CHARACTERIZATION OF SUBSTANCE P-INDUCED BRONCHOCONSTRICTION IN THE GUINEA-PIG: A COMPARISON WITH ACETYLCHOLINE

Substance P (0.5-8.0 micrograms/kg, i.v.) induced bronchoconstriction in anaesthetized, mechanically-ventilated guinea-pigs, comprising increases in airways resistance and decreases in dynamic compliance. These bronchoconstrictor responses were unaffected by bilateral vagotomy, pretreatment with pheniramine (2 mg/kg, i.v.) or by pretreatment with atropine (100 micrograms/kg, i.v.). Acetylcholine-induced (4-32 micrograms/kg, i.v.) bronchoconstriction was prevented by atropine pretreatment, whereas bilateral vagotomy inhibited responses to acetylcholine. Ganglionic blockade using hexamethonium (20 mg/kg, i.v.) potentiated both substance P and acetylcholine on airways resistance and dynamic compliance. Indomethacin (1 or 5 mg/kg, i.v.) did not affect substance P-induced bronchoconstriction, whereas the higher dose enhanced acetylcholine-induced increases in airways resistance. In addition, aspirin pretreatment (20 mg/kg, i.v.) did not alter the bronchoconstrictor potency for either substance P or acetylcholine. On the other hand, the combined cyclo-oxygenase/lipoxygenase inhibitors eicosatetraynoic acid (ETYA, 20 mg/kg, i.v.) and BW755C (20 mg/kg, i.v.) potentiated both acetylcholine and substance P on airways resistance and dynamic compliance. The results suggest that substance P-induced bronchoconstriction may be modulated by the sympathetic nervous system and does not appear to be influenced by vagal or histaminergic mechanisms. The failure of indomethacin or aspirin to affect substance P-induced bronchoconstriction, together with the enhancing effects of ETYA and BW755C pretreatments, provide evidence consistent with the existence of a bronchodilator mechanism which may be inhibited by compounds inhibiting lipoxygenase enzymes.     

Evidence for a role of bradykinin in experimental pain models.

Pretreatment with captopril, a kininase II inhibitor, at 10 mg/kg i.p. or s.c., significantly increased the writhing response induced by a minimum effective dose (0.75 mg/kg i.p.) of phenylbenzoquinone (PBQ), by 91-148%. 1,10-Phenanthroline, a carboxypeptidase B inhibitor (2 mg/kg i.p.), in combination with captopril enhanced the algesic effect of PBQ by 309-360%. Captopril also doubled the number of writhes induced by a minimum effective dose of BK (5 micrograms/kg i.p.) in PGE2-pretreated mice. The writhing responses induced by higher doses of PBQ or BK were not affected by these inhibitors. The hyperalgesic effect of BK (1 micrograms) injected into the hindpaw of rats was significantly increased and prolonged by coinjection of captopril (30 micrograms) and 1,10-phenanthroline (30 micrograms) and was prevented by carboxypeptidase B (1 mg). These data indicate that BK plays a role in pain in these models, a role which appears of greatest relevance at threshold algesic stimulation.     

Clonidine-induced hypoactivity and mydriasis in mice are respectively mediated via pre- and postsynaptic alpha 2-adrenoceptors in the brain

Since brain alpha 2-adrenoceptors occur both pre- and postsynaptically, experiments were carried out to determine the synaptic locations of those receptors mediating clonidine-induced hypoactivity and mydriasis. Intraperitoneal (i.p.) injection of clonidine (1-3000 micrograms/kg) to mice dose dependently induced these two responses and also decreased brain concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG). The ED50 values were: 120 micrograms/kg for hypoactivity (95% confidence limits 103-140 micrograms/kg), 54 micrograms/kg for mydriasis (95% confidence limits 40-74 micrograms/kg) and 18 micrograms/kg for MHPG reduction (95% confidence limits 8-36 micrograms/kg) suggesting that these responses could all be presynaptically mediated. However, methamphetamine which increases noradrenaline turnover was found to dose dependently produce mydriasis, but not hypoactivity, after peripheral (0.1-5 mg/kg i.p.) or central (0.5-10 micrograms i.c.v.) injection. The mydriasis produced by methamphetamine (0.5 mg/kg i.p.) was abolished by i.c.v. injection of 1 micrograms idazoxan or yohimbine, but not 2.5 micrograms prazosin or pindolol, showing this effect was mediated by central alpha 2-adrenoceptors. Methamphetamine (1-10 micrograms i.c.v.) potentiated the mydriasis induced by clonidine (50 micrograms/kg i.p.) suggesting this was a postsynaptic alpha 2-adrenoceptor response. By contrast, methamphetamine (1-10 micrograms i.c.v.) dose dependently reversed clonidine (100 micrograms/kg i.p.) hypoactivity indicating this response was mediated by presynaptic alpha 2-adrenoceptors. These hypotheses were confirmed by destruction of noradrenergic neurones using DSP-4 (100 mg/kg i.p. x 2). This treatment prevented the mydriasis response to methamphetamine (0.5 mg/kg i.p.), but not clonidine (100 micrograms/kg i.p.) and markedly attenuated clonidine (100 micrograms/kg i.p.) hypoactivity.     

