Ventilatory effects of low-dose paraoxon result from central muscarinic effects.

Paraoxon induces respiratory toxicity. Atropine completely reversed parathion- and paraoxon-induced respiratory toxicity. The aim of this study was to assess the peripheral or central origin of ventilatory effects of low-dose paraoxon. Male Sprague-Dawley rats were given paraoxon 0.215 mg/kg subcutaneously and treated with either atropine (10 mg/kg sc) or ascending doses of methylatropine of 5.42 (equimolar to that of atropine), 54.2, and 542 mg/kg administered subcutaneously 30 min after paraoxon. Ventilation at rest was assessed using whole-body plethysmography and rat temperature using infra-red telemetry. Results are expressed as mean+/-SE. Statistical analysis used two-way ANOVA for repeated measurements. Paraoxon induced a significant decrease in temperature 30 min after injection lasting the 90 min of the study period. This effect was partially corrected by atropine, but not by methylatropine whatever the dose. Paraoxon induced a decrease in respiratory rate resulting from an increase in expiratory time associated with an increase in tidal volume. Atropine completely reversed the ventilatory effects of low-dose paraoxon while the equimolar dose of methylatropine had no significant effects. The 54.2 and 542 mg/kg doses of methylatropine had no significant effects. Atropine crosses the blood-brain barrier and reverses peripheral and central muscarinic effects. In contrast, methylatropine does not cross the blood-brain barrier. Atropine completely reversed the ventilatory effects of low-dose paraoxon, while methylatropine had no significant effects at doses up to 100-fold the equimolar dose of atropine. We conclude that the ventilatory effects of low-dose paraoxon are mediated by disrupted muscarinic signaling in the central nervous system.

The peripheral sympathetic nervous system is the major target of cannabinoids in eliciting cardiovascular depression.

Our objective was to identify the sites of interaction of cannabinoids with cardiovascular sympathetic regulation in the rat. Effects on sympathetic tone were first determined in anaesthetised animals following i.v. administration of the drugs. Central effects were evaluated in anaesthetised rats receiving microinjections of cannabinoids into brain stem nuclei. Peripheral effects were identified in pithed rats with electrically stimulated sympathetic outflow. In anaesthetised and artificially ventilated rats, i.v. injection of the cannabinoid agonists WIN55212-2 and CP55940 decreased mean arterial pressure, heart rate and the plasma noradrenaline concentration. These effects were antagonized by the CB(1) cannabinoid receptor antagonist SR141716A. The bradycardia was abolished by the muscarinic acetylcholine receptor antagonist methylatropine. The decreases in mean arterial pressure and heart rate caused by cannabinoids in ventilated rats were much less pronounced than in spontaneously breathing rats. Microinjection of WIN55212-2 into the nucleus tractus solitarii had no effect. Microinjected into the rostral ventrolateral medulla oblongata, WIN55212-2 lowered mean arterial pressure slightly without changing other parameters. In pithed rats, WIN55212-2 inhibited the increases in mean arterial pressure, heart rate and the plasma noradrenaline concentration evoked by electrical stimulation of the sympathetic outflow. Our results show that activation of CB(1) cannabinoid receptors induces sympathoinhibition and enhancement of cardiac vagal tone, leading to hypotension and bradycardia. Presynaptic inhibition of noradrenaline release from terminals of postganglionic sympathetic neurons is the major component of the sympathoinhibition, but an effect in the rostral ventrolateral medulla oblongata may also contribute. The cannabinoid-evoked cardiovascular depression depends strongly on the respiratory state of the animals.

Cardiovascular studies on different classes of soft drugs.

