Effects Of Moxonidine Research Articles

Moxonidine displays a presynaptic alpha-2-adrenoceptor-dependent synergistic sympathoinhibitory action at imidazoline-1 receptors.

The function of presynaptic imidazoline-1 receptors (I1-R) in the heart remains unclear. In rat hearts, UK14.304 and moxonidine reduced norepinephrine (NE) release. AGN192403 had no influence on NE, whereas rilmenidine, agmatine, rauwolscine, and efaroxan increased NE. These effects of moxonidine and rilmenidine were not affected by AGN192403 adminstration. Conversely, after pretreatment with UK14.304, only moxonidine displayed a pronounced inhibitory action on NE release (sensitive to AGN192403), indicating a synergistic inhibitory action at I1-R under conditions of a stimulated alpha2-adrenergic autoinhibition.

Involvement of Forebrain Imidazoline and a2‐Adrenergic Receptors in the Antidipsogenic Response to Moxonidine

We investigated the participation of central alpha(2)-adrenoceptors and imidazoline receptors in the inhibition of water deprivation-induced water intake in rats. The alpha(2)-adrenoceptor and imidazoline antagonist idazoxan (320 nmol), but not the alpha(2)-adrenoceptor antagonist yohimbine, abolished the antidipsogenic effect of moxonidine (alpha(2)-adrenoceptor and imidazoline agonist, 20 nmol) microinjected into the medial septal area. Yohimbine abolished the antidipsogenic effect of moxonidine intracerebroventricularly. Therefore, central moxonidine may inhibit water intake acting independently on both imidazoline receptors and alpha(2)-adrenoceptors at different forebrain sites.

Moxonidine and central α 2 adrenergic receptors in sodium intake

Central injections of the α 2 adrenergic/imidazoline receptor agonist moxonidine inhibit water and NaCl intake in rats. In the present study, we investigated the possible involvement of central α 2 adrenergic receptors on the inhibitory effect of moxonidine in 0.3 M NaCl intake induced by 24 h sodium depletion. Male Holtzman rats with stainless-steel cannulas implanted into the lateral ventricle (LV) were used. Sodium depletion was produced by the treatment with the diuretic furosemide (20 mg/kg of body weight) injected subcutaneously +24 h of sodium-deficient diet. Intracerebroventricular (icv) injections of moxonidine (20 nmol/1 μl) reduced sodium depletion-induced 0.3 M NaCl intake (6.6±1.9 ml/120 min vs. vehicle: 12.7±1.7 ml/120 min). Pre-treatment with the α 2 adrenoreceptor antagonists RX 821002 (80 nmol/1 μl), SK&F 86466 (640 nmol/1 μl) and yohimbine (320 nmol/3 μl) injected icv abolished the inhibitory effect of icv moxonidine on sodium depletion-induced 0.3 M NaCl intake (13.3±1.4, 15.7±1.7 and 11.8±2.2 ml/120 min, respectively). The results show that the activation of α 2 adrenoreceptors is essential for the inhibitory effect of central moxonidine on sodium depletion-induced NaCl intake.

Effects of moxonidine and metoprolol in penile circulation in hypertensive men with erectile dysfunction: results of a pilot study.

Centrally acting (moxonidine) and peripherally acting (metoprolol) sympatholytic agents might have different actions upon penile circulation in hypertensive men with erectile dysfunction. A total of 11 nonsmoking, hypertensive but otherwise healthy men with erectile dysfunction were studied after 8 weeks on moxonidine monotherapy (0.4 mg per day, increased to 0.6 mg if needed) and then after 8 weeks of metoprolol monotherapy (100 mg per day, increased to 200 mg if needed) in a crossover design. At the end of each treatment phase, the subjects were asked about their subjective erectile capacity (nocturnal and coital erections), and resting and stimulated (after intracavernosal injection of a mixture of alprostadil and phentolamine) penile deep artery diameters and systolic peak velocities were measured by color Doppler ultrasonography. There were no significant differences in blood pressure after either therapy. The change from earlier antihypertensive therapy, moxonidine produced significant subjective amelioration of sexual dysfunction in 9/11 of the men (< or = 0.001), whereas 9/11 returned to impaired dysfunction after crossover to metoprolol treatment. Resting and stimulated deep penile diameters and peak systolic velocities were higher after moxonidine treatment compared with metoprolol (diameters: < or = 0.004, < or = 0.0001; velocities: < or = 0.008, < or = 0.038). The centrally acting sympatholytic agent moxonidine seems to improve erectile function both subjectively and objectively and has a better effect on penile circulation compared with the peripherally acting sympatholytic agent metoprolol.

