A comparison of the effects of verapamil and cinnarizine upon responses elicited by selective alpha 1- and alpha 2-adrenoceptor agonists in the autoperfused canine hindlimb

In an attempt to extend the hypothesis that activation of vascular postsynaptic alpha 2-adrenoceptors requires an influx of Ca2+ ions, the effects of 2 calcium entry blocking drugs verapamil and cinnarizine have been examined as inhibitors of the pressor responses to methoxamine and B-HT 920 in autoperfused dog hindlimb preparations. Verapamil (0.1-1 mg i.a.) selectively antagonized responses to B-HT 920 and had little or no effect upon responses to methoxamine, thus supporting this hypothesis. However cinnarizine, over the dose range studied (0.1-1 mg/kg i.a.) produced quantitatively similar inhibitions of the hindlimb responses to B-HT 920 and methoxamine. These results suggest that cinnarizine may have a different site of action to verapamil in resistance vessels of the dog hindlimb.     

Effect of verapamil on cardiac protein kinase C activity in diabetic rats

We examined the effect of verapamil treatment on cardiac protein kinase C (PKC) activity in streptozocin-induced diabetic rats. Basal cardiac PKC activity in diabetes increased in both cytosolic (by 94%, P < 0.01) and membrane (by 41%, P < 0.05) fractions as compared with that in controls. Subcutaneous administration of 8 mg/kg verapamil twice a day for 8 weeks induced a significant decrease in both cytosolic (by 59%, P < 0.01) and membrane (by 50%, P < 0.01) PKC activity in diabetes as compared with the activity in the non-treated diabetic groups. In contrast, cardiac cytosolic PKC activity in control rats was significantly (P < 0.01) decreased by 41% as compared with that of the non-treated control group without there being any change in membrane PKC activity. Our data demonstrate that verapamil treatment may ameliorate the abnormal activation of cardiac PKC in diabetes.     

Effects of ondansetron administration on opioid withdrawal syndrome observed in rats

This study tested whether a 5-HT₃ receptor antagonist could reverse the signs of precipitated opioid withdrawal. Rats were treated with either saline or morphine for 4 days. After the four days, half of the rats in each group received naloxone and half received saline. Each animal also received one of four doses of ondansetron (0, 1, 2 and 4 mg/kg i.p.). Administration of ondansetron to rats receiving naloxone after chronic morphine decreased the intensity of withdrawal signs such as increased defecation, jumping and wet-dog shakes, elevated the nociceptive threshold values which were decreased by precipitated withdrawal, but produced no change in urination, rectal temperature or salivation. The effects exhibited by ondansetron administration may be explained through interference of its 5-HT₃ receptor antagonist activity with serotoninergic mechanisms involved in the regulation of these withdrawal symptoms. The use of this drug is thus suggested as a possible treatment of opioid withdrawal signs in heroin addicts.     

Comparison of abstinence syndromes precipitated by flumazenil and PK 11195 in female diazepam-dependent rats

 The abilities of the central (CBR) and the peripheral (PBR) benzodiazepine receptor antagonists, flumazenil (FLU) and PK 11195 (PK), to precipitate an abstinence syndrome in diazepam (DZ)-dependent rats have been evaluated. Female rats were exposed for 5 weeks to DZ slowly released from SC implanted silastic capsules (90 mg/capsule per week) and thereafter they were challenged in weekly intervals with IV injections of FLU (10, 20, 40 mg/kg) or PK (5, 10, 20 mg/kg), respectively. The maximum abstinence scores tended to increase with the dose of FLU but not with the dose of PK. Although FLU and PK precipitated some common abstinence signs, there were marked differences between these antagonists. FLU evoked dose-related tonic-clonic and clonic convulsions (five out of six rats), whereas PK (10 mg/kg) induced convulsions in only one rat (out of five); tachypnea tended to increase with the dose of both FLU and PK; twitches and jerks, backing and writhing had a significant regression on the dose of FLU; rearing tended to decrease with the dose of PK whereas FLU-evoked head bobbing and PK-evoked twitches and jerks had inverse U-shaped dose-response curves. In comparison to FLU, similar doses of PK (10 and 20 mg/kg) induced a lower precipitated abstinence score (P<0.05) and a less intense tachypnea (P<0.05).The data indicate that the chronic continuous exposure to DZ (and/or its active metabolites) affects both CBR and PBR in the rat; however, the abstinence syndromes produced by the CBR and PBR antagonists, FLU and PK, differ in overall intensities and in the diversity of evoked abstinence signs. Received: 5 November 1996 / Final version: 25 April 1997     

