancement induced by adenosine, while the second had an inhibitory effect. It is concluded that adenosine has both excitatory and inhibitory modulatory effects on airway responsiveness to excitatory non-adrenergic non-cholinergic (e-NANC) stimuli. The excitatory effects, revealed with substance P and capsaicin, support the hypothesis that adenosine may play a role as an asthma mediator.     

Ambroxol Improves the Broncho-spasmolytic Activity of Clenbuterol in the Guinea-Pig

The effects of ambroxol on the spasmolytic action of clenbuterol were investigated on acetylcholine-induced bronchospasm in guinea-pigs. Ambroxol (50 mg kg^?1 day^?1) or vehicle was administered orally for 14 days. Approximately 45 min after the final dose on day 14, the animals were anaesthetized and the spasmolytic effects of clenbuterol (3, 6 or 12 μg kg^?1 injected intravenously) were determined by use of acetylcholine (40 μg kg^?1, i.v.)-induced bronchoconstriction. For both vehicle- and ambroxol-treated animals, a positive linear relationship was observed between the log-dose of clenbuterol and the percent inhibition of bronchospasm. The calculated ED25 of clenbuterol (i.e. the dose producing 25% inhibition of the acetylcholine-induced bronchospasm) was 3.98 μg kg^?1 (3.29 to 4.82 μg kg^?1, 95% confidence interval) in the presence of ambroxol and 5.81 μg kg^?1 (4.98 to 6.79 μg kg^?1) in the absence of ambroxol. The linear regressions with or without ambroxol differed from each other (P < 0001) but ran parallel (covariance analysis), enabling us to calculate a relative potency, the value of which was 1.46 (1.16 to 1.84). These results demonstrate that the spasmolytic activity of clenbuterol is significantly improved in animals pretreated with ambroxol.     

The mechanism of the hypothermic effect of amantadine in rats and mice

Amantadine (25–100 mg kg^?1, i.p.) given to rats at an ambient temperature of 4°, or mice at 21°, caused a marked fall in rectal temperature. Prior administration of pimozide (1–2 mg kg^?1, s.c.) did not block hypothermia due to amantadine in rats or mice; in contrast, hypothermia due to apomorphine (2 mg kg^?1, i.p.) and piribedil (10–40 mg kg^?1, i.p.) in rats was blocked by pimozide pretreatment. Amphetamine (5 mg kg^?1, i.p.) given 2 h after reserpine (2 mg kg^?1, i.p.) caused a reversal of the hypothermic effect of reserpine in mice, but a reversal was not obtained with amantadine (50 mg kg^?1, i.p.). Direct injection of amantadine (4–8 mg kg^?1) into the cerebral ventricles (i.c.v.) of mice caused marked hypothermia which was not blocked by pimozide, but intravenous injection of the same dose of amantadine did not cause hypothermia. Rimantadine, a congener of amantadine but without anti-parkinsonian activity, also caused pimozide insensitive hypothermia in mice at doses of 50 mg kg^?1, intraperitoneally or 2–4 mg kg^?1, intracerebroventricularly. The main conclusion drawn from these results is that in causing hypothermia amantadine acts in the cns but not on dopamine receptors.     

An analysis of the mechanism of 5-hydroxytrypt-amine-induced vasopressor responses in ganglion-blocked anaesthetized dogs

5-Hydroxytryptamine (5-HT) administered intravenously (i.v., 1–30 μg kg^?1) to ganglion-blocked anaesthetized dogs produced dose-related increases in diastolic blood pressure and we have analysed the mechanism involved. Cyproheptadine and methysergide (10–100 μg kg^?1 i.v.) were potent and specific antagonists of the 5-HT induced rise in blood pressure, while the α-adrenoceptor blocking agent phentolamine (0·3–3 mg kg^?1 i.v.) also caused dose-related inhibition. Syrosingopine pretreatment converted the vasopressor action of 5-HT to a vasodepressor action and acute bilateral adrenalectomy caused a marked reduction in the 5-HT-induced rise in blood pressure. In two dogs, 5-HT (30 μg kg^?1 i.v.) markedly increased the venous plasma concentrations of noradrenaline and adrenaline. We concluded that the 5-HT-induced rise in diastolic pressure in the ganglion blocked anaesthetized dog is due largely to the release of catecholamines of which a substantial component is from the adrenal gland. The rise in diastolic blood pressure is specifically blocked by low doses of cyproheptadine and methysergide suggesting that the release of catecholamines is mediated by specific 5-HT receptors located mainly within the adrenal medulla.     