Clonidine produces mydriasis in conscious mice by activating central alpha 2-adrenoceptors

Intraperitoneal (i.p.) injection of the alpha 2-adrenoceptor agonist clonidine (1-3000 micrograms/kg) produced dose-dependent pupil dilatation in conscious C57/Bl/6 mice with an ED50 of 54 micrograms/kg (95% confidence limits 40-74 micrograms/kg). This response was rapid in onset and of approximately 30 min duration. The alpha 2-adrenoceptor antagonists idazoxan (1 or 3 mg/kg i.p.) and yohimbine (1 or 3 mg/kg i.p.) both produced dose-related miosis, but the alpha 1- and beta-adrenoceptor antagonists prazosin (1 or 3 mg/kg i.p.) and pindolol (1 or 3 mg/kg i.p.) were without effect. These doses of idazoxan and yohimbine potently reversed the mydriasis induced by clonidine (100 micrograms/kg i.p.), while prazosin and pindolol were again ineffective. Clonidine-induced mydriasis was also unaltered by the 5-HT antagonists, methysergide (2.5 mg/kg i.p.) and ketanserin (0.1 mg/kg i.p.) or 0.1 mg/kg i.p. of the dopamine antagonists, haloperidol, SCH 23390 and BRL 34778. A dose of 0.25 microgram clonidine, which was ineffective when administered i.p., produced marked mydriasis after intracerebroventricular (i.c.v.) injection. In addition, the mydriasis produced by i.p. injection of clonidine (100 micrograms/kg) was abolished by i.c.v. dosing of 2.5 micrograms idazoxan or yohimbine, but again not by prazosin or pindolol. Together, these data provide strong evidence to indicate that clonidine-induced mydriasis is exclusively mediated via central alpha 2-adrenoceptors and that this response provides a useful model for studying the function of these receptors.     

Neurogenic plasma leakage in mouse airways

1. This study sought to determine whether neurogenic inflammation occurs in the airways by examining the effects of capsaicin or substance P on microvascular plasma leakage in the trachea and lungs of male pathogen-free C57BL/6 mice. 2. Single bolus intravenous injections of capsaicin (0.5 and 1 micromol kg(-1), i.v.) or substance P (1, 10 and 37 nmol kg(-10, i.v.) failed to induce significant leakage in the trachea, assessed as extravasation of Evans blue dye, but did induce leakage in the urinary bladder and skin. 3. Pretreatment with captopril (2.5 mg kg(-1), i.v.), a selective inhibitor of angiotensin converting enzyme (ACE), either alone or in combination with phosphoramidon (2.5 mg kg(-1), i.v.), a selective inhibitor of neutral endopeptidase (NEP), increased baseline leakage of Evans blue in the absence of any exogenous inflammatory mediator. The increase was reversed by the bradykinin B2 receptor antagonist Hoe 140 (0.1 mg kg(-1), i.v.). 4. After pretreatment with phosphoramidon and captopril, capsaicin increased the Evans blue leakage above the baseline in the trachea, but not in the lung. This increase was reversed by the tachykinin (NK1) receptor antagonist SR 140333 (0.7 mg kg(-1), i.v.), but not by the NK2 receptor antagonist SR 48968 (1 mg kg(-1), i.v.). 5. Experiments using Monastral blue pigment as a tracer localized the leakage to postcapillary venules in the trachea and intrapulmonary bronchi, although the labelled vessels were less numerous in mice than in comparably treated rats. Blood vessels of the pulmonary circulation were not labelled. 6. We conclude that neurogenic inflammation can occur in airways of pathogen-free mice, but only after the inhibition of enzymes that normally degrade inflammatory peptides. Neurogenic inflammation does not involve the pulmonary microvasculature.     