Differential classical conditioning of abstinence syndrome in morphine-dependent rats

Independent groups of addicted rats were placed repeatedly in a conditioning procedure: pairings of non-rotatable activity wheels with periods of either 0–11 or 12–23 h of morphine deprivation. Controls consisted of a saline-injected group exposed to the same training stimuli and conditioning procedure, and a morphine addicted group not receiving such training. Subsequently, morphine-addicted animals were withdrawn until primary abstinence signs disappeared, and all groups were tested in unlocked wheels for differential activity resulting from reexposure to previous training environments.Experimental groups not only were found to exhibit significantly increased wheel turning over controls, but subjects having greater morphine deprivation during training were more resistant to extinction than a low deprivation group. Motivational interpretations and methodological artifacts in designs of this nature are discussed.A lengthy review of the literature encompassing the area of the present study, as well as a more thorough discussion of its theoretical aspects, were included in a Ph. D. thesis submitted to the Department of Psychology at the University of Denver, 1969, by the author.     

Role of catecholaminergic mechanisms in the expression of the morphine abstinence syndrome in rats

The effect of various drugs affecting catecholaminergic mechanisms on the precipitated morphine withdrawal syndrome was studied in rats which had developed a medium degree of dependence. Administration of low doses of d-amphetamine, cocaine, and L-Dopa shortly before precipitating withdrawal by levallorphan induced a dose-dependent increase of dominant withdrawal signs such as jumping and a decrease of recessive signs such as wet dog shaking; signs such as diarrhea and ptosis decreased, whereas rhinorrhea, salivation and lacrimation increased. A qualitatively very similar change in withdrawal signs occurred when withdrawal was precipitated in extremely highly dependent rats and/or increasing doses of the antagonist were administered. Therefore, the effects of the above drugs are interpreted as potentiation of withdrawal. Pretreatment with higher doses of the same drugs provoked strong stereotyped behaviour which obviously suppressed the occurrence of other motor signs.Activation of noradrenergic or dopaminergic mechanisms with desipramine or apomorphine induced an increase in the intensity of withdrawal, which was, however, much more pronounced after the former than the latter drug. When catecholamines (CA) were previously depleted by alpha-methyl-para-tyrosine (AMT), apomorphine lost a great part of its effectiveness. Blockade of CA synthesis by AMT alone resulted in decreased jumping while at the same time writhing largely increased, thus, inducing a profile of signs characteristic for a weak withdrawal. Selective inhibition of noradrenaline synthesis by FLA-63 resulted in a reduction in withdrawal intensity. Ro 4-4602 + L-Dopa, given after AMT, antagonized and reversed the reduction of withdrawal, but this effect was not so pronounced when by additional pretreatment with FLA-63 NA levels remained low. It is concluded that of both brain CA especially noradrenaline is involved in the manifestation of the morphine withdrawal syndrome.     

Enhanced bioavailability of verapamil after oral administration with hesperidin in rats

The aim of this study was to investigate the effects of hesperidin on the pharmacokinetics of verapamil and its major metabolite, norverapamil, in rats. The pharmacokinetic parameters of verapamil and norverapamil in rats were measured after the oral administration of verapamil (9 mg/kg) in the presence or absence of hesperidin (3 or 10 mg/kg). Compared to the control group, the presence of hesperidin significantly (p<0.01) increased the area under the plasma concentration-time curve (AUC) of verapamil by 71.1–96.8% and the peak concentration (C_max) of verapamil by 98.3–105.2%. Hesperidin significantly (p<0.01) decreased the total plasma clearance (CL/F) of verapamil by 41.6–49.2% in rats. However there was no significant change in the time to reach the peak plasma concentration (T_max), the elimination rate constant (K_el) and the terminal half-life (T_1/2) of verapamil in the presence of hesperidin. The AUC and C_max of norverapamil were significantly (p<0.05) higher in rats coadministrated with hesperidin than those of the control. Consequently hesperidin significantly enhanced bioavailability of verapamil in rats. These results might be due to the decreased efflux and metabolism of verapamil in the intestine. Drug interactions should be concerned in the clinical setting when verapamil is used concomitantly with hesperidin or hesperidin-containing dietary.     

