Prazosin Pretreatment Research Articles

Prazosin Protects the Liver Against Renal Ischemia/Reperfusion Injury in Rats.

Acute kidney injury (AKI) is a common subsequent problem after many medical conditions. AKI is associated with distant organ dysfunction where systemic inflammation and oxidative stress play major roles. In this study, the effect of Prazosin, an α1-Adrenergic receptor antagonist, was investigated on the liver injury induced by kidney ischemia-reperfusion (I/R) in rats. Male adult Wistar rats (n=21) were divided into three groups: sham, kidney I/R, and kidney I/R pre-treated with Prazosin (1 mg/kg). Kidney I/R was induced by vascular clamping of the left kidney for 45 min to reduce the blood flow. Oxidative and antioxidant factors along with apoptotic (Bax, Bcl-2, caspase3), and inflammatory (NF-κβ, IL-1β, and IL-6) factors were measured in the liver at protein levels. Prazosin could reserve liver function (p<0.01) and increase glutathione level (p<0.05) after kidney I/R significantly. Malonil dialdehyde (MDA), a lipid peroxidation marker, was diminished more significantly in Prazosin-treated rats compared to the kidney I/R group (p<0.001). Inflammatory and apoptotic factors were diminished by Prazosin pre-treatment in the liver tissue (p<0.05). Pre-administration of Prazosin could preserve liver function and decrease its inflammatory and apoptotic factors under kidney I/R conditions.

Regulation of Aqueous Humor Secretion by Melatonin in Porcine Ciliary Epithelium.

Secretion of melatonin, a natural hormone whose receptors are present in the ciliary epithelium, displays diurnal variation in the aqueous humor (AH), potentially contributing to the regulation of intraocular pressure. This study aimed to determine the effects of melatonin on AH secretion in porcine ciliary epithelium. The addition of 100 µM melatonin to both sides of the epithelium significantly increased the short-circuit current (Isc) by ~40%. Stromal administration alone had no effect on the Isc, but aqueous application triggered a 40% increase in Isc, similar to that of bilateral application without additive effect. Pre-treatment with niflumic acid abolished melatonin-induced Isc stimulation. More importantly, melatonin stimulated the fluid secretion across the intact ciliary epithelium by ~80% and elicited a sustained increase (~50-60%) in gap junctional permeability between pigmented ciliary epithelial (PE) cells and non-pigmented ciliary epithelial (NPE) cells. The expression of MT3 receptor was found to be >10-fold higher than that of MT1 and MT2 in porcine ciliary epithelium. Aqueous pre-treatment with MT1/MT2 antagonist luzindole failed to inhibit the melatonin-induced Isc response, while MT3 antagonist prazosin pre-treatment abolished the Isc stimulation. We conclude that melatonin facilitates Cl- and fluid movement from PE to NPE cells, thereby stimulating AH secretion via NPE-cell MT3 receptors.

Prazosin Treatment Protects Brain and Heart by Diminishing Oxidative Stress and Apoptotic Pathways After Renal Ischemia Reperfusion.

Acute kidney injury (AKI) is a major medical challenge caused from renal ischemia-reperfusion (IR) injury connected with different cellular events in other distant organs. Renal IR-related oxidative stress and inflammation followed by cell apoptosis play a crucial role in IR-induced distant organ pathological damages. Prazosin has shown protective effects against IR-injuries. Thus, the current study intended to investigate the possible protective role of prazosin against the consequents of renal IR in the heart and brain tissues. To reach this goal, rats were randomly divided into 3 groups (n=7): Sham, IR and prazosin pretreatment-IR animals (1 mg/kg intraperitoneally injection of prazosin 45 min before IR induction). After 6 h reperfusion, lipid peroxidation and antioxidant markers levels were evaluated in the both, brain and heart tissue. Moreover, apoptotic pathway in the heart and brain tissues were assessed by western blotting. Accordingly, prazosin pretreatment in IR model rats could significantly increase the antioxidant capacity and attenuate apoptotic pathways by increasing the bcl-2 levels and decreasing the expression of Bax and caspase 3 enzymes (P<0.05). Thus, prazosin suppressed cellular damages of heart and brain tissues post kidney IR by anti-oxidative and anti-apoptotic effects, which suggests the plausible use of prazosin in improving the clinical outcomes during AKI after further investigations.

