Antagonism of pre- and postjunctional responses to neuropeptide Y and sympathetic stimulation by D-myo-inositol-1,2,6-trisphosphate in the anaesthetised dog.

Pre- and postjunctional responses to nerve released or exogenous neuropeptide Y (NPY) were measured in the anaesthetised dog before and after administration of D-myo-inositol-1,2,6-trisphosphate (PP56) a putative NPY antagonist. The inhibition of the increase in pulse interval evoked by vagal stimulation was used as a measure of prejunctional action of NPY and the magnitude of increase in blood pressure was used as a measure of postjunctional action of NPY (direct action or constrictor potentiating). Elevated plasma levels of PP56 were maintained throughout the course of the experiment. PP56 significantly reversed the inhibitory effect of NPY (nerve released or exogenous) on cardiac vagal action, and significantly inhibited the pressor response to exogenous NPY. PP56 did not affect the pressor response to intravenous phenylephrine, a selective alpha-adrenoceptor agonist. PP56 therefore significantly antagonises both pre- and postjunctional effects of NPY (nerve released and exogenous) and, with respect to its postjunctional antagonism, this action is selective for NPY.     

Comparison of affinities of muscarinic antagonists to pre- and postjunctional receptors in the guinea-pig ileum

The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was preincubated with [3H]choline, then superfused and stimulated electrically (1 Hz 120 pulses). Oxotremorine reduced the evoked outflow of [3H]acetylcholine in a concentration-dependent manner. Each of the six antagonists (scopolamine, methylatropine, trihexyphenidyl, 4-DAMP, clozapine, pirenzipine) produced parallel shifts of the concentration-response curves for the prejunctional effects of oxotremorine. Similarly, in contraction experiments, the antagonists competitively antagonized the postjunctional responses to oxotremorine. The pre- and postjunctional pA2 values did not differ significantly for any of the antagonists. It is concluded that pre- and postjunctional muscarinic receptors in the guinea-pig ileum are pharmacologically similar.     

Effects of phosphorothioated neuropeptide Y Y1-receptor antisense oligodeoxynucleotide in conscious rats and in human vessels.

1. Metabolically stabilized (phosphorothioate) human and rat NPY Y1 receptor oligodeoxynucleotides (ODNs) complimentary to the rat or human Y1 mRNA were synthesized; [sense (rY1-SODN, 5'-AATTCAACTCTGTTCTCC-3'), antisense (hY1-ASODN, 5'-CCTGGGAAAATAATGTTG-3' and rY1-ASODN, 5'-GGAGAACAGAGTTGAATT-3') and mismatches (hY1-MMODN, 5'-CCTGAGATAA-TAAGGTTG-3' and rY1-MM 5'-GTAGATCAGAGATGAAGT-3')] and used to modulate cardiovascular function in vitro in human vessels as well as in vivo in the rat. 2. The objectives of the experiments were to assess the influence of the NPY Y1 receptor on vasomotor function human resistance arteries in vitro and to investigate the contribution of the NPY receptor system to cardiovascular haemodynamics in vivo. 3. Human subcutaneous resistance arteries removed from patients who underwent surgery for nonvascular diseases were incubated in vitro with the stabilized phosphorothioated hY1-receptor ASODN or MMODN (10(-7) TO 10(-5) M). 4. In human resistance vessels preincubated with hY1-AS (10(-7) to 10(-5) M), the contractile response to NPY was significantly reduced in a dose-dependent fashion. No effects were observed in the hY1-MMODN-incubated vessels at lower concentrations (10(-7) M to 10(-6) M). 5.The haemodynamic effects of the phosphorothioated rY1-ASODN, SODN or MMODN were investigated in conscious rats during 48 h of continuous infusions. The continuous infusion with rY1-ASODN did not change MAP while the rY1-SODN unexpectedly induced an early (10-20) increase in ambulatory MAP and the rY1-MMODN a late (24-44 h) increase. 6. Contractile responses to NPY (2, 4, 8, 16 and 32 micrograms kg-1) were significantly reduced in the rats treated with long-term infusion of rY1-ASODN (2.1 mg kg-1 h-1, i.v. infusion for 48 h) compared with animals treated with rY1-SODN and MMODN, as well as animals treated with saline and glucose. Notably, the group infused with the rY1-SODN showed an exaggerated response to tested doses of NPY. 7. We conclude that the incubation of human subcutaneous arteries with a metabolically stabilized 18 base pair hY1-ASODN and long-term infusion with a corresponding rY1-ASODN attenuate NPY-induced vasoconstriction.     

