3H]noradrenaline release evoked by selegiline ((-)-deprenyl) in the isolated main pulmonary artery of the rabbit

High concentrations of selegiline[-)-deprenyl) (greater than 10(-5) M) enhanced the nerve stimulation (2 Hz)-evoked release of [3H]noradrenaline from the isolated main pulmonary artery of the rabbit. This facilitation of stimulation-evoked [3H]noradrenaline release by selegiline was reduced by exogenous (-)-noradrenaline, an agonist of presynaptic alpha 2-adrenoceptors. This inhibitory action of (-)-noradrenaline was partly antagonized by yohimbine, a selective alpha 2-adrenoceptor blocker. When the stimulation-evoked [3H]noradrenaline release had already been increased by inhibition of Na+-pump (K+-free solution), selegiline further enhanced the nerve-evoked release of labelled neurotransmitter.     

Corticotropin releasing factor (CRF) has a peripheral site of action for antinociception

In the rat carrageenan model of inflammation, systemically administered CRF significantly reduced hyperalgesia, edema and hyperthermia. While hypophysectomy had no effect, adrenalectomy blocked the effects of systemic CRF on edema and hyperthermia, and tended to reduce the peptide's ability to suppress hyperalgesia. When CRF was injected into one of two bilaterally inflamed hindpaws, it significantly inhibited hyperalgesia via a peripheral mechanism. In this model of inflammation, the antinociceptive effects of CRF are peripherally mediated, while the anti-inflammatory effects are dependent on the adrenal gland.     

Effect of 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine on noradrenaline release from vascular sympathetic nerves

1. The effects of 9-(6,7-dideoxy-beta-D-allo-hept-5-ynofuranosyl)adenine (HAK2701), a selective and potent ligand for P3 receptor-like protein, on the release of endogenous noradrenaline (NA) from electrically stimulated rat mesenteric artery and rabbit ear artery were compared with those of a number of purinoceptor agonists. 2. In the rat mesenteric artery, the P1 receptor agonists 2-chloroadenosine (2CA) and 5'-N-ethylcarboxamidoadenosine (NECA) and the P2 purinoceptor agonists beta,gamma-methylene ATP (betagammamATP) and 2-methylthio ATP (2mSATP) significantly inhibited the release of NA in a xanthine-sensitive manner. HAK2701 did not significantly inhibit the release of NA, the relative order of potency being betagammamATP > NECA > 2CA > 2mSATP > HAK2701. 3. In the rabbit ear artery, both P1 and P2 receptor agonists significantly facilitated the release of NA in a xanthine-sensitive manner. HAK2701 also significantly facilitated the release of NA, the relative order of potency being HAK2701 > betagammamATP > 2CA > 2mSATP > NECA. 4. These findings suggest that HAK2701 may be a potent and selective agonist for facilitatory prejunctional purinoceptors, but not for inhibitory purinoceptors, on adrenergic nerve terminals.     

Anti-HIV activity of dextran sulphate as determined under different experimental conditions

Dextran sulphate is a potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1). Its anti-HIV-1 activity has been investigated under varying experimental conditions. MT-4 cells were infected with HIV-1 at different multiplicities of infection (MOI), and treated with either dextran sulphate, 3'-azido-2',3'-dideoxythymidine (AZT), or anti-HIV-1 serum obtained from an ARC patient. Dextran sulphate suppressed HIV-1 replication (as monitored by viral antigen expression) when the MOI was 0.01 or 0.1. It was ineffective at an MOI of 1.0. The anti-HIV-1 serum was only partially effective at an MOI of 0.01 and ineffective at an MOI of 0.1 or 1.0. AZT proved effective at all three MOIs. Co-cultures of uninfected and HIV-1-infected MT-4 cells were protected against destruction by dextran sulphate at a concentration of 10 and 100 micrograms/ml. To fully suppress viral antigen expression a concentration of 100 micrograms/ml was needed. When used at this concentration, a 1-h contact of dextran sulphate with the cells during the virus adsorption period sufficed to suppress HIV-1 antigen expression. In this sense, dextran sulphate behaved like the anti-HIV-1 serum. Dextran sulphate also behaved like OKT-4A in that they both inhibited HIV-1 attachment to the MT-4 cells, whereas OKT-4 failed to do so. However, dextran sulphate did not affect the binding of OKT-4A to the cells. The present results support the concept that dextran sulphate owes its anti-HIV-1 activity mainly to inhibition of virus binding to its target cells. The anti-HIV-1 activity of dextran sulphate is highly dependent on its sulphate content.     