Presynaptic effects of moxonidine in isolated buffer perfused rat hearts: role of imidazoline-1 receptors and alpha2-adrenoceptors.

Numerous studies support the concept that centrally acting antihypertensive drugs, such as imidazolines, mediate sympathoinhibition not only via activation of central nervous alpha2-adrenoceptors (alpha2-AR) but also via imidazoline-1 receptors (I1-R). An additional presynaptic involvement in sympathetic neurotransmission of imidazolines, via I1-R independent of alpha2-AR, is still controversial and remains to be clarified in the heart. Concentration response curves on endogenous norepinephrine (NE) overflow evoked by stimulation of epicardial postganglionic sympathetic nerves in isolated buffer-perfused rat hearts were performed for brimonidine, moxonidine, rauwolscine, 2-endo-amino-3-exo-isopropylbicyclo[2.2.1]heptane (AGN192403), and efaroxan. To unmask an I1-R-mediated effect of moxonidine, hearts were pre-exposed in additional experiments with brimonidine or rauwolscine with or without AGN192403 or efaroxan, respectively. Moxonidine reduced stimulated NE overflow (log EC50: -6.15 +/- 0.14). AGN192403, a selective ligand at I1-R, had no influence on the dose-response curve of moxonidine (log EC50: -6.01 +/- 0.25). After pre-exposure to brimonidine [ stimulation 1 (S1) + stimulation 2 (S2); 10(-5) M], the inhibitory action of moxonidine was potentiated compared with control (32.0 +/- 2.8 versus 73.13 +/- 3.0%) and completely abolished with AGN192403 or efaroxan. This effect was also totally inhibited by pre-exposure with indomethacin (10(-7) M) and tricyclodecan-9-yl-xanthogenate (D-609), an inhibitor of phosphatidylcholine-selective phospholipase C (PC-PLC; 10(-7) M). Conversely, moxonidine was without modulating efficacy under alpha2-AR-blockade by rauwolscine. In summary, we demonstrate that moxonidine reduces NE release independently of I1-R, demonstrating the prominent effect of alpha2-AR in cardiac tissue under basal conditions. We also demonstrate that I1-R are involved in NE release under conditions of alpha2-AR-stimulation involving both a pathway of prostaglandins and PC-PLC.

Central α2 adrenergic receptors and cholinergic-induced salivation in rats

Salivation induced by intraperitoneal (i.p.) injections of pilocarpine (cholinergic agonist) is reduced by intracerebroventricular (i.c.v.) injections of moxonidine ( α 2 adrenergic and imidazoline receptor agonist). In the present study, we investigated the involvement of central α 2 adrenergic receptors in the inhibitory effect of i.c.v. moxonidine on i.p. pilocarpine-induced salivation. Male Holtzman rats with stainless steel cannula implanted into the lateral ventricle (LV) were used. Saliva was collected using pre-weighted small cotton balls inserted into the animal’s mouth under ketamine (100 mg kg −1) anesthesia. Salivation was induced by i.p. injection of pilocarpine (4 μmol kg −1). Pilocarpine-induced salivation was reduced by i.c.v. injection of moxonidine (10 nmol) and enhanced by i.c.v. injections of either RX 821002 (160 nmol) or yohimbine (320 nmol). The inhibitory effect of i.c.v. moxonidine on pilocarpine-induced salivation was abolished by prior i.c.v. injections of the α 2 adrenergic receptor antagonists, RX 821002 (160 nmol) or yohimbine (160 and 320 nmol). The α 1 adrenergic receptor antagonist prazosin (320 nmol) injected i.c.v. did not change the effect of moxonidine on pilocarpine-induced salivation. The results suggest that moxonidine acts on central α 2 adrenergic receptors to inhibit pilocarpine-induced salivation, and that this salivation is tonically inhibited by central α 2 adrenergic receptors.

