Angiotensin II blocks memory consolidation through an AT<Subscript>2</Subscript> receptor-dependent mechanism

Rationale and objectives Several studies suggest that the brain renin–angiotensin system is involved in memory consolidation. However, the participation of angiotensin II (AII) in this process is controversial. This is probably due to the fact that many of the studies carried out to elucidate this matter employed multitrial learning paradigms together with pretraining intracerebroventricular infusions, and therefore were unable to distinguish between consolidation and retrieval related events and lacked anatomical specificity. To circumvent this problem, we analyzed the role played in memory consolidation by AII using the hippocampal-dependent, one-trial, step-down inhibitory avoidance task (IA) in combination with stereotaxically localized intrahippocampal infusion of drugs.Methods and results Rats bilaterally implanted with infusion cannulae into the CA1 region of the dorsal hippocampus (CA1) were trained in IA and tested for memory retention 24 h later. We found that when infused into CA1 immediately or 30 min after training but not later, AII produced a dose-dependent amnesic effect without altering locomotor activity, exploratory behavior or anxiety state. The amnesic effect of AII was not mimicked by angiotensin IV (AIV) and was totally blocked by the AII-type 2 receptor (AT₂) antagonist, PD123319, but not by the AII-type 1 receptor (AT₁) antagonist, losartan. Importantly, when infused alone, neither PD123319 nor losartan produced any effect on memory retention.Conclusions Our data indicate that, when given into CA1, AII blocks memory formation through a mechanism involving activation of AT₂ receptors; however, endogenous AII does not seem to participate in the consolidation of IA long-term memory.     

NMDA or AMPA/kainate receptor blockade prevents acquisition of conditioned place preference induced by D<Subscript>2/3</Subscript> dopamine receptor stimulation in rats

Rationale Recent experiments from this laboratory demonstrated synergistic effects of AMPA/kainate receptor blockade and D_2/3 dopamine (DA) receptor stimulation on brain stimulation reward and locomotor activity.Objectives Using place conditioning, this study explored further the interaction between DA and glutamate (Glu) using the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801, the AMPA/kainate receptor antagonist NBQX, and the D_2/3 DA receptor agonist 7-OH-DPAT.Methods Effects of these compounds, alone and combined, were measured in male Sprague–Dawley rats using an unbiased two-compartment place conditioning procedure.Results 7-OH-DPAT (0.03–5.0 mg kg^–1, s.c.) administered immediately prior to conditioning was ineffective; when administered 15 min prior to conditioning, only the highest dose (5.0 mg kg^–1, s.c.) induced conditioned place preference (CPP). Acquisition of 7-OH-DPAT-induced CPP was blocked by MK-801 (0.06 or 0.13 mg kg^–1, i.p.) or NBQX (0.5 g) microinjected into the nucleus accumbens (NAS) shell subregion. Intra-NAS shell administration of 7-OH-DPAT (5.0 g) or NBQX (0.5 g), alone or combined, failed to induce place conditioning, and this lack of effect was not due to state dependency. Administration of MK-801 or 7-OH-DPAT (5.0 mg kg^–1) during the conditioning phase acutely increased horizontal activity, but neither compound, alone or combined, induced conditioned locomotor effects.Conclusions Acquisition of place conditioning induced by systemic administration of 7-OH-DPAT is blocked by systemic NMDA receptor antagonism by MK-801 or by the AMPA/kainate receptor antagonist NBQX microinjected into the NAS shell subregion.Anna-Maria Biondo and Robert L.H. Clements contributed equally to this work.     

Angiotensin II receptor blockade blocker pre-treatment largely prevents injury from gradual renal ablation in rats.