Lack of inotropic effects of neuropeptide Y in human myocardium

The sympathetic co-transmitter neuropeptide Y (NPY) inhibits cardiac contractility in vivo in the rat heart. We tested whether NPY alters the force of contraction or the activity of adenylate cyclase in the isolated human right atrium. Neuropeptide Y did not affect basal-or isoproterenol-stimulated force of contraction and did not inhibit forskolin-stimulated adenylate cyclase activity. We conclude that NPY does not directly decrease cardiac contractility in humans. The inhibitory cardiac effects of NPY are likely to be secondary to coronary vasoconstriction, presynaptic inhibition of catecholamine release, and/or baroreflex activity.     

The effects of age on human venous responsiveness to neuropeptide Y

AIMS: Neuropeptide Y (NPY) is a sympathetic neurotransmitter released with noradrenaline during sympathetic stimulation. Ageing has been shown to be associated with a reduction in alpha2 and beta-adrenoceptor mediated responses in veins, but it is not known whether NPY responsiveness is also altered with increasing age. METHODS: Using a dorsal hand vein technique, we examined NPY receptor responsiveness in 24 normal, healthy subjects (20-72 years; 10 males, 14 females). Graded infusions of NPY (25-2000 pmol min(-1)) were administered (5 min at each dose) into a dorsal hand vein. Venous distension at 45 mmHg was measured at 3-5 min of each infusion. Dose-response curves to NPY were constructed and the peak venoconstriction was calculated. RESULTS: Dose-dependent venoconstriction was seen in all but one subject. The peak venoconstriction observed with NPY was significantly and negatively correlated with the age of the normal subjects (r=-0.63, P<0.01). When subjects were ranked from youngest to oldest and divided into tertiles, (20-40 years, n = 8; 41-55 years, n = 8; 56-72 years, n = 8), mean dose-response curves were different with the oldest tertile being significantly less responsive (P<0.05). The peak venoconstriction observed (% of control) was 65.1+/-7.0, 46.5+/-9.4, and 24.4+/-4.8%, respectively. The oldest tertile had a significantly decreased peak venoconstriction compared with the youngest tertile (P<0.01). Infusion of NPY into a dorsal hand vein had no systemic effects on heart rate or blood pressure in any of the subjects studied. CONCLUSIONS: Hand vein responsiveness to exogenously infused NPY in normal subjects is decreased as age increases. The reduction of NPY-receptor-mediated responses with age may influence sympathetic nervous system control of the venous system with advancing age.     

The effects of neuropeptide Y on myocardial contractility and coronary blood flow.

1. This study was designed to assess the effects of exogenous neuropeptide Y (NPY) on cardiac contractility and coronary blood flow (CBF) in anaesthetized dogs and to evaluate the effect of NPY on the responses to sympathetic and parasympathetic stimulation and to inotropic agents. 2. Bolus doses of NPY (500 micrograms), administered via the femoral vein, increased mean arterial pressure. The pressor effect was associated with reductions in heart rate, CBF and cardiac contractility. 3. The effects of NPY (500 micrograms) on contractility and CBF were compared with that of vasopressin (VP) (1 unit). For similar reductions in CBF, NPY and VP had similar negative inotropic effects. Thus, it is likely that the negative inotropic response to NPY is not due to a direct effect of NPY on the heart muscle but is largely due to coronary vasoconstriction. 4. In the presence of NPY (500 micrograms, i.v.), there was an inhibition of the positive inotropic response to stimulation of the left cardiac sympathetic nerve (2 or 5 Hz, 0.05 ms). NPY also inhibited the negative inotropic response and chronotropic response to vagal stimulation (2, 3 or 5 Hz, 0.05 ms). 5. Dose-response curves were obtained for the inotropic, chronotropic and pressor responses to cumulative infusions of noradrenaline (n = 6) and dobutamine (n = 6). NPY had no effect on these dose-response curves. 6. The effect of NPY on the responses to salbutamol and impromidine was assessed. NPY did not alter the positive inotropic, chronotropic or depressor responses to these agonists.(ABSTRACT TRUNCATED AT 250 WORDS)     