Behavioural Profile of Two Potential Antidepressant Pyridazine Derivatives Including Arylpiperazinyl Moieties in Their Structure,in Mice

The potential antidepressant effects of two pyridazine derivatives, 5-benzyl 6-methyl 2-[4-(3-trifluoro-methyl phenyl) piperazin-1-yl] methylpyridazin-3-one (PC4) and 5-benzyl 6-methyl 2-[4-(3-chlorophenyl) piperazin-1-yl] methylpyridazin-3-one (PCI3), were evaluated using classical psychopharmacological tests in mice. The intraperitoneal LD50 values of PC4 and PC13 were respectively 1125·8 and 429-6mg kg^?1. Only at intraperitoneal doses of 100mg kg^?1 did PC4 or PC13 significantly decrease locomotor activity. Both compounds (5–20 mg kg^?1, i.p.) reduced the duration of immobility of mice in the forced swimming test, antagonized reserpine (2–5 mg kg^?1, i.p.)-induced ptosis, and potentiated reserpine (2–5 mg kg^?1, i.p.)-induced hypothermia. PC4 and PCI3 (20mg kg^?1, i.p.) partly reversed hypothermia induced by low dose apomorphine (5 mg kg^?1, s.c.) but were less effective for higher doses of apomorphine (16 mg kg^?1, s.c). At 200 mg kg^?1, intraperitoneal PC13 enhanced the toxic effects of yohimbine (30 mg kg^?1, s.c), while PC4 was inactive. Head twitches produced either by L-5-hydroxytryptophan (4 mg kg^?1, i.p.) in mice pretreated with pargyline (100mg kg^?1, i.p.) or by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (3 mg kg^?1, i.p.) were antagonized by both pyridazine derivatives (20 mg kg^?1, i.p.). PC4 and PC13 showed analgesic properties in the phenylbenzoquinone-induced abdominal constriction test (50 < ED50 < 5-5mg kg^?1, i.p.) and in the hot-plate test (10 to 37% of analgesia at 10 mg kg^?1, i.p.). These antinociceptive effects were not significantly diminished by naloxone (1 mg kg^?1, i.p.). Furthermore, acute intraperitoneal administration of both compounds (20 mg kg^?1 for PC4 and 5mg kg^?1 for PC13) potentiated morphine (7–5 mg kg^?1, s.c.) analgesia in the hot-plate test. Thus, these results suggest that PC4 and PC 13 possess potential antidepressant effects related to different aminergic mechanisms, especially at the 5-HT₂ receptor level.     

The Action of 1,2,3,5,6,11b-Hexahydro-[1]benzothieno [3,2-g]indolizine Hydrochloride (ADT 16) on Peripheral and Central Responses Mediated by 5-Hydroxytryptaminergic and Adrenergic Systems of the Rat

Abstract— Some acute pharmacological effects have been examined of racemic ADT 16 (1,2,3,5,6,11b-hexahydro[1]benzothieno[3,2-g]indolizine hydrochloride), on peripheral and central responses mediated by 5-HT and adrenergic systems in the rat. In-vitro, ADT 16(10–1000 Nm ), similarly to mianserin, antagonized the inhibitory responses to B-HT 920 of the electrically-stimulated rat isolated prostatic vas deferens. High concentrations of ADT 16 (10 μm ), also resembled those of mianserin by potentiating twitch responses to electrical stimulation of the tissue. Contractile responses to phenylephrine of rat isolated epididymal vas deferens were antagonized by ADT 16 (0·3–1 μm ). In the rat stomach fundus strip, ADT 16 (1–3 μm ) antagonized contractions due to 5-HT. ADT 16 (0·1–1 μm ) had no effect on responses to acetylcholine of the guinea-pig isolated ileum. In-vivo, in spinalized, decerebrated rats, fenfluramine- or clonidine-induced facilitation of flexor reflex activity of the anterior tibialis muscle was attenuated by ADT 16 (3 and 10 mg kg^?1, i.v., and 3 mg kg^?1, i.v. respectively). In the anaesthetized rat, l -3,4-dihydroxyphenylalanine (l -dopa)- or l -5-hydroxytryptophan (l -5-HTP)-induced increases in the frequency of spontaneous twitches of the anterior digastricus muscle were attenuated by ADT 16 (1 and 3 mg kg^?1, i.v.; n = 4). It is concluded that ADT 16, similarly to mianserin, is a novel peripherally and centrally active antagonist of 5-HT and adrenergic responses in the rat.     

