Gene expression and morphological changes in surgically injured carotids of spontaneously hypertensive rats

The expression profiles of genes involved in cell proliferation, differentiation and programmed death were investigated in carotids of spontaneously hypertensive rats (SHR) treated with a model of surgical injury that mimics events occurring during arterial grafts, endarterectomy and organ transplantation. The mRNA level of the c-myc, angiotensin II receptor 1 (AT1), Rb/p105, Rb2/p130, Bcl-2 and Bax-alpha genes was assessed by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) technique at different times up to 48 h after injury, while the morphological changes were evaluated 30 days after injury. The proliferation marker c-myc increases almost immediately, peaks after 4 h and returns to basal levels after 24 h; the AT1 receptor mRNA reaches its maximal level 48 h after injury. The level of cell cycle exit markers Rb/p105 and Rb2/p130 gradually decreases after injury. The apoptosis marker Bcl-2/Bax-alpha ratio shows a significant reduction only 4 h after injury, resuming the initial value after 24 and 48 h. Morphological analysis reveals that surgical injury in SHR induces adventitial and medial constrictive remodeling changes rather than intima proliferation as in balloon angioplasty. Both molecular and histological data show substantial differences with respect to normotensive rats.

Interaction between metabotropic and NMDA glutamate receptors in the periaqueductal grey pain modulatory system

The formalin test was used to investigate the interactive role of periaqueductal grey (PAG) N-methyl-D-aspartate (NMDA) and metabotropic glutamate (mGlu) receptors in the modulation of persistent noxious stimulation in mice. Intra-PAG microinjections of 1 or 3 nmol NMDA, a selective agonist at NMDA-subtype receptors, decreased the nociceptive response (-94+/-5% with 3 nmol) during the latter phase of the test. This effect was antagonized by MK-801, a selective antagonist at NMDA receptors. No change in the early nociceptive phase was observed after NMDA injection. Pretreatment either with 2-methyl-6-phenylethynylpyridine (MPEP, 25 nmol/mouse), a selective antagonist at mGlu5 receptors, or with (2S)-alpha-ethylglutamic acid [(2S)-alpha-EGlu, 30 nmol/mouse], a selective antagonist at group-II mGluRs, prevented the NMDA-induced antinociceptive effect during the late hyperalgesic phase. Pretreatment with (R,S)-alpha-methylserine-O-phosphate [(R,S)-alpha-MSOP, 70 nmol/mouse], a selective antagonist at group-III mGlu receptors, had no effect on the NMDA-induced antinociception. None of the antagonists changed the formalin-induced nociceptive behaviour per se with the dosages used in combination with NMDA. MPEP at 50 nmol/mouse, however, potentiated the early nociceptive phase whilst 100 nmol/mouse attenuated the late phase. Similarly, at the higher dose of 140 nmol/mouse, (R,S)-alpha-MSOP decreased the late hyperalgesic phase. These results provide additional evidence that NMDA and mGlu receptors participate in modulating the hyperalgesia induced by peripheral noxious stimulation. In particular, mGlu receptors may modulate the NMDA receptors in the PAG since their physiological stimulation seems to be required for the NMDA-induced effect. This suggests that, together with ionotropic glutamate receptors, mGlu receptors also play a role in modulating a type of spinal cord neuroplasticity (i.e. wind-up) that has been proposed to mediate hyperalgesia.

[Drugs interfering with somatostatin receptors]

The use of drugs interfering with somatostatin receptors (ssR) is now consolidated practice in diagnostics and therapy, stimulating the development of new and more efficient molecules offering improved pharmacodynamics. Over the years, we have passed from the use of native somatostatin to mini-somatostatin and then octapeptides, above all octreotide. Subsequently, peptides were synthesized with specific affinities for a single receptorial subtype, like compound BIM23268 and compound CH275. More recently, somatostatin analogs were synthesized with a non-peptide structure. Another important aspect in the history of sst analogs is represented by the development of new pharmaceutical formulas for these drugs in order to improve patient compliance by reducing dose frequency.

High glucose induces ventricular instability and increases vasomotor tone in rats

AIMS/HYPOTHESIS

To investigate cardiac repolarization time in streptozotocin-induced diabetic rats and isolated hearts perfused with high glucose concentration.