The in vitro genotoxic and cytotoxic effects of remeron on human peripheral blood lymphocytes

Remeron (Mirtazapine) is an antidepressant drug which exerts its action by blocking presynaptic α-2-adrenergic receptors and postsynaptic serotonin types 2 and 3 receptors. In this in vitro analysis, human peripheral blood lymphocytes was treated by remeron (10, 25, 40 and 55 μg/mL) for 24 hours and 48 hours periods, then it was attempted to study of genotoxic and cytotoxic effects of the substance on human peripheral blood lymphocytes by some tests such as sister chromatid exchange (SCE), chromosomal abnormalities (CA) and micronucleus (MN) tests. Also proliferating effect of the substance was investigated. Remeron didn’t significantly cause chromosomal abnormalities and sister chromatid exchange while caused micronucleus at 40 μg/mL concentration and 24?h periodic time and increased proliferation index of the both 24 and 48 hours treated cells was decreased in a concentration manner. Also, exposing to the remeron for 24 and 48 hours leaded to a decrease in mitotic index and nucleus division index in the cells by concentration dependent manner. These findings showed that remeron did not have significantly genotoxic effects on human peripheral blood lymphocytes while it showed cytotoxic effects on the cells, which is the first report on genotoxic and cytotoxic properties of remeron.     

Pharmacology of neuropeptide Y receptor antagonists. Focus on cardiovascular functions

Neuropeptide Y is one of the most abundant mammalian neuropeptides identified to date. The possible actions of neuropeptide Y, that is co-localized and released with noradrenaline, as a sympathetic co-transmitter has attracted much attention during the last decade. In recent years, several non-peptide antagonists with high subtype selectivity for neuropeptide Y receptors have been introduced. With them, the status of neuropeptide Y as a sympathetic transmitter has been established, and so have profound cardiovascular effects mediated by neuropeptide Y Y(1) and Y(2) receptors. Significant release of neuropeptide Y occurs especially upon stronger sympathetic activation, and recent data suggest that the importance of neuropeptide Y seems enhanced in stress-related cardiovascular disorders. The true significance of neuropeptide Y has thus started to unfold, owing to the presence of the first generation of selective neuropeptide Y receptor antagonists. This review concerns the pharmacology of these agents, what we have learnt from them, and might find out in the future.     

An investigation of age-related changes in pre- and postjunctional alpha-adrenoceptors in human saphenous vein

The responsiveness of prejunctional alpha 2-, postjunctional alpha 1- and postjunctional alpha 2-adrenoceptors was examined in human isolated saphenous veins from male patients in the age range 37-70. There was no age-related alteration in the prejunctional potency of the alpha 2-adrenoceptor agonist xylazine for inhibiting the stimulation-evoked overflow of tritium in tissues preincubated with [3H]noradrenaline. The alpha 2-adrenoceptor antagonist yohimbine (0.01-1 microM) and the alpha 1-adrenoceptor antagonist prazosin (0.1-1 microM) significantly reduced stimulation-evoked contractions in a concentration-dependent manner. There was no significant age-related correlation for the potency of prazosin but there was a significant negative correlation between the potency of yohimbine and age (r = 0.70, n = 11, P less than 0.05), i.e. the potency of yohimbine decreased with increasing age. The decreased postjunctional potency of yohimbine may reflect a loss of alpha 2-adrenoceptors with increasing age.     