INTRODUCTION: Reduction in renal mass in rats results in progressive proteinuria, hypertension, focal-segmental glomerulosclerosis (FSG), atrophy of tubules (AT), and interstitial expansion. We reported that slow reduction of renal tissue in rats (slow ablation) ending in the removal of 1.5 kidneys is associated, over the next six months, with higher albumin excretion rates (AER) and accelerated development of FSG lesions compared to sudden equivalent renal mass reduction. It was hypothesised that slow reduction of nephron numbers allows for a process of conditioning of residual nephrons that increases their susceptibility to subsequent injury. METHODS: To test this idea we treated Münich-Wistar rats with the angiotensin receptor blocker (ARB) losartan for six weeks during the gradual staged surgical removal of 1.5 kidneys, and compared them to sham operated controls, and parallel groups untreated by losartan. RESULTS: Despite discontinuation of losartan over the subsequent six months, ARB pre-treatment completely prevented proteinuria and hypertension in these slow renal ablation rats. ARB pre-treatment also largely prevented the subsequent development of FSG, AT, and interstitial expansion in these animals. Both losartan-treated and untreated renal ablation groups had glomerular enlargement and compensatory hyperfiltration and this was uninfluenced by losartan. CONCLUSION: Temporary ARB administration during gradual renal mass reduction resulted in long-term prevention of hypertension and albuminuria and greatly reduced FSG and tubular and interstitial lesions. We hypothesise that the preconditioning of residual nephrons in the gradual ablation model which facilitates their subsequent injury, is blunted by renin-angiotensin system blockade.     

Effect of dopamine D<Subscript>3</Subscript> receptor blockade on renal function and glomerular size in diabetic rats

Dopamine D₂-like receptors, including D₂, D₃, and D₄ receptors, are involved in the regulation of glomerular hyperfiltration due to diabetes mellitus. These hemodynamic alterations represent a risk factor for the later development of diabetic nephropathy. The aim of the present study was to determine whether the D₃ receptor subtype modulates the diabetes-induced increase in glomerular filtration rate (GFR) in rats. Renal function was studied in Sprague–Dawley rats 14 days after induction of a moderate diabetes mellitus (DM) by streptozotocin and in non-diabetic controls (CON). Rats were orally treated either with the peripherally acting, selective dopamine D₃ receptor antagonist BSF 135170 (BSF, 10 mg/kg per day for 2 weeks) or with vehicle (VHC). Perfusion-fixed kidneys were used for estimation of glomerular volume. In conscious rats, which were treated with BSF, the DM-induced increase in fluid intake, urinary output, and renal sodium excretion was significantly less pronounced than in the vehicle group (DM-VHC). In the clearance experiments, GFR in CON was about 0.84±0.04 ml/min per 100 g body weight. The DM-VHC group presented a significant glomerular hyperfiltration (1.09±0.04 ml/min per 100 g body weight). Treatment with BSF significantly lowered GFR towards levels of CON. The estimated glomerular volume was 0.73±0.03×10⁶ m³ in the CON-VHC group and 0.86±0.04×10⁶ m³ in the DM-VHC animals. Interestingly, treatment with BSF decreased the glomerular volume in both groups. Irrespective of BSF treatment, kidney wet weight related to body weight was about 36% higher in DM animals compared with CON animals. We conclude that dopamine D₃ receptors represent a target for the modulation of diabetes-induced glomerular hyperfiltration. Therefore, the results encourage the testing of the possible beneficial effects of long-term D₃ receptor blockade on the development of diabetic nephropathy.     

Angiotensin II type 1 receptor blockade restores nitric oxide-dependent renal vascular responses in renovascular hypertension

It was previously reported that enhancement of renal vascular responses to angiotensin II in hypertensive rats is related to decreased release of nitric oxide. Thus, it was suggested that impairment of nitric oxide synthesis during development of hypertension is related to a decreased nitric oxide synthase mRNA expression by an angiotensin II-dependent mechanism. The current study evaluated whether the blockade of angiotensin II type 1 receptor during the development of hypertension restored nitric oxide synthase mRNA expression, nitric oxide synthesis, and nitric oxide-dependent modulation of angiotensin II vasoconstrictor effects. It was shown that losartan treatment prevented increased vascular responses to angiotensin II in hypertensive rats and that this effect was associated with restoration of nitric oxide synthase mRNA expression and nitric oxide synthase activity. Furthermore, angiotensin II-dependent nitric oxide release in hypertensive rats was potentiated by losartan treatment. Angiotensin II (1 microg) released renal nitrites by 485 +/- 178, 470 +/- 150, 185 +/- 45, and 515 +/- 100 nmol/ml/30 s in the kidneys from normotensive, losartan-treated normotensive rats, hypertensive, and losartan-treated hypertensive rats, respectively. The data suggest that during development of hypertension, angiotensin II downregulates nitric oxide synthase mRNA expression, blunting nitric oxide vasodilatory tone and increasing vascular sensitivity to vasoconstrictor agents in the renal circulation.     