METHODS

We studied the effects of streptozotocin-induced diabetes on the cardiac repolarisation time (Q-T interval) in Sprague-Dawley rats during a 4-day period of hyperglycaemia and a subsequent 4-day period of normoglycaemia. The Q-T interval was also evaluated in isolated hearts of non-diabetic rats, in condition of high glucose concentration.

RESULTS

Hyperglycaemia in streptozotocin rats increased mean blood pressure and led to a significant (p < 0.001) prolongation of Q-T values, which normalized after 4 days of normoglycaemia with intravenous insulin infusion. Perfusion of isolated hearts in condition of high glucose concentration caused a significant prolongation of Q-T values and increased coronary perfusion pressure (p < 0.001). The effects of high glucose were completely prevented by glutathione and almost completely by L-arginine, the natural precursor of nitric oxide. In a condition of normal glucose, L-NAME, an inhibitor of endogenous nitric oxide synthesis, increased both Q-T and CPP values to levels similar to those induced by high glucose (p < 0.001). Verapamil completely prevented Q-T lengthening and reduced by about two-thirds CPP values (p < 0.001).

CONCLUSION/INTERPRETATION

Streptozotocin-diabetes in rats produces significant haemodynamic and electric perturbations that are reversed by normoglycaemia. Moreover, high glucose increases Q-T and CPP values in the isolated hearts of non-diabetic rats. The latter effects are reversed by glutathione and L-arginine, partially reversed by verapamil and mimicked by L-NAME. By increasing the production of free radicals, high glucose could reduce nitric oxide availability to target cells inducing a state of increased vasomotor tone and ventricular instability.

Metabotropic and NMDA glutamate receptors participate in the cannabinoid-induced antinociception

The purpose of this study was to evaluate the possible contribution of metabotropic glutamate receptors (mGluRs) to cannabinoid-induced antinociception in the periaqueductal grey (PAG) matter of rats. Intra-PAG microinjection of WIN 55,212-2, a cannabinoid receptor agonist, increased the latency of the nociceptive reaction (NR) in a dose-dependent fashion in the plantar test. This effect was prevented by pretreatment with SR141716A, a selective antagonist of CB1 receptors. When injected alone, SR141716A produced, with the highest dosage used, a significant reduction in the latency of the NR. CPCCOEt, a selective mGlu1 receptor antagonist, was unable to prevent the analgesia produced by WIN 55,212-2. On the contrary, MPEP, a selective mGlu5 receptor antagonist, completely antagonized the effect of WIN 55,212-2. However, the analgesia induced by CHPG, a selective mGlu5 receptor agonist, was blocked by MPEP but not by SR141716A. When injected alone, CPCOOEt produced no effect, whereas MPEP produced, with the highest dosage used, a significant reduction in the latency of the NR. These data emphasize that mGlu5 receptors, but not mGluR1, may modulate nociception in the PAG. Similarly, a pretreatment with either 2-(S)-alpha-EGlu or (RS)-alpha-MSOP, selective antagonists for group II and III mGluRs, respectively, prevented the WIN 55,212-2-induced analgesia. When the higher dosage of (RS)-alpha-MSOP was used a decrease in the latency of the NR was observed. This was not the case for 2-(S)-alpha-EGlu. Pretreatment with DL-AP5, a selective antagonist of N-methyl-D-aspartate (NMDA) receptors, blocked the effect of WIN 55,212-2, and by increasing the dosage strongly reduced per se the latency of the NR. This study suggests that endogenous glutamate could tonically modulate nociception through mGlu and NMDA receptors in the PAG matter. In particular, the physiological stimulation of these receptors seems to be required for the cannabinoid-induced analgesia in this midbrain area.

Molecular analysis of arterial stenosis in rat carotids

A new model of surgical injury for the induction and development of stenosis in common rat carotids is described. This model differs from balloon angioplasty or vein graft systems currently applied on animals to develop stenosis, since it involves the entire vessel wall layers and mimics the injury occurring during arterial grafts, endarterectomy or organ transplantation. At different times following arterial damage, the pattern of expression of genes already known to be involved in the proliferation, differentiation, and apoptosis of smooth muscle cells (c-myc, Angiotensin II receptor 1, Bcl-2 and Bax alpha), as well as of Rb and Rb2 genes, whose pattern of expression after arterial injury has not yet been reported, was analyzed by semi-quantitative reverse transcription-polymerase chain reaction technique. Histological and histochemical analysis on carotid sections shows the morphological changes which occurred 30 days after surgical injury in the vessel wall. Molecular and histological data demonstrate that this model of surgical injury induces neointimal proliferation in about 30% of rats. In about 70% of the remaining rats, it induces the processes responsible for negative remodelling, namely the significant accumulation of extracellular matrix and fibers and disorganization of arterial tunics. This model is therefore available for further studies on the expression of genes involved in the arterial stenotic process, as well as for testing drugs aimed at limiting this recurrent pathophysiological phenomenon.