Effects of moxonidine on sympathetic activity, and metabolic and hemodynamic variables in obese hypertensive patients

Effects of moxonidine on sympathetic activity, and metabolic and hemodynamic variables in obese hypertensive patients

Pharmacological evidence of a role for prejunctionalimidazoline (I1) receptors in ocular function

Imidazoline and guanidiniun-substituted isoindoline compounds have been reported to demonstrate affinity for the putative imidazoline receptors (I 1) and alpha-2 (a 2) adrenoceptors. The purpose of this study was to determine the relative contribution of I 1 receptors to ocular actions of moxonidine (MOX) and brimonidine (BRIM) by utilizing relatively selective a 2 and I 1 antagonists. MOX, an a 2 /I 1 receptor agonist, BRIM, a selective a 2 agonist, efaroxan (EFA), an I 1 /a 2 antagonist and rauwolscine (RAU), a relatively selective a 2 antagonist, were utilized to study alterations in sympathetically evoked contractions of the cat nictitating membrane (CNM). MOX (1-10 µg) suppressed, dose dependently, contractions of the CNM elicited by electrically stimulating the cervical preganglionic sympathetic trunk. The suppressive effect of MOX was antagonized more effectively by EFA (333 µg) than by rauwolscine (333 µg). In contrast, RAU, but not EFA, completely reversed the suppressive effects of BRIM on electrically induced contractions of the CNM. In conclusion, these in vivo data suggest that I 1 receptors are involved in the pre-junctional (neuronal) modulation of contractions in the CNM (Supported by NIH grant EY06338).

Effect of the imidazoline receptor agonist moxonidine on hemodynamics, coronary circulation, metabolic ischemia markers and the neurohumoral system in patients with essential hypertension. Effects of moxonidine on coronary circulation

Moxonidine is a new centrally active imidazoline-receptor agonist being effectively applied in the treatment of arterial hypertension due to its sympathicolytic potency. This is the first investigation regarding the effects of moxonidine on coronary and systemic hemodynamics, metabolic markers of ischemia and neurohumoral parameters in patients with essential hypertension (WHO I-II). We studied moxonidine (single dose of 0.4 mg p.o.) in 22 patients with left ventricular (LV) hypertrophy, ST segment depressions during exercise, pectanginal complaints and negative coronarograms. Assessments included arterial blood pressure, cardiac output, pulmonary artery pressure mean (PAPm), pulmonary capillary wedge pressure (PCWP) and coronary sinus flow (CSF) by intravascular Doppler technique. The moxonidine-induced parameter changes 2 hours later were as follows: a decrease in systolic/diastolic pressure by 28/10 mmHg, and in heart rate by 5 bpm, associated with a decline of PAPm by 17% and of PCWP by 26%. LV work was reduced by 26%, MVO2 by 18% and CSF by 16%. Average peak velocity in CS fell by 18% and coronary flow reserve (with adenosine) increased by 12%. CS-O2 saturation rose by 4%, accompanied by an increase in lactate extraction by 17%, a decrease in norepinephrine spillover by 30% and in arterial endotheline by 20%. In conclusion, moxonidine produces clinically relevant sympathicolysis with beneficial effects on hemodynamics, coronary circulation and neurohumoral parameters.

Site of action of moxonidine in the rat nephron.