Kinetics of monosodium glutamate in human volunteers under different experimental conditions

The kinetics of glutamic acid (GA) in plasma was studied in human volunteers after administration of monosodium glutamate (MSG) at different doses--43 mg/kg (3 g/70 kg) and 64 mg/kg (4.5 g/70 kg)--and in bouillon solutions of different concentrations (1.5-3.5%). MSG was administered to the subjects either during fasting or immediately after a standard meal. In the fasted subjects MSG administration caused a dose-dependent increase in plasma GA levels. In contrast, ingestion of MSG with a meal did not result in any significant increases in plasma GA levels in comparison with the wide variations observed in plasma GA after ingestion of a meal without added MSG.     

Effects of 4-(o-benzylphenoxy)-N-methylbutylamine hydrochloride (MCI-2016, bifemelane hydrochloride) on spontaneous motor activity under different experimental conditions

Effects of MCI-2016 on SMA changes were examined under several experimental conditions (normal conditions, hypoxia and head injury). Under normal conditions, MCI-2016 showed a significant increase of SMA after single administration of 12 mg/kg, i.p. Other doses (12.5-50 mg/kg, p.o. and 3-6 mg/kg, i.p.) of MCI-2016 were without significant effect. Under the same condition, MCI-2016 produced a dose-dependent increase of SMA after repeated doses of 12.5 to 50 mg/kg, p.o. (9-10 days administrations). After 5 days repeated administration, MCI-2016 significantly improved the decreased SMA due to hypoxia (rats) at 50 to 100 mg/kg, p.o. Furthermore, the drug also improved the decreased spontaneity due to head injury (mice) at 50 to 400 mg/kg, p.o. These improving effects of MCI-2016 were superior to those of Ca-hopantenate. The SMA increasing effect of MCI-2016 (12 mg/kg, i.p.) was antagonized more strongly by phenoxybenzamine than by haloperidol. In addition, the drug was shown to be rather antagonistic to the effects of anticholinergic agents. These effects may indicate the existence of qualitative differences between MCI-2016 and methamphetamine in the SMA increasing actions. It is also suggested that MCI-2016 may exhibit the above pharmacological effects through possible activation of noradrenergic and/or cholinergic mechanisms.     

Release of endogenous dopamine from rat isolated striatum: effect of clorgyline and (-)-deprenyl

High performance liquid chromatography with electrochemical detection was used to measure the release and content of dopamine and dihydroxyphenylacetic acid (DOPAC) from rat isolated striatum. The effects of the monoamine oxidase (MAO) inhibitors clorgyline and (-)-deprenyl on dopamine and DOPAC release and contents, and the IC50 values of these compounds for inhibition of dopamine deamination in rat striatum were determined. Dopamine release was significantly increased by elevated KCl (22 mM) in a Ca2+-dependent manner, and by ouabain (20 muM), whereas the release of DOPAC remained constant. The loss in striatal dopamine content during the incubation period (67% of initial content) was far greater than the amount of dopamine recovered in the incubation fluid (16% of initial content), suggesting that much of the DOPAC, released during incubation originated from the conversion of dopamine to DOPAC within the striatum. A concentration-dependent decrease in DOPAC efflux, both during rest and stimulation periods, was observed in the presence of clorgyline (10(-8)M-10(-7)M) and (-)-deprenyl (10(-5)M-10(-4)M). Higher concentrations of clorgyline (10(-7)M) and (-)-deprenyl (10(-4)M), which inhibited dopamine deamination by 85-90%, enhanced both the resting and KCl-induced release of dopamine. The total amount of dopamine plus DOPAC that was released in the presence of clorgyline or (-)-deprenyl did not differ from control values, suggesting that the increase in dopamine release elicited by MAO inhibitors might result from reduced degradation of dopamine to DOPAC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dual mechanism of the stimulant action of N,N-dimethyl-5-hydroxy-tryptamine (bufotenine) on cardiac sympathetic nerves

The indirect sympathomimetic effects of N,N-dimethyl-5-hydroxytryptamine (bufotenine) have been analysed on the rabbit heart perfused in vitro by the Langendorff technique. Comparisons have been made with the effects of 5-hydroxytryptamine (5-HT), which activates tryptamine receptors, and dimethylphenylpiperazinium (DMPP), which stimulates nicotine receptors. Bufotenine, 5-HT and DMPP stimulated the rate and force of cardiac contraction but whereas all were powerful stimulants of cardiac rate, bufotenine and DMPP were much stronger stimulants of atrial and particularly ventricular tension than 5-HT. Responses to 5-HT were markedly reduced by perfusion of hearts with an excess of 5-HT, and those to DMPP, during perfusion with hexamethonium. A combination of 5-HT with hexamethonium was necessary to abolish the effects of bufotenine. The data suggest a dual mechanism of stimulant action of bufotenine on the cardiac sympathetic nerves of the rabbit heart involving activation of receptors sensitive to 5-HT and nicotine receptors.     