A pharmacological differentiation between postjunctional (AT<Subscript>1A</Subscript>) and prejunctional (AT<Subscript>1B</Subscript>) angiotensin II receptors in the rabbit aorta

The effects of angiotensin II and angiotensin III were compared at prejunctional and postjunctional AT₁ receptors of the rabbit thoracic aorta. Furthermore, the influence of PD123319, losartan and eprosartan on these effects was also compared. To study prejunctional effects, the tissues were preincubated with (³H)-noradrenaline, superfused and electrically stimulated (1 Hz, 2 ms, 50 mA, 5 min). To study postjunctional effects, non-cumulative concentration–response curves were determined. Both angiotensin II and angiotensin III were more potent prejunctionally than postjunctionally. In the case of angiotensin II, the EC₅₀ was 12 times lower at the prejunctional than at the postjunctional level, while that of angiotensin III was 30 times lower prejunctionally. Furthermore, whereas angiotensin II was about 33 times more potent than angiotensin III postjunctionally, it was only 12 times more potent than angiotensin III prejunctionally. Eprosartan did not differentiate between prejunctional and postjunctional effects of both angiotensins. In contrast, PD123319 and losartan did differentiate; however, whereas PD123319 concentration-dependently antagonised the facilitation of tritium release caused by angiotensin II and angiotensin III and had no influence on the contraction of the aortic rings elicited by the peptides, losartan did the opposite: it concentration-dependently antagonised the contractions caused by the peptides on the aortic rings and exerted no influence on the facilitatory effect of angiotensin II and angiotensin III. These results show that prejunctional and postjunctional receptors for angiotensin II and angiotensin III are different and underline the hypothesis that postjunctional AT₁ receptors belong to the AT_1A subtype, while prejunctional AT₁ receptors belong to the AT_1B subtype.     

Ramipril prevents the detrimental sequels of chronic NO synthase inhibition in rats: hypertension,cardiac hypertrophy and renal insufficiency

Inhibition of the angiotensin converting enzyme (ACE) with ramipril was studied in male Wistar rats during long-term inhibition of nitric oxide (NO) synthase by N^G-nitro-l-arginine methyl ester (l-NAME). Chronic treatment with l-NAME in a dose of 25 mg/kg per day over 6 weeks caused myocardial hypertrophy and a significant increase in systolic blood pressure (245 ± 16 mmHg) as compared to controls (155+4 mmHg). Animals receiving simultaneously l-NAME and ramipril were protected against blood pressure increase and partially against myocardial hypertrophy. L-NAME caused a significant reduction in glomerular filtration rate (GFR: 2.56+0.73 ml·kg^–1·min^–1) and renal plasma flow (RPF: 6.93±1.70ml·kg^–1·min^–1) as compared to control (GFR: 7.29±0.69, RPF: 21.36±2.33ml·kg^–1·min^–1). Addition of ramipril prevented l-NAME-induced reduction in GFR and renal plasma flow. l-NAME produced an elevation in urinary protein excretion and serum creatinine and a decrease in potassium excretion which was antagonised by ramipril. L-NAME-induced increase in plasma renin activity (PRA) was further elevated with ramipril treatment. Isolated hearts from rats treated with l-NAME showed increased post-ischaemic reperfusion injuries. Compared to controls duration of ventricular fibrillation was increased and coronary flow reduced. During ischaemia the cytosolic enzymes lactate dehydrogenase and creatine kinase, as well as lactate in the venous effluent were increased. Myocardial tissue values of glycogen, ATP, and creatine phosphate were decreased, whereas lactate was increased. Coadministration of ramipril reversed these effects. l-NAME treatment reduced the cyclic GMP content in urine and renal arteries, and was not changed by additional ramipril-treatment. In the kidney hyalinosis of arterioles and of glomerular capillaries, as well as mesangial expansion and tubular atrophies seen after long-term inhibition of NO synthase were reduced by coadministration of ramipril. In conclusion, long-term ACE inhibition by ramipril prevented l-NAME-induced hypertension and cardiac hypertrophy, and attenuated functional and morphological changes in the kidneys. In addition, cardiac-dynamic and -metabolic deterioration induced by L-NAME was normalised by co-treatment with ramipril. Correspondence to: Max Hropot at the above address     

