Activation of α-adrenoceptors depresses synaptic transmission of myelinated afferents and inhibits pathways mediating primary afferent depolarization (PAD) in the in vitro mouse spinal cord.

Somatosensory afferent transmission strength is controlled by several presynaptic mechanisms that reduce transmitter release at the spinal cord level. We focused this investigation on the role of α-adrenoceptors in modulating sensory transmission in low-threshold myelinated afferents and in pathways mediating primary afferent depolarization (PAD) of neonatal mouse spinal cord. We hypothesized that the activation of α-adrenoceptors depresses low threshold-evoked synaptic transmission and inhibits pathways mediating PAD. Extracellular field potentials (EFPs) recorded in the deep dorsal horn assessed adrenergic modulation of population monosynaptic transmission, while dorsal root potentials (DRPs) recorded at root entry zone assessed adrenergic modulation of PAD. We found that noradrenaline (NA) and the α1-adrenoceptor agonists phenylephrine and cirazoline depressed synaptic transmission (by 15, 14 and 22%, respectively). DRPs were also depressed by NA, phenylephrine and cirazoline (by 62, 30, and 64%, respectively), and by the α2-adrenoceptor agonist clonidine, although to a lower extent (20%). We conclude that NA depresses monosynaptic transmission of myelinated afferents onto deep dorsal horn neurons via α1-adrenoceptors and inhibits interneuronal pathways mediating PAD through the activation of α1- and α2-adrenoceptors. The functional significance of these modulatory actions in shaping cutaneous and muscle sensory information during motor behaviors requires further study.

Involvement of monoaminergic targets in the antidepressant- and anxiolytic-like effects of the synthetic alkamide riparin IV: Elucidation of further mechanisms through pharmacological, neurochemistry and computational approaches.

Despite recent advances, current antidepressants have considerable limitations: late onset of action and the high profile of refractoriness. Biomedical research with natural products has gained growing interest in the last years, and had provide useful candidates for new antidepressants. Riparins are a group of natural alkamides obtained from Aniba riparia, which had marked neuroactive effects, mainly as antidepressant and antinociceptive agents. We made modifications of the basic structure of riparins, originating a synthetic alkamide, also known as riparin IV (RipIV). RipIV demonstrated a superior analgesic effect than its congeners and a marked antidepressant-like effect. However, the basic mechanism for the central effects of RipIV remains unknown. Here, we aimed to investigate the participation of monoaminergic neurotransmission targets in the antidepressant-like effects of RipIV. To do this, we applied a combined approach of experimental (classical pharmacology and neurochemistry) and computer-aided techniques. Our results demonstrated that RipIV presented antidepressant- and anxiolytic-like effects without modifying locomotion and motor coordination of mice. Also, RipIV increased brain monoamines and their metabolite levels. At the higher dose (100 mg/kg), RipIV increased serotonin concentrations in all studied brain areas, while at the lower one (50 mg/kg), it increased mainly dopamine and noradrenaline levels. When tested with selective receptor antagonists, RipIV antidepressant effect showed dependence of the activation of multiple targets, including D1 and D2 dopamine receptors, 5-HT2A/2, 5-HT3 receptors and α2 adrenergic receptors. Molecular docking demonstrated favorable binding conformation and affinity of RipIV to monoamine oxidase B (MAO-B), serotonin transporter (SERT), α1 receptor, D2 receptor, dopamine transporter (DAT) and at some extent GABA-A receptor. RipIV also presented a computationally predicted favorable pharmacokinetic profile. Therefore, this study demonstrated the involvement of monoaminergic targets in the mechanism of RipIV antidepressant-like action, and provide evidence of it as a promising new antidepressant.

Effects of lidocaine associated with detomidine on sedation of horses undergoing dental procedures / Efeitos da lidocaína associada a detomidina na sedação de equinos submetidos a procedimentos odontológicos