The central GABAergic system and control of food intake under different experimental conditions

Intracerebroventricular injections of gamma-aminobutyric acid (GABA) and of the GABA-transaminase inhibitor, ethanolamine-O-sulphate (EOS), decreased the food intake of freely-fed (GABA and EOS) and food-deprived rats (EOS). The effect, still evident 24 h after treatment, was not decreased by the GABA receptor-blocker bicuculline. In contrast, intracerebroventricular injections of the GABA receptor-agonist, muscimol, caused an increase in food intake of freely-fed rats that was antagonized by bicuculline. The eating of animals receiving only bicuculline was stimulated in free-feeding and depressed in food-deprived conditions. These opposite results suggest that muscimol binds preferentially to some GABA receptors, probably those within the satiety-controlling areas (i.e. ventromedial hypothalamus), and that bicuculline influences mainly those postsynaptic neurons where GABAergic inputs prevail.These observations and the data from EOS- and GABA-treated rats provide evidence for involvement of GABA neurons in the regulation of feeding behaviour. The balance of the different effects produced in each of these areas by this modulation appears to be a decrease in feeding behaviour.     

Histamine H(3) receptors mediate inhibition of noradrenaline release from intestinal sympathetic nerves

1. The present study investigates whether presynaptic histamine receptors regulate noradrenaline release from intestinal sympathetic nerves. The experiments were performed on longitudinal muscle-myenteric plexus preparations of guinea-pig ileum, preincubated with [(3)H]-noradrenaline. 2. In the presence of rauwolscine, electrically-induced [(3)H]-noradrenaline release was inhibited by histamine or R-alpha-methylhistamine, whereas it was unaffected by pyridylethylamine, impromidine, pyrilamine, cimetidine, thioperamide or clobenpropit. The inhibitory effects of histamine or R-alpha-methylhistamine were antagonized by thioperamide or clobenpropit, but not by pyrilamine or cimetidine. In the absence of rauwolscine, none of these drugs modified the release of [(3)H]-noradrenaline. 3. The modulatory action of histamine was attenuated by pertussis toxin and abolished by N-ethylmaleimide. Tetraethylammonium or 4-aminopyridine enhanced the evoked tritium outflow and counteracted the inhibitory effect of histamine. However, the blocking effects of tetraethylammonium and 4-aminopyridine were no longer evident when their enhancing actions were compensated by reduction of Ca(2+) concentration in the superfusion medium. 4. Histamine-induced inhibition of tritium output was enhanced by omega-conotoxin or low Ca(2+) concentration, whereas it was not modified by nifedipine, forskolin, rolipram, phorbol myristate acetate, H7 or lavendustin A. 5. The present results indicate that presynaptic H(3) receptors, located on sympathetic nerve endings, mediate an inhibitory control on intestinal noradrenergic neurotransmission. It is suggested that these receptors are coupled to G(i)/G(o) proteins which modulate the activity of N-type Ca(2+) channels through a direct link, thus reducing the availability of extracellular Ca(2+) at the level of noradrenergic nerve terminals.     

The effect of (-) deprenyl (selegiline) on different behavioral changes induced by dopamine agonists in the rat

The effect of (-) deprenyl was investigated both on the stereotyped behavior and on other types of activities induced by various dopamine (DA) agonists. (-) Deprenyl was given in a single dose, 1 h prior to the DA agonists. 1-2 mg/kg sc (-) deprenyl decreased the stereotypy induced by amphetamine (AMPH, 2.5 mg/kg sc), but 20 mg/kg was needed to reduce the stereotypy-inducing effect of apomorphine (APO, 0.3 mg/kg sc). The stereotypy-inducing effect of phenyl-ethyl-amine (PEA, 40 mg/kg sc) was significantly enhanced by 0.25 mg/kg sc (-) deprenyl pretreatment. The PEA or AMPH-induced increase in the horizontal activity (locomotion) and the vertical activity (rearing) remained unchanged after a single dose of (-) deprenyl, showing that this drug acts primarily on the nigro-striatal dopaminergic system.     