MECHANISMS OF CAPTOPRIL-INDUCED POTENTIATION OF THE DEPRESSOR RESPONSES TO ARACHIDONIC ACID IN RATS

The mechanisms underlying potentiation by captopril of the depressor responses to arachidonic acid were studied in chloralose-anaesthetized rats. Captopril, in a dose (0.5 mg/kg, i.v.) which inhibited the pressor responses to angiotensin I (0.03-1 microgram/kg, i.v.), enhanced the depressor responses to bradykinin (3-300 micrograms/kg, i.v.) and potentiated the hypotensive action of arachidonic acid (3 mg/kg, intravenously). This phenomenon was observed not only when captopril and arachidonic acid were administered intravenously, but also when these compounds were injected directly into the aortic arch. The enhancement of arachidonic acid-induced hypotension by captopril was not significantly affected by pretreatment with a low dose of aprotinin (3 mg/kg, i.v.), but was abolished by bilateral nephrectomy or by pretreatment with a higher dose of aprotinin (6 mg/kg, i.v.). It is suggested that captopril augments the depressor responses to arachidonic acid by inhibiting angiotensin converting enzyme. This results in accumulation of bradykinin which in turn increases release of vasodilator prostaglandins, originating most probably, from the kidneys. The possibility that blockade of angiotensin II formation by captopril may leave the vasodilator action of prostaglandin unopposed cannot be excluded.     

SENSORY NERVES IN THE AIRWAYS AS A TARGET FOR DRUG DEVELOPMENT

1. Electrical stimulation (2.5-10 Hz, 80 V, 1 ms for 15 s) within the spinal canal of the pithed guinea-pig pretreated with atropine, D-tubocurarine and pentolinium caused a bronchoconstrictor response, indicated by a rise of insufflation pressure. 2. The magnitude of these non-cholinergic neuronal bronchoconstrictor responses were frequency-dependent, capsaicin-sensitive and temperature-dependent. 3. Responses could be inhibited by the alpha 2-adrenoceptor agonist B-HT920 (3 mg/kg, i.v.) and the mu-opioid agonist H-Tyr-D-Arg-Phe-Lys-NH2 (DALDA; 1 mg/kg, i.v.) and the attenuation observed could be overcome by use of the respective antagonists idazoxan (3 mg/kg, i.v.) and naloxone (3 mg/kg, i.v.). 4. Substance P-induced bronchoconstriction (0.3 micrograms/kg, i.v.), but not that due to electrical stimulation, was attenuated by indomethacin (3 mg/kg, i.v.), indicating an indirect action of substance P via a product of arachidonic acid metabolism. 5. The prostanoid product of the substance P response was probably thromboxane A2. 6. Hence, novel drug development could be directed towards tachykinin receptors or to the synthesis, release and degradation of neuropeptides.     

Possible mechanisms underlying the hypertensive response to clonidine in freely moving, normotensive rats

Possible mechanisms underlying the hypertensive response to intracerebroventricular (i.c.v.) or intravenous (i.v.) injection of clonidine were investigated in freely moving, normotensive rats. In conscious rats, clonidine (2-20 micrograms) injected i.c.v. caused a dose-dependent and long-lasting pressor response associated with bradycardia. A similarly long-lasting pressor response was induced following an initial rapid rise in mean blood pressure after i.v. bolus injections of clonidine (5-50 micrograms/kg). In pentobarbital-anesthetized rats, the prolonged pressor responses to i.v. and i.c.v. injected clonidine at high doses were significantly smaller than those in conscious rats. Low doses of clonidine caused only depressor responses which developed gradually. No significant changes in concentrations of plasma norepinephrine and epinephrine were found during the pressor period after i.c.v. injection of clonidine (20 micrograms). Systemic (2 mg/kg, i.v.) or central (100 micrograms, i.c.v.) pretreatment with phentolamine abolished only the prolonged pressor response to both i.c.v. (20 micrograms) and i.v. (50 micrograms/kg) injected clonidine. The prolonged pressor response to clonidine (20 micrograms, i.c.v.) was enhanced by pretreatment with hexamethonium (25 mg/kg, i.v.), methylatropine (1 mg/kg, i.v.) or atropine (1 mg/kg, i.v.) and it was not affected by pretreatment with saralasin (300 micrograms/kg and 25 micrograms/kg/min, i.v.), d(CH2)5Tyr(Me)-arginine-vasopressin, a vasopressin antagonist (50 micrograms/kg, i.v.) or naloxone (1 mg/kg, i.v.). Neither adrenalectomy nor adrenal demedullation had an effect on the pressor response to clonidine (20 micrograms, i.c.v.). In adrenalectomized rats, systemic pretreatment with hexamethonium (25 mg/kg, i.v.) caused a potentiation of the pressor response to clonidine (20 micrograms, i.c.v.). These results suggest that clonidine induces the pressor response through activation of central alpha-adrenoceptors, probably the alpha 2 subtype, without an increase in sympatho-adrenomedullary activity. It is speculated that the response may be mediated by vasoactive humoral substance(s).     

