The effect of papaverine on sodium-potassium adenosine triphosphatase and the ouabain sensitive electrical properties of crayfish nerve.

The effect of cyclic and non-cyclic nucleotides and phosphodiesterase inhibitors on (Na-K)-adenosine triphosphatase (ATPase) activity of crayfish nerve membrane fragments and on the ouabain sensitive electrical properties of the intact crayfish giant axon was investigated. Only papaverine (1 × 10^?7?2 × 10^?4m), of the phosphodiesterase inhibitors stimulated the adenosine triphosphatase to approximately 2.5 times its control level. The methylxanthine inhibitors (caffeine and aminophylline) had no effect. The papaverine induced stimulation did not alter substrate or ionic activation kinetics or the ouabain sensitivity of the ATPase activity. Cyclic and non-cyclic nucleotides, slightly but significantly inhibited the (Na-K)-adenosine triphosphatase if the membrane preparation was preincubated with these agents prior to activation of enzyme activity. Addition of 3 mm adenosine triphosphate to the incubation medium simultaneous with test nucleotides prevented the inhibition. Addition of the phosphodiesterase inhibitors in conjunction with the nucleotides had no effect on adenosine triphosphatase activity other than that accounted for by the nucleotides alone. Papaverine (1?10 × 10^?6m) increased the membrane resistance and the temperature dependence of the membrane potential of the intact axon. The action of papaverine was totally prevented if the axon was pretreated with 0.5–1 mm ouabain. The papaverine stimulated axon was more sensitive to ouabain inhibition than the untreated control axon.The results suggest (a) papaverine acts to stimulate the (Na-K)-adenosine triphosphatase of the membrane fragments and the ouabain sensitive electrogenic transport properties of the intact axon and, (b) papaverine does not appear to act through a cyclic adenosine monophosphate mediated mechanism to stimulate the (Na-K)-adenosine triphosphatase.     

Sex differences in mouse heart rate and body temperature and in their regulation by adenosine A1 receptors

Aim: To examine cardiac function, body temperature and locomotor behaviour in the awake adenosine A₁ receptor knock out mouse of both sexes. Methods: Male and female A₁R (+/+) and (−/−) mice, instrumented with telemetric devices, were recorded during basal conditions and after drug administration. Results: Female mice had higher heart rate, body temperature and locomotion, both during daytime and during the night. Awake A₁R (−/−) mice had a slightly elevated heart rate, and this was more clear‐cut in males. Heart rate was also higher in Langendorff‐perfused denervated A₁R (−/−) hearts. Body temperature was higher in A₁R (−/−) males and females; locomotor activity was higher in A₁R (−/−) females, but not in males. The adenosine receptor agonist R‐PIA (0.2 mg kg⁻¹) decreased heart rate and body temperature, but less in A₁R (−/−) animals than in A₁R (+/+) mice (P < 0.001 in both parameters). The unselective adenosine receptor antagonist caffeine had a minor stimulatory effect on heart rate in lower doses, but depressed it at a dose of 75 mg kg⁻¹. Body temperature was increased after a low dose (7.5 mg kg⁻¹) of caffeine in both sexes and genotypes, and markedly reduced after a high dose (75 mg kg⁻¹) of caffeine. An intermediary dose of caffeine 30 mg kg⁻¹ increased or decreased body temperature depending on genotype and sex. Locomotor responses to caffeine were variable depending both on genotype and sex. Conclusion: Thus, the adenosine A₁ receptor is involved in the regulation of heart rate, body temperature and locomotor activity, but the magnitude of the involvement is different in males and females.     