Based on the inactive metabolite approach, three different classes of soft drugs were designed and synthesized. Their cardiovascular effects and duration of actions were studied in anesthetized male Sprague-Dawley rats compared to the traditional drugs. During the experiments ECG (leads II, aVF) and beat-to-beat blood pressure (BP) from the left carotid artery were recorded (except during the anticholinergic studies). The soft anticholinergic methoxycarbonylphenylcyclopentyl-N,N-dimethyltropinium methyl sulfate was as potent as atropine in the prevention of carbachol induced bradycardia; however, its action only lasted up to 15-30 min, compared to 2 h of that of atropine. In the isoproterenol-induced tachycardia model, while bufuralol at an i.v. dose of 3.8 mumol/kg (1 mg/kg) diminished heart rate (HR) for at least 2 h, the effects of the soft drugs lasted for only 30-40 min at equimolar doses. The methyl-, ethyl-, isopropyl-, and tert-butyl ester-analogs of the carboxylic acid metabolite of bufuralol showed the highest beta-blocking potencies (i.e., 30-50% of that of bufuralol). When these compounds were infused for 10 min at doses ranging from 2-4 mumol/kg/min, they caused a 20-40% decrease in HR and a 30-40% reduction in mean arterial pressure (MAP). These effects were similar to those elicited by esmolol at a dose of 20 mumol/kg/min in respect of the kinetics and in the extent of the reductions in heart rate and MAP. The isopropyl-, the sec-butyl-, and the neopentyl-esters of the acidic metabolite of amiodarone, with plasma hydrolytic half-lives of 60, 240 and 300 min, were tested in the benzene/adrenaline induced ventricular tachycardia (VT) model of the rat. All drugs were administered at a dose of 5 mumol/kg i.v. bolus immediately followed by an infusion at 15 mumol/kg/h for 2 h. It was found, that amiodarone resulted a complete suppression of VTs at 30 min after the start of drug administration, but its effect lasted up to the total course of the experiment (up to 180 min). On the contrary, both the sec-butyl and the isopropyl-analog resulted in complete suppression of VTs already during the first benzene/adrenaline challenge after drug administration (i.e., at 5 min). However, their effects disappeared between 15 and 30 min after discontinuation of the drug infusions in accordance with the enzymatic inactivation (ester hydrolysis) of these soft drugs. All these three classes of soft cardioactive drugs are good examples for highly potent but short acting drugs whose side effects might also be reduced via the retrometabolism based drug design.

Soft drugs--XVI. Design, evaluation and transdermal penetration of novel soft anticholinergics based on methatropine.

Atropine has been reported to produce unwanted systemic side effects on topical administration into the eye. The same problem could arise when atropine is used topically as a suppressant of eccrine sweating. In this study, the principles of soft drug design were applied to methatropine. A hypothetical carboxylate metabolite of methatropine was reactivated by esterification with cyclic and alicyclic alcohols to yield a series of compounds (3a-g). In vitro evaluation by guinea pig ileum assay indicated that the compounds are potent anticholinergics and the lead carboxylate metabolite is about 60 times less potent than the most active compound of the series. The activity was found to decrease with the increasing side chain length. The n-octanol/water partition coefficients were found to be directly dependent on the chain length for the compounds made with straight chain alcohols. The transdermal permeability coefficients across the hairless mice skin were found to be directly dependent on the partition coefficients. The soft drugs are found to metabolize extensively during the penetration process compared to the unmetabolizable nature of methatropine. The soft drugs reported in this study will probably be able to elicit a local action at the site of application but will probably be metabolized rapidly in the systemic circulation, thereby avoiding the systemic side effects with a consequent increase in the therapeutic index.

Análisis de las propiedades antihipertensivas del ácido-3-nitropropionico: un compuesto proveniente de plantas del género Astragalus / Antihypertensive properties of 3-nitropropionic acid: a compound derived from the astragalus plant

El ácido 3-nitropropiónico (ANP) es un compuesto proveniente de plantas del género Astragalus que ocasionó relajación dependiente de la concentración en anillos precontraídos de aorta de conejo. La remoción del endotelio o la presencia de atropina, propranolol o bromofeniramina no afectaron el efecto vasodilatador del ANP, el cual fue claramente inhibido por el azul de metileno. Por otra parte, la administración i.v. aguda de ANP en ratas normotensas o crónica por vía oral en perros hipertensos renales, provocó disminución en la presión sanguínea y bradicardia. Finalmente, el ANP ocasionó efectos inotrópicos negativos en aurículas aisladas de cobayos que no fueron bloqueados por atropina e inhibió los incrementos en fuerza y frecuencia de contracción cardíaca provocados por el isoproterenol. Los resultados indican que el ANP posee propiedades vasodilatadoras y antihipertensivas. La actividad vasodilatadora parece ser consecuencia de activación de la guanilato ciclasa, ya que se inhibió con azul de metileno. El efecto hipotensor del ANP fue independiente de la especie del animal o ruta de administración empleada. La bradicardia apreciada en ratas y perros y los efectos inotrópicos y cronotrópico negativos observados en aurículas aisladas, sugieren que el efecto hipotensor del ANP es una mezcla de acciones vasodilatadoras y cardiodepresoras. Los efectos cardíacos del ANP parecen relacionarse con inhibición de las respuestas mediadas por receptores ß-adrenérgicos

Opioid receptor agonists D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin and ethylketocyclazocine in the brain accentuate digoxin-induced arrhythmias.