A central site of action for benzamide facilitation of gastric emptying

Gastric emptying of the fed guinea-pig was measured using a non-invasive X-ray fluoroscopic technique to determine passage from the stomach of polystyrene-coated barium sulphate spheroids. Peripherally administered metoclopramide (0.1-10 mg/kg i.p.), clebopride (1-10 mg/kg i.p.), (-)-sulpiride (40 mg/kg i.p.), haloperidol (1 mg/kg i.p.) and domperidone (1-10 mg/kg i.p.) failed to modify gastric emptying. Stress inhibited emptying, and this was considered to explain the effects of eserine and high dose metoclopramide. Gastric emptying was decreased by peripherally administered atropine (0.5 mg/kg i.p.) and apomorphine (0.1-0.5 mg/kg s.c.); the apomorphine response was antagonised by pretreatment with haloperidol, domperidone, (-)-sulpiride, metoclopramide and clebopride but not by prazosin + propranolol. Gastric emptying was facilitated by intracerebroventricular (i.c.v.) administrations of metoclopramide and clebopride (40, 100 and 200 micrograms) but not by i.c.v. domperidone, haloperidol, fluphenazine or (-)-sulpiride (100, 200 micrograms) and was inhibited by i.c.v. apomorphine (100, 200 micrograms); the response to i.c.v. apomorphine was antagonised by i.c.v. pretreatments with haloperidol, domperidone, (-)-sulpiride, metoclopramide and clebopride (40-50 micrograms). Facilitation of emptying by i.c.v. metoclopramide was prevented by peripheral pretreatment with atropine (0.5 mg/kg i.p.). It is concluded that the actions of apomorphine and metoclopramide/clebopride to respectively inhibit and facilitate gastric emptying may be mediated, at least in part, via central mechanisms. Whilst apomorphine's action may be mediated via dopamine receptor mechanisms, metoclopramide and clebopride act at additional unspecified sites, metoclopramide's action being expressed via cholinergic mechanisms.     

Comparison of acute cardiovascular effects of cadmium and captopril in relation to oxidant and angiotensin converting enzyme activity in rats

Cadmium (0.1, 0.32, 1.0 mg/kg i.v.) produced dose dependent hypertensive response in pentobarbitone anesthetized Sprague-Dawley (S-D) rats. The peak hypertensive effect was observed within 15 min of cadmium administration. This response gradually decreased over 1-h observation period. Heart rate did not change significantly. Serum malondialdehyde (MDA) levels increased with cadmium administration. The lower dose of cadmium (0.1 mg/kg i.v.) increased serum MDA to 0.14 +/- 0.02 nmol/mL as compared to 0.12 +/- 0.01 nmol/mL in the control group and was not statistically significant. However, mid (0.32 mg/kg i.v.) and high doses (1.0 mg/kg i.v.) raised serum MDA levels significantly (P < 0.01). Cadmium inhibited serum angiotensin converting enzyme (ACE) levels at all the three tested doses and was statistically significant (P < 0.01). Captopril (1.0, 3.2 mg/kg i.v.) produced a dose dependent mild hypotensive response. The peak effect was observed within 5 min. Cadmium produced inhibition of serum ACE levels, however, a dose response effect was not observed. Captopril (3.2 mg/kg i.v.) decreased serum ACE levels to 5.4 +/- 1.1 U/mL (control levels 10.7 +/- 1.4 U/mL). Serum MDA levels were decreased by captopril treatment. A correlation between serum ACE and MDA following higher dose of cadmium was found. These results indicate that acute administration of cadmium, an inorganic blocker of ACE and calcium channels cadmium produced hypertensive response while captopril produced mild hypotensive response in rats.     