α1-AR overactivation induces cardiac inflammation through NLRP3 inflammasome activation.

Acute sympathetic stress causes excessive secretion of catecholamines and induces cardiac injuries, which are mainly mediated by β-adrenergic receptors (β-ARs). However, α1-adrenergic receptors (α1-ARs) are also expressed in the heart and are activated upon acute sympathetic stress. In the present study, we investigated whether α1-AR activation induced cardiac inflammation and the underlying mechanisms. Male C57BL/6 mice were injected with a single dose of α1-AR agonist phenylephrine (PE, 5 or 10 mg/kg, s.c.) with or without pretreatment with α-AR antagonist prazosin (5 mg/kg, s.c.). PE injection caused cardiac dysfunction and cardiac inflammation, evidenced by the increased expression of inflammatory cytokine IL-6 and chemokines MCP-1 and MCP-5, as well as macrophage infiltration in myocardium. These effects were blocked by prazosin pretreatment. Furthermore, PE injection significantly increased the expression of NOD-like receptor protein 3 (NLRP3) and the cleavage of caspase-1 (p20) and interleukin-18 in the heart; similar results were observed in both Langendorff-perfused hearts and cultured cardiomyocytes following the treatment with PE (10 μM). Moreover, PE-induced NLRP3 inflammasome activation and cardiac inflammation was blocked in Nlrp3-/- mice compared with wild-type mice. In conclusion, α1-AR overactivation induces cardiac inflammation by activating NLRP3 inflammasomes.

Potential of novel phytoecdysteroids isolated from Vitex doniana in the treatment depression: Involvement of monoaminergic systems

Vitex doniana Sweet (Verbanaceae) is used in traditional African medicine for the treatment of neurological disorders including depression. In our previous studies, three new phytoecdysteroids were isolated from methanol stem bark extract of V. doniana (VD) (11β-hydroxy-20-deoxyshidasterone, 21-hydroxyshidasterone, and 2,3-acetonide-24-hydroxyecdysone) along with known ecdysteroids. This study was designed to investigate antidepressant-like effect of VD and the isolated phytoecdysteroids in behavioral models of despair, forced-swim test (FST) and tail-suspension test (TST) in mice. VD (100 and 200mg/kg, p.o.) treatment reduced (P<0.05) the duration of immobility in both tests without affecting the locomotor activity and exploratory behavior as observed in the open field test. Similarly, 21-hydroxyshidasterone, 11β-hydroxy-20-deoxyshidasterone, ajugasterone and 24-hydroxyecdysone acute oral treatments significantly reduced immobility time with peak effect at 10mg/kg, which was similar to the effect of conventional antidepressants (imipramine and fluoxetine) in the FST. Conversely, pretreatment of mice with yohimbine (1mg/kg, i.p., α2-adrenoceptor antagonist), ketanserin (5mg/kg, i.p., 5-HT2A/2C receptor antagonist) or sulpiride (dopamine D2 receptor antagonist) prevented the antidepressant-like effect of 21-hydroxyshidasterone while the effects of 11β-hydroxy-20-deoxyshidasterone and 24-hydroxyecdysone were blocked by yohimbine or ketanserin in the FST. Moreover, the anti-immobility effect elicited by ajugasterone was prevented by prazosin (62.5μg/kg, i.p., α1-adrenoceptor antagonist) pretreatment. Our findings demonstrated that V. doniana and its phytoecdysteroids constituents elicited antidepressant-like effect in behavioral paradigm of despair. Furthermore, 21-hydroxyshidasterone produces its antidepressant-like effect through interaction with α2-adrenoceptor, 5-HT2A/2C receptor and dopamine D2-receptors but 11β-hydroxy-20-deoxyshidasterone and 24-hydroxyecdysone effects depend on interaction with α2-adrenoceptor and 5-HT2A/2C receptors while ajugasterone produces its action through interaction with post-synaptic α1-adrenoceptors. Thus, phytoecdysteroids could play a pivotal role in the treatment of major depression.