Nuclear factor-kappaB mediates simultaneous induction of inducible nitric-oxide synthase and Up-regulation of the cationic amino acid transporter CAT-2B in rat alveolar macrophages

The connection between the regulation of L-arginine transport and nitric oxide (NO) synthesis was studied in rat alveolar macrophages. Lipopolysaccharides (LPSs) and interferon-gamma stimulated in the same concentration- and time-dependent manner NO synthesis (measured by nitrite accumulation) and L-[(3)H]arginine uptake. This correlated with an increased mRNA expression for iNOS and the cationic amino acid transporter CAT-2B (analyzed by reverse transcription-polymerase chain reaction), with the same kinetics observed for the up-regulation of both mRNAs. Because nuclear factor-kappaB (NF-kappaB) is essential for induction of iNOS its role for the regulation of CAT-2B expression and L-arginine transport was investigated. The NF-kappaB inhibitors pyrrolidine dithiocarbamate and N(alpha)-p-tosyl-L-lysine chloromethyl ketone abrogated LPS- and interferon-gamma-induced increase of nitrite accumulation and L-[(3)H]arginine uptake as well as up-regulation of iNOS and CAT-2B mRNA. LPS-induced increase in iNOS and CAT-2B mRNA was also suppressed by specific NF-kappaB decoy oligodesoxynucleotides, confirming the essential role of NF-kappaB for iNOS and CAT-2B expression. Dexamethasone did not affect the initial (5 h) LPS-induced increase of iNOS and CAT-2B mRNA, but down-regulated both mRNAs after prolonged (20 h) exposure and this was accompanied by partial inhibition of LPS-stimulated nitrite accumulation and L-[(3)H]arginine uptake. These findings demonstrate parallel regulation of the expression of iNOS and CAT-2B, and of NO synthesis and L-arginine uptake in rat alveolar macrophages. NF-kappaB is an essential transcription factor not only for the induction of iNOS, but also for the up-regulation of CAT-2B. The simultaneous up-regulation of CAT-2B with iNOS is considered as a mechanism to ensure a high substrate supply for iNOS.

Effects of persistent nociception on periaqueductal gray glycine release

Glycine is a candidate nociception inhibitory transmitter in specific brain regions, like for example the spinal cord, the thalamic nuclei and the periaqueductal gray matter. However, quantitative changes in glycine released in these brain regions during peripheral inflammation episodes have not been characterized in awake animals. To address this issue, an in vivo microdialysis study was carried out in freely moving rats in order to analyse periaqueductal gray matter extracellular glycine concentration following unilateral formalin injection into the dorsal skin of the right hind-paw. The extracellular concentration of glutamine was also evaluated in order to analyse whether or not a non-neurotransmitter amino acid was equally modified. Intra-periaqueductal gray matter tetrodotoxin perfusion reduced extracellular glycine concentration (-44+/-5%), but did not change the glutamine dialysate values. Peripheral injection of formalin reduced the glycine release during the early phase (-62+/-8%) and the late phase (-36+/-6%) of hyperalgesia, although not during the analgesic period. Perfusion with naloxone (300microM) neither prevented the formalin-induced decreases in extacellular glycine concentration, nor modified the perfusate basal values of glycine and glutamine. These results show that, contrary to what has been recognized on the interactive role of opioids and GABA into the periaqueductal gray matter (i.e. opioid disinhibition), endogenous opioids seem not to modulate the activity of glycinergic neurons in the same midbrain area. In the light of these preliminary data, it is reasonable to suppose that GABA and glycine are probably not co-released at the level of periaqueductal gray matter of the rat.