Prejunctional and postjunctional effects of neuropeptide Y at the noradrenergic neuroeffector junction of the perfused mesenteric arterial bed of the rat

The effect of neuropeptide Y (NPY) on periarterial nerve stimulation-induced release of norepinephrine (NE) and increase in perfusion pressure in the perfused mesenteric arterial bed of the rat was examined. Perfusate effluents were continuously collected and assayed for endogenous NE by high-pressure liquid chromatography (HPLC) coupled to electrochemical detection. Perfusion pressure was continuously monitored by means of a pressure transducer. Periarterial nerve stimulation (8 or 16 Hz, 60 V, 2-ms duration for 30 s) resulted in a readily detectable increase in NE release and perfusion pressure that was attenuated by the prior administration of tetrodotoxin (TTX) (10(-5) M) or guanethidine (5 X 10(-5) M). NPY exerted both prejunctional and postjunctional effects on noradrenergic neurotransmission in this preparation. The peptide produced a concentration-dependent reduction in the release of NE over a concentration range of 10(-10) - 10(-7) M. A similar inhibition effect occurred at 8, 10, and 16 Hz. In contrast, low concentrations (10(-10) and 10(-9) M) decreased the effect of nerve stimulation on perfusion pressure, whereas higher concentrations (10(-7) M) produced a marked potentiation. The alpha 2-adrenoceptor antagonist, yohimbine, did not alter the inhibitory effect of NPY on evoked NE release or the effect on perfusion pressure. Prazosin similarly did not alter the inhibitory effect of NPY on NE release but prevented the increase in perfusion pressure. We conclude that NPY modulates noradrenergic neurotransmission in the mesenteric arterial bed by decreasing the evoked release of NE and producing a concentration-dependent biphasic response on vascular smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The actions of 5-hydroxytryptamine receptor agonists and antagonists at pre- and postjunctional level on the canine saphenous vein

Summary The prejunctional and postjunctional 5-HT receptors of the canine saphenous vein were studied. The release of ³H-noradrenaline (³H-NA) from incubated saphenous vein strips was inhibited by 5-hydroxytryptamine (5-HT) in a concentration-dependent way (5-HT concentrations: 0.01, 0.1 and 1.0 mol · l^–1), but not by the selective 5-HT_1A agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT; 1 and 10 mol · l^–1). The inhibitory effect of 5-HT was antagonized by metitepine and methysergide, but not by yohimbine, (–)-pindolol or ketanserin. In strips preincubated with 5-HT (1.2 mol · l^–1), the fractional release of ³H-NA was slightly reduced (paired experiments). 5-HT and 8-OH-DPAT caused concentration-dependent contractions of the saphenous smooth muscle. A parallel shift of the concentration-response curve for 8-OH-DPAT to the right was caused by metitepine and yohimbine, but not by ketanserin. The contractions caused by 5-HT were antagonized by metitepine and yohimbine (parallel displacement of the curves to the right), as well as by ketanserin and methysergide (with a depression of the upper part of the curve). Blockade of -adrenoceptors (due to prazosin plus a low concentration of yohimbine) also resulted in a weak antagonistic effect. Ketanserin and metitepine displaced the noradrenaline concentration-response curve to the right. We conclude that the saphenous vein of the dog is endowed with prejunctional receptors of the 5-HT₁ type which can not be classified as belonging either to the 1 A or 1 B subtype; and that at the postjunctional level 5-HT₁ (possibly of the 1D subtype) and 5-HT₂ receptors are present. 5-HT is able to activate all these receptors.Supported by INIC (Centro de Farmacologia e Biopatologia Química da Universidade do Porto) Send offprint requests to M. Q. Paiva at the above address     

Inhibition of proliferation of human peripheral blood mononuclear cells by calcium antagonists. Role of interleukin-2

To evaluate the role of interleukin-2 (IL-2) in the inhibition of the proliferation of human peripheral blood mononuclear cells (PBMC) by calcium channel blockade, the effect of nifedipine, which blocks the L-type calcium channel on the proliferation, the IL-2 expression and the IL-2 production in human PBMC, was compared with the effect of mibefradil, which blocks both L- and T-type calcium channels with a more selective blockade of T-type channels. The rate of [3H]-thymidine incorporation into control and concanavalin A-induced PBMC in the presence or absence of the calcium channel blockers nifedipine or mibefradil (1, 10 or 50 microM) was assayed in the cells cultured for 3 days. The cellular cytotoxicity and the cell number in growing cultures was also determined in nifedipine- or mibefradil-treated control or stimulated cells. Restoration of the proliferative response in nifedipine- or mibefradil-treated cells was investigated by addition of exogenous IL-2. IL-2 receptor expression in the cells was monitored using antiactivated T-cell antigen (Tac) antibody, and the IL-2 production in the cell supernatants of the cultures was determined by an enzyme amplified sensitive immunoassay. Nifedipine and mibefradil concentration-dependently reduced the cell number and [3H]-thymidine incorporation or the do novo DNA synthesis in control and concanavalin A-stimulated human PBMC. The proliferative response of nifedipine- or mibefradil-treated cells was restored by addition of exogenous IL-2. The normal expression of IL-2 receptors was preserved while the IL-2 production was blocked in the presence of nifedipine or mibefradil.     