Due to the growing increase in the dental routine in equine medicine, along with the need for patient sedation to perform this procedure, this study aimed to assess sedation by detomidine alone and/or associated with lidocaine under continuous infusion. Twenty-two horses from the dental routine of the veterinary hospital of the institution of origin were used. A jugular catheter was implanted on the day of study and animals were allocated into two distinct groups (n=11): GD, which received detomidine (20 µg kg−1), followed by continuous infusion (20 µg kg−1 h−1); and GDL, animals which received detomidine (10 µg kg−1) and lidocaine (1.3 mg kg−1), followed by continuous infusion of detomidine (10 µg kg−1 h−1) and lidocaine (25 µg kg−1 min−1). The assessed moments were as follows: M0, before catheter placement; M1, 5 minutes after bolus and beginning of infusion; M2, placement of mouth speculum; and M3, wear with an electric rasp. The assessed parameters were heart rate (HR), respiratory rate (f), systolic blood pressure (SBP), and intestinal motility. In addition to the clinical parameters, sedation was assessed by measuring head height in relation to the ground before (M0) and after treatment administration (M1) and during the dental procedure using a scale adapted for dental procedures. Statistical analysis was performed using the Shapiro-Wilk normality test by applying one-way RM ANOVA, followed by the Dunnett test for comparison in relation to M0, t-test, and Mann-Whitney test between groups (p ≤ 0.05). HR decreased by 20% at M2 and M3 compared to M0 only in GD, while SBP increased 35% at the same moments compared to M0 in GD and 27, 42, and 27% at M1, M2, and M3 compared to M0 in GDL, respectively. Intestinal motility decreased by 75% at all moments compared to M0 in both groups. Head height decreased by 67% in GD and 60% in GDL, with no difference between groups. Sedation scores provided by the scale did not differ between groups, with values of 1 [0­3] in GD and 3 [0­4] in GDL at M2 and 1 [0­3] in GD and 1 [1.5­3] in GDL at M3. Thus, sedation by the association between detomidine and lidocaine allowed reducing detomidine dose in half but offering similar results for dental procedures.(AU)

Devido ao crescente aumento da rotina odontológica na medicina equina, juntamente com a necessidade de sedação dos pacientes para a realização destes procedimentos, objetivou-se avaliar a sedação promovida pela detomidina isolada e, ou, associada com lidocaína sob regime de infusão contínua. Foram utilizados 22 equinos provindos da rotina odontológica do hospital veterinário da instituição de origem. No dia do estudo, foi implantado um cateter na jugular, alocando-se os animais em 2 grupos distintos (n = 11): GD, os quais receberam detomidina (20 µg kg-1) seguido de infusão contínua (20 µg kg-1 h-1); GDL, os quais receberam detomidina (10 µg kg-1) e lidocaína (1,3 mg kg-1), seguido de infusão contínua de detomidina (10 µg kg-1 h-1) e lidocaína (25 µg kg-1 min-1). Os momentos avaliados foram: M0, antes da colocação do cateter; M1, 5 minutos após o bolus e início da infusão; M2, no momento da colocação do abre bocas; M3, momento do desgaste com a grosa elétrica. Os parâmetros avaliados foram: frequência cardíaca (FC), frequência respiratória (f), pressão arterial sistólica (PAS) e motilidade intestinal. Além dos parâmetros clínicos, foi avaliada a sedação medindo-se a altura de cabeça em relação ao solo antes (M0) e após a administração dos tratamentos (M1), assim como durante o procedimento odontológico através de uma escala adaptada para procedimentos odontológicos. A análise estatística foi realizada através do teste de normalidade Shapiro-Wilk, aplicando-se One Way RM ANOVA seguido por Dunnet para comparação em relação ao M0, teste de t e Mann-Whitney entre grupos (p ≤ 0,05). A FC reduziu 20% no M2 e M3 em relação ao M0 somente no GD, já a PAS aumentou 35% nos mesmos momentos em relação ao M0 no GD e no M1, M2 e M3 do GDL também houve um aumento de 27%, 42% e 27%, respectivamente, em relação ao M0. A motilidade intestinal reduziu 75% em todos os momentos em relação ao M0 em ambos os grupos. A altura da cabeça diminuiu 67% no GD e 60% no GDL, sem diferença entre os grupos. Os escores de sedação fornecidos pela escala não diferiram entre os grupos, sendo este no M2 de 1 [0 ­ 3], no GD, e 3 [0 ­ 4], no GDL, e no M3, no GD 1 [0 ­ 3], e 1 [1,5 ­ 3], no GDL. Conclui-se que a sedação ofertada pela associação de detomidina e lidocaína reduziu a dose de detomidina pela metade, oferecendo sedação similar para procedimentos odontológicos.(AU)

Uso e efeitos da dexmedetomidina na anestesia de ratos e camundongos / Use and effects of dexmedetomidine in rats and mice anesthesia