In vivo effects of partial phosphorothioated AT1 receptor antisense oligonucleotides in spontaneously hypertensive and normotensive rats

Partial phosphorothioate (PS) antisense oligodeoxynucleotides (ODNs) targeted against rat AT1 receptor mRNA have been used to control blood pressure in normotensive (WKY) and spontaneously hypertensive (SHR) rats. Molecules were injected intracerebroventricularly (i.c.v., right lateral ventricle) in freely moving animals. The antisense ODN lowered the mean arterial pressure (MAP) 24 hours (-43 mmHg+/-10) and 48 hours (-30 mmHg+/-13) after injection, while the control ODN molecule had no significant effects. The observed decrease of blood pressure was due to a specific inhibition of AT1 receptor gene expression, since the level of its mRNA, monitored by reverse transcription (RT)- polymerase chain reaction (PCR), was significantly reduced by antisense molecule (-40%), compared to sense one. In normotensive rats no effect on MAP have been observed, while AT1 receptor gene expression is reduced (-40%) by antisense treatment. It is known that SHRs have an enhanced basal activity of the central renin-angiotensin system that induces an increase in central sympathetic outflow. Instead in WKY rats the central sympathetic outflow is not conditioned by the enhanced activity of brain renin-angiotensin system. Therefore in normotensive rats although partial PS ODN reduces the AT1 mRNA level this will not result in a modification of the sympathetic outflow and no change in MAP level would be observed.

Periaqueductal gray matter metabotropic glutamate receptors modulate formalin-induced nociception

The role played by periaqueductal gray (PAG) matter metabotropic glutamate receptors (mGluRs) in the modulation of persistent noxious stimulation was investigated in mice. The formalin test was used as a model of persistent pain. Intra-PAG microinjections of (S)-3, 5-DHPG (25 and 50 nmol/mouse) and L-CCG-I (30 and 60 nmol/mouse), agonists of group I and group II mGluRs, respectively, decreased the nociceptive response (-92+/-6% and -89+/-8%, respectively) during the late phase. No change of the early nociceptive phase was observed after (S)-3,5-DHPG or L-CCG-I treatments. These effects were antagonized by a pretreatment with CPCCOEt (40 nmol/mouse) and (2S)-alpha-EGlu (30 nmol/mouse). CPCCOEt is a selective antagonist of group I mGlu receptors, while (2S)-alpha-EGlu is an antagonist of group II. Intra-PAG microinjections of L-SOP (60 and 120 nmol/mouse), a selective agonist of group III mGluRs, induced an increase of the nociceptive response (+95+/-7%) during the late hyperalgesic phase. (R,S)-alpha-M-SOP (70 nmol/mouse), a selective antagonist of group III mGluRs, completely antagonized the L-SOP-induced effect. These results show that PAG mGluRs participate in modulating the late hyperalgesic behaviours induced by formalin. It seems, therefore, possible that group I and group II mGluRs positively modulate PAG antinociceptive descending pathway following a persistent noxious stimulation, while group III mGluRs modulate it negatively.

Cardiotoxicity of doxorubicin: effects of 21-aminosteroids

The purposes of this study were to investigate in vivo the effects of two lazaroids,U-74389G (21-[4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl]-pregna-1,4,9 (11)-triene-3,20-dione (2)-2-butenenedionate) and U-83836E (-)-2-[[4-(2,6-di-1-pyrrlidinyl-4-pyrimidinyl)-1-piperazinyl]methy l]-3,4-dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-6-ol, dihydrochloride against the cardiotoxicity induced by doxorubicin in rat and the mechanisms underlying such a toxicity. Doxorubicin (DXR) administered intraperitoneally (5 mg/kg 4 times per week for 1 week) induced significant decrease of body weight, ECG alterations and 100% mortality. The lazaroids used in this study did not protect from DXR-induced cardiotoxicity. Our results showed that the compound U-74389G delayed, but did not reduce DXR-induced mortality, and did not prevent body weight loss and ECG changes. The compound U-83836E was unable to modify any toxic effects induced by DXR. These data indicate that oxygen free radicals and the subsequent increase in intracellular calcium are only steps of DXR progressive general toxicity that leads to cardiac injury. In conclusion, we propose that the 21-aminosteroids, potent inhibitors of membrane lipid peroxidation, alone are not enough to protect from DXR toxic effects.