Moxonidine is a centrally acting antihypertensive agent which has been found to exert its blood pressure lowering effect by interaction with (alpha2-adrenoceptors and imidazoline receptors of the I(1)-type. These receptors have also been demonstrated to be present in the rat kidney. In the present study, clearance and micropuncture techniques were applied to anaesthetized rats to localize the site of action of moxonidine within the nephron. The clearance data show that moxonidine (0.25 mg/kg i.v., followed by a continuous i.v. infusion of 0.25 mg/h) induced a marked increase in urine flow and urinary excretion of sodium, chloride and potassium. The changes in urine flow and urinary solute excretion were accompanied by an enhanced glomerular filtration rate. The micropuncture experiments revealed that moxonidine significantly increased glomerular filtration rate of superficial nephrons, and significantly inhibited fractional reabsorption of fluid, sodium, potassium and chloride by similar amounts (by 9.0%-9.8%) in superficial proximal tubules. Regarding fluid and sodium reabsorption, the proximal effect of moxonidine was continuously weakened by a compensatory increase of reabsorption in the loop of Henle and the subsequent distal nephron segments. The inhibitory effect of moxonidine on fractional proximal potassium reabsorption was completely compensated in the loop of Henle, but the drug induced a net secretion of potassium into the segments lying beyond the early distal tubule, probably as a consequence of the increased tubule fluid and sodium load delivered to them. The experiments have identified the proximal tubule as the principal nephron site where the diuretic action of moxonidine arises. The proximal effect may be related to the increased glomerular filtration rate and to a direct inhibitory interaction of moxonidine with the proximal Na+/H+ exchanger.

Role of I(1)-imidazoline receptors and alpha2-adrenoceptors in hemodynamic effects of moxonidine administration into the rostroventrolateral medulla.

Local injection of 4 nmol moxonidine (unilaterally) into the rostroventrolateral medulla of spontaneously hypertensive rats (SHR-SP) decreased mean blood pressure and heart rate by 24+/-3 and 3+/-4%, respectively. Pretreatment with the I1/alpha2-receptor antagonist efaroxan abolished the moxonidine-induced decrease in mean blood pressure, but had no effect on heart rate. Yohimbine blocked hypotension, delayed bradycardia (8 nmol), or completely inhibited the effects of moxonidine (16 nmol). Our results indicate that both I1-imidazoline receptors and alpha2-adrenoceptors of the rostroventrolateral medulla are involved in the realization of moxonidine-induced changes.

Moxonidine versus placebo as an aid in smoking cessation.

This study assessed the effects of moxonidine as an aid in smoking cessation in 166 heavily addicted smokers who were motivated to quit smoking completely. Recruitment was via advertisement. Patients were randomly allocated to receive double-blind placebo or moxonidine (0.1 mg once or twice daily) for 6 weeks. Brief counseling was provided. An encouragement letter was sent prior to the quit date. Success was defined as not smoking any cigarettes during weeks 3 - 6, an expired carbon monoxide level of < 10 ppm, and a plasma cotinine level of < 25 ng/ml. The study failed to demonstrate a statistically significant effect for moxonidine on either nicotine withdrawal symptoms or smoking cessation. Reported side effects were not different with moxonidine than with placebo, however. Copyright 2000 John Wiley & Sons, Ltd.

Chronic administration of moxonidine suppresses sympathetic activation in a rat heart failure model

Excessive sympathetic activity contributes to cardiovascular abnormalities, which negatively affect the prognosis of heart failure. The present study evaluated the effects of moxonidine, an imidazoline I 1 receptor agonist, on sympathetic activation and myocardial remodelling in a rat heart failure model. Rats were subjected to coronary artery ligation, and treated with moxonidine, 3 or 6 mg/kg/day, from 1 to 21 days after myocardial infarction. After 21 days, heart rate and blood pressure were measured in conscious, chronically instrumented rats. Plasma catecholamine levels were determined by high-performance liquid chromatography. Effects on post-myocardial infarction remodelling were evaluated from the ventricular weight body weight ratio and interstitial collagen deposition, measured morphometrically in the interventricular septum remote from the infarcted area. Moxonidine dose-dependently decreased myocardial infarction induced tachycardia but did not affect myocardial infarction reduced blood pressure. Plasma noradrenaline levels, which were elevated after myocardial infarction, decreased below sham-values with 6 mg/kg/day moxonidine. Ventricular weight–body weight ratio as well as interstitial collagen were significantly elevated in myocardial infarcted rats, and restored to sham values with 6 mg/kg/day moxonidine. These data suggest that moxonidine suppresses myocardial infarction induced sympathetic activation in a dose-dependent way as indicated by reduced heart rate and plasma noradrenaline levels. Furthermore, post-myocardial infarction remodelling may be attenuated at a higher dose-range of moxonidine as shown by normalisation of ventricular weight body weight ratio and interstitial collagen.