O uso de agonistas dos receptores α-2 adrenérgicos possui ampla difusão no campo da medicina veterinária, tendo a xilazina como principal representante deste grupo anestésico. A dexmedetomidina, um isômero da medetomidina, demonstra altíssima especificidade aos adrenorreceptores α-2 e com isso vem ganhando espaço devido a seus potentes efeitos analgésicos e anestésicos e sua utilização em ratos e camundongos. Seu uso é justificado tanto como agente isolado, bem como associado a outros fármacos, visando reduzir as doses e os efeitos indesejados. A praticidade da existência de um reversor específico, o atipamezole, juntamente com a disponibilidade de administração por diversas vias, faz da dexmedetomidina uma droga adequada para utilização em roedores. Sua resposta é dose-dependente, e, por isso, deve-se avaliar cautelosamente o tipo de anestesia desejada previamente à sua administração. A dexmedetomidina demostra uma série de efeitos anti-inflamatórios e protetores sistêmicos, visto que inibe citocinas pró-inflamatórias. No entanto, tais mecanismos de ação ainda não foram completamente elucidados. A especificidade da dexmedetomidina aliada a seu potente potencial analgésico e anestésico, além de seus efeitos secundários como anti-inflamatório e protetor sugerem sua utilização na anestesia de ratos e camundongos de forma segura.(AU)

The use of α-2 agonist adrenoreceptors is widespread in veterinary, and xilazine represents the major role of the group. Dexmedetomidine, a medetomidine isomer, is highly specific to the α-2 adrenoreceptors and due to analgesic and anesthetic effects, its use in rats and mice can be seen as single agent or associated with other drugs, to reduce dose and minimize the side effects. The convenience of having a specific revert drug, atipamezole, makes dexmedetomidine a safe drug to be administered to rodents, besides the possibility of being administered by multiple ways. The response of dexmedetomidine is dose-dependent and, because of that, the anesthesia protocol should be careful evaluated before its administration. Besides, the drug shows several anti-inflammatory and protective effects decurrent of its use, inhibiting pro-inflammatory citokines, but the mechanisms havent been completely elucidated. The high specifity of dexmedetomidine associated to the analgesic and anesthetic effects, plus its secondary effects as anti-inflammatory and protector suggests a safe use in rats and mice anesthesia.(AU)

Natural Diterpenes from Coffee, Cafestol, and Kahweol Induce Peripheral Antinoceception by Adrenergic System Interaction.

Cafestol and kahweol are diterpenes found only in the non-saponified lipid fraction of coffee. They are released during boiling and retained in the filtration process. Previous studies have shown peripheral antinociception induced by endogenous opioid peptides released by these diterpenes. Considering that the activation of the opioid system leads to a noradrenaline release, the aim of this study was to verify the participation of the noradrenergic system in the peripheral antinociception induced by cafestol and kahweol. Hyperalgesia was induced by an intraplantar injection of prostaglandin E2 (2 µg). Cafestol or kahweol (80 µg/paw) were administered locally into the right hindpaw alone, and after the agents α 2-adrenoceptor antagonist yohimbine (5, 10 and 20 µg/paw), α 2 A-adrenoceptor antagonist BRL 44 408 (40 µg/paw), α 2B-adrenoceptor antagonist imiloxan (40 µg/paw), α 2 C-adrenoceptor antagonist rauwolscine (10, 15 and 20 µg/paw), α 2D-adrenoceptor antagonist RX 821 002 (40 µg/paw), α 1-adrenoceptor antagonist prazosin (0.5, 1 and 2 µg/paw), or ß-adrenoceptor antagonist propranolol (150, 300 and 600 ng/paw), respectively. Noradrenaline reuptake inhibitor reboxetine (30 µg/paw) was administered prior to cafestol or kahweol low dose (40 µg/paw) and guanetidine 3 days prior to the experiment (30 mg/kg, once a day), depleting the noradrenaline storage. Intraplantar injection of cafestol or kahweol (80 µg/paw) induced a peripheral antinociception against hyperalgesia induced by PGE2. This effect was reversed by intraplantar injections of yohimbine, rauwolscine, prazosin and propranolol. Reboxetine injection intensified the antinociceptive effect of cafestol or kahweol low-dose, and guanethidine reversed almost 70 % of the cafestol or kahweol-induced peripheral antinociception. This study gives evidence that the noradrenergic system participates in cafestol and kahweol-induced peripheral antinociception with the release of endogenous noradrenaline.

Specific role of α2A - and α2B -, but not α2C -, adrenoceptor subtypes in the inhibition of the vasopressor sympathetic out-flow in diabetic pithed rats.