α1 adrenoceptor activation by norepinephrine inhibits LPS‐induced cardiomyocyte TNF‐α production via modulating ERK1/2 and NF‐κB pathway

Cardiomyocyte tumour necrosis factor α (TNF-α) production contributes to myocardial depression during sepsis. This study was designed to observe the effect of norepinephrine (NE) on lipopolysaccharide (LPS)-induced cardiomyocyte TNF-α expression and to further investigate the underlying mechanisms in neonatal rat cardiomyocytes and endotoxaemic mice. In cultured neonatal rat cardiomyocytes, NE inhibited LPS-induced TNF-α production in a dose-dependent manner. α1-adrenoceptor (AR) antagonist (prazosin), but neither β1-nor β2-AR antagonist, abrogated the inhibitory effect of NE on LPS-stimulated TNF-α production. Furthermore, phenylephrine (PE), an α1-AR agonist, also suppressed LPS-induced TNF-α production. NE inhibited p38 phosphorylation and NF-κB activation, but enhanced extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and c-Fos expression in LPS-treated cardiomyocytes, all of which were reversed by prazosin pre-treatment. To determine whether ERK1/2 regulates c-Fos expression, p38 phosphorylation, NF-κB activation and TNF-α production, cardiomyocytes were also treated with U0126, a selective ERK1/2 inhibitor. Treatment with U0126 reversed the effects of NE on c-Fos expression, p38 mitogen-activated protein kinase (MAPK) phosphorylation and TNF-α production, but not NF-κB activation in LPS-challenged cardiomyocytes. In addition, pre-treatment with SB202190, a p38 MAPK inhibitor, partly inhibited LPS-induced TNF-α production in cardiomyocytes. In endotoxaemic mice, PE promoted myocardial ERK1/2 phosphorylation and c-Fos expression, inhibited p38 phosphorylation and IκBα degradation, reduced myocardial TNF-α production and prevented LPS-provoked cardiac dysfunction. Altogether, these findings indicate that activation of α1-AR by NE suppresses LPS-induced cardiomyocyte TNF-α expression and improves cardiac dysfunction during endotoxaemia via promoting myocardial ERK phosphorylation and suppressing NF-κB activation.

Prazosin-induced blockade of extraneuronal uptake facilitates dopaminergic modulation of muscle twitches in rat vas deferens.

Preliminary findings in our laboratory have shown that prazosin augmented the inhibitory effects of dopamine on the electrically-evoked muscle twitches in rat vas deferens. In this study, we opted to investigate the underlying mechanism and whether a prazosin-induced blockade of extraneuronal uptake process may be involved. Cumulative additions of dopamine (1.8 x 10(-7)-4.4 x 10(-5) M) elicited slight (< 30%) but dose-related inhibition of electrically-evoked (0.05 Hz, 1 ms duration and supramaximal voltage) muscle twitches of the vas deferens. Pretreatment with cocaine (10 microM), prazosin (50 nM) or oestradiol (10 microM) produced comparable potentiation of the inhibitory responses of dopamine; the pD2 values to dopamine amounted to 4.47 +/- 0.20, 4.72 +/- 0.21 and 4.56 +/- 0.19, respectively. A lower concentration of prazosin (5 nM) failed to alter dopaminergic responses. Further potentiation of dopamine responses was demonstrated in tissues preincubated with a combination of cocaine plus prazosin (50 nM), or cocaine plus oestradiol (pD2, 5.40 +/- 0.11 and 5.42 +/- 0.05, respectively). However, a mixture of all three drugs failed to elicit any further increase in dopamine responses, a finding that may suggest an extraneuronal uptake blocking activity for prazosin. Inhibition of muscle twitches evoked by bromocriptine, a dopaminoceptor agonist which is not a substrate for extraneuronal uptake, was not affected by prazosin (50 nM) pretreatment. The findings presented in this study emphasize the role of dopamine in modulating noradrenergic neurotransmission in rat vas deferens. More importantly, the results suggest that prazosin may act to block the extraneuronal uptake at noradrenergic sites, an effect that may account for its capability to facilitate dopaminergic modulation of noradrenergic neurotransmission.