Adenosine receptor-induced cAMP changes in D384 astrocytoma cells and the effect of bradykinin thereon

In human D384 astrocytoma cells, cyclic AMP accumulation can be conveniently studied after labelling of the adenosine triphosphate pool (15 fmol cell^-1) with [³H]adenine. In this study, adenosine had a biphasic effect on cyclic AMP accumulation, which was scarcely altered by blocking adenosine uptake and metabolism. Low concentrations of adenosine led to an inhibition of cyclic AMP accumulation, and higher concentrations led to stimulation. No effect of adenosine on cyclic AMP was observed unless phosphodiesterase was inhibited by rolipram. The A₁ receptor antagonist DPCPX attenuated the inhibitory phase of adenosine response, and enhanced the cyclic AMP accumulation induced by adenosine analogues. The cyclic AMP accumulation was stimulated by NECA > ADO > CGS 21680 > CV 1808 > CPA ≥ CHA, indicating mediation by A, receptors. The stimulatory effect of NECA was much more effectively blocked by the combined A₁ and A₂ receptor antagonist CGS 15943 (K_B 4 nmol I^-1) than by the A₁ antagonist DPCPX (K_B 110 nmol 1^-l). Treatment of the cells with pertussis toxin (0.2 μg ml^-1 for 2.5 h) potentiated the cyclic AMP response to adenosine analogues significantly. The cyclic AMP response to NECA was enhanced by the protein kinase C activator phorbol dibutyrate even after pertussis toxin treatment. By contrast, nanomolar concentrations of bradykinin, which increases Ca²⁺-levels and protein kinase C activity in D384 cells, reduced NECA-induced cyclic AMP accumulation in control and pertussis toxin-treated cells. Thus, D384 cells possess both A₁ and A₂ adenosine receptors influencing cyclic AMP in opposite directions. A₂ receptor-mediated cyclic AMP accumulation can be stimulated by activating protein kinase C and inhibited by raising Ca²⁺. Neither the effects of protein kinase C activation nor those of bradykinin required pertussis toxin-sensitive G-proteins.     

Local infusion of the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione does not block D1 dopamine receptor-mediated increases in immediate early gene expression in the dopamine-depleted striatum

Administration of selective agonists of D1 dopamine receptors increases immediate early gene expression in striatal neurons, a response which is particularly robust in the dopamine-depleted striatum. Although interactions between dopamine and glutamate receptor-mediated responses in striatal neurons have been demonstrated in a number of experimental paradigms, our previous findings indicate that N-methyl-D-aspartate antagonists do not block D1 receptor-mediated induction of immediate early genes in the dopamine-depleted striatum. In the present study, we therefore examined interactions between D1 dopamine receptors and the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate subtypes of glutamate receptor by determining whether striatal infusion of the (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione would block D1 receptor-mediated induction of the immediate early genes c-fos and zif268 in the dopamine-depleted striatum. Striatal infusion of 6-cyano-7-nitroquinoxaline-2,3-dione (1 mM) completely blocked (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate-induced c-fos and zif268 expression. However, 6-cyano-7-nitroquinoxaline-2,3-dione (1 microM-1 mM) did not significantly affect induction of c-fos and zif268 by D1 receptor stimulation (SKF 38393, 2 mg/kg, i.p.) in the dopamine-depleted striatum. To more generally block excitatory input, tetrodotoxin (10 microM) was infused into the striatum of rats receiving a D1 agonist. Local infusion of tetrodotoxin had minimal effect on induction of c-fos and zif268 in the dopamine-depleted striatum. In contrast, tetrodotoxin abolished induction of c-fos and zif268 messenger RNAs by the D2 antagonist eticlopride (0.5 mg/kg, i.p.) in both intact rats and dopamine-depleted rats receiving continuous D2 agonist treatment (quinpirole, 0.5 mg/kg/day). The results indicate that D1 receptor-mediated induction of immediate early genes in the dopamine-depleted striatum occurs by mechanisms that are independent of excitatory input through (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptors.     

The relationship between intracellular cyclic AMP concentrations and the in vitro growth of macrophages

The addition of cholera toxin, prostaglandins, or one of a series of xanthine phosphodiesterase inhibitors to bone marrow-derived macrophages maintained in liquid culture caused a dose-dependent decrease in colony formation measured 7-10 days following seeding. The growth inhibitory effects of xanthines were in the same order of potency (caffeine less than theophylline less than isobutylmethylxanthine) as their reported ability to inhibit cyclic AMP phosphodiesterase. The relationship between the magnitude of the increases in intracellular concentrations of cyclic AMP observed following the addition of the drugs and the degree of growth inhibition was complex. Combinations of cholera toxin and phosphodiesterase inhibitors caused synergistic elevations in cyclic AMP levels after a lag of approximately 3 days. However, the growth rate was decreased immediately following the addition of the combination of drugs, and thus seemed to be independent of the nucleotide levels. A cyclic AMP-resistant variant of a cloned nontransformed macrophage cell line was found to be also resistant to the growth inhibitory actions of both cholera toxin and prostaglandins. However, resistance to the inhibitory effects of cyclic AMP did not render the cells resistant to a xanthine-induced growth inhibition.     