The dopamine D<Subscript>1</Subscript> receptor agonist and D<Subscript>2</Subscript> receptor antagonist LEK-8829 attenuates reinstatement of cocaine-seeking in rats

Various dopaminergic drugs have been studied for their efficacy in the treatment of cocaine addiction. Pretreatment with either selective dopamine D₁ receptor agonists or selective dopamine D₂ receptor antagonists prevents reinstatement of cocaine-seeking in animal models of drug craving and relapse. We tested a novel ergoline derivative with combined D₁ agonistic and D₂ antagonistic effects, 9,10-didehydro-N-methyl-N-(2-propynyl)-6-methyl-8-aminomethylergoline bimaleate (LEK-8829), for its effects on cocaine-seeking in the intravenous cocaine self-administration model in rats. Pretreatment with systemic injections of LEK-8829 attenuated reinstatement of cocaine-seeking induced by cocaine priming injections and diminished cocaine intake in cocaine self-administration sessions. LEK-8829 itself did not induce reinstatement of cocaine-seeking and did not maintain intravenous self-administration. The results of our study indicate that LEK-8829 is a candidate medication for the treatment of cocaine craving in cocaine addiction.     

Angiotensin type 1 receptor blockade prevents endocardial dysfunction of rapidly paced atria in rats.

INTRODUCTION: Atrial fibrillation (AF) per se causes atrial endocardial dysfunction leading to local coagulation imbalance on the internal surface of the atrium, which contributes to thrombus formation in the fibrillating left atrium. MATERIALS AND METHODS: To test a hypothesis that blockade of angiotensin II type 1 receptor (AT1-receptor) prevents the endocardial dysfunction by AF, we examined the effects of olmesartan on the expression of tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), endothelial nitric oxide synthase (eNOS) and plasminogen activator inhibitor-1 (PAI-1) in the endocardium of the rapidly paced rat atria. RESULTS: Rapid pacing induced a significant decrease in TFPI, TM and eNOS and an increase in PAI-1 protein in the left atrium. Pre-administration of low-dose olmesartan significantly prevented the down-regulation of TFPI, TM and eNOS and also attenuated the up-regulation of PAI-1. Immunohistochemistry identified these changes predominantly in the atrial endocardium. While the drug was without any effect on mRNA levels of TFPI, TM and eNOS, there was a significant decrease in its PAI-1 mRNA expression. CONCLUSIONS: AT1-receptor blocker could partially prevent the atrial endocardial dysfunction by rapid atrial pacing, which would provide one theoretical basis for beneficial effects for stroke prevention in AF.     

Simvastatin reduces adrenal catecholamine secretion evoked by stimulation of cholinergic nicotinic and angiotensinergic AT<Subscript>1</Subscript> receptors