Amitriptyline and Acute Inflammation: A Study Using Intravital Microscopy and the Carrageenan-Induced Paw Edema Model

Background/Aims: Antidepressants are reported to exhibit antiinflammatory effects. However, mechanisms involved in this action have not been elucidated. Thus, the objectives of the present study were (a) to evaluate the effects of amitriptyline on the acute inflammatory process, and (b) to investigate the participation of α₁-adrenergic receptors and glucocorticoids as possible mechanisms implicated in the amitriptyline action on inflammation. Methods and Results: Single and multiple doses of amitriptyline were administered to rats submitted to the carrageenan-induced paw edema model. The results showed a significant antiedematous reaction to amitriptyline, mainly when administered at each elimination half-life. The next step was to evaluate its effects on leukocyte behavior, using intravital microscopy. Amitriptyline produced a significant effect on leukocyte behavior. To investigate possible mechanisms involved, a glucocorticoid receptor antagonist (RU-486) and an α₁-adrenergic receptor antagonist (prazosin) were used. RU-486 administration lacked the ability to decrease the amitriptyline antiinflammatory effects in the carrageenan-induced paw edema model. Prazosin pretreatment potentiated the amitriptyline antiinflammatory effect without presenting an effect per se. Conclusion: The present study shows the ability of amitriptyline to decrease edema and affect leukocyte behavior in an acute inflammatory process; and, for the first time to our knowledge, we suggest the involvement of α₁-adrenoceptors in the antiinflammatory effects of amitriptyline.

Preoptic norepinephrine mediates the febrile response of guinea pigs to lipopolysaccharide

Norepinephrine (NE) microdialyzed in the preoptic area (POA) raises core temperature (T(c)) via 1) alpha(1)-adrenoceptors (AR), quickly and independently of POA PGE(2), and 2) alpha(2)-AR, after a delay and PGE(2) dependently. Since systemic lipopolysaccharide (LPS) activates the central noradrenergic system, we investigated whether preoptic NE mediates LPS fever. We injected LPS (2 microg/kg iv) in guinea pigs prepared with intra-POA microdialysis probes and determined POA cerebrospinal (CSF) NE levels. We similarly microdialyzed prazosin (alpha(1) blocker, 1 microg/microl), yohimbine (alpha(2) blocker, 1 microg/microl), SC-560 [cyclooxygenase (COX)-1 blocker, 5 microg/microl], acetaminophen (presumptive COX-1v blocker, 5 microg/microl), or MK-0663 (COX-2 blocker, 0.5 microg/microl) in other animals before intravenous LPS and measured CSF PGE(2). All of the agents were perfused at 2 microg/min for 6 h. T(c) was monitored constantly. POA NE peaked within 30 min after LPS and then returned to baseline over the next 90 min. T(c) increased within 12 min to a first peak at approximately 60 min and to a second at approximately 150 min and then declined over the following 2.5 h. POA PGE(2) followed a concurrent course. Prazosin pretreatment eliminated the first T(c) rise but not the second; PGE(2) rose normally. Yohimbine pretreatment did not affect the first T(c) rise, which continued unchanged for 6 h; the second rise, however, was absent, and PGE(2) levels did not increase. SC-560 and acetaminophen did not alter the LPS-induced PGE(2) and T(c) rises; MK-0663 prevented both the late PGE(2) and T(c) rises. These results confirm that POA NE is pivotal in the development of LPS fever.

Involvement of alpha1-adrenergic receptors in tranylcypromine enhancement of nicotine self-administration in rat

The mechanisms mediating tobacco addiction remain elusive. Nicotine, the psychoactive component in tobacco, is generally believed to be the main cause of reward and addiction. However, tobacco smoke contains thousands of constituents, some of which may interact with nicotine to enhance reward. It has previously been shown that monoamine oxidase (MAO) inhibition, known to result from smoking, can enhance nicotine self-administration. The aim of the present study was to evaluate the role of noradrenergic systems in mediating this enhancement of nicotine reward. The objective of this study was to test the hypothesis that MAO inhibitor pretreatment enhances nicotine self-administration by activation of noradrenergic pathways that regulate dopamine release in the nucleus accumbens (NAc). The effect of prazosin (0.0625-0.5 mg/kg, i.p.), a specific alpha1-adrenergic receptor antagonist, was examined on male rats pretreated with tranylcypromine (3 mg/kg), an irreversible inhibitor of MAO A and B. Acquisition of nicotine (10 mug kg(-1) inj(-1), i.v.) self-administration behavior was examined over a 5-day period. Nicotine (60 mug kg(-1) inj(-1), i.v.)-induced increase in NAc extracellular dopamine levels was examined by in vivo microdialysis in non-self-administering animals. We have shown that (1) tranylcypromine enhances nicotine self-administration, (2) prazosin pretreatment blocks both the acquisition and the expression of nicotine self-administration, and (3) prazosin pretreatment diminishes nicotine-induced dopamine release in the NAc. These data indicate that the stimulation of alpha1-adrenergic receptors is critical for tranylcypromine enhancement of nicotine reward and suggest a critical interplay between the noradrenergic and dopaminergic systems in tobacco addiction.