Differential effects of reserpine and 6-hydroxydopamine on neuropeptide Y (NPY) and noradrenaline in peripheral neurons

The effects of 6-hydroxydopamine (6-OHDA) and reserpine pretreatment on peripheral neuropeptide Y (NPY)- and noradrenaline (NA)-containing neurons were studied in guinea-pigs. Ten days after 6-OHDA pretreatment, a 60-80% reduction of the NA content was observed in the right atrium of the heart, stellate ganglion and spleen. The content of NPY-like immunoreactivity (LI) was reduced by about 50% in the heart, not changed in the spleen while it increased to 200% of control in the stellate ganglion. Immunohistochemistry showed a pronounced loss of NPY- and tyrosinehydroxylase (TH)-immunoreactive (IR) nerves in the heart but not in the spleen. Increased NPY-IR was seen in axons and cell bodies of the stellate ganglion. Reserpine pretreatment (thereshold dose 0.5 mg X kg-1) caused a dose- and time-dependent reduction of the content of NPY-LI in the heart. A maximal depletion of NPY-LI (about 80%) was observed 5 days after reserpine. Reserpine pretreatment also reduced the content of NPY-LI in the spleen, while no significant change was observed in the adrenal gland or vas deferens. The levels of NPY-LI increased in the stellate ganglion to about 180% of control 5 days after reserpine. Immunohistochemical analysis revealed an almost total loss of NPY-IR nerve fibres in the heart as well as around blood vessels in the lung and skeletal muscle. No detectable changes were observed in perivascular NPY-IR nerves in the spleen, vas deferens or kidney. TH-IR nerves remained unchanged after reserpine, thus indicating that the observed loss of NPY-IR nerves was due to a depletion of NPY and not a degeneration. No change in the levels of substance P-LI was observed in the right atrium 5 days after reserpine. NA was, in contrast to NPY, markedly depleted in all tissues investigated after reserpine treatment. The depletion of NA was more extensive, and occurred more rapidly and at much lower doses as compared to the effects on NPY-LI. Ligations of the sciatic nerve revealed that NPY-LI was transported axonally with a rapid rate (3 mm/h). Reserpine pretreatment significantly increased the amount of accumulated NPY-IR above the ligation, suggesting an increase in axonal transport. High performance liquid chromatography revealed that the NPY-LI consisted of two major peaks in the stellate ganglia, while only one peak closely corresponding to porcine NPY was seen in the right atrium. In conclusion, 6-OHDA pretreatment depletes NPY-LI in certain terminal regions and increases NPY-LI in ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vitro cytopathic effects of mycotoxin T-2 on human peripheral blood T lymphocytes

The trichothecene mycotoxin T-2 is reported to exhibit immunotoxic activity. The potential presence of T-2 in foods renders it as public health hazard and its toxicity needs to be better understood. We investigated the in vitro effects of T-2 at sub-toxic (0.1 ng/ml) and toxic (10 ng/ml) levels on freshly isolated human peripheral blood lymphocytes (PBLs). We observed no direct influence on untreated PBLs. The toxic dose of T-2, however, totally inhibited phytohemagglutinin-induced T lymphocyte proliferation and caused early apoptosis that peaked after 8 h of exposure. Both major T lymphocyte subsets (CD4⁺ and CD8⁺) were affected as they appeared to show a positive response to T-2 at 8 h followed by their sharp reduction after 96 h. Further investigation on the naïve (CD45RA⁺) and memory (CD45RO⁺) subpopulations confirmed these observations and indicated that T-2 affected equally all the subpopulations studied, although PHA preferentially stimulated CD45RO⁺ T lymphocytes. Sub-toxic T-2 appeared to exhibit co stimulatory properties to PHA-stimulated cells. These results support the hypothesis that T-2 affects the activation-induced cell death mechanism of T lymphocytes.     