Effect of YM934, a Novel Potassium-Channel Opener,in Various Experimental Asthma Models in Guinea-pigs

YM934 is a novel synthetic potassium-channel opener. We have investigated its anti-asthma effect after intravenous (i.v.) and oral (p.o.) administration in various experimental asthma models in the guinea-pig, and compared the results with those for lemakalim, theophylline and salbutamol. In an ovalbumin-active sensitization anaphylaxis asthma model, YM934, lemakalim, theophylline and salbutamol dose-dependently prolonged the time before the occurrence of asthma attacks and reduced the mortality rate. The respective ED50 values (dose required to prolong by 50% the time before the occurrence of attacks) of the anti-asthma effects of YM934, lemakalim, theophylline and salbutamol were 6, 340, 30 000, and 45 μg kg^?1 (i.v.); the efficacy ratios were YM934 (1) > salbutamol (1/9) > lemakalim (1/57) » theophylline (1/5000). YM934 also prolonged the period before the occurrence of attacks in the anti-BSA (bovine serum albumin) serum-passive sensitization anaphylaxis, histamine-induced and methacholine-induced asthma models, with respective ED50 values for these models of 15, 22 and 20 μg kg^?1 (i.v.). Among these models a reduction in mortality rate was seen in the histamine- and methacholine-induced asthma models. After oral administration, YM934 showed an anti-asthma effect in the ovalbumin-active sensitization anaphylaxis, histamine-induced and methacholine-induced asthma models, with respective ED50 values of 38, 44 and 193 μg kg^?1. YM934 was 5–6 times more potent than salbutamol. These results indicate that YM934 has potent anti-asthma activity, and that this activity is mainly attributable to bronchodilation, most likely mediated through its potassium-channel opening activity.     

An α-adrenoceptor-mediated mechanism of hypoactivity induced by β-amyrin palmitate

Abstract— Inhibitory effects of β-amyrin palmitate in locomotor activity of mice were studied by combining this compound with α-adrenergic agonists or antagonists and a dopaminergic agonist. β-Amyrin palmitate (2·5, 5·0 and 10·0 mg kg^?1, i.p.) decreased locomotor activity of mice in a dose-dependent manner. It enhanced hypoactivity of mice treated with clonidine (0·025 mg kg^?1, i.p.) and antagonized hyperactivity produced by phenylephrine (40 μg, i.c.v.). The inhibitory action of β-amyrin palmitate was not affected by yohimbine (1·5 mg kg^?1, i.p.), but was potentiated by prazosin (0·75 mg kg^?1, i.p.). When combined with a dopaminergic agonist, apomorphine (2·0 mg kg^?1, i.p.), β-amyrin palmitate (5·0 and 10·0 mg kg^?1, i.p.) did not affect locomotor stimulation produced by apomorphine. These results suggest that β-amyrin palmitate might inhibit α₁-adrenoceptors.     

Constipation Evoked by 5-HT3-Receptor Antagonism: Evidence for Heterogeneous Efficacy among Different Antagonists in Guinea-pigs