The role of adrenergic agonists on glycogenolysis in rat hepatocyte cultures and possible involvement of NO

Certain liver metabolic diseases point to the presence of disturbances in glycogen deposition. Epinephrine raises the cAMP level that activates protein kinase A leading to the activation of phosphorylase and glycogen breakdown. In the present report, we sought to investigate whether NO is produced during adrenoceptor agonist-induced glycogenolysis in rat hepatocytes in cultures. Isolated glycogen rich rat hepatocytes in cultures were used. NO production (NO(2)(-)) was assessed under the effect of adrenergic agonists and adrenergic agonist/antagonist pairs, dibutyryl cyclic AMP sodium-potassium salt (db-cAMP), NO synthase (NOS) inhibitors N(omega)-nitro-L-arginine methyl ester (L-NAME), aminoguanidine (AG) and the NO donor S-nitroso-N-acetyl penicillamine (SNAP). The inducible NO synthase (iNOS) mRNA was examined by the reverse transcription-polymerase chain reaction (RT-PCR). Glycogenolysis was quantified by glucose levels released into medium. The amount of glucose and NO(2)(-) released by hepatocytes was increased as a result of epinephrine, phenylephrine or db-cAMP treatments. The increase in glucose and NO(2)(-) released by epinephrine or phenylephrine was blocked or reduced by prazosin pretreatment and by NOS inhibitors aminoguanidine and L-NAME. iNOS gene expression was up-regulated by epinephrine. It can be concluded that glycogenolysis occurs through -adrenoceptor stimulation and a signaling cascade may involve NO production.

Daytime Prazosin Reduces Psychological Distress to Trauma Specific Cues in Civilian Trauma Posttraumatic Stress Disorder

Persons with posttraumatic stress disorder (PTSD) whose trauma-related nightmares improve or resolve with bedtime administration of the alpha-1 adrenergic antagonist prazosin often continue to experience PTSD symptoms during the day. This study addressed whether daytime prazosin compared to placebo would alleviate psychological distress provoked experimentally by a trauma-related word list included in the emotional Stroop (E-Stroop) paradigm. Eleven persons with civilian trauma PTSD who continued to experience daytime PTSD symptoms despite a stable bedtime prazosin dose that suppressed trauma-related nightmares were studied. Prazosin and placebo were administered on two different occasions in the early afternoon followed two hours later by the E-Stroop. Effects of drug on psychological distress were assessed by the Profile of Mood States (POMS). POMS total score and an "emotional distress" POMS subscale score following trauma-related words were significantly lower in the prazosin than placebo condition. There were no treatment effects on E-Stroop completion time. In 10 subjects who continued open label daytime prazosin, there was a reduction in global PTSD illness severity at 2-week follow-up. Daytime prazosin pretreatment reduced psychological distress specifically to trauma cues. Adding daytime prazosin to bedtime prazosin may further reduce overall PTSD illness severity and distress.