The role of A3 adenosine receptors in central regulation of arterial blood pressure

1. Pharmacological studies have suggested that A3 receptors are present on central neurons. Recently this adenosine receptor subtype has been identified in the rat and its presence in the central nervous system has been confirmed. 2. In this study we investigated the effects of acute intracerebroventricular (i.c.v.) injections of N6-2-(4-aminophenyl)-ethyladenosine (APNEA), a non-selective A3 adenosine receptor agonist, on arterial blood pressure (ABP) and heart rate (HR), after treatment with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective antagonist of A1 adenosine receptors. 3. Anaesthetized rats, after DPCPX (12 microg(-1) kg i.c.v.), were treated with APNEA (0.4-4 microg kg(-1) i.c.v.) resulting in a transitory and dose-dependent decrease in arterial blood pressure without a change in heart rate. APNEA also induced hypotensive responses after i.c.v. pretreatment with aminophylline, at a dose of 20 microg kg(-1). In contrast, pretreatment 48 h before, with 4 microg kg(-1) i.c.v. of pertussis toxin reduced the hypotensive effect induced by APNEA. Administration of APNEA at a higher dose (20 microg kg(-1) i.c.v.), after DPCPX, induced a decrease in ABP of -66+/-5.4 mmHg and after 3 min a decrease in heart rate of -62+/-6.0 beats min(-1). Transection of the spinal cord abolished this significant fall in ABP, but not the decrease of HR. 4. These results suggest that a population of A3-receptors is present in the CNS, whose activation induces a decrease in blood pressure with no change of heart rate.

Role of vasopressin on excitatory amino acids mediated pressor responses in the periaqueductal gray area

In order to evaluate the role played by vasopressin on pressor responses elicited by stimulation of the periaqueductal gray (PAG) area by excitatory amino acids we carried out in vivo studies in genetically vasopressin deficient rats (Brattleboro). Microinjections of 1-glutamic acid (glutamate, 0.6 to 60 nmol/rat) or N-methyl-d-aspartic acid (NMDA, 0.07 to 7 nmol/rat) into the PAG area of freely moving Brattleboro rats induced increases of arterial blood pressure values significantly lower than those obtained in Long Evans rats (control) (glutamate in Brattleboro rats: from +2+/-1 mmHg to 16+/-3 mmHg; glutamate in Long Evans rats: from +16+/-2 mmHg to +36+/-4 mmHg; NMDA in Brattleboro rats: from +5+/-2 mmHg to +34 +/-8 mmHg; NMDA in Long Evans rats: from +18+/-7 mmHg to 80+/-9 mmHg; n=5). Similarly, in anaesthetized Brattleboro rats (urethane 1.2 g/kg i.p.) pressor responses to NMDA microinjections (0.7 nmol/rat) into the PAG area were significantly lower than in Long Evans rats (controls) (+15+/-3 mmHg vs +24+/-4 mmHg). In Long Evans rats NMDA injection also reversed blood pressure decrease induced by ganglionic blocker, hexamethonium and/or losartan (3 mg/kg i.v.), an AT1 receptor antagonist. In Brattleboro rats, NMDA injection did not reverse blood pressure decreases induced by hexamethonium (5 mg/kg i.v.). Moreover, hexamethonium induced blood pressure decrease was not reversed by acetylcholine injection (137 nmol/rat) into the PAG area of anaesthetized Long Evans rats, but if injected before hexamethonium, acetylcholine was able to increase blood pressure (+25+/-3 mmHg). Our results document: i) the importance of the PAG area in the control of cardiovascular system; ii) the involvement of excitatory amino acids in the neural control of vasopressin release; iii) the close relationship between glutamate and vasopressin in the central blood pressure regulation.

Bioavailability of timolol and aceclidine after ocular instillation in the rabbit

The bioavailability of timolol and aceclidine after the ocular instillation of each drug (timolol 0.5% or aceclidine 2%) or both combined (timolol 0.5% + aceclidine 2%) has been evaluated in rabbits. 15 male albino rabbits were treated by the instillation of timolol and aceclidine alone or combined in the conjunctival sac of the right eye. Timolol concentrations in humor aqueous were assayed at 10 min, 30 min, 1 hr, 2 hr, 4 hr and 6 hr after instillation by high-performance liquid chromatography (HPLC). Aceclidine was assayed by a pharmacodynamic method: pupillary diameter at the following time intervals 0 (basal value), 1 min, 5 min, 30 min, 1 hr, 2 hr, 4 hr, 6 hr after treatment. Our results demonstrated that no differences in timolol and aceclidine bioavailability were found between simple-drug preparations and their combination.