Several lines of evidence have shown an association of diabetes with a catecholamines' aberrant homeostasis involving a drastic change in the expression of adrenoceptors. This homeostatic alteration includes, among other things, atypical actions of α2 -adrenoceptor agonists within central and peripheral α2 -adrenoceptors (e.g. profound antinociceptive effects in diabetic subjects). Hence, this study investigated the pharmacological profile of the α2 -adrenoceptor subtypes that inhibit the vasopressor sympathetic out-flow in streptozotocin-pre-treated (diabetic) pithed rats. For this purpose, B-HT 933 (up to 30 µg/kg min) was used as a selective α2 -adrenoceptor agonist and rauwolscine as a non-selective α2A/2B/2C -adrenoceptor antagonist; in addition, BRL 44408, imiloxan and JP-1302 were used as subtype-selective α2A -, α2B - and α2C -adrenoceptor antagonists, respectively (all given i.v.). I.v. continuous infusions of B-HT 933 inhibited the vasopressor responses induced by electrical sympathetic stimulation without affecting those by i.v. bolus injections of noradrenaline in both normoglycaemic and diabetic rats. Interestingly, the ED50 for B-HT 933 in diabetic rats (25 µg/kg min) was almost 1-log unit greater than that in normoglycaemic rats (3 µg/kg.min). Moreover, the sympatho-inhibition induced by 10 µg/kg min B-HT 933 in diabetic rats was (i) abolished by 300 µg/kg rauwolscine or 100 and 300 µg/kg BRL 44408; (ii) partially blocked by 1000 µg/kg imiloxan; and (iii) unchanged by 1000 µg/kg JP-1302. Our findings, taken together, suggest that B-HT 933 has a less potent inhibitory effect on the sympathetic vasopressor responses in diabetic (compared to normoglycaemic) rats and that can probably be ascribed to a down-regulation of α2C -adrenoceptors.

Assessment of mechanisms involved in antinociception produced by the alkaloid caulerpine.

In previous works we showed that oral administration of caulerpine, a bisindole alkaloid isolated from algae of the genus Caulerpa, produced antinociception when assessed in chemical and thermal models of nociception. In this study, we evaluated the possible mechanism of action of this alkaloid in mice, using the writhing test. The antinociceptive effect of caulerpine was not affected by intraperitoneal (i.p.) pretreatment of mice with naloxone, flumazenil, l-arginine or atropine, thus discounting the involvement of the opioid, GABAergic, l-arginine-nitric oxide and (muscarinic) cholinergic pathways, respectively. In contrast, i.p. pretreatment with yohimbine, an α2-adrenoceptor antagonist, or tropisetron, a 5-HT3 antagonist, significantly blocked caulerpine-induced antinociception. These results suggest that caulerpine exerts its antinociceptive effect in the writhing test via pathways involving α2-adrenoceptors and 5-HT3 receptors. In summary, this alkaloid could be of interest in the development of new dual-action analgesic drugs.

Stress alone or associated with ethanol induces prostanoid release in rat aorta via alpha2-Adrenoceptor.

BACKGROUND: Stress and ethanol are both, independently, important cardiovascular risk factors. OBJECTIVE: To evaluate the cardiovascular risk of ethanol consumption and stress exposure, isolated and in association, in male adult rats. METHODS: Rats were separated into 4 groups: Control, ethanol (20% in drinking water for 6 weeks), stress (immobilization 1h day/5 days a week for 6 weeks) and stress/ethanol. Concentration-responses curves to noradrenaline - in the absence and presence of yohimbine, L-NAME or indomethacin - or to phenylephrine were determined in thoracic aortas with and without endothelium. EC50 and maximum response (n=8-12) were compared using two-way ANOVA/Bonferroni method. RESULTS: Either stress or stress in association with ethanol consumption increased the noradrenaline maximum responses in intact aortas. This hyper-reactivity was eliminated by endothelium removal or by the presence of either indomethacin or yohimbine, but was not altered by the presence of L-NAME. Meanwhile, ethanol consumption did not alter the reactivity to noradrenaline. The phenylephrine responses in aortas both with and without endothelium also remained unaffected regardless of protocol. CONCLUSION: Chronic stress increased rat aortic responses to noradrenaline. This effect is dependent upon the vascular endothelium and involves the release of vasoconstrictor prostanoids via stimulation of endothelial alpha-2 adrenoceptors. Moreover, chronic ethanol consumption appeared to neither influence noradrenaline responses in rat thoracic aorta, nor did it modify the increase of such responses observed as a consequence of stress exposure.