Peripheral GABAA receptor-mediated effects of sodium valproate on dural plasma protein extravasation to substance P and trigeminal stimulation.

1. The GABA transaminase inhibitor and activator of glutamic acid decarboxylase, valproic acid is being used for the treatment of migraine. Its mechanism of action is unknown. We tested the effects of sodium valproate and GABAA-agonist muscimol on dural plasma protein ([125I]-bovine serum albumin) extravasation evoked by either unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min) or substance P (SP) administration (1 nmol kg-1,i.v.) in anaesthetized Sprague-Dawley rats. 2. Intraperitoneal (i.p.) injection of sodium valproate or muscimol, but not baclofen (< or = 10 mg kg-1, i.p.) dose-dependently reduced dural plasma protein extravasation caused either by electrical trigeminal stimulation (ED50: 6.6 +/- 1.4 mg kg-1, i.p., and 58 +/- 18 micrograms kg-1, i.p. for valproate or muscimol, respectively) or by intravenous substance P administration (ED50: 3.2 +/- 1.4 mg kg-1, i.p. and 385 +/- 190 micrograms kg-1, i.p. for valproate or muscimol, respectively). 3. Valproate (6.6 mg kg-1, i.p.) or muscimol (58 micrograms kg-1, i.p.) had no effect on mean arterial blood pressure or heart rate when measured for 30 min after i.p. administration. 4. The GABAA-antagonist bicuculline (0.01 mg kg-1, i.p.) completely reversed the effect of valproate and muscimol on plasma extravasation following electrical stimulation or substance P administration, whereas the GABAB-receptor antagonist, phaclofen (0.01-1 mg kg-1, i.p.) did not. Bicuculline or phaclofen, given alone, did not alter the plasma extravasation response after either electrical stimulation or SP administration. 5. Valproate decreased plasma extravasation following substance P administration in adult animals, neonatally treated with capsaicin by a bicuculline-reversible mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Some behavioural effects of captopril in rats

1. Effects of inhibition of angiotensin converting enzyme (ACE, EC 3.4.15.1) in brain on psychomotor, exploratory, stereotyped and cognitive behaviour in rats were investigated. To inhibit brain ACE captopril (D-3-mercaptopropanoyl-L-proline) was given orally (p.o., 50 mg/kg) or intracerebroventricularly (i.c.v., 5 micrograms/rat). 3. Captopril given p.o. but not i.c.v. significantly enhanced stereotypy, overall number of conditioned avoidance responses, and decreased blood pressure. 4. No statistically significant influence of captopril given by either route on the number of crossings, rearings and bar approaches in the open field, performance of passive avoidance and number of correct choices as well as the speed of running for food in the T-maze was observed. 5. In conclusion, a small decrease of the activity of nigrostriatal dopaminergic system caused by the decrease of AII and/or increase of bradykinin, substance P, enkephalins and neurotensin in brain resulting from ACE inhibition is postulated.     

PHARMACOLOGICAL EVALUATION OF TWO NOVEL ANALOGUES OF MIANSERIN: 2-N-CARBOXAMIDINONORMIANSERIN(FCC5) AND 2-N-CARBOXAMIDONORMIANSERIN (FCC13)