We investigated the influence of simvastatin, a statin, on the secretion of catecholamines (CA) in rat adrenal glands, and clarified its action mechanism. Simvastatin suppressed acetylcholine (ACh)-evoked CA release in a dose- and time-dependent fashion. In the presence of simvastatin, CA secretion evoked by 1.1-dimethyl-4-phenyl piperazinium iodide (DMPP), angiotensin II, high K⁺, veratridine, and Bay-K-8644 was time-dependently inhibited. However, in the simultaneous presence of simvastatin and Nω-nitro-l-arginine methyl ester hydrochloride, CA secretion evoked by angiotensin II and DMPP recovered to control levels. Adrenal NO release was increased by simvastatin-treatment. Simvastatin-inhibited CA secretion was not affected by treatment with mevalonate. Pravastatin did not influence ACh-evoked CA secretion, while atorvastatin reduced it. In the simultaneous presence of simvastatin and fimasartan, ACh-induced CA release was markedly reduced compared to that of fimasartan-treatment alone. We present the first evidence that simvastatin reduces adrenal CA secretion induced by stimulation of nicotinic and AT₁-receptors. Simvastatin-induced inhibition seems to involve reducing the influx of both Ca²⁺ and Na⁺ into adrenochromaffin cells, partly via the elevation of NO production by NO synthase activation, without inhibition of 3-hydroxy-methylglutaryl coenzyme A reductase. Co-administration of simvastatin and fimasartan may be clinically helpful for the treatment of cardiovascular diseases.     

Non-uniform blockade of intrastriatal D<Subscript>2</Subscript>/D<Subscript>3</Subscript> receptors by risperidone and amisulpride

Rationale Atypical antipsychotic drugs have been shown to preferentially affect extrastriatal (mesolimbic) D₂/D₃ receptors over those within the striatum (nigrostriatal). The striatum does not contain exclusively nigrostriatal dopamine tracts, however. The caudate nucleus and ventral parts of the striatum primarily contain limbic and associative dopamine pathways more relevant to psychosis. Objectives We tested the hypothesis that two pharmacologically distinct atypical antipsychotic drugs, amisulpride and risperidone, would preferentially occupy of D₂/D₃ dopamine receptors in limbic and associative regions of the striatum. Methods Eight amisulpride-treated patients, six risperidone-treated patients and six age- and sex-matched healthy controls were recruited. Dynamic SPET studies were performed after bolus injection of [¹²³I]epidepride. Binding potential (BP) images were generated using a modified Logan method and aligned between subjects. Regions of interest (ROIs) were placed around head of caudate and putamen bilaterally on an average BP map derived from aligned control images. These ROIs were then applied user-independently to the BP maps for each subject to calculate BP for head of caudate and putamen. Mean occupancy of D₂/D₃ receptors in each ROI was determined by reference to the drug-free healthy volunteer group. Occupancy values for head of caudate and putamen were compared using paired Student’s t test. Results D₂/D₃ receptor occupancy was 42% in caudate and 31% in putamen for risperidone (t=5.9, df=11, p=0.0001) and 51% in caudate and 37% in putamen for amisulpride (t=11.1, df=15, p<0.0001). Conclusions Amisulpride and risperidone both show selective occupancy for limbic and associative D₂/D₃ receptors within the striatum.     

Central mediation and differential blockade by cannabinergics of the discriminative stimulus effects of the cannabinoid CB<Subscript>1</Subscript> receptor antagonist rimonabant in rats

Rationale  

Discovery of an endocannabinoid signaling system launched the development of the blocker rimonabant, a cannabinoid CB1 receptor (CB₁R) antagonist/inverse agonist. Due to untoward effects, this medication was withdrawn and efforts have been directed towards discovering chemicals with more benign profiles.     

Angiotensin II type 1 receptor blockade prevents decrease in adult stem-like cells in kidney after ureteral obstruction

Infusion of renal side population (SP) cells, enriched with adult stem-like cells, can ameliorate acute renal failure. We investigated the effects of an angiotensin II type 1 (AT(1)) receptor antagonist, valsartan on SP cell changes in renal injury by ureteral obstruction. Renal SP fraction was reduced by 38%, and the number of cells expressing CD45, a marker of hematopoietic system, in renal SP cells was increased in obstructed kidneys. Valsartan attenuated renal injury and the associated SP profile changes. Angiotensin AT(1) receptor blockade may exert regenerative effect by preserving adult stem-like cells such as SP cells in the kidney.     