Inhibition of sodium appetite by lipopolysaccharide: involvement of alpha2-adrenoceptors.

Lipopolysaccharide (LPS), an endotoxin from the wall of Escherichia coli, produces a general behavioral inhibition and affects several aspects of fluid-electrolyte balance. LPS inhibits thirst; however, it is not clear if it also inhibits sodium appetite. The present results show that LPS (0.3-2.5 mg/kg body wt) injected intraperitoneally produces a dose-dependent reduction of sodium appetite expressed as 0.3 M NaCl intake induced by sodium depletion (furosemide plus removal of ambient sodium for 24 h). The high doses of LPS (1.2-2.5 mg/kg) also produced transient hypothermia at the beginning of the sodium appetite test; however, no dose produced hyperthermia. LPS also increased the stomach liquid content (an index of gastric emptying) after a load of 0.3 M NaCl given intragastrically by gavage to sodium-depleted rats. The α(2)-adrenoceptor antagonist yohimbine (5 mg/kg ip) abolished the effect of LPS on 0.3 M NaCl intake, without changing the effect of LPS on gastric emptying. Injection of RX-821002 (160 nmol), another α(2)-adrenoceptor antagonist, in the lateral cerebral ventricle (LV) also reversed the inhibition of sodium appetite produced by LPS. Yohimbine intraperitoneally or RX-821002 in the LV alone had no effect on sodium intake. Although yohimbine plus LPS produced a slight hypotension, RX-821002 plus LPS produced no change in arterial pressure, suggesting that the blockade of the effects of LPS on sodium intake by the α(2)-adrenoceptor antagonists is independent from changes in arterial pressure. The results suggest an inhibitory role for LPS in sodium appetite that is mediated by central α(2)-adrenoceptors.

Alpha-2B adrenergic receptor mediated hemodynamic profile of etomidate.

Etomidate has been used since 1972 as an inductor and in maintaining anesthesia. There are multiple mechanisms that account for the biologic effects of etomidate. One of the most prominent features of this drug is that it provides anesthesia without gross changes in hemodynamic parameters. This feature allows using etomidate in patients with considerable cardiopulmonary compromise avoiding the characteristic hypotension produced by other anesthetics. The mechanism that provides the basis for its cardiovascular stability is the capacity to bind and stimulate peripheral alpha-2B adrenergic receptors with a subsequent vasoconstriction. Alterations in the function or number of these receptors may account for abnormal responses during etomidate induction.

DA1 receptors modulation in rat isolated trachea.

We have previously demonstrated that low dose of inhaled dopamine (0.5-2 microg kg(-1) min(-1)) induces broncodilatacion in patients with acute asthma attack, suggesting that this dopamine effect is mediated by dopaminergic rather than by adrenergic receptors. To understand better these dopamine effect, rat tracheal smooth muscle was used as a model to evaluate the responses of beta2-, alpha1-, alpha2-adrenergic and DA1 and DA2 dopaminergic antagonists. Tracheal rings from male Sprague-Dawley rats (n = 90) were excised and placed in an organ bath containing modified Krebs-Ringer bicarbonate buffer at 37 degrees C, and gassed with O2 (95%) and CO2 (5%). Contractile responses were recorded with an isometric transducer in a polygraph (Letica, Spain). Contraction was induced by accumulative doses of acetylcholine (0.1, 0.3, 1, 3, 10 mM) or by electric field stimulation (10 Hz at 2 milliseconds), and accumulative doses of dopamine were added to the bath. Low concentration (0.1-0.3 mM) elicited a small initial contraction, followed by a marked relaxation. Cholinergic contraction was completely reversed at 6 mM of dopamine. This biphasic dopaminergic response was not blocked by incubation with beta2-adrenergic antagonist propranolol (0.1 microM), alpha1-antagonist, terazosin (0.1 mM), alpha2-antagonist, yohimbine (0.1 mM), or by DA2 antagonist metoclopramide (1-8 mM); DA1 antagonist SCH23390 (0.1 microM) produced a sustained increase of basal tone but did not block initial dopaminergic contraction and partially inhibited bronchodilator effect of dopamine. Dopaminergic relaxation in rat trachea is mediated by DA1 rather than by DA2 receptors; and adrenergic receptors are not involved in such dopamine-induced response. Finally, DA1 antagonist SCH23390 exerts intrinsic contractile activity on airway smooth muscle that deserves further research.

Gastroprotective effect of lupeol on ethanol-induced gastric damage and the underlying mechanism.