Effects of repeated withdrawal from continuous amphetamine administration on brain reward function in rats

RATIONALE: The study of the effects of repeated amphetamine administration and withdrawal on brain reward function has relevance to both amphetamine dependence and non-drug-induced depressions. OBJECTIVES: The purpose of this study was to investigate the effects of continuous amphetamine administration and withdrawal on brain stimulation reward thresholds, and the changes that occur with repeated amphetamine exposures. METHODS: Rats were prepared with bipolar electrodes in the lateral hypothalamus and trained in a discrete-trial reward threshold procedure. Then, rats underwent two separate periods of amphetamine administration via subcutaneous osmotic mini-pumps. RESULTS: Continuous amphetamine administration was associated with lowering in brain reward thresholds and decreases in response latencies, while withdrawal was associated with threshold elevations. These effects changed with subsequent amphetamine administration and withdrawal. CONCLUSIONS: The results of this study indicated that with the amphetamine administration regime used here, rats developed increased sensitivity to the effects of acute amphetamine administration and tolerance to the effects of amphetamine withdrawal.     

Effects of peripheral and central administration of calcium channel blockers in the naloxone-precipitated abstinence syndrome in morphine-dependent rats

The effects of two calcium channel blockers (verapamil and flunarizine) were evaluated on the naloxone-precipitated syndrome in morphine-dependent rats. The withdrawal signs in saline-treated rats were mainly diarrhea, body weight loss, jumping and ptosis. On i.p. administration, verapamil and flunarizine prevented diarrhea and body weight loss but not jumping. Verapamil also reduced the incidence of ptosis at the highest dose tested (40 mg/kg). Administered i.c.v., 160 micrograms verapamil reduced the body weight loss and the number of jumps without modifying diarrhea or ptosis. The results show that calcium channel blockers inhibit morphine abstinence syndrome manifestations through both peripheral and central mechanisms.     

Pharmacodynamics of acute intranasal administration of verapamil: comparison with i.v. and oral administration

The present study was conducted in order to examine the intranasal administration of verapamil and compare this route to oral and intravenous administration in a 3 way crossover protocol in five dogs. Unanesthetized, adult mongrel dogs were given verapamil intravenously (0.5 mg/kg), orally (2.5 mg/kg) and intranasally (0.75 mg/kg) with at least a 3-4 day washout period between each administration. Blood samples were collected over a 10 hour period and analyzed for verapamil using HPLC with fluorescence detection. A lead II ECG was monitored to determine the effects of verapamil on heart rate and P-R interval. Following intravenous administration, verapamil was distributed according to a two compartment model. Bioavailability (corrected for dose and elimination rate constant) following intranasal administration (36% +/- 7%) was approximately 3 fold that after oral administration (13% +/- 3%). Absorption from the nasal cavity appeared instantaneous compared to an absorption half-life of 50 +/- 6 min after oral administration. All three routes of administration resulted in significant increases in heart rate and increases in the P-R interval. Maximal P-R interval prolongation occurred after peak plasma concentrations of verapamil. The results of this study suggest that the intranasal route is a viable alternative route of administration for verapamil.     