Renal hemodynamics in hemorrhagic hypotension: studies on the effects of pre- and postjunctional dopamine receptor agonists

The present study was conducted to determine if selective prejunctional dopamine receptor agonists will be useful in improving renal hemodynamics in acute hemorrhagic shock in anesthetized mongrel dogs. Both bromocriptine and N-n-propyl-N-n-butyl dopamine (PBDA) effectively increased renal blood flow, due to a decrease in renal vascular resistance in intact anesthetized dogs. However, these two agents failed to increase renal blood flow after acute hemorrhage in the innervated or denervated kidneys. Dopamine was effective in increasing renal blood flow in both intact and hemorrhaged animals. However, this action of dopamine in hemorrhaged animals was associated with a significant increase in arterial blood pressure. These data could be explained based on the observations that the reduction in renal blood flow following hemorrhage was primarily due to a decrease in blood pressure as a result of the decrease in cardiac output and was not due to an increase in renal vascular resistance. Because elevation of sympathetic tone appeared to play little role, prejunctional inhibition by bromocriptine and/or PBDA of sympathetic nerve function was ineffective in altering renal vascular resistance. Dopamine was effective in increasing renal blood flow, not because of its pre- or postjunctional actions on dopamine receptors on renal nerves or vasculature, but because of its ability to increase cardiac output and arterial pressure. Based on the experimental model employed in these studies, it is concluded that agents such as PBDA and bromocriptine, which are considered to be selective prejunctional dopamine agonists, may not be clinically useful in improving renal circulation during hemorrhagic shock.     

Amphetamine-induced effects on neuropeptide Y in the rat brain

Repeated (+)-amphetamine sulfate (AMPH) administration (5 mg/kg sc twice daily for 6 days and once on day 7) markedly and reversibly decreased (until 96 h after the final dose) neuropeptide Y-like immunoreactivity (NPY-LI) in the rat striatum (caudate-putamen) and nucleus accumbens, and had no effect on NPY-LI in the hippocampus. No significant alterations were detected in the hybridization signal of NPY mRNA4 and 24 h after the end of AMPH treatment. A single dose of AMPH (5 mg/kg sc) administered to rats 4 and 24 h prior to sacrifice had no effect on NPY-LI in the brain structures studied. Moreover, AMPH injected 8 days after the last dose of repeated AMPH administration did not change NPY-LI up to 72 h. The minimal dose of haloperidol, the strong mixed dopaminergic D2/D1 receptor antagonist, (0.75 mg/kg injected ip 30 min before each of the multiple AMPH administrations) that was sufficient to completely block stereotypy and hyperlocomotion elicited by multiple AMPH administrations enhanced the AMPH-induced decrease in the striatal and accumbens NPY-LI. Our results suggest that NPY neurons in the striatum, nucleus accumbens and hippocampus are not directly involved in the acute behavioral response to AMPH (stereotypy and hyperlocomotion) as well as in the initiation and expression of AMPH-induced behavioral sensitization.     

Compared effects of calcium entry blockers on calcium-induced tension in rat isolated cerebral and peripheral resistance vessels