The effect of lupeol, a natural pentacyclic triterpene on ethanol-induced gastric damage in mice was evaluated. The gastroprotection was assessed by determination of changes in mean gastric lesion area, quantification of mucosal non-protein sulfhydryls (NP-SH), and characterized using drugs that influence the endogenous prostaglandins, alpha(2)-adrenoceptors, nitric oxide, K(ATP)-channels, and intracellular calcium. Orally administered lupeol (3, 10, and 30 mg/kg) significantly and dose-dependently attenuated the ethanol-induced gastric damage by 39-69%, whereas the positive control N-acetylcysteine (NAC, 300 mg/kg, i.p.) afforded 32% protection. Both lupeol and NAC restored the NP-SH depleted by ethanol but the lupeol effect was only marginal. Lupeol gastroprotection was attenuated by indomethacin and L-NAME, the respective COX and NO-synthase inhibitors and was weakly sensitive to alpha(2)-adrenergic antagonist yohimbine and K(ATP)-channel blocker glibenclamide, but more profoundly to calcium blocker verapamil. These pharmacological effects of lupeol may synergistically contribute to alleviating the ethanol-associated gastric damage, which is multifactorial.

Adenosine modulates alpha2-adrenergic receptors through a phospholipase C pathway in brainstem cell culture of rats.

Adenosine acts in the nucleus tractus solitarii (NTS), one of the main brain sites related to cardiovascular control. In the present study we show that A(1) adenosine receptor (A(1R)) activation promotes an increase on alpha(2)-adrenoceptor (Alpha(2R)) binding in brainstem cell culture from newborn rats. We investigated the intracellular cascade involved in such modulatory process using different intracellular signaling molecule inhibitors as well as calcium chelators. Phospholipase C, protein kinase Ca(2+)-dependent, IP(3) receptor and intracellular calcium were shown to participate in A(1R)/Alpha(2R) interaction. In conclusion, this result might be important to understand the role of adenosine within the NTS regarding autonomic cardiovascular control.

Use of transgenic (knockout) mice reveals a site distinct from the alpha2A-adrenoceptors for agmatine in the vas deferens.

The inhibitory effect of agmatine on electrically induced contractions was studied in vas deferens of Adra 2a transgenic mice lacking alpha(2A)-adrenoceptors. Agmatine and clonidine caused a concentration-dependent inhibition of twitches. However, while agmatine showed a similar pIC(50) value in control and transgenic mice, the pIC(50) value for clonidine was about 30-fold lower in knockout mice. In both strains, yohimbine shifted the curve for clonidine, but not for agmatine, even when a 100-fold higher concentration of yohimbine was employed. Our results indicate that inhibition by agmatine in mouse vas deferens is not simply due to interactions with alpha(2)-adrenoceptors in our experimental conditions.

Involvement of central alpha1-adrenoceptors on renal responses to central moxonidine and alpha-methylnoradrenaline.

Moxonidine (alpha2-adrenoceptor/imidazoline receptor agonist) injected into the lateral ventricle induces diuresis, natriuresis and renal vasodilation. Moxonidine-induced diuresis and natriuresis depend on central imidazoline receptors, while central alpha1-adrenoceptors are involved in renal vasodilation. However, the involvement of central alpha1-adrenoceptors on diuresis and natriuresis to central moxonidine was not investigated yet. In the present study, the effects of moxonidine, alpha-methylnoradrenaline (alpha2-adrenoceptor agonist) or phenylephrine (alpha1-adrenoceptor agonist) alone or combined with previous injections of prazosin (alpha1-adrenoceptor antagonist), yohimbine or RX 821002 (alpha2-adrenoceptor antagonists) intracerebroventricularly (i.c.v.) on urinary sodium, potassium and volume were investigated. Male Holtzman rats (n = 5-18/group) with stainless steel cannula implanted into the lateral ventricle and submitted to gastric water load (10% of body weight) were used. Injections of moxonidine (20 nmol) or alpha-methylnoradrenaline (80 nmol) i.c.v. induced natriuresis (196 +/- 25 and 171 +/- 30, respectively, vs. vehicle: 101 +/- 9 microEq/2 h) and diuresis (9.0 +/- 0.4 and 12.3 +/- 1.6, respectively, vs. vehicle: 5.2 +/- 0.5 ml/2 h). Pre-treatment with prazosin (320 nmol) i.c.v. abolished the natriuresis (23 +/- 4 and 76 +/- 11 microEq/2 h, respectively) and diuresis (5 +/- 1 and 7.6 +/- 0.8 ml/2 h, respectively) produced by i.c.v. moxonidine or alpha-methylnoradrenaline. RX 821002 (320 nmol) i.c.v. abolished the natriuretic effect of alpha-methylnoradrenaline, however, yohimbine (320 nmol) did not change renal responses to moxonidine. Phenylephrine (80 nmol) i.c.v. induced natriuresis and kaliuresis that were blocked by prazosin. Therefore, the present data suggest that moxonidine and alpha-methylnoradrenaline acting on central imidazoline receptors and alpha2-adrenoceptors, respectively, activate central alpha1-adrenergic mechanisms to increase renal excretion.