Effects of moxonidine on corticocerebral blood flow under normal and ischemic conditions in conscious rabbits.

Hypertension associated with excessive liberation of circulating and tissue catecholamines is an independent risk factor for further cardiovascular complications and an important predictor of stroke. Moxonidine is a centrally acting anti-hypertensive drug with potent action on I1-imidazoline receptors. It inhibits catecholamine release and is therefore expected to exert an antiadrenergic effect at various levels in the regulation of the cardiovascular system. The aim of this study was to investigate the effect of moxonidine (0.025-0.1 mg/kg, i.v.) on the normal and unilateral carotid occlusion-induced impaired corticocerebral blood flow (cCBF) determined by hydrogen polarography, on mean arterial blood pressure (MABP) and heart rate (HR) in conscious rabbits. Moxonidine produced a reduction of MABP and HR. On the other hand, after administration of the drug, a significant increase in the normal and impaired cCBF was observed. Because the improvement in cCBF was conspicuous in both normal and ischemic conditions, moxonidine might be beneficial not only in the treatment of hypertension but also in the management of cerebral ischemia.

Effects of the I 1 imidazoline/ α2-adrenergic receptor agonist moxonidine in comparison with clonidine in the formalin test in rats

Moxonidine is a mixed I 1 imidazoline/ α 2-adrenergic receptor agonist structurally related to clonidine. In the present studies, moxonidine, like clonidine, produced a dose- and time-related inhibition of formalin-induced behaviors after subcutaneous administration. Moxonidine was equiefficacious to both clonidine and morphine in inhibiting formalin-induced behaviors. The order of potencies of these analgesics was clonidine>moxonidine=morphine. The I 1 imidazoline preferring antagonist efaroxan produced a dose-dependent antagonism of both moxonidine (5.0 mg/kg) and clonidine (0.5 mg/kg). In addition, the α 2-adrenergic receptor antagonist yohimbine produced a dose-related antagonism of moxonidine, but only partially antagonized clonidine. Prazosin failed to block the effects of either moxonidine or clonidine, indicating a lack of involvement of α 1 as well as α 2B and α 2C receptors. The present results suggest that α 2-adrenergic receptors play an important role in mediating the effects of moxonidine in producing antinociception in the formalin test. Further, the present results demonstrate that the mechanism of action of moxonidine and clonidine differ in that clonidine, but not moxonidine, produces an antinociceptive effect through a yohimbine-insensitive mechanism in the formalin test.

Prototypical imidazoline-1 receptor ligand moxonidine activates alpha2-adrenoceptors in bulbospinal neurons of the RVL.