Opposite tonic modulation of dopamine and adenosine on c-fos gene expression in striatopallidal neurons

The impulse flow-dependent dopamine release in the striatum was acutely blocked by unilateral lesion of the medial forebrain bundle with 6-hydroxydopamine. Within 45 min this disruption reduced the striatal extracellular dopamine levels by 80% as determined by in vivo voltammetry. A strong induction of c-fos messenger RNA was detected in the ipsilateral dorsolateral striatum 75 min after 6-hydroxydopamine injection by in situ hybridization. Double labelling demonstrates that this induction was confined to neurons expressing the dopamine D2 receptor messenger RNA. At this time-point, there were no changes in the striatal levels of either tyrosine hydroxylase immunoreactivity or dopamine D2 receptor messenger RNA. The c-fos messenger RNA expression induced by acute 6-hydroxydopamine injection was abolished by intraperitoneal pretreatment with the dopamine D2 receptor agonist, quinelorane (2 mg/kg) and strongly reduced by administration of the selective adenosine A2A receptor antagonist SCH-58261 (5 mg/kg). The results reported here show, by using a novel methodological approach, that an acute decrease of dopamine release causes an induction of c-fos messenger RNA in dopamine D2 receptor-containing striatopallidal neurons. This, together with previous findings, demonstrates that the c-fos gene expression is tonically inhibited by the impulse flow-dependent dopamine release via D2 receptors. In addition, this study provides evidence that endogenous adenosine, acting via adenosine A2A receptors, induces striatal c-fos messenger RNA when extracellular dopamine levels are strongly reduced. Thus endogenous dopamine and adenosine exert opposite effects on the activity of the D2-containing striatopallidal neurons.     

The stimulatory effects of caffeine with oseltamivir (Tamiflu) on light–dark behavior and open-field behavior in mice

Abnormal behaviors and death associated with the use of oseltamivir (Tamiflu^®) have emerged as a major issue in influenza patients taking the drug. Here, we investigated the mechanisms underlying the effects of oseltamivir on the behavior of mice using light–dark and open-field preference tests. Oseltamivir (75 and 150 mg/kg, intraperitoneally (i.p.)) alone affected neither time spent in the open area in the light–dark preference test nor ambulation in the open-field test at 2 h post-injection. However, a non-selective adenosine A₁/A₂ receptor antagonist, caffeine (10 mg/kg, i.p.) in combination with oseltamivir (150 mg/kg, i.p.) increased time spent in the open area in the light–dark preference test. This enhancement was not inhibited by a benzodiazepine receptor antagonist, flumazenil (10–20 mg/kg, subcutaneously (s.c.)). Enhancement of ambulation in the open-field test was also observed when caffeine (10 mg/kg, i.p.) was combined with oseltamivir (150 mg/kg, i.p.). This enhancement was inhibited by a dopamine D₂ receptor antagonist, haloperidol (0.1 mg/kg, s.c.). Furthermore, an adenosine A₂ receptor antagonist, SCH58261 (3 mg/kg, i.p.) in combination with oseltamivir (150 mg/kg, i.p.) increased ambulation in the open-field test, while an adenosine A₁ receptor antagonist, DPCPX (1–3 mg/kg, i.p.) did not. These findings suggest that the actions of oseltamivir may involve the dopamine and adenosine systems. Our findings suggest that due to the interaction between central blockade of adenosine A₂ receptors by caffeine, and oseltamivir-induced behavioral changes, patients being treated with oseltamivir should be closely monitored.     

Ergogenic effect of varied doses of coffee-caffeine on maximal aerobic power of young African subjects

Background

Caffeine one of the readily available stimulants consumed daily by more than 80% of the world''s population, making it the most widely consumed drug in history. The objective of this study was to determine the effects of different doses (5, 10 &15 mg.kg⁻¹) of caffeine per kilogram body weight on maximal aerobic power of normal young black African (Nigerian) male adults.