The effects of chronic administration of ethanol on startle thresholds in rats

The thresholds for startle responses to electric shock were measured in adult male Wistar strain rats given ethanol daily in doses rising from 3 to 7 g/kg over a 30-day period, and in controls receiving equicaloric doses of sucrose. Tests made 23, 36, or 47 h after ethanol (i.e., during partial or complete ethanol withdrawal) gave threshold values significantly lower than those obtained with sucrose-treated controls. The difference became greater after longer ethanol treatment and larger doses. However, when threshold measurements were made under the acute influence of ethanol in the experimental group, the mean values were virtually equal to those of the sucrose controls. This normalization, by ethanol, of a disturbance produced by absence of ethanol in a chronically treated animal is indicative of physical dependence. Following termination of ethanol treatment there was a gradual return of startle thresholds almost to control values over a relatively short period, indicating that the changes underlying the hyperexcitability are readily reversible.     

Effect of pioglitazone on the pharmacokinetics of verapamil and its major metabolite,norverapamil, in rats

Pioglitazone, a thiazolidinedione antidiabetic drug, inhibits cytochrome P450 (CYP) 2C8 and CYP3A4 enzymes in vitro. This study investigated the effect of pioglitazone on the pharmacokinetics of verapamil and its major metabolite, norverapamil, in rats, after oral administration of verapamil (9 mg/kg) in the presence or absence of pioglitazone (0.3 or 1.0 mg/kg). Pioglitazone altered verapamil pharmacokinetics compared with verapamil alone. The presence of 1.0 mg/kg of pioglitazone significantly (p < 0.05) increased the area under the plasma concentration-time curve (AUC) and the peak concentration (C(max)) of verapamil by 49.0% and 46.8%, respectively, and significantly (p < 0.05) decreased the total plasma clearance (CL/F) of verapamil by 32.8%. The metabolite-parent AUC ratio in the presence of pioglitazone (1.0 mg/kg) significantly (p < 0.05) decreased by 21.9% compared to the control group. Thus, coadministration of pioglitazone inhibited the CYP3A4-mediated metabolism of verapamil.     

Transient disruption of attentional performance following escalating amphetamine administration in rats

Rationale Attentional deficits are thought to be critically involved in the development of positive symptoms in schizophrenia. The present experiment tests the general hypothesis that sensitization of the mesolimbic dopaminergic system contributes to the attentional deficits in schizophrenia.Objectives The present study assessed attentional performance following administration of an escalating amphetamine regimen and subsequent challenge amphetamine administration in rats.Methods Rats were trained to perform a two-lever sustained attention task that involved discrimination of visual signals and no signal presentation. After reaching criterion, subjects were assigned to receive escalating amphetamine or saline. Attentional performance was assessed immediately following escalating amphetamine, following challenge amphetamine administration (1.0 mg/kg) to amphetamine-pretreated rats, and for 3 days after the challenge session. At the end of this experiment, a dose-response study was conducted with saline-pretreated rats to confirm the appropriateness of the challenge dose.Results Amphetamine-pretreated animals demonstrated a transient increase in errors on non-signal trials following escalating amphetamine administration. The latency to press a lever was decreased during and after challenge amphetamine administration. Administration of 1.0 mg/kg amphetamine did not alter accuracy of amphetamine-pretreated animals or of saline-pretreated animals in the dose-response experiment.Conclusions Prior escalating amphetamine administration transiently disrupted attention, increasing incorrect claims for a signal on trials when no signal was presented. The present data support the existing literature that escalating amphetamine regimens may be useful to model the attentional deficits that contribute to the psychotic symptoms in schizophrenia.     

Effects of smoking abstinence on adult smokers with and without attention deficit hyperactivity disorder: results of a preliminary study

Rationale Individuals with attention deficit hyperactivity disorder (ADHD) smoke at higher rates than the general population; however, little is known about the mechanisms underlying this comorbidity. Objective This study evaluated the effects of overnight abstinence on withdrawal symptoms and cognitive performance in adult smokers with and without ADHD. Materials and methods Individuals smoking ≥15 cigarettes per day were recruited from the community and underwent an evaluation to establish a diagnosis of ADHD (n = 12) or not (n = 14). Withdrawal symptoms, mood, craving, cognitive performance, and smoking cue reactivity were measured during two laboratory sessions—in a ‘Satiated’ condition participants smoked up to and during the session while in an ‘Abstinent’ condition, participants were required to be smoking abstinent overnight and remain abstinent during the session. Results The effects of abstinence on ADHD and non-ADHD smokers did not differ for withdrawal symptom severity, mood, craving or cue reactivity. Significant Group × Condition interactions were observed for measures of attention and response inhibition on the Conners’ CPT. For reaction time (RT) variability and errors of commission, the ADHD group exhibited greater decrements in performance after overnight abstinence compared to the non-ADHD group. The effects of abstinence on other cognitive measures (e.g., rapid visual information processing task, cued Go/No-Go task) did not differ between the two groups. Conclusion This preliminary study is the first to systematically evaluate the effects of acute smoking abstinence in adult smokers diagnosed with ADHD. Individuals with the disorder may smoke at higher rates due to greater worsening of attention and response inhibition after abstinence.     