Abstract— The abilities of selective 5-HT₃-receptor antagonists to evoke constipation were examined in conscious guinea-pigs and in preparations of guinea-pig isolated colon. Compared with vehicle-treated guinea-pigs, acute doses of granisetron (0·1, 1 and 10 mg kg^?1, i.p.) and tropisetron (10 mg kg^?1, i.p., but not 1 and 0.1 mg kg^?1, i.p.) significantly (P < 0·05) reduced the total number of faecal pellets excreted during a 12-h observation period. By contrast, BRL 46470 (0·1–10 mg kg^?1, i.p.) had no significant effect on the incidence of defecation. Mid-to-distal lengths of guinea-pig isolated colon spontaneously expelled faecal pellets. Granisetron (0·1 and 1 μm ) and tropisetron (1 μm ) reduced or prevented the rate at which they were spontaneously expelled. Morphine (0·1 μm ) and clonidine (10 nm ) also slowed faecal pellet transit time. Naloxone (0·1 μm ) had no effects alone, but reversed the actions of granisetron, morphine and clonidine. BRL 46470 (1 μm ) had no significant effect on the transit of faecal pellets in guinea-pig isolated colon. In segments of guinea-pig isolated colon which did not contain faecal pellets, granisetron, tropisetron and BRL 46470 antagonized the ability of 5-HT to evoke cholinergically-mediated contractions of the longitudinal muscle. The respective pA₂ values and slopes of the Schild plots were 8·5 ± 0·05, slope 1·06 ± 0·03; 8·5 ± 0·1, slope 0·91 ± 0·04; and 7·9 ± 0·1, slope 0·93 ± 0·05. Our experiments suggest that not all 5-HT₃-receptor antagonists are the same. In particular, BRL 46470 does not prevent defecation or faecal pellet expulsion in guinea-pig colon, even though this compound is an effective 5-HT₃-receptor antagonist in the same tissue. For the 5-HT₃-receptor antagonists which did cause constipation, the effects can be at least partly attributed to an indirect opioid-dependent action within the colonic enteric nervous system.     

Sympathomimetic Effects of Scoparia dulcis L. and Catecholamines Isolated from Plant Extracts

The herb Scoparia dulcis L. is used in Brazilian folk medicine to treat bronchitis, gastric disorders, haemorrhoids, insect bites and skin wounds, and in oriental medicine to treat hypertension. A previous study has shown that extracts of S. dulcis have analgesic and anti-inflammatory properties; in this work the sympathomimetic activity of an ethanolic extract of Scoparia dulcis L. has been investigated in rodent preparations in-vivo and in-vitro. Administration of the extract (0.5-2 mg kg^?1, i.v.) to anaesthetized rats produced dose-related hypertension blocked by the α-adrenoceptor antagonist prazosin (1 mg kg^?1). Partition of the extract in chloroform-water yielded an aqueous phase 20 times more potent than the extract; this produced hypertension in either reserpine-treated or pithed rats. In untreated and reserpine-treated rats the same fraction (1–3 × 10³ μg mL^?1) produced concentration-dependent contractions of the vas deferens musculature parallel to those obtained with noradrenaline (10^?8-10^?4 m ). Prazosin (10^?7 m ) reduced the maximum contractile effect of the aqueous fraction, and shifted the concentration-response curves for noradrenaline to the right. The aqueous fraction (25 and 50 μg mL^?1) increased the inotropism of electrically driven left atria of rats, the effect being blocked by propranolol (0.4 μg mL^?1). In preparations of guinea-pig tracheal rings the aqueous fraction (1–3 × 10³ μg mL^?1) relaxed the muscle contraction induced by histamine (10^?4 m ) in proportion to the concentration. The effect was antagonized competitively by propranolol (1.5 μm ). High-performance liquid-chromatographic analysis of the aqueous fraction revealed the presence of both noradrenaline and adrenaline in the plant extract. The results indicated that both catecholamines may account for the hypertensive and inotropic effects obtained after parenteral administration of S. dulcis extracts. This sympathomimetic activity is, however, unrelated to the previously reported analgesic and anti-inflammatory properties of the plant extract, but may explain its effectiveness upon topical application in the healing of mucosal and skin wounds.     

Pharmacokinetic study of a tripeptide HIV-1 protease inhibitor,KNI-174, in rats after intravenous and intraduodenal administrations

Recently, as a new type of anti-AIDS drug, an HIV-1 protease inhibitor, KNI-174, has been synthesized; it shows a potent and selective HIV-1 protease inhibitory activity in vitro. In this study, we developed an HPLC assay system for KNI-174 in rat plasma and examined the pharmacokinetics of KNI-174 in rats using this assay method after both intravenous (i.v.) and intraduodenal (i.d.) administrations to obtain the disposition characteristics and bioavailability of this new anti-AIDS drug. This HPLC assay method is specific to KNI-174 and the standard curve was linear from 0.02 to 30 μg ml^?1 plasma. After i.v. administration, 10.0 mg kg^?1, KNI-174 disappeared from the rats' plasma in a three-exponential decay. The mean terminal elimination half-life, t_1/2ÀZ, was 3.97 ± 0.19 (S.E.)h, the total body clearance, CL_tot, was 9.53 ± 1.08 ml min^?1 and the distribution volume at steady state, V_{d, ss}′ was 7070 ± 960 ml kg^?1. In the case of the i.d. administration, 10.0 mg kg^?1, the mean peak plasma concentration, C_max, and the peak time, t_max, were 0.196 ± 0.076 μg ml^?1 and 0.444 ± 0.193 h, respectively. The bioavailability of KNI-174 till infinity, BA^(0-infinity), was 5.37 per cent. Because the IC₅₀ of KNI-174 against HIV-1 in PHA-PBM was 138 ng ml^?1, the time needed for maintaining the concentrations above IC₅₀ after a single i.d. administration of KNI-174 is estimated to be 0.350 ± 0.184 h.     