1. The pharmacological properties have been examined of FCC5 (2-N-carboxamidinonormianserin) and FCC13 (2-N-carboxamidonormianserin), two novel analogues of mianserin. 2. FCC5 or FCC13 (100 micrograms/kg, i.v.) caused long-lasting (greater than 1 h) abolition of 5-hydroxytryptamine (5-HT) and histamine-induced bronchoconstriction in the anaesthetized guinea-pig. Both analogues had no effect (up to 1 mg/kg, i.v.) on bronchoconstriction caused by acetylcholine (25-50 micrograms/kg, i.v.). 3. The pressor effects of 5-HT in pithed rats were significantly attenuated by FCC5 (0.1 mg/kg, i.v.) or FCC13 (0.5 mg/kg, i.v.). 4. Oedema in the rat hind paw caused by intraplantar 5-HT was inhibited by FCC5 (ID50 0.76 mg/kg, i.p.; 2.7 mg/kg, p.o.) or FCC13 (ID50 0.65 mg/kg, i.p.; 5.8 mg/kg, p.o.). 5. In the central nervous system (CNS), FCC13 caused antagonism of 5-HT activity. It inhibited: (i) L-5-hydroxytryptophan (L-5-HTP)-induced head twitches in mice (ID50 1.85 mg/kg, i.p.), (ii) fenfluramine-induced facilitation of flexor reflex activity (FRA) in spinalized decerebrate rats (SDR) (IC50 0.57 mg/kg, i.p.). 6. FCC5 (less than or equal to 30 mg/kg, i.p. and less than or equal to 3 mg/kg, i.p., respectively) had no effect in either test. In contrast to mianserin, it also had no overt central actions as (less than or equal to 30 mg/kg, i.p.) had no effect on: (i) morphine-induced catalepsy (MIC) or (ii) clonidine-induced facilitation of FRA in SDR. However, high doses of FCC13 inhibited MIC (ID50 20 mg/kg, i.p.), but had no effect on (ii) (less than or equal to 10 mg/kg, i.p.). 7. Thus, FCC5 and FCC13 are potent, orally active H1 and 5-HT receptor antagonists. However, in contrast to FCC13 and mianserin, FCC5 did not cause CNS-mediated effects.     

The rise of body temperature induced by the stimulation of dopamine D1 receptors is increased in acutely reserpinized mice

In naive mice, the selective D1 agonist, SK&F 38393 (7.5-30 mg/kg s.c.), induced a significant rise of body temperature (0.5-1 degree C) which was antagonized by SCH 23390 (100 micrograms/kg s.c.) and by flupenthixol (0.4 mg/kg i.p.). In mice treated with reserpine (5 mg/kg s.c.) 18 h before testing, which on its own caused intense hypothermia (10-12 degrees C), SK&F 38393 (1.87-30 mg/kg s.c.) induced a dose-dependent and more marked rise of body temperature (5-7 degrees C). Similarly, SK&F 38393 (30 mg/kg s.c.) partially prevented reserpine-induced hypothermia. The central origin of the SK&F 38393 effects in reserpine-treated mice is indicated by the rise of body temperature induced by the i.c.v. administration of the drug (12.5-50 micrograms per mice). The SK&F 38393-induced rise of body temperature in acutely reserpinized mice was antagonized by SCH 23390 (50-200 micrograms/kg s.c.), clozapine (1.87-30 mg/kg i.p.) or chlorpromazine (2-32 mg/kg i.p.) but not by metoclopramide (25 or 100 mg/kg i.p.) or amisulpride (12.5 or 50 mg/kg). In naive mice, apomorphine (1 mg/kg s.c.) or LY 171555 (0.4 mg/kg s.c.) induced hypothermia which was antagonized by amisulpride (12.5 mg/kg i.p.); a transiently increased body temperature was even measured 30 min after apomorphine injection in amisulpride-treated mice. Apomorphine (1 mg/kg s.c.) induced a rise of body temperature in acutely reserpinized mice which was significantly reduced by SCH 23390 (50 and 200 micrograms/kg s.c.) and significantly increased by amisulpride (12.5 and 50 mg/kg i.p.). These data suggest that pharmacologically different dopamine receptor subtypes mediate different effects on body temperature in mice: D1 dopamine receptors mediate a rise of body temperature which is increased in hypothermic reserpinized animals and dopamine receptors of the D4 subtype mediate the decrease of body temperature in naive mice.     

Captopril potentiates the vasodepressor action of Met-enkephalin in the anaesthetized rat

The transient vasodepressor action of Met-enkephalin (10-80 micrograms kg-1, i.v.) in anaesthetized rats was significantly potentiated by the angiotensin-converting enzyme inhibitor, captopril (2 mg kg-1, i.v.); at this dose, it failed to modify the transient vasodepressor action of the non-specific vasodilator, nitroprusside (2.5, 5.0, 10 micrograms kg-1, i.v.). Captopril (2 mg kg-1, i.v.) caused a slow, progressive fall in the blood pressure of anaesthetized spontaneously hypertensive (SH) rats when compared to vehicle-treated controls. Pretreatment with naloxone (1.5 mg kg-1, i.v.) 30 min earlier failed to alter significantly the hypotensive action of captopril in anaesthetized SH rats. It was concluded that although captopril potentiated the vasodepressor action of Met-enkephalin in anaesthetized normotensive rats, potentiation of endogenous opioids does not appear to be involved in the hypotensive action of captopril in anaesthetized SH rats.     