Multiple sites of action of ( +)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine (( +)-3PPP) in blood vessels

Functional effects of the σ ligand, (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ((+)-3PPP), were explored in perfused rat tail and rabbit ear arteries in vitro. In the rat tail artery (+)-3PPP inhibited contractile responses to adrenergic nerve stimulation, an effect which was reversed to potentiation by the dopamine D₂ receptor antagonist sulpiride. In the rabbit ear artery, however, (+)-3PPP potentiated contractile responses to nerve stimulation, an effect which was unchanged by sulpiride. In the rat tail artery, blockade of norepinephrine uptake by cocaine and deoxycorticosterone in the presence of sulpiride revealed two additional actions of (+)-3PPP. First, an inhibitory action on the monoamine uptake site was confirmed by direct measurement of [³H]norepmephrine accumulation. Second, at higher concentrations, an action to inhibit contractile responses to adrenergic nerve stimulation was manifested at a still unidentified site. These studies demonstrate that the observed functional effect of (+)-3PPP results from its combined actions on three individual sites with the net effect dependent on the relative densities of these different receptor sites in each type of vessel.     

Modulation of noradrenaline release from the sympathetic nerves of human right atrial appendages by presynaptic EP3- and DP-receptors

Strips of human right atrial appendages were preincubated with [³H]noradrenaline and then superfused with physiological salt solution containing inhibitors of uptake₁ and uptake₂. Tritium overflow was evoked by transmural electrical stimulation (standard frequency: 2 Hz). Prostaglandin E₂ (PGE₂) inhibited the electrically evoked tritium overflow; at the highest concentration investigated, tritium overflow was reduced by about 80% and the pIC_50% value was 7.14. The effect of PGE₂ was not affected by rauwolscine, which, by itself, increased the evoked overflow. Naproxen failed to affect the evoked tritium overflow and its inhibition by PGE₂. The inhibitory effect of PGE₂ on the electrically evoked tritium overflow was mimicked by prostaglandin E₁, the EP₁/EP₃-receptor agonist sulprostone and the EP₂/EP₃-receptor agonist misoprostol with the rank order of potency (pEC_50%): sulprostone (7.68) > misoprostol (7.10) > PGE₁ (6.39). In contrast, PGF_2α, the IP/EP₁-receptor agonist iloprost and the stable thromboxane A₂ analogue U46619 (9,11-dideoxy-11α,9α-epoxy-methanoprostaglandin F_2α) did not change evoked tritium overflow. PGD₂ caused facilitation. These results suggest that the sympathetic nerve fibres innervating human atrial appendages are endowed with presynaptic inhibitory EP₃ and facilitatory DP-receptors. The EP₃-receptors appear not to be tonically activated and do not interact with the α₂-autoreceptors. Received: 11 May 1998 / Accepted: 29 July 1998     

Studies on the possible contribution of a peripheral presynaptic action of clonidine and dopamine to their vascular effects under in vivo conditions

Summary The functional consequences of drug-induced stimulation under in vivo conditions of -adrenoceptors and dopamine receptors at vascular adrenergic nerve endings (presynaptic receptors) was studied in the autoperfused hindquarters or hindlegs of cats anaesthetized with urethane. The changes in perfusion pressure in response to electrical stimulation of the lumbar sympathetic chain were taken as a measure of noradrenaline release from the vascular adrenergic nerves. Presynaptic inhibitory -adrenoceptors and dopamine receptors were activated by clonidine and dopamine, respectively. According to in vitro experiments these two drugs are more potent stimulants of peripheral presynaptic than postsynaptic receptors. The lowest frequency of stimulation of the lumbar sympathetic chain which yielded a reproducible pressor response was 4 Hz for the autoperfused hindquarters and 1 Hz for the hindlegs. Clonidine was tested over a wide dose range (1–100 g/kg i.v.). A reduction of the stimulation-induced pressor response in the autoperfused hindquarters or hindlegs was observed only after the rather high dose of 100 g/kg of clonidine. The inhibition was marked at low frequencies of stimulation (1–4 Hz) and weak or absent at high frequencies (16 and 32 Hz). The dose of clonidine (100 g/kg) which proved to be effective at presynaptic receptors produced a transient increase in blood pressure and in perfusion pressure of the hindquarters and hindlegs and virtually abolished spontaneous sympathetic nervous activity. In spinal cats, the clonidine-induced increases in blood pressure and perfusion pressure were very pronounced and of rather long duration. Thus, under in vivo conditions clonidine showed no selectivity for presynaptic -adrenoceptors in a blood-perfused vascular bed, and its presynaptic action was negligible as compared to its powerful central sympatho-inhibitory effect.Dopamine was constantly infused into the autoperfused hindquarters or hindlegs at increasing rates until a vasoconstriction due to stimulation of vascular (postsynaptic) -adrenoceptors occurred. The monoamine did not inhibit the stimulation-induced increases in perfusion pressure of the autoperfused hindquarters or hindlegs and, thus, an effect on presynaptic receptors was not found. The results underscore the importance of in vivo experiments for assessing the therapeutic significance of drug-induced stimulation of presynaptic receptors.Part of the results has been presented at the 16th Spring Meeting of the German Pharmacological Society in Mainz (Haeusler, 1975)     