Method

Twenty apparently healthy young male adults volunteers, participated. A repeated measure four randomized crossover (counter balanced) double blind design was used in data collection. Subjects engaged in 20 meter shuttle run test (20 MST) one hour post caffeine (5, 10 & 15 mg.kg⁻¹) and placebo doses ingestion. Endurance performance index (VO₂ max, run time & number of exercise laps) were measured and recorded.

Result

Repeated measures ANOVA was used to assess the level of significant difference between caffeine doses and placebo dose in VO₂ max, run time and number of exercise laps. The result showed no significant effect of caffeine doses over placebo dose.

Conclusion

It was concluded that caffeine dose of up to 15mg/kg seems not to have any ergogenic effect on maximum aerobic power of young black African male adults.     

l-Arginine-induced hypotension in the rat: evidence that NO synthesis is not involved

l -Arginine is the biological precursor for nitric oxide (NO). NO is formed continuously in endothelial cells and maintains a certain degree of vasodilator tone under physiological conditions. Although the formation of NO is not primarily controlled by precursor availability, the extent to which extra supplementation with l -arginine may affect endothelial NO formation, and hence, vasodilator tone and systemic blood pressure, is not entirely clear. To address this issue, we infused l -arginine i.v. in anaesthetized normotensive rats pretreated with N^G-nitro-l -arginine methyl ester (l -NAME, 50 or 200 mg^-1) and in untreated controls, under continued recording of mean arterial pressure (MAP). In control animals l -arginine (25 or 100 mg kg^-1 min^-1) had no effect on systemic MAP (111 ± 3 mm Hg), while l -arginine (200 mg kg^-1 min^-1) lowered MAP (to 70 ± 6mmHg). D-Arginine (200 mg kg^-1 min^-1) also induced hypotension; during infusion of D-arginine MAP fell from 106 ± 4 to 64 ± 4 mm Hg. Pretreatment with l -NAME (50 and 200mgkg^-1) elevated MAP to 140 ± 2 and 147 ± 3 mm Hg, respectively, but failed to affect the hypotensive response to l -arginine; during infusion of l -arginine (200 mg kg^-1 min^-1) in rats pretreated with l -NAME (50 and 200 mg kg^-1) MAP fell to 86 ± 9 and 104 ± 6 mm Hg, respectively. Plasma levels of the NO metabolite, nitrate, were 18 ± 4 and 17 ± 3μmol l^-1, respectively, before and after infusion of l -arginine (200 mg kg^-1 min^-1). Trapping of NO to haemoglobin (HbNO) could not be detected, either before or after infusion of l -arginine (200 mg kg^-1 min^-1). We conclude that a high dose of l -arginine may act hypotensive in normotensive rats. This effect does, however, not seem to be based on an augmented formation of NO.     

Systemic effects of angiotensin III in conscious dogs during acute double blockade of the renin-angiotensin-aldosterone-system

Aims: The study was designed to determine (i) whether the effects of angiotensin III (AngIII) are similar to those of angiotensin II (AngII) at identical plasma concentrations and (ii) whether AngIII operates solely through AT₁‐ receptors. Methods: Angiotensin II (3 pmol kg^?1 min^?1–3.1 ng kg^?1 min^?1) or AngIII (15 pmol kg^?1 min^?1–14 ng kg^?1 min^?1) was infused i.v. during acute inhibition of angiotensin converting enzyme (enalaprilate; 2 mg kg^?1) and of aldosterone (canrenoate; 6 mg kg^?1 plus 1 mg kg^?1 h^?1). Arterial plasma concentrations of angiotensins were determined by radioimmunoassay using a cross‐reacting antibody to AngII. During ongoing peptide infusion, candesartan (2 mg kg^?1) was administered to block the AT₁‐receptors. Results: Angiotensin immunoactivity in plasma increased to 60 ± 10 pg mL^?1 during infusion of AngII or infusion of AngIII. AngII significantly increased mean arterial blood pressure (+14 ± 4 mmHg) and plasma aldosterone by 79% (+149 ± 17 pg mL^?1) and reduced plasma renin activity and sodium excretion (?41 ± 16 mIU L^?1 and ?46 ± 6 μmol min^?1 respectively). AngIII mimicked these effects and the magnitude of AngIII responses was statistically indistinguishable from those of AngII. All measured effects of both peptides were blocked by candesartan. Conclusion: At the present arterial plasma concentrations, AngIII is equipotent to AngII with regard to effects on blood pressure, aldosterone secretion and renal functions, and these AngIII effects are mediated through AT₁‐ receptors. The metabolic clearance rate of AngIII is five times that of AngII.     