Summary The effects of the calcium entry blockers verapamil (V), diltiazem (D), nifedipine (NF) and nicardipine (NC) have been studied on calcium concentration-effect curves elicited in depolarized (K⁺, 40 mmol/l) and in serotonin-exposed (6 mol/l) rat middle cerebral arteries (RMCA) in order to compare the relative potencies of the blockers against these two calcium channel activating mechanisms. In control conditions, Ca²⁺ sensitivity expressed as pD₂ and maximal active wall tension (AWT) were not significantly different in depolarized and in 5-HT-exposed vessels: pD₂: 3.39 ±0.08 vs 3.50 ± 0.06 and AWT: 0.93 ± 0.15 mN · mm^–1 vs 0.90 ± 0.16 mN · mm^–1 respectively. V, D, NF and NC displaced Ca²⁺ control curves to the right and depressed the maximum contractile response in the two experimental conditions, which suggests a noncompetitive type of antagonism. All the blockers were more potent inhibitors of Ca²⁺-induced contractions in depolarized than in serotonin-exposed middle cerebral arteries. The IC₅₀ values (concentration of blockers producing a 50% inhibition of maximal control contractile response) were (nmol/l) : V = 20, D = 120, NF = 0.4, NC = 1 and V = 400, D = 10000, NF = 20, NC = 7 in depolarized and serotonin-exposed arteries respectively. From these IC₅₀ values, the relative order of potency of the CEB's was not the same in the two experimental conditions suggesting that while serotonin and K⁺ both promote the entry of Ca²⁺ into vascular smooth muscle cells of RMCA, they either activate a different gating mechanism associated with a single common channel or perhaps distinct channels. Comparison of the results obtained in this study for depolarized rat middle cerebral arteries with those previously obtained in depolarized rat mesenteric resistance arteries (RMRA) revealed that while Ca²⁺-induced contractile responses were inhibited in a similar non-competitive manner by the four CEB's, the respective IC₅₀ values showed that potencies and rank of relative potency of the blockers were different in the two types of vessels. D and NC were equally potent in both preparations (IC₅₀ ratio = 2.5 and 3 respectively) but RMCA were more sensitive to V and NF than RMRA (IC₅₀ ratio = 6.5 and 11 respectively). These results are discussed and it is proposed that regional differencies in the conformation and/or the activation of the voltage-gated Ca²⁺ channels may exist in different vascular beds. Send offprint requests to J. L. Freston     

Neuroprotective effects of MTEP, a selective mGluR5 antagonists and neuropeptide Y on the kainate-induced toxicity in primary neuronal cultures

The majority of studies on neuroprotection tested potentially protective compounds given before, simultaneously or shortly after damage. Such procedures are greatly different from the situation faced in clinical practice. In the present study, we tried to find out whether two compounds, a selective mGluR5 antagonist 3-[(2-methyl-1, 3-thiazol-4-yl) ethynyl]-pyridine (MTEP) and neuro-peptide Y (NPY) elicit neuroprotective action against excitotoxic damage in the mouse neocortical and hippocampal neuronal cultures after delayed treatment. In order to evoke toxic effects, primary cultures were exposed to 150 munic acid (KA) for 24 h (hippocampus) or for 48 h (neocortex). MTEP (1, 10 and 100 microM), or NPY (0.5 microM and 1 microM) were applied 30 min before, or 30 min, 1 h, 3 h or 6 h after KA. Kainate neurotoxicity was measured by lactate dehydrogenase (LDH) efflux from the damaged cells into the culture media. The results of our studies showed that MTEPor NPY treatment attenuated the kainate-induced LDH release in mouse neocortical and hippocampal cultures. The effect was observed when the compounds were added not only before, but also 30 min to 6 h after KA. Moreover, both MTEP and NPY displayed antiapoptotic activity as they prevented the KA-induced increase in the expression of caspase-3 activity in the cultures under study. Summing up, our data showed that MTEP and NPY were neuroprotective in wide time schedule. The effectiveness of late treatment with these compounds opens a new perspective for their potential therapeutic use.     

Novel human neuropeptide Y Y5 receptor antagonists for the treatment of obesity. Synthesis and biological evaluation of pyridine hydrazide derivatives

A series of new pyridine hydrazide derivatives with high and selective antagonist activity at the human neuropeptide Y Y5 receptor were developed. Introduction of electron-withdrawing groups into the arylsulfonamide rest, together with the 3-pyridyl analogue in the hydrazide moiety, led to a significant improvement of potency and solubility, affording trans-N-(4-[N'-(pyridine-3-carbonyl)hydrazino-carbonyl]cyclohexylmethyl)-2,4-dichloro-benzenesulfonamide (14), which binds to the hY5 receptor with an IC50 value of 7.44 nmol/L.