Modulation of noradrenaline release from the sympathetic nerves of the human saphenous vein and pulmonary artery by presynaptic EP3- and DP-receptors.

1. Spirally cut strips of the human saphenous vein and pulmonary artery were used to determine the pharmacological properties of the presynaptic prostanoid receptors involved in the modulation of sympathetic [3H]-noradrenaline release. Strips preincubated with [3H]-noradenaline were superfused with physiological salt solution containing inhibitors of uptake1 and uptake2 and rauwolscine to eliminate involvement of presynaptic alpha 2-adrenoceptors. Tritium overflow was evoked by transmural electrical stimulation (standard frequency: 2 Hz). 2. In the saphenous vein, prostaglandin E2 (PGE2) inhibited the electrically-evoked tritium overflow; at the highest concentration investigated, tritium overflow was inhibited by more than 75% and the pEC50 value was 7.00. These effects were mimicked by prostaglandin E1, the EP1/EP3 receptor agonist, sulprostone and the EP2/EP3 receptor agonist, misoprostol with the rank order (pEC50): sulprostone (8.60) > PGE1 (7.25) > misoprostol (6.96). This rank order of potency suggests that the inhibitory effect of the drugs is mediated by presynaptic EP3-receptors. In contrast, PGF2 alpha did not inhibit evoked tritium overflow; the IP/EP1 receptor agonist iloprost and the stable thromboxane A2 analogue U 46619 (9, 11-dideoxy-11 alpha,9 alpha-epoxy-methanoprostaglandin F2 alpha) produced inhibition only at concentrations above 1 microM. 3. The EP1-receptor antagonist, AH 6809 (6-isopropoxy-9-oxoxanthene-2-carboxylic acid) had no effect on the evoked tritium overflow nor did it modify the inhibitory effect of PGE2, further excluding involvement of inhibitory presynaptic EP1-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of (+/-)-2-(dimethylamino)-1-[[o-(m-methoxyphenethyl)phenoxy] methyl]ethyl hydrogen succinate on experimental models of peripheral obstructive disease

Peripheral obstructive disease in tail or hind limb was experimentally induced by intravenous injection of kappa-carrageenin or intra-arterial injection of sodium laurate in rats, and the suppressive effect of (+/-)-2-(dimethylamino)-1-[[o-(m-methoxyphenethyl)phenoxy] methyl]ethyl hydrogen succinate (MCI-9042, CAS 125926-17-2) on the peripheral obstructive diseases was examined. The injection of kappa-carrageenin induced a thrombotic infarction of the tail vessel in rats. The administration of MCI-9042 dose-dependently suppressed the peripheral infarction with an ED50 value of 16 mg/kg p.o. Ticlopidine, a reference antiplatelet drug, did not affect the peripheral infarction even at 50 mg/kg p.o. Cyproheptadine, however, an S2-serotonergic antagonist, potently suppressed the peripheral infarction with an ED50 of 3.5 mg/kg p.o. After the injection of sodium laurate into the femoral artery in rats peripheral lesions of the paw were generated and extended. MCI-9042 significantly prevented the progression of the disease at doses of 10 mg/kg p.o. and above. When the daily administration of MCI-9042 was started from 1 day after the laurate injection, it was also effective as well as by pretreatment. Ticlopidine was significantly effective only at 100 mg/kg p.o. as pretreatment. From the present study, it is considered that platelet-derived serotonin plays an important role in the development of peripheral obstructive disease and MCI-9042 suppressed the disease through its S2-serotonergic antagonism.