CB<Subscript>1</Subscript> receptor mediation of cannabinoid behavioral effects in male and female rats

Rationale Cannabinoids have been shown to produce greater behavioral effects in female than male rats. Although central nervous system CB₁ receptors are known to mediate cannabinoid-induced behavioral effects in male rats, it is not known whether the same is true for females.Objective To determine if cannabinoid-induced antinociception and catalepsy are similarly mediated by central CB₁ receptors in male and female rats.Methods The ability of SR141716A, a CB₁ receptor selective antagonist, administered ICV (1–1000 g) or IT (1–600 g) to block 10 mg/kg IP ⁹-THC-induced antinociception (paw pressure) and catalepsy (bar test), was compared in male and female rats.Results ⁹-THC alone produced slightly greater antinociception, and significantly greater catalepsy in females than males. When administered ICV, SR141716A partially antagonized ⁹-THC-induced antinociception in both females and males. IT SR141716A also antagonized ⁹-THC-induced antinociception in both sexes; it was slightly more potent in males but equally effective in males and females. SR141716A antagonized ⁹-THC-induced catalepsy in a similar manner in males and females when given ICV or IT.Conclusions These results confirm that ⁹-THC-induced behavioral effects are mediated by central CB₁ receptors in male and female rats.     

D<Subscript>2</Subscript> but not D<Subscript>1</Subscript> dopamine receptor stimulation augments brain signaling involving arachidonic acid in unanesthetized rats

Rationale and objectives Signal transduction involving the activation of phospholipase A₂ (PLA₂) to release arachidonic acid (AA) from membrane phospholipids, when coupled to dopamine D₁- and D₂-type receptors, can be imaged in rats having a chronic unilateral lesion of the substantia nigra. It is not known, however, if the signaling responses occur in the absence of a lesion. To determine this, we used our in vivo fatty acid method to measure signaling in response to D₁ and D₂ receptor agonists given acutely to unanesthetized rats. Methods [1-¹⁴C]AA was injected intravenously in unanesthetized rats, and incorporation coefficients k* for AA (brain radioactivity/integrated plasma radioactivity) were measured using quantitative autoradiography in 61 brain regions. The animals were administered i.v. the D₂ receptor agonist, quinpirole (1 mg kg⁻¹, i.v.), the D₁ receptor agonist SKF-38393 (5 mg kg⁻¹, i.v.), or vehicle/saline. Results Quinpirole increased k* significantly in multiple brain regions rich in D₂-type receptors, whereas SKF-38393 did not change k* significantly in any of the 61 regions examined. Conclusions In the intact rat brain, D₂ but not D₁ receptors are coupled to the activation of PLA₂ and the release of AA.     

Discriminative stimulus effects of the cannabinoid CB<Subscript>1</Subscript> receptor antagonist rimonabant in rats

OBJECTIVE: To examine the discriminative stimulus effects of the cannabinoid CB(1) receptor (CB(1)R) antagonist/inverse agonist rimonabant (SR141716A) using a discriminated taste aversion (DTA) procedure. MATERIALS AND METHODS: Groups of rats were trained to discriminate between drug (5.6 or 3 mg/kg) and vehicle in DTA (t' = 20 min). The 30-min drinking opportunity after rimonabant pretreatment was followed by injection of lithium chloride (120 mg/kg) in the experimental (EXP) animals. When offered fluid after vehicle pretreatment, EXP animals subsequently were given intraperitoneal saline (NaCl, 10 ml/kg). Post-drinking treatment for controls (CONT) was NaCl irrespective of the pretreatment condition (rimonabant or vehicle). Tests examined other doses and drugs (t' = 20 min). RESULTS: The rimonabant analog AM251 (1 to 5.6 mg/kg) substituted for rimonabant. AM281 also appeared to substitute, but interpretation is complicated by unconditioned effects (drinking suppressed also in the CONT group). The CB(2)R antagonists SR144528 (18 and 30 mg/kg), AM630 (1 to 10 mg/kg), and the CB(1)R agonist methanandamide (mAEA, 3 and 10 mg/kg) did not substitute. There was a dose-related attenuation of the rimonabant-induced suppression of saccharin drinking when Delta9-tetrahydrocannabinol (Delta9-THC; 0.3 to 5.6 mg/kg), but not mAEA (1 to 10 mg/kg), was given together with rimonabant (3 mg/kg). Unconditioned effects occurred with the mAEA-rimonabant combination, not evident for combinations of rimonabant and Delta9-THC. mAEA (10 mg/kg) plus AM251 (5.6 mg/kg) resulted in strong unconditioned effects. CONCLUSION: Rimonabant induces a discriminative stimulus in DTA that continues to show potential for further examination of cannabinoid receptor antagonism.     