Effect of P-glycoprotein inhibitor, verapamil, on oral bioavailability and pharmacokinetics of irinotecan in rats

The objective of present investigation was to study the effect of verapamil on the pharmacokinetics of irinotecan in order to evaluate the role of P-glycoprotein (P-gp) in irinotecan disposition. An in vitro study using Caco-2 intestinal cell monolayer was first carried out to determine the effect of verapamil on the function of intestinal P-gp. Verapamil (25 mg/kg) was administered orally 2 h before irinotecan oral (80 mg/kg) or intravenous (20 mg/kg) dosing in female Wistar rats. Plasma and biliary samples were collected at specified time points from control and treated animals to determine irinotecan and its metabolite, SN-38 concentrations. Bi-directional transport and inhibition studies in Caco-2 cells indicated irinotecan to be a P-gp substrate and the function of intestinal P-gp was significantly inhibited in presence of verapamil. After oral irinotecan dosing, the mean area under the plasma concentration–time curve (AUC) was found to be 14.03 ± 2.18 μg h/ml which was increased significantly, i.e. 61.71 ± 15.0 μg h/ml when verapamil was co-administered (P < 0.05). Similarly, the mean maximum plasma concentration of irinotecan increased from 2.93 ± 0.37 μg/ml (without verapamil) to 10.75 ± 1.0 μg/ml (with verapamil) (P < 0.05). There was approximately 4–5-folds increase in apparent bioavailability. On the other hand, the intravenous irinotecan administration with verapamil resulted in small but statistically significant effect on AUC (10.76 ± 2.0 to 23.3 ± 3.8 μg h/ml; P < 0.05) and systemic clearance (1206.4 ± 159.7 to 713.5 ± 78.2 ml/(h kg)). In addition, SN-38 showed significant change in oral pharmacokinetic parameters and minor changes in intravenous pharmacokinetic profile. Biliary excretion curves of both irinotecan and SN-38 were lowered by verapamil. The mean percent of irinotecan excreted into bile over 5 h following intravenous and oral administration was found to be 8% and 1%, respectively, which was further reduced to half when treated with verapamil. These results are quite stimulating for further development of a clinically useful oral formulation of irinotecan based on P-gp inhibition.     

Intravenous verapamil kinetics in rats: Marked arteriovenous concentration difference and comparison with humans

The pharmacokinetics of verapamil, a calcium channel blocker, were studied in male Sprague—Dawley rats following i.v. administration at a dose of 1 mg kg^?1. Both arterial and venous blood were collected and the plasma drug concentrations were determined by reversed-phase high-performance liquid chromatography. Verapamil was distributed to the extravascular tissues very rapidly as indicated by the large V_dss (2.99±0.57 1 kg^?1) and V_dβ (5.08 ± 0.541 kg^?1). The apparent terminal plasma T_1/2, MRT_iv, and CL_p were 1.59 ± 0.46, 1.26 ± 0.12 h, and 40.4 ± 9.73 ml min^?1 kg^?1, respectively. Marked arterial/venous differences were found with a considerable influence on the MRT and V_dss, and the terminal phase venous levels were higher than arterial levels by 103, 69, and 90%, respectively, for the three rats studied. The distribution of verapamil between plasma and erythrocytes occurred very rapidly and was identical in vitro and in vivo. The average blood to plasma and plasma to blood cell concentration ratios were 0.85 and 1.47, respectively. In contrast to propranolol, blood data rather than plasma data should be used to predict the hepatic extraction ratio of verapamil (0.87). The plasma protein binding of verapamil in humans (90%) and rats (95%) were quite similar and constant over the wide concentration range studied. A comparison of some pharmacokinetic parameters between rats and humans is presented and the potential shortcomings of using T_1/2 or CL_p and the advantage of using CL_u (unbound plasma clearance) in interspecies scaling is also discussed.     