OBJECTIVE: To examine the potential effects of two opioid receptor agonists in the brain on digoxin-induced cardiac arrhythmias and to explore cholinergic mechanisms in any potential effect on arrhythmias. METHODS AND RESULTS: Digoxin-induced arrhythmias were produced in guinea pigs (weighing between 280 and 350 g) that received digoxin 50 micrograms/kg intravenous bolus plus digoxin 500 micrograms/kg/h intravenously. Animals received D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin (FK 33,824) (50 or 100 micrograms/kg), ethylketocyclazocine (EKC) (50, 10 or 1 micrograms/kg) or saline (control) into the lateral cerebroventricle prior to digoxin. FK 33,824 produced significant (P less than 0.05) dose-dependent reductions in the threshold for digoxin-induced arrhythmias. The mean digoxin dosage at the development of fatal arrhythmias after the 100 micrograms/kg of FK 33,824 was 30% lower than the control group. EKC also produced significant (P less than 0.05) dose-dependent reductions in the threshold for digoxin-induced arrhythmias and the mean dose at development of fatal arrhythmias was 67% lower than the control group after 50 micrograms/kg of EKC. In the absence of digoxin, the highest dosages of each of these opioids did not produce arrhythmias. Changes in blood pressure and heart rate were unlikely explanations for the observed actions of these opioids because D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin accentuated the increase in blood pressure that accompanied digoxin while EKC reduced the blood pressure response to digoxin and neither altered the heart rate response to digoxin. In the control group, fatal digoxin-induced arrhythmias were ventricular tachyarrhythmias in two-thirds of cases and complete heart block in the remainder. These opioids accentuated the development of complete heart block. The role of the cholinergic system was explored for only EKC because both opioids produce similar effects on arrhythmias, using atropine sulphate which crosses the blood brain-barrier and atropine methylnitrate which does not enter the central nervous system. Atropine sulphate, but not atropine methylnitrate, slightly blunted but did not reverse the action of EKC. CONCLUSIONS: These data indicate that: two opioids in the brain--D-Ala-2-Me-Phe-4-Met-(O)-ol enkephalin and EKC--alter the threshold for development of digoxin-induced arrhythmias, specifically accentuating development of complete heart block produced by digoxin; and cholinergic mechanisms play only a small role in modulating the action of EKC on digoxin-induced bradyarrhythmias.

Extended middle ear drug delivery. A new concept; a new device.

The authors present the development of a new device that consists of a biodegradable support matrix incorporating a therapeutically releasable amount of ampicillin. This device is in an insertable shape that allows easy placement into the middle ear. Once in the middle ear cavity it expands, contacts the walls, and provides extended sustained release of ampicillin. In vitro studies over three months documented the consistent release of therapeutically effective levels of ampicillin. In vivo efficacy was demonstrated in the cat otitis media induced by eustachian tube obstruction. Cultures of normal cat middle ear cavities prior to obstruction revealed no microflora. Cultures after obstruction of the middle ears of animals treated with this device had no growth of bacteria as early as one week after obstruction (10 out of 12 cats). The contralateral untreated ears became culture negative at two weeks post obstruction, suggesting that the effect of the device is not limited to the treated ear. Histopathological studies showed the effect of the device as early as one week post obstruction in treated ears and after two weeks in the contralateral ear. Both ears became normal at three months, while obstructed untreated animals (controls) developed chronic irreversible otitis media changes. In addition, histopathological findings documented a lack of inflammatory reaction from the device itself, and its capacity of being biodegradable. Topical extended middle ear drug delivery can become a significant form of treatment for middle ear disease and has the potential of being useful as a source for inner ear drug delivery.

Short acting soft mydriatics.