Protection against paracetamol-induced hepatic injury by prazosin pre-treatment in CD-1 mice

A synergistic depletion of glutathione has been suggested to be one critical factor in the hepatic injury in mice induced by non-toxic doses of paracetamol (APAP) when co-administered with α-adrenergic agonists. Prazosin (an α-adrenergic antagonist) could confer hepatoprotection following a toxic APAP dose (530 mg/kg) by increasing glutathione levels and enhancing bioinactivation by glucuronidation and glutathione conjugation. The effect of prazosin pre-treatment on APAP-induced gluthathione depletion and bioinactivation in vivo was assessed. Prazosin (15 mg/kg) pre-treatment provided protection against APAP-induced hepatic injury as evidenced by a significant decrease in serum transaminase (ALT) levels after 5 h ( p < 0.05). Interestingly, prazosin pre-treatment did not prevent the dramatic depletion of glutathione by high dose APAP and it had no effect on the quantity of the glutathione conjugate formed. However, prazosin pre-treatment caused a significant increase in recovery of the administered dose (530 mg/kg) as the glucuronide metabolite ( p < 0.05). UDP-glucuronosyltransferase (UGT) is involved in the bioinactivation of APAP by glucuronidation and we showed that prazosin had no effect on microsomal UGT kinetics. Thus, prazosin had no effect on either APAP-mediated glutathione depletion or the extent of APAP-glutathione conjugate formation and may be affecting other mechanisms to reduce oxidative stress caused by a toxic dose of APAP.

Noradrenergic modulation of ephedrine-induced hypophagia.

The hypophagic action of the sympathomimetic amine ephedrine (EPH) in the rat may reflect actions on central dopaminergic (DA) and noradrenergic (NE) systems. EPH indirectly facilitates DA and NE activity and acts as a partial agonist at alpha(1)-adrenergic receptors. Two approaches were used to assess the possible contribution of NE and DA pathways to EPH-induced hypophagia. In the first, regression analyses of published archival data were computed to characterize the relation between the hypophagic potency values of (-)-(EPH) and related sympathomimetic drugs, including (+)-amphetamine, aminorex, mazindol, and phentermine (data derived from Blosser JC et al., 1987) and the most potent action of these drugs on facilitating NE activity or DA activity in rat brain (data derived from Rothman RB et al., 2001). In the NE analyses, the ED(50) values for these drugs for the inhibition of eating in rats were significantly related (r = 0.91, P = 0.03) to the potency of each drug in facilitating NE activity (either release or inhibition of [(3)H]NE reuptake), whereas in the DA analyses the correlation between ED(50) values and DA activity for these drugs was also significant (r = 0.98, P = 0.003). The regression analyses are thus supportive of a role for NE or DA in the hypophagic capacity of EPH. Although an earlier study noted that administration of the putative DA antagonist pimozide in rats attenuated EPH hypophagia, pimozide exerts similar potency in antagonizing DA receptors and alpha(1)-adrenergic receptors. To clarify the role of alpha(1)-adrenoceptors in EPH-induced hypophagia, adult male rats were pretreated with the alpha(1)-adrenergic receptor antagonist prazosin (0.0.5 and 2 mg/kg) prior to the administration of (-)-EPH (0, 5, 10, or 20 mg/kg, IP). Prazosin pretreatment at 2.0 mg/kg significantly attenuated the hypophagia, but not the hypodipsia, induced by administration of 10 mg/kg and by 20 mg/kg (-)-EPH. Collectively, these results confirm a critical contribution of of alpha(1)-adrenoceptors to the hypophagic action of (-)-EPH in rats.

Adrenoceptor mechanisms underlying imipramine-induced memory deficits in rats

The post-training administration of tricyclic antidepressant imipramine impairs memory consolidation in the passive avoidance task. The present study investigated the effects of intrahippocampal (i.h.) injection of adrenoceptor agents on imipramine-induced (2-8 microg/rat) amnesia. The administration of the alpha1-adrenoceptor agonist phenylephrine (0.05 microg/rat) and the alpha1-adrenceptor antagonist prazosin (0.5 microg/rat) did not alter the effect of imipramine. The lower doses of phenylephrine (0.005 and 0.015 microg/rat) impaired, while the higher dose of the drug (0.025 and 0.05 microg/rat) improved retention. The effect of phenylephrine was not altered by prazosin (0.5 and 1 microg/rat) pretreatment, although prazosin alone decreased retention latencies. The alpha2-adrenoceptor antagonist yohimbine (0.5 and 1 microg/rat) decreased the response induced by imipramine. However, the alpha2-adrenoceptor agonist clonidine (0.08 microg/rat) did not alter the effect of the drug. Clonidine (0.15 and 0.3 microg/rat) by itself decreased, while yohimbine (1 and 2 microg/rat) increased retention latencies. Yohimbine pretreatment attenuated the effect of clonidine. It is concluded that alpha2-adrenoceptor mechanism(s) may be involved in imipramine-induced impairment of memory.