Potent Antinociceptive Activity of a Hydroalcoholic Extract of Phyllanthus corcovadensis

Abstract— This study analyses the analgesic effect of a hydroalcoholic extract (HE) from Phyllanthus corcovadensis in several models of pain in mice. HE (3–60 mg kg^?1, i.p.) or (100–500 mg kg^?1, p.o.) caused a graded and potent analgesic effect against the abdominal constriction response caused by acetic acid and acetylcholine with an ID50 of about 3 and 100 mg kg^?1, respectively. In the tail-flick model HE (up to 500 mg kg^?1, p.o.) was without effect, while morphine (1–10 mg kg^?1, s.c.) caused a graded increase in pain latency (ID50, 3 mg kg^?1). HE (1–300 mg kg^?1) given both intraperitoneally and orally caused a potent and graded inhibition of the second phase of formalin-induced persistent pain in mice with an ID50 of 1 and 80 mg kg^?1, respectively. In contrast, morphine (1–5 mg kg^?1, s.c.) inhibited both phases of formalin-induced pain with an ID50 of 2·5 mg kg^?1. Indomethacin (1–10 mg kg^?1, i.p.) only inhibited the second phase of formalin-induced pain with an ID50 of about 3 mg kg^?1. The analgesic effect of indomethacin, but not that caused by morphine and HE was accompanied by a graded inhibition of formalin-induced mouse paw oedema. In addition, HE up to 1 g kg^?1 failed to prevent carrageenan- and dextran-induced rat hindpaw oedema. It is concluded that HE exhibits a potent antinociceptive profile, either when given intraperitoneally or orally. The mechanisms that underly its analgesic effect are unclear at present, but appear to be unrelated to inhibition of synthesis of arachidonic acid via cyclo-oxygenase or to activation of opioid receptors.     

The Protective Effect of Glycine in Cisplatin Nephrotoxicity: Inhibition with NG-Nitro-l-arginine Methyl Ester

Abstract— The effect of glycine on the acute changes in renal haemodynamics and nephrotoxicity produced by cisplatin was investigated in the rat. Cisplatin (6·0 mg kg^?1, i.v.) injection in anaesthetized rats produced, over a period of 2 h, falls of approximately 50% in renal blood flow (RBF) and the clearance of [³H]inulin (CL_IN), effects which were prevented by co-administration of glycine (1·0 g kg^?1). Infusion of the nitric oxide (NO) synthase-inhibitor N^G-nitro-l -arginine methyl ester, l -NAME (10 μg min^?1 kg^?1, i.v.), abolished glycine's ability to maintain RBF in cisplatin-injected rats whilst partially inhibiting the ability of glycine to preserve CL_IN. Treatment of cisplatin-injected rats with glycine (1·0 g kg^?1, i.v.) significantly ameliorated the nephrotoxic effects of cisplatin (6·0 mg kg^?1) as judged by improvements in a range of indices of renal function which included plasma urea and creatinine concentrations, urine output, sodium excretion, CL_IN and the clearance of [¹⁴C]p-aminohippurate. Administration of l -NAME (1·0 mg kg^?1, i.v.) to rats which received cisplatin and glycine significantly inhibited the reno-protective effect of glycine. However, l -NAME administration to rats which were treated only with cisplatin did not result in any potentiation of cisplatin nephrotoxicity. The findings of this study suggest that glycine can block the acute falls in RBF and C_IN produced by cisplatin by a mechanism which involves the production of NO. Furthermore, the results indicate that these renal haemodynamic actions of glycine are responsible, at least in part, for the ability of this amino acid to ameliorate cisplatin nephrotoxicity.