beta-1 and beta-2, but not alpha-1 and alpha-2, adrenoceptor blockade delays rat cutaneous wound healing.

The sympathetic nervous system plays an important role in wound healing, but its mechanism of action is poorly understood. The aim of this study was to investigate the effects of beta- and alpha-adrenoceptor blockade on cutaneous wound healing. Male rats were treated with propranolol (beta1- and beta2-antagonist), atenolol (beta1-antagonist), or phentolamine (alpha1- and alpha2-antagonist) dissolved in drinking water. A full-thickness excisional lesion was created and the wound area was measured. Fourteen days after wounding, lesions and adjacent skin were removed, formalin-fixed, and paraffin-embedded. Sections were stained with hematoxylin-eosin and toluidine blue, and immunostained for alpha-smooth muscle actin and proliferating cell nuclear antigen. Wound contraction was delayed in propranolol- and atenolol-treated animals but not in phentolamine-treated animals. Reepithelialization was decreased only in propranolol-treated animals. beta1- and beta2-adrenoceptor blockade delayed leukocyte migration, epidermal and connective tissue cell proliferation, myofibroblastic differentiation, and mast cell migration. The volume density of blood vessels was increased in the propranolol- and atenolol-treated animals compared with controls. The levels of matrix metalloproteases (MMP-2 and MMP-9) decreased in the propranolol- and atenolol-treated animals. alpha1- and alpha2-adrenoceptor blockade only affected leukocyte migration, epithelial and connective tissue cell proliferation, and pro-MMP-9 levels. In conclusion, beta-1 and beta-2, but not alpha-1 and alpha-2, adrenoceptor blockade delays cutaneous wound healing.

Pharmacological profile of the clonidine-induced inhibition of vasodepressor sensory outflow in pithed rats: correlation with alpha(2A/2C)-adrenoceptors.

BACKGROUND AND PURPOSE: Resistance blood vessels are innervated by sympathetic and primary sensory nerves, which modulate vascular tone through the release of noradrenaline and calcitonin gene-related peptide (CGRP), respectively. Moreover, electrical stimulation of the perivascular sensory outflow in pithed rats results in vasodepressor responses which are mainly mediated by CGRP release. The present study has investigated the role of alpha(2)-adrenoceptors in the inhibition of these vasodepressor responses. EXPERIMENTAL APPROACH: 144 pithed male Wistar rats were pretreated with hexamethonium (2 mg kg(-1) min(-1)) followed by i.v. continuous infusions of either methoxamine (15 and 30 microg kg(-1) min(-1)) or clonidine (3, 10 and 30 microg kg(-1) min(-1)). Under these conditions, electrical stimulation (0.56-5.6 Hz; 50 V and 2 ms) of the spinal cord (T(9)-T(12)) resulted in frequency-dependent decreases in diastolic blood pressure. KEY RESULTS: The infusion of clonidine (10 microg kg(-1) min(-1)), as compared to those of methoxamine (15 or 30 microg kg(-1) min(-1)), inhibited the vasodepressor responses to electrical stimulation without affecting those to i.v. bolus injections of alpha-CGRP (0.1-1 microg kg(-1)). This inhibition by clonidine was: (i) antagonized by 300 microg kg(-1) rauwolscine (alpha(2A/2B/2C)), 300 and 1000 microg kg(-1) BRL44408 (alpha(2A)), or 10 and 30 microg kg(-1) MK912 (alpha(2C)); and (ii) unaffected by 1 ml kg(-1) saline, 100 microg kg(-1) BRL44408, 3000 and 10,000 microg kg(-1) imiloxan (alpha(2B)) or 3 microg kg(-1) MK912. CONCLUSIONS AND IMPLICATIONS: The inhibition produced by 10 microg kg(-1) min(-1) clonidine on the vasodepressor (perivascular) sensory outflow in rats may be mainly mediated by prejunctional alpha(2A)/alpha(2C)-adrenoceptors.