Endogenous Adenosine Curtails Lipopolysaccharide-Stimulated Tumour Necrosis Factor Synthesis

Recent studies have demonstrated the inhibitory effect of exogenous adenosine on TNF production. During inflammation endogenous adenosine levels are elevated and may be one of several anti-inflammatory mediators that reduce TNF synthesis. In the present study the authors investigated this role of adenosine in freshly isolated human PBMC. The effect of endogenous adenosine on TNF formation was studied by four different approaches. First, adenosine deaminase was added to LPS-stimulated mononuclear cells. This enzyme specifically deaminates extracellular adenosine to the inactive metabolite inosine. TNF production was augmented from baseline stimulation (LPS alone) of 3.5 ± 0.4 ng ml^?1— 5.2 ± 0.9 ng ml^?1 in the presence of 10 U ml^?1 adenosine deaminase. Second, TNF production was determined after stimulation in the presence of dipyridamole, an inhibitor of cellular re-uptake of adenosine which increases extracellular concentrations. TNF synthesis was reduced dose-dependently from 3.1 ± 0.9 ng ml^?1— 1.1 ± 0.2 ng ml^?1 by 10 μm dipyridamole. Third, the adenosine A₂ receptor antagonist 8-(3-chlorostyryl)caffeine (100 nm ) enhanced TNF synthesis from a baseline of 3.7 ± 0.5 ng ml^?1— 5.5 ± 0.9 ng ml^?1. In contrast, no increase resulted from the addition of 100 nm of the specific A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine. Finally, the authors were able to show that suppression of TNF formation by the specific type IV phosphodiesterase inhibitor rolipram can be completely reversed by adenosine deaminase or by the application of the A₂ receptor antagonist. The authors conclude that endogenous adenosine controls TNF production. This effect of adenosine may not only have a physiological role but also appears to contribute to the pharmacological inhibition of TNF synthesis by exogenous agents such as the specific type IV phosphodiesterase inhibitor rolipram.     

Caffeine reverses antinociception by oxcarbazepine by inhibition of adenosine A1 receptors: Insights using knockout mice

Oxcarbazepine is an anticonvulsant drug that has been explored as a novel therapeutic agent to treat neuropathic pain in humans. It produces antinociception in several preclinical models of pain, and these actions are blocked by methylxanthine adenosine receptor antagonists which implicates adenosine it its actions. In this study, the antinociceptive effect of oxcarbazepine, and the ability of caffeine to reverse its actions, were examined using the formalin test (2%) in wild-type mice and in mice lacking adenosine A₁ receptors by way of further exploring the involvement of adenosine in its actions. Oxcarbazepine produced dose-related suppression of formalin-evoked flinching responses in wild-type mice following both systemic and intraplantar administration, and this action was reversed by systemic and intraplantar administration of caffeine, respectively. The ability of oxcarbazepine to inhibit flinching after systemic and intraplantar administration was unaltered in homozygous (−/−) and heterozygous (+/−) adenosine A₁ receptor knockout mice. However, caffeine no longer reversed this antinociception. Our results indicate that, while adenosine A₁ receptors are not required for oxcarbazepine to produce antinociception in knockout mice, such receptors are essential in order to see caffeine reversal of this antinociceptive effect.     

Heme oxygenase-1/biliverdin/carbon monoxide pathway downregulates hypernociception in rats by a mechanism dependent on cGMP/ATP-sensitive K<Superscript>+</Superscript> channels

Objective and design

To investigate the role of heme oxygenase-1 (HO-1), carbon monoxide (CO), and biliverdin (BVD) in the zymosan-induced TMJ arthritis in rats.