Captopril given intracerebroventricularly, subcutaneously or by gavage inhibits angiotensin-converting enzyme activity in the rat brain

In rats with permanent brain cannulas intracerebroventricular (i.c.v.) injections of 2 microgram captopril nearly abolished drinking responses elicited by i.c.v. injections of 1 mUnit hog renin, 10 pmol synthetic renin substrate or 10 pmol angiotensin I but did not reduce drinking elicited by 10 pmol angiotensin II. Inhibition of the response to precursors of angiotensin II was long-lasting (at least 2 h) and dose-dependent (20 ng-2 microgram captopril). Captopril was 3-5 times more potent than SQ 20,881 i.c.v. Subcutaneous injections of captopril in doses 0.1 to 1.0 mg/kg reduced pressor responses to intravenous injections of angiotensin I without attenuating drinking elicited by i.c.v. injections of angiotensin precursors. Higher doses of captopril, however, given subcutaneously (5-50 mg/kg) or by gavage (10 mg/kg) did not reduce drinking to i.c.v. injections of renin or angiotensin I (but not angiotensin II). We conclude that captopril inhibits angiotensin-converting enzyme activity in the brain even when given subcutaneously or by gavage in doses commonly used in the rat.     

The effect of the selective PAF antagonist CIS-19 on PAF- and antigen-induced bronchoconstriction, microvascular leakage and bronchial hyperreactivity in guinea-pigs

We investigated the effects of a novel platelet-activating factor (PAF) receptor antagonist, CIS-19 [cis-2-(3, 4-dimethoxyphenyl)-6-isopropoxy-7-methoxy-1-(N-methylformamido)-1, 2, 3, 4-tetrahydronaphthalene], on PAF-, histamine-, substance P- and antigen-induced bronchoconstriction and microvascular leakage, as well as PAF- and antigen-induced bronchial hyperreactivity to methacholine in urethane-anesthetized guinea-pigs. Administration of CIS-19 (0.5–5 mg/kg, i.v.) inhibited the increase in lung resistance induced by PAF (30 ng/kg, i.v.) in a dose-dependent manner, but failed to inhibit the increase induced by histamine (30 μg/kg, i.v.) or substance P (6.5 μg/kg, i.v.). CIS-19 (5 mg/kg, i.v.) did not inhibit the increase in lung resistance induced by ovalbumin (2 mg/kg, i.v.) in actively sensitized guinea-pigs. PAF (30 ng/kg, i.v.)-induced microvascular leakage, measured by the extravasation of Evans blue dye, was dose-dependently inhibited by CIS-19 (0.5–5 mg/kg, i.v.) in the trachea, main bronchi and intrapulmonary airways, but it did not affect histamine (30 μg/kg, i.v.)- or substance P (6.5 μg/kg, i.v.)-induced microvascular leakage at all airway levels. CIS-19 (2.5 and 5 mg/kg) did not affect ovalbumin (2 mg/kg, i.v.)-induced microvascular leakage in all airway levels in actively sensitized guinea-pigs. CIS-19 (2.5 and 5 mg/kg, i.v.) significantly inhibited PAF-induced enhancement of the bronchial response to methacholine, but had no effect on ovalbumin (0.05 mg/kg, i.v.)-induced bronchial hyperreactivity in actively sensitized guinea-pigs. It is concluded that CIS-19 is a potent PAF receptor antagonist which inhibits PAF- but not antigen-induced bronchoconstriction, microvascular leakage and bronchial hyperreactivity. These results suggest that PAF plays little or no role in early airway responses following antigen challenge. Received: 29 April 1996 / Accepted: 10 October 1996     

The potentiation of cardiodepressant and hypotensive effects of bradykinin by enalapril and captopril both in vitro and in vivo.