Moxonidine is an antihypertensive drug that lowers sympathetic vasomotor tone by stimulating either alpha2-adrenergic (alpha2-AR) or imidazoline I1 receptors within the rostral ventrolateral medulla (RVL). In this study, we investigated the effects of moxonidine (10 microM) on RVL neurons in brain stem slices of neonatal rats. We recorded mainly from retrogradely labeled RVL bulbospinal neurons (putative presympathetic neurons) except for some extracellular recordings. Prazosin was used to block alpha1-adrenoceptors. Moxonidine inhibited the extracellularly recorded discharges of all spontaneously active RVL neurons tested (bulbospinal and unidentified). This effect was reversed or blocked by the selective alpha2-AR antagonist SKF 86466 (10 microM). In contrast, the I1 imidazoline ligand AGN 192403 (10 microM) had no effect on the spontaneous activity. In whole cell recordings (holding potential -70 mV), moxonidine produced a small and variable outward current (mean 7 pA). This current was observed in both tyrosine hydroxylase-immunoreactive and other bulbospinal neurons and was blocked by SKF 86466. Excitatory postsynaptic currents (EPSCs) evoked by focal electrical stimulation were isolated by incubation with gabazine and strychnine, and inhibitory postsynaptic currents (IPSCs) were isolated with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Moxonidine reduced the amplitude of the evoked EPSCs (EC(50) = 1 microM; 53% inhibition at 10 microM) but not their decay time constant (5.6 ms). The effect of moxonidine on EPSCs persisted in barium (300 microM) and was reduced approximately 80% by SKF 86466. Moxonidine also reduced the amplitude of evoked IPSCs by 63%. In conclusion, moxonidine inhibits putative RVL presympathetic neurons both presynaptically and postsynaptically. All observed effects in the present study are consistent with an alpha2-AR agonist activity of moxonidine.

The effects of moxonidine, a novel imidazoline, on plasma norepinephrine in patients with congestive heart failure

OBJECTIVETo evaluate the dose response relationship of moxonidine on plasma concentration of norepinephrine during acute and chronic administration in patients with congestive heart failure (CHF).BACKGROUNDSympathetic activation is increased in heart failure. Moxonidine is an imidazoline ligand acting on the central nervous system (CNS) receptors to decrease sympathetic activation.METHODSNinety-seven patients with heart failure and New York Heart Association class II–III symptoms and ejection fraction <40% were randomized to placebo or one of three target doses of moxonidine, 0.1, 0.2 or 0.3 mg administered twice daily. An initial dose of moxonidine 0.1 mg twice a day (b.i.d.) was followed by weekly increments of 0.1 mg b.i.d. until target dose. The second and third study days occurred after four weeks (at target dose) and after 12 weeks, respectively. At each study day, repeated blood samples were drawn.RESULTSThere was a significant dose-related decrease of systolic blood pressure across all three study days. Heart rate decreased significantly on study day 3 in a dose-related manner. The acute 2 h decrease in plasma norepinephrine in response to all three doses of moxonidine was significantly different compared with placebo after four and 12 weeks. There was a significant linear relation between dose and plasma norepinephrine after four and 12 weeks in both 2 h peak and the time averaged effect (>8 h). The number of adverse events was similar in the moxonidine and placebo groups.CONCLUSIONSThe increased sympathetic activation in CHF can be reduced by moxonidine through CNS inhibition.

Metabolic effects of moxonidine and other centrally acting antihypertensives.

Diabetes, Obesity and MetabolismVolume 1, Issue 6 p. 317-322 Metabolic effects of moxonidine and other centrally acting antihypertensives Michael Schachter, Michael Schachter Department of Clinical Pharmacology and Therapeutics, Imperial College School of Medicine, St Mary’s Hospital, London, UKSearch for more papers by this author Michael Schachter, Michael Schachter Department of Clinical Pharmacology and Therapeutics, Imperial College School of Medicine, St Mary’s Hospital, London, UKSearch for more papers by this author First published: 25 December 2001 https://doi.org/10.1046/j.1463-1326.1999.00042.xCitations: 6 Dr M. Schachter, Department of Clinical Pharmacology, St Mary’s Hospital, London W2 1NY, UK. E-mail:M.Schachter@ic.ac.uk Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume1, Issue6November 1999Pages 317-322 RelatedInformation

Presynaptic cannabinoid and imidazoline receptors in the human heart and their potential relationship.