CB<Subscript>1</Subscript>- and CB<Subscript>2</Subscript>-cannabinoid receptor-independent lipolysis induced by WIN 55,212-2 in male rat adipocytes

The expression of genes encoding the cannabinoid CB₁ and CB₂ receptors and fatty acid amide hydrolase (FAAH) and the lipolytic activity of cannabinoid agonists were investigated in rat adipose tissue.RT-PCR studies indicated that the genes encoding CB₁ and CB₂ receptors and FAAH are not expressed in epididymal adipocytes. In functional studies, the non-selective cannabinoid receptor agonist WIN 55,212-2 concentration-dependently (0.01–30 µM) induced glycerol release above baseline (E _max 96.1±6.2% of isoprenaline-induced lipolytic response). The selective CB₂ agonist JWH-015 (0.01–30 µM) had no lipolytic activity while the endocannabinoid 2-arachidonoylglycerol and the stable anandamide derivative, R(+)-methanandamide had, only a weak lipolytic effect at the highest concentrations employed (10 and 30 µM). The concentration/response relationship for WIN 55,212-2-mediated lipolytic activity, mimicked by the S(–)-enantiomer WIN 55,212-3, was shifted significantly to the right by the CB₁ antagonist AM 251 only at 10 µM, but was not modified by the -adrenoceptor antagonist propranolol (1 µM). The protein kinase inhibitor H-89, but not the two adenylyl cyclase inhibitors (±)N ⁶-R-phenylisopropyladenosine (R-PIA, 1 µM, a selective A₁ adenosine receptor agonist) or SQ 22,536 (50 µM) significantly reduced the glycerol efflux induced by WIN 55,212-2.Our data suggest that the cannabinoid drug WIN 55,212-2 may exert lipolytic activity in male rat adipocytes via an intracellular mechanism, not activated by CB₁ or CB₂ receptor stimulation, significantly reversed by H-89 but not clearly linked to stimulation of adenylyl cyclase.     

Angiotensin II stimulation of phospholipase D in rat renal mesangial cells is mediated by the AT1 receptor subtype

Angiotensin II stimulated a biphasic 1,2-diacylglycerol formation in [³H]arachidonic acid-labelled mesangial cells. In contrast, in cells labelled with [³H]myristic acid, a tracer that preferentially marks phosphatidylcholine, angiotensin II induced a delayed monophasic production of 1,2-diacylglycerol. This delayed peak of 1,2-diacylglycerol generation was associated with a concomitant increase in choline formation, suggesting that stimulation of mesangial cells with angiotensin II causes a phospholipase D-mediated phosphatidylcholine hydrolysis. This conclusion is supported by the observation that angiotensin II stimulated the accumulation of phosphatidylethanol, when ethanol was added to mesangial cells. The production of choline and phosphatidylethanol stimulated by angiotensin II was completely blocked by the angiotensin II AT₁ receptor-selective antagonist DuP 753 with an IC₅₀ value of 8 nM, but not by the angiotensin II AT₂ receptor selective ligand CGP 42112A. Furthermore, angiotensin(1–7) and angiotensin(1–6) had only weak effects on choline generation. These data clearly indicate that angiotensin II AT₁ receptors trigger phospholipase D-mediated phosphatidylcholine hydrolysis in rat mesangial cells.     

GABA<Subscript>B</Subscript> receptor blockade in the hippocampus affects sensory and sensorimotor gating in Long-Evans rats

Rationale  

Sensory and sensorimotor gating deficits are observed in schizophrenia. GABA_B receptor deficiency is also detected in the hippocampus of schizophrenic patients.