Stimulatory effect of puerarin on alpha1A-adrenoceptor to increase glucose uptake into cultured C2C12 cells of mice.

Effects of puerarin, an active principle contained in the roots of Pueraria lobata (Leguminosae), on the regulation of glucose metabolism in an insulin deficient state were investigated in cultured myoblast C 2 C 12 cells using glucose uptake as indicator. Puerarin enhanced the uptake of radioactive glucose into C 2 C 12 cells in a concentration-dependent manner, which was abolished by prazosin pretreatment. Activation of alpha 1 -adrenoceptors by puerarin was further indicated by the displacement of [ 3H]prazosin binding in C 2 C 12 cells. The stimulatory action of puerarin on glucose uptake was also reduced in C 2 C 12 cells pre-incubated with the antagonists, both WB 4101 and RS 17 056, at concentrations sufficient to block alpha 1A -adrenoceptor (alpha 1A -AR). An activation of alpha 1A -AR seems responsible for the action of puerarin in C 2 C 12 cells. Pharmacological inhibition of phospholipase C (PLC) by U73312 resulted a concentration-dependent decrease of puerarin-stimulated glucose uptake in C 2 C 12 cells. This inhibition of glucose uptake by U73122 was specific because the inactive congener, U73343, failed to block puerarin-stimulated glucose uptake. Moreover, both chelerythrine and GF 109203X diminished the action of puerarin at concentration sufficient to inhibit protein kinase C (PKC). The obtained data suggest that an activation of alpha 1A -AR by puerarin in C 2 C 12 cells may increase the glucose uptake via the PLC-PKC pathway.

Effects of cocaine administration on VTA cell activity in response to prefrontal cortex stimulation.

The repeated use of psychostimulants in humans has been associated with progressive enhancement of anxiety, panic attacks, and eventually paranoid psychosis. The appearance of such behaviors has been termed behavioral sensitization, which forms part of the basic pathological mechanisms involved in drug addiction. Psychostimulants act via a circuit involving the ventral tegmental area (VTA), prefrontal cortex (PFC), and nucleus accumbens. The PFC sends glutamatergic projections that activate dopaminergic neurons in the VTA. These projections provide an extremely important excitatory drive necessary for the development of sensitization. The effects of cocaine administration on the response of dopaminergic VTA cells to activation of the PFC have not been reported. Here the effects of acute cocaine administration on VTA cell response to PFC stimulation are examined. Statistical analysis of the changes in spontaneous activity and evoked response revealed a significant decrease in spontaneous activity at 1.0 mg/kg i.v. after cocaine treatment compared to baseline levels. The net effect was an increase in signal-to-noise ratio. Treatment with MK-801 at a dose of 2 mg/kg showed that the excitatory response was, at least partially, NMDA-mediated. Prazosin pretreatment (0.5 mg/kg i.p.) did not prevent a significant decrease in spontaneous activity brought about by cocaine (15 mg/kg, i.p.). Nonetheless, prazosin alone induced a significant decrease in the response to PFC stimulation when compared to baseline. In addition, iontophoretic application of norepinephrine (NE) onto VTA cells revealed that NE potentiated (19.2%), enhanced (26.9%), or suppressed (46.2%) the glutamate-evoked response in VTA cells. The results suggest that a possible role of cocaine in the process of sensitization might be to amplify the PFC-induced excitation at the VTA. Since the iontophoretic release of NE in almost half of the sampled cells produced similar effects to those of cocaine it may suggest a possible NE-mediated mechanism for cocaine actions.