Segments of human right atrial appendages preincubated with [3H]noradrenaline and superfused with physiological salt solution containing desipramine and corticosterone were used to examine whether the cardiac sympathetic nerves are endowed with cannabinoid receptors and to further study pharmacological properties of presynaptic imidazoline receptors. The cannabinoid CB1 receptor agonists CP55,940, HU210 and anandamide inhibited evoked [3H]noradrenaline release. The inhibition by CP55,940 and anandamide was abolished by the CB1 receptor antagonists SR141716A (1 microM) and LY320135 (1 microM). Rauwolscine at the imidazoline receptor-blocking concentration of 30 microM abolished the inhibitory effect of CP55,940 and anandamide. After blockade of alpha2-adrenoceptors with 1 microM rauwolscine, the imidazoline binding site ligand S23230, which is the (-)-enantiomer of the racemic oxazoline derivative S22687, exhibited low potency in inhibiting electrically evoked [3H]noradrenaline release (pIC30%=4.96), whereas the (+)-enantiomer S23229 and the racemate S22687 were ineffective. In the presence of 30 microM rauwolscine, S23230 did not significantly inhibit evoked release. The imidazoline receptor-mediated inhibitory effect of BDF 6143 and aganodine on evoked [3H]noradrenaline release was abolished by 1 microM SR141716A and by 1 microM LY320135. The inhibitory effect of moxonidine on evoked [3H]noradrenaline release, which is exclusively mediated via activation of alpha2-autoreceptors, was not antagonized by 1 microM SR141716A. In conclusion, inhibitory cannabinoid CB1 receptors are present on the sympathetic axon terminals of human atrial appendages. Presynaptic imidazoline receptors share the property of other receptors in that they can be stereoselectively activated. The cross-antagonism of imidazoline receptor agonists/antagonists with CB1 receptor antagonists/agonists suggests that these receptors may have certain binding domains in common or that they interact with each other in an unknown manner.

Central moxonidine on water and NaCl intake

In this study we investigated: (a) the effects of intracerebroventricular (i.c.v.) injections of moxonidine (an α 2-adrenergic and imidazoline receptor agonist) on the ingestion of water and NaCl induced by 24 h of water deprivation; (b) the effects of i.c.v. injection of moxonidine on central angiotensin II (ANG II)- and carbachol-induced water intake; (c) the effects of the pre-treatment with i.c.v. idazoxan (an α 2-adrenergic and imidazoline receptor antagonist) and RX 821002 (a selective α 2-adrenergic antagonist) on the antidipsogenic action of central moxonidine. Male Holtzman rats had stainless steel cannulas implanted in the lateral cerebral ventricle. Intracerebroventricular injection of moxonidine (5 and 20 nmol/1 μl) reduced the ingestion of 1.5% NaCl solution (4.1 ± 1.1 and 2.9 ± 2.5 ml/2 h, respectively vs. control = 7.4 ± 2.1 ml/2 h) and water intake (2.0 ± 0.6 and 0.3 ± 0.2 ml/h, respectively vs. control = 13.0 ± 1.4 ml/h) induced by water deprivation. Intracerebroventricular moxonidine (5 nmol/1 μl) also reduced i.c.v. ANG II-induced water intake (2.8 ± 0.9 vs. control = 7.9 ± 1.7 ml/1 h) and i.c.v. moxonidine (10 and 20 nmol/1 μl) reduced i.c.v. carbachol-induced water intake (4.3 ± 1.7 and 2.1 ± 0.9, respectively vs. control = 9.2 ± 1.0 ml/1 h). The pre-treatment with i.c.v. idazoxan (40 to 320 nmol/1 μl) abolished the inhibitory effect of i.c.v. moxonidine on carbachol-induced water intake. Intracerebroventricular idazoxan (320 nmol/1 μl) partially reduced the inhibitory effect of moxonidine on water deprivation-induced water intake and produced only a tendency to reduce the antidipsogenic effect of moxonidine on ANG II-induced water intake. RX 821002 (80 and 160 nmol/1 μl) completely abolished the antidipsogenic action of moxonidine on ANG II-induced water intake. The results show that central injections of moxonidine strongly inhibit water and NaCl ingestion. They also suggest the involvement of central α 2-adrenergic receptors in the antidipsogenic action of moxonidine.