Three soft drug analogs of atropine have been tested for mydriatic activity in rabbits' eyes and their in vitro metabolic pathway has been investigated in rat, rabbit and human blood. The three soft drugs were found to produce an equieffective mydriatic activity to atropine and tropicamide. At equieffective concentrations, their durations were shorter with AUC's 12-21% that of 0.25% atropine and 44-80% that of 0.2% tropicamide. The untreated control eyes were observed to dilate after unilateral ocular administration of atropine, but not with unilateral soft drug treatment. In vitro stability studies showed that the soft ethyl analog was less stable in rat blood and rat liver homogenate than in rabbit or human blood. The metabolic product of the soft ethyl derivative in biological media was proven to be the corresponding inactive acidic metabolite predicted by the soft drug design. The ultrashort durations and the potentially nontoxic systemic properties of the soft mydriatics offer promise for use in ophthalmoscopy and in other ocular procedures where a short acting anticholinergic type of mydriatic would be indicated.

Vasomotor rhinitis and the systemic absorption of ipratropium bromide.

Plasma concentrations of nasally administered ipratropium bromide were analyzed in 10 subjects suffering from severe vasomotor rhinitis and 10 age-sex matched control subjects. The rate of salivary secretion and heart rate were monitored in order to measure systemic anticholinergic effects. A total dose of 360 micrograms of ipratropium bromide (60 micrograms into each nostril, repeated twice at 15 min intervals) were administered nasally to the subjects in randomized order. Ipratropium bromide was rapidly absorbed from the nasal mucosa into the systemic circulation in both groups. The peak plasma concentrations were detected within 10 min after the last drug administration. The peak concentrations were about 50% higher (380 +/- 153 pg/ml) in patients than in control subjects (245 +/- 134 pg/ml). The AUCs/0-15 min (1970 +/- 1140 pg/ml X min) in patients were about 100% higher than in the control subjects (960 +/- 560 pg/ml X min). During the experiment there was a small decrease in the heart rate (8 bpm) and salivary secretion (10%) in both groups. In conclusion, the vasomotor rhinitis increases the systemic absorption of nasally administered ipratropium bromide, but the small increase in the absorption is not likely to have any clinical consequences.

Pharmacokinetics of ipratropium bromide after single dose inhalation and oral and intravenous administration.

Single doses of ipratropium bromide were administered intravenously, orally and by slow inhalation to ten healthy male volunteers. The plasma level after oral administration followed a low but broad plateau persisting for several hours. After i.v. administration the kinetic parameters were: Vc = 25.9 l, V alpha = 13.1 l, V beta = 3.38 l, t1/2 alpha = 3.85 min, t1/2 beta = 98.4 min, AUC = 15.0 h.ng/ml, kel = 11.8 l/h and total clearance is 2325 ml/min. The bioavailability was 3.3% (range 0.9-6.1%) on comparing the plasma AUCs following i.v. and 20 mg oral administration. The cumulative renal excretion (0-24 h) after i.v. administration was compared with that after oral administration and inhalation. Following oral administration, the apparent systemic availability was around 2%, and after inhalation it was 6.9%. In comparison with oral placebo administration, only after i.v. administration was there a significant change in heart rate (from 63.7 to 90.2 beats/min). The systolic blood pressure rose from 115.1 to 119.6 mm Hg and the diastolic blood pressure from 68.3 to 78.3 mm Hg.

Evaluation of the systemic anticholinergic activity of nasally administered ipratropium bromide.

Plasma concentrations of nasally inhaled ipratropium bromide were analyzed in eight healthy volunteers by using a sensitive radioreceptor assay (RRA). The rate of saliva secretion, heart rate and changes in visual accommodation were quantitated in order to measure possible systemic anticholinergic drug effects. 240 micrograms of ipratropium bromide (40 micrograms each nostril, repeated twice at 15 min intervals) were inhaled nasally in a double blind, randomized, placebo-controlled experiment. Ipratropium bromide absorbed fast, and peak plasma concentrations of the drug (257 +/- 55 pg/ml) were detected as soon as 5 min after the last inhalation (at 35 min from the beginning). The plasma levels of ipratropium bromide decreased rapidly, being only 86 +/- 7 pg/ml one hour after the last inhalation. These low concentrations of ipratropium bromide indicate that only a small portion of it absorbs after nasal application, which is consistent with the lack of any systemic anticholinergic drug effects in our subjects. It is concluded that nasally applied ipratropium bromide is not likely to cause systemic anticholinergic side-effects, even in doses exceeding the therapeutic recommendations.