Hypotension caused by therapeutic doses of venlafaxine: case report and proposed pathophysiological mechanisms.

Although venlafaxine is usually associated with modest increases in blood pressure and not so often clinical hypertension, there are a few reported cases of hypotension related to overdoses of this specific antidepressant. The case study of a young female patient with a history of Major Depressive Disorder who initiated treatment with venlafaxine 75 mg/day and developed hypotension when the dosage was titrated up to 225 mg/day is described. The patient did not present comorbid diseases nor use other medication. A temporal association and a dose-dependent relationship between the hypotension and the use of venlafaxine is shown. To the best of the knowledge of the authors,this is the first case report that specifically associates regular doses of venlafaxine with the presence of hypotension. A pathophysiological mechanism is proposed, involving the participation of presynaptic alpha2-adrenergic receptors and the presence of a possible genetic polymorphism of cytochrome P4502D6, which is associated with lower drug metabolization, to explain the relationship between venlafaxine in regular dosage and development of hypotension.

Adenosine modulates alpha2-adrenergic receptors within specific subnuclei of the nucleus tractus solitarius in normotensive and spontaneously hypertensive rats.

Adenosine is known to modulate neuronal activity within the nucleus tractus solitarius (NTS). The modulatory effect of adenosine A1 receptors (A1R) on alpha2-adrenoceptors (Adr2R) was evaluated using quantitative radioautography within NTS subnuclei and using neuronal culture of normotensive (WKY) and spontaneously hypertensive rats (SHR). Radioautography was used in a saturation experiment to measure Adr2R binding parameters (Bmax, Kd) in the presence of 3 different concentrations of N6-cyclopentyladenosine (CPA), an A1R agonist. Neuronal culture confirmed our radioautographic results. [3H]RX821002, an Adr2R antagonist, was used as a ligand for both approaches. The dorsomedial/dorsolateral subnucleus of WKY showed an increase in Bmax values (21%) induced by 10 nmol/L of CPA. However, the subpostremal subnucleus showed a decrease in Kd values (24%) induced by 10 nmol/L of CPA. SHR showed the same pattern of changes as WKY within the same subnuclei; however, the modulatory effect of CPA was induced by 1 nmol/L (increased Bmax, 17%; decreased Kd, 26%). Cell culture confirmed these results, because 10(-5) and 10(-7) mol/L of CPA promoted an increase in [3H]RX821002 binding of WKY (53%) and SHR cells (48%), respectively. DPCPX, an A1R antagonist, was used to block the modulatory effect promoted by CPA with respect to Adr2R binding. In conclusion, our study shows for the first time an interaction between A1R that increases the binding of Adr2R within specific subnuclei of the NTS. This may be important in understanding the complex autonomic response induced by adenosine within the NTS. In addition, changes in interactions between receptors might be relevant to understanding the development of hypertension.

The role of local and systemic renin angiotensin system activation in a genetic model of sympathetic hyperactivity-induced heart failure in mice.

Sympathetic hyperactivity (SH) and renin angiotensin system (RAS) activation are commonly associated with heart failure (HF), even though the relative contribution of these factors to the cardiac derangement is less understood. The role of SH on RAS components and its consequences for the HF were investigated in mice lacking alpha(2A) and alpha(2C) adrenoceptor knockout (alpha(2A)/alpha(2C)ARKO) that present SH with evidence of HF by 7 mo of age. Cardiac and systemic RAS components and plasma norepinephrine (PN) levels were evaluated in male adult mice at 3 and 7 mo of age. In addition, cardiac morphometric analysis, collagen content, exercise tolerance, and hemodynamic assessments were made. At 3 mo, alpha(2A)/alpha(2C)ARKO mice showed no signs of HF, while displaying elevated PN, activation of local and systemic RAS components, and increased cardiomyocyte width (16%) compared with wild-type mice (WT). In contrast, at 7 mo, alpha(2A)/alpha(2C)ARKO mice presented clear signs of HF accompanied only by cardiac activation of angiotensinogen and ANG II levels and increased collagen content (twofold). Consistent with this local activation of RAS, 8 wk of ANG II AT(1) receptor blocker treatment restored cardiac structure and function comparable to the WT. Collectively, these data provide direct evidence that cardiac RAS activation plays a major role underlying the structural and functional abnormalities associated with a genetic SH-induced HF in mice.