Effects of imipramine on raphe nuclei and prefrontal cortex extracellular serotonin levels in the rat

The effect of acute administrations of three doses of imipramine (1, 5 and 10 mg/kg s.c.), a widely used tricyclic antidepressant, on extracellular levels of serotonin (5-HT) has been studied by intracerebral microdialysis in raphe nuclei and prefrontal cortex of conscious rats. Imipramine 1 mg/kg s.c. did not change extracellular 5-HT in either raphe nuclei and prefrontal cortex. However, with the dose of 5 mg/kg s.c. imipramine induced in raphe nuclei, a brief increase of extracellular 5-HT followed by a lowering (55-65% basal release) of the neurotransmitter. The same dose of imipramine decreased (60-70% of basal value) extracellular 5-HT in prefrontal cortex. Imipramine 10 mg/kg s.c. significantly increased 5-HT levels in both raphe nuclei (190 +/- 20% above basal value) and prefrontal cortex (280 +/- 15% above basal value). Pretreatment with (-)pindolol (5 mg/kg s.c.), a non-selective 5-HT1A subtype receptor antagonist, 30 min before imipramine 5 mg/kg, modified the effect of the antidepressant: an increase, instead of a decrease, on prefrontal cortex dialysate 5-HT was observed. (-)Pindolol (10 mg/kg s.c.) increased extracellular 5-HT in both raphe nuclei (155 +/- 20% above basal value) and prefrontal cortex (160 +/- 8% above basal value). These data show that acute administration of imipramine modifies extracellular 5-HT at the level of the raphe nuclei and prefrontal cortex. 5-HT1A autoreceptors in the raphe nuclei, which this study suggests to be tonically active, may be stimulated after systemic administration of high doses of imipramine.

[Local administration of somatostatin in joint diseases in athletes]

Somatostatin is a hormone produced by the hypothalamus, and is widely diffused outside the CNS. It inhibits the secretion of many glands. Recently it has been shown that somatostatin has been proposed in the treatment of phlogistic diseases of the joints by intra-articular administration. The authors show the results of a study conducted in 16 patients (athletes) with arthrosynovitis or tendinitis of the knee or of the ankle, in which somatostatin was administered (250 mg/treatment, 1 treatment/week). Somatostatin significantly reduced pain, improved movement function and decreased the effects of pain on daily activities. The treatment was very well tolerated locally and generally. In conclusion, somatostatin may be considered useful in the treatment of articular and tendineous phlogistic diseases, almost in athletes.

Research on heterocyclic compounds. XXXVIII. Synthesis and pharmacological activity of imidazo[1,2-b]pyridazine-2-carboxylic derivatives

A series of imidazo[1,2-b]pyridazine-2-carboxylic acids, esters and amides was synthesized and tested for antiinflammatory, analgesic and ulcerogenic activities. The ethyl esters were prepared by cyclocondensation of some 3-aminopyridazines with ethyl bromopyruvate, followed by hydrolysis or ammonolysis in order to obtain the corresponding acids and amides. The inhibitory activity on the carrageenan-induced edema in the rat paw and on writhes induced by acetic acid in mice was evaluated, as well as the ulcerogenic action on the rat gastric mucosa. The pharmacological activity was discussed in terms of structure-activity relationships. In particular, the analgestic activity shown by these carboxylic derivatives was compared with that found in other series of imidazo[1,2-b]pyridazine analogues previously examined.

AT1 receptors mediate pressor responses induced by angiotensin II in the periaqueductal gray area of rats

Microinjection of angiotensin II (ANGII) (0.01 to 1 nmol) into the periaqueductal gray area (PAG) of anaesthetised rats caused dose-dependent increases in blood pressure. Preinjection (10 min before) of losartan (a selective non-peptide AT1 receptor antagonist; 50 nmol) to the PAG reduced the pressor response to ANGII whereas PD123319 (a selective non-peptide AT2 receptor antagonist; 50 nmol) did not affect the ANGII-induced hypertension. Thus, our data suggest that the activation of AT1 but not AT2 receptors mediates ANGII-induced blood pressure changes in the PAG area.