1. Bradykinin (cumulative concentrations of 0.007-0.09 micrograms ml-1) produced a dose-related, but statistically insignificant depression of the isometric contraction of the isolated, spontaneously beating atria of the guinea-pig. The same concentrations of bradykinin did not change the atrial rate, but a tendency to a slight decrease was observed. 2. Enalapril (4.06 or 13.54 mumol l-1), produced a dose-related potentiation of the effect of the highest concentration of bradykinin on the isometric contraction. 3. Captopril (equimolar concentrations) also potentiated the effect of the highest concentration of bradykinin on the isometric contraction. This effect of captopril was not dose-related. 4. Both enalapril and captopril did not change the effect of bradykinin on the heart rate. 5. Bradykinin induced dose-related hypotensive responses in anaesthetized cats (0.03-1.0 microgram/kg b.w., i.v.) with a tendency towards bradycardia. 6. Enalapril (0.3 and 1.0 mg/kg b.w., i.v.) significantly potentiated bradykinin-induced hypotension and bradycardia. However, the potentiating effect of enalapril was not dose-dependent. 7. Captopril (0.1, 0.3 and 1.0 mg/kg b.w., i.v.) significantly potentiated bradykinin-induced hypotension and bradycardia. Also, the potentiating effect of captopril was not dose-dependent. 8. The failure of ACE inhibitors to potentiate the cardiodepressant and hypotensive effects of bradykinin in a dose-dependent manner is explained with some other mechanism(s) independent of ACE inhibition.     

Protective effects of benidipine on arachidonic acid-induced acute cerebral ischemia in rats.

Acute cerebral ischemia was produced in rats by injection of arachidonic acid (AA) into the internal carotid artery. Evans blue (EB) was intravenously injected and its extravasation into the brain was determined as an indicator of disturbances in the blood-brain barrier and endothelial cells. Control animals showed severe cerebral edema and marked blue staining of the brain. Benidipine (30 micrograms/kg, i.p.) suppressed the increase in cerebral water content and the extravasation of EB. Similarly nicardipine (100 micrograms/kg, i.p.) suppressed the elevation of water content and the extravasation of EB. Furthermore, both benidipine (30 micrograms/kg, i.p.) and nicardipine (100 micrograms/kg, i.p.) improved the neuronal injuries following AA-injection. An antiplatelet agent, ticlopidine (100 mg/kg, i.p.), and a thromboxane A2 synthetase inhibitor, OKY-1581 (3 mg/kg, i.p.), also suppressed the elevation of cerebral water content. A lipoxygenase inhibitor, AA-561 (200 mg/kg, p.o.), and a cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.p.), did not prevent the increase in cerebral water content. Neither benidipine (3-30 micrograms/kg, i.v.) nor nicardipine (100 micrograms/kg, i.v.) inhibited the AgNO3-induced thrombus formation of the abdominal aorta, whereas ticlopidine (100 mg/kg, p.o.) and OKY-1581 (3 mg/kg, i.v.) prevented the thrombus formation. From the present results, it is suggested that benidipine, as well as nicardipine, may protect against AA-induced acute cerebral infarction via a mechanism independent of antithrombotic action.     

Effects of the analgesic agent tramadol in normal and arthritic rats: comparison with the effects of different opioids, including tolerance and cross-tolerance to morphine

The effects of the analgesic agent tramadol (0.1-1 mg/kg i.v.) were compared to those of the mixed agonist-antagonist analgesics nalbuphine (1 mg/kg i.v.) and buprenorphine (3 micrograms/kg i.v.) in the vocalization threshold to paw pressure test. Normal and Freund's adjuvant-induced arthritic rats were used. We have shown previously that these animals used as a model of clinical pain exhibit an enhanced sensitivity to morphine (0.1-1 mg/kg i.v.), with a rapid development of tolerance after repetitive low doses, a response not observed in normal rats. In the present study, the antinociceptive effects of tramadol, buprenorphine and nalbuphine were enhanced (by 2- to 5-fold) in arthritic compared to normal rats. In this model, these effects were significantly reduced by a dose of naloxone (0.1 mg/kg i.v.) that completely antagonized the effect of morphine. In this model, the antinociceptive effect of tramadol (1 mg/kg i.v.) was comparable to that of nalbuphine (1 mg/kg i.v.), buprenorphine (3 micrograms/kg i.v.) and morphine (1 mg/kg i.v.). Repeated administration of low doses of tramadol twice daily for 4 days to arthritic rats did not induce tolerance, in contrast to nalbuphine, buprenorphine, and morphine. In addition, no cross-tolerance between tramadol and morphine was observed in these animals.