An in vivo binding assay to determine central α 1-adrenoceptor occupancy using [ 3H]prazosin

An alpha 1 adrenoceptor (α 1-AdR) assay using [ 3H]prazosin binding in mouse brain is described which allows in vivo determination of central α 1-AdR occupancy for ligands with α 1-AdR affinity. Binding of [ 3H]prazosin in rat and mouse brain membranes in vitro was used to characterise the pharmacological profile of α 1-AdRs in order to determine any potential species variations. Saturation and displacement studies yielded comparable affinity and pharmacological profile for [ 3H]prazosin binding in mouse and rat brain homogenates. These studies confirmed the absence of species variation for ligands in central α 1-AdR pharmacology which is in good agreement with previous studies in rat brain. Subsequently, in vivo binding of [ 3H]prazosin in mouse whole brain was used to measure the occupancy of a number of AdR ligands. Timecourse studies revealed that a [ 3H]prazosin (5 μCi/mouse) pretreatment time of at least 20 min following intravenous (i.v.) administration was required for optimal specific binding. Ligands were administered systemically 40 min prior to i.v. administration of radiolabel. The α 1-adrenoceptor ligands prazosin (ED 50=0.15 mg/kg i.p.), benoxathian (0.52 mg/kg i.p.) and phentolamine (51 mg/kg i.p.) were all able to block in vivo [ 3H]prazosin binding from mouse brain. In addition, receptor occupancy values for a number of compounds including haloperidol (ED 50=0.83 mg/kg s.c.), clozapine (2.2 mg/kg s.c.) and MDL-100 907 [ R(+)-α-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine-methanol], (10 mg/kg s.c.)], which possess high to moderate affinity at α 1-adrenoceptors, were also determined. These results suggest that in the mouse, [ 3H]prazosin binding can be used to measure in vivo receptor occupancy of ligands with affinity at central α 1-adrenoceptors.

Cortical alpha 1-adrenergic regulation of acute and sensitized morphine locomotor effects.

The role of alpha1-adrenergic transmission was tested on locomotor effects of acute or repeated morphine (5 mg/kg, i.p.) administration. Prazosin, an alpha1-adrenergic antagonist, administered 30 min before morphine, either systemically (0.5 mg/kg, i.p.) or locally and bilaterally into the prefrontal cortex (200 pmol/side) reduced the stimulatory influence of morphine on locomotion. The progressive increase of the locomotor response induced by repeated morphine injections was blocked by a prazosin pretreatment but not the behavioral sensitization on the test day. These data suggest that blockade of cortical alpha1-adrenergic receptors reduces the expression of acute and sensitized locomotor responses to morphine, but does not prevent the induction of behavioral sensitization.

Critical role of alpha1-adrenergic receptors in acute and sensitized locomotor effects of D-amphetamine, cocaine, and GBR 12783: influence of preexposure conditions and pharmacological characteristics.

Psychostimulant-induced locomotor hyperactivity is commonly associated with an inhibition of dopamine reuptake. However, a physiological coupling between noradrenergic and dopaminergic neurons occurring through the stimulation of alpha1-adrenergic receptors has recently been proposed. This possibility was tested on locomotor responses induced either by D-amphetamine and cocaine, which both interfere with noradrenergic and dopaminergic transmissions, or by GBR 12783, a specific dopamine reuptake inhibitor. In an attempt to control the effects of stress and novelty on noradrenergic neurons activity, rats were submitted to habituation procedures consisting of either a 15-h period of habituation to the experimental environment ("long-habituation") or to repeated exposure to intraperitoneal saline injections for 3 consecutive days ("three-session"). Three-session-exposed animals exhibited a pronounced locomotor reactivity to saline injection which did not occur after noradrenergic depletion, clonidine (20 microg/kg) or prazosin (0.5 mg/kg) pretreatments, or in long-habituation-preexposed animals. Cocaine and GBR 12783 locomotor hyperactivities were doubled in three-session vs. long-habituation-preexposed rats, whereas D-amphetamine responses were similar in both conditions. Prazosin (0.5 mg/kg) pretreatment reduced the acute locomotor effects of the three psychostimulants in both procedures and blocked the behavioral sensitization induced by repeated injections of D-amphetamine (0.75 mg/kg) or cocaine (5 mg/kg). GBR 12783 (5 mg/kg) failed to induce significant behavioral sensitization. In addition to their role in the acute and sensitized locomotor responses to psychostimulants possessing different pharmacological characteristics, alpha1-adrenergic receptors are involved in animal reactivity to previously experimented procedures. This suggests an implication of noradrenergic neurons in the vulnerability to psychostimulants.