Evidence that A(2a) and not A(2b) purinoceptors are coupled to production of nitric oxide in the central regulation of blood pressure

In a previous study we reported that nitric oxide (NO) partially mediates centrally the decrease of arterial blood pressure induced by adenosine A(2) subtype receptor stimulation. The present study confirms the earlier suggestion and shows that in adult male normotensive anaesthetized rats 5'-N-ethylcarboxamidoadenosine (NECA), a non-selective adenosine receptor agonist, centrally injected induced a significant decrease of arterial blood pressure. Moreover, the observation that intracerebroventricular (i.c.v.) administration of N(ω)-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor, +8-(3-chlorostyryl)-caffeine (CSC), antagonist of A(2a) receptors, did not reduce furthermore the hypotensive effect induced by NECA injection, demonstrated that NO is involved only via A(2a) and not via A(2b) adenosine subtype receptors in the central regulation of blood pressure.

Angiotensin II, via an action at AT1 receptors, may modulate the behavioural effects of ET-1 in conscious rats

The injection of endothelin-1 (ET-1) (1 pmol/rat) into the dorsolateral periaqueductal gray (PAG) area of freely moving rats induced rotation along the long axis of the body (barrel-rolling). Preinjection (10 min before) of losartan (a selective AT1 receptor antagonist; 50 nmol) to the PAG area reduced the behavioural response to ET-1. In contrast, pretreatment with PD123319 (a selective AT2 receptor antagonist; 50 nmol) did not affect the ET-1-induced barrel-rolling. These results indicate that endogenous angiotensin II, via an action on AT1 receptors, contributes to the barrel-rolling of ET-1 within the brain.

Involvement of nitric oxide in cardiorespiratory regulation in the nucleus tractus solitarii

The aim of this study was to investigate whether nitric oxide (NO) is involved in cardiorespiratory regulation in the nucleus tractus solitarii (NTS). Unilateral microinjections (50 nl) of the NO-donor, sodium nitroprusside (SNP, 40-100-200 mM), into the NTS of anaesthetized rats elicited dose-dependent apnea (7.3 +/- 2.3 sec; 28.6 +/- 5.7 sec; 35.6 +/- 6.4 sec, respectively; n = 6) and a decrease in arterial blood pressure (8.4 +/- 3.1 mmHg; 18.2 +/- 5.8 mmHg; 25.8 +/- 6.7 mmHg, respectively; n = 6). Similarly, unilateral micro-injections (50 nl) of another NO-donor, 3-morpholinosydnonimine (SIN-1, 20-40-100 mM), also induced apnea (5.1 +/- 2.4 sec; 8.7 +/- 4.3 sec; 26.3 +/- 6.4 sec, respectively; n = 6) and a decrease in arterial blood pressure (6.2 +/- 2.3 mmHg; 11.1 +/- 3.3 mmHg; 18.3 +/- 6.1 mmHg, respectively; n = 6). The SNP- and SIN-1-induced apnea and arterial blood pressure decrease were significantly (p < 0.01) blocked by a 3 min pretreatment with two calcium-channel blockers, diltiazem (0.1 mM) and cobalt (10 mM), while lower doses (diltiazem 0.01 and cobalt 1) were ineffective. Microinjections of diltiazem (0.01 mM) and cobalt (1 mM) alone did not induce any change in basal cardiorespiratory values like diltiazem (0.1 mM) and cobalt (10 mM). These data suggest that NO may be involved in NTS cardiorespiratory regulation via calcium-channel activation.

Endothelin-1 in periaqueductal gray area of mice induces analgesia via glutamatergic receptors

The aim of the study was to examine whether endothelin-1 (ET-1) injected into dorsolateral periaqueductal gray (PAG) area of mice produces antinociception. ET-1, from 1 to 4 pmol/mouse, induced antinociceptive effect in a dose-dependent manner. This antinociceptive effect was prevented by NMDA receptor antagonists (2-APV and MK-801) injected in the same area (2-APV) or by intraperitoneal route (MK-801). CNQX, a non-NMDA receptor antagonist, did not inhibit the ET-1 effects. Prazosin, an alpha 1-adrenergic blocking agent, also prevented the ET-1 antinociceptive effect. We suggest that the activation of NMDA glutamatergic receptors in the PAG area may be a necessary step for ET-1 induced antinociception.