Effect of verapamil in obstructive airways disease

Summary Lung resistance and the ECG were studied before and after i.v. injection of verapamil in six healthy subjects and in nine patients with obstructive airways disease. No systematic effect on lung resistance was found in any of the groups. There was prolongation of atrio-ventricular conduction time in those healthy subjects who received a larger dose of verapamil. Inhalation of isoprenaline caused a significant decrease of lung resistance in patients with obstructive airways disease. It is concluded that verapamil is not contraindicated in the latter disease. The results support the hypothesis that verapamil causes quantitatively different effects on the same type of tissue at different sites.     

Influence of different benzodiazepines on the experimental morphine abstinence syndrome

The abuse of benzodiazepines by narcotic addicts has been well documented. However, the pharmacological basis of this abuse is not clear. In this study the effects of different benzodiazepines (flunitrazepam: 0.5, 1 and 2 mg/kg; nitrazepam: 0.5, 1, 2.5, 5 and 10 mg/kg; diazepam: 0.5, 1, 2.5, 5 and 10 mg/kg; chlordiazepoxide: 0.5, 1, 2.5, 5 and 10 mg/kg; and triazolam: 0.5, 1 and 2 mg/kg) on the morphine withdrawal syndrome in mice have been compared. Drugs were administered 30 min before naloxone-induced withdrawal. All benzodiazepines tested induced similar changes in some of the signs of morphine abstinence: decreased jumping behavior and increased wet dog shake frequency. Jumping behavior was particularly decreased by triazolam and wet dog shakes were mainly increased by flunitrazepam and nitrazepam. Forepaw treading was reduced by flunitrazepam, diazepam and triazolam, increased by nitrazepam and not changed by chlordiazepoxide. Tremor was effectively reduced by diazepam but less reliably by the other benzodiazepines. Teeth chattering was reduced by flunitrazepam and diazepam. These results indicate that benzodiazepines can interfere with the expression of the morphine withdrawal syndrome.     

Dose, duration and pattern of nicotine administration as determinants of behavioral dependence in rats

Rationale Relatively little is known about the role of dose, duration, and pattern of nicotine exposure in the development of dependence. Disruption of learned behavior during antagonist-precipitated withdrawal can be a sensitive, quantitative measure of behavioral dependence. Objectives The present study sought to determine whether behavioral dependence upon nicotine could be induced in rats and, if so, what exposure conditions were essential for inducing it. Our primary focus was on whether continuous exposure over several days was necessary to produce dependence. Methods Male Sprague–Dawley rats were trained to lever press under fixed-ratio 10 schedules of food reinforcement during daily, 15-min experimental sessions. Nicotine was then administered s.c. via osmotic minipumps that delivered various nicotine dosage regimens, some including 24-h nicotine-free periods, to manipulate pattern of exposure. The presence of dependence was tested with challenges with the nicotinic acetylcholine receptor antagonist, mecamylamine, or during spontaneous withdrawal. Results After 7 days of 3, 6, and 12 mg kg⁻¹ day⁻¹ nicotine administration, response rates were significantly reduced in nicotinized, but not in saline-treated rats following mecamylamine challenges. Subsequent studies demonstrated that 4 days, but not 3 days, of cumulative 3 mg kg⁻¹ day⁻¹ nicotine administration was sufficient to induce dependence. The induction of dependence could be prevented by imposing a nicotine-free period between the first and second days during these 4-day regimens but not at other times. Conclusion Behavioral dependence upon nicotine can be induced in the rat, and its induction is dependent upon its cumulative duration and pattern of exposure suggesting that tobacco dependencies could be controlled by similar determinants.