Materials and Methods

Mechanical threshold was assessed before and 4 h after TMJ arthritis induction in rats. Cell influx, myeloperoxidase activity, and histological changes were measured in the TMJ lavages and tissues. Trigeminal ganglion and periarticular tissues were used for HO-1, TNF-α, and IL-1β mRNA time course expression and immunohistochemical analyses. Hemin (0.1, 0.3, or 1 mg kg^?1), DMDC (0.025, 0.25, or 2.5 µmol kg^?1), biliverdin (1, 3, or 10 mg kg^?1), or ZnPP-IX (1, 3 or 9 mg kg^?1) were injected (s.c.) 60 min before zymosan. ODQ (12.5 µmol kg^?1; s.c.) or glibenclamide (10 mg kg^?1; i.p.) was administered 1 h and 30 min prior to DMDC (2.5 µmol kg^?1; s.c), respectively.

Results

Hemin (1 mg kg^?1), DMDC (2.5 µmol kg^?1), and BVD (10 mg kg^?1) reduced hypernociception and leukocyte migration, which ZnPP (3 mg kg^?1) enhanced. The effects of DMDC were counteracted by ODQ and glibenclamide. The HO-1, TNF-α, and IL-1β mRNA expression and immunolabelling increased.

Conclusions

HO-1/BVD/CO pathway activation provides anti-nociceptive and anti-inflammatory effects on the zymosan-induced TMJ hypernociception in rats.

     

Cholinergic system of rats treated with vincristine sulphate and nandrolone decanoate

This study aimed to detect brain and red blood cell acetylcholinesterase activity (AChE and RBC-AChE, respectively) of rats treated with vincristine sulphate and different doses of nandrolone decanoate. Thirty rats were divided into six groups (n = 5). The treatments were applied once a week for 2 weeks. Sample collection was performed in the third week. The groups were divided in: G1, physiologic solution (PS) (first and second week); G2, vincristine sulphate (4 mg/m²) in the first week and PS in the second week; G3, PS in the first week and nandrolone decanoate (1.8 mg/kg⁻¹) in the second week; G4, PS in the first week and nandrolone decanoate (10 mg/kg⁻¹) in the second week; G5, vincristine sulphate (4 mg/m²) in the first week and nandrolone decanoate (1.8 mg/kg⁻¹) in the second week; and G6, vincristine sulphate (4 mg/m²) in the first week and nandrolone decanoate (10 mg/kg⁻¹) in the second week. The isolated use of nandrolone decanoate and its use in association with vincristine sulphate altered brain AChE and RBC-AChE activity. These results suggest that there is interference in cholinergic neurotransmission, which could cause an alteration of its neurotransmitter, as well as a low or high stimulation of post-synaptic receptors. The serum RBC-AChE activity results presented in this study are similar to those exhibited by brain tissue.     

Intravenous injection of AlbunexR microspheres causes thromboxane mediated pulmonary hypertension in pigs,but not in monkeys or rabbits

østensen , J., Hede , R., Myreng , Y., Ege , T. & Holtz , E. 1992. Intravenous injection of Albunex^R microspheres causes thromboxane-mediated pulmonary hypertension in pigs, but not in monkeys or rabbits. Acta Physiol Scand 144 , 307–315. Received J April 1991, accepted 7 October 1991. ISSN 0001–6772. Nycomed AS Research and Development, Oslo, Norway. Intravenous injection of the ultrasound contrast agent Albunex^R (manufactured by Nycomed AS, Oslo, Norway; 400 million air-filled albumin microspheres per ml, mean diameter 4 ± 1 μm) caused a dose-dependent increase of mean pulmonary arterial pressure in nine pigs. The highest dose (0.014 ± 0.002 ml kg^-1) increased mean pulmonary arterial pressure from 17± mmHg to 42 ± 3 mmHg and decreased mean systemic arterial pressure from 111±9 to 93± 12 mmHg. The pressure responses began 22 ± 1 s after particle injection, and reached maximum after 51 ±3 s. No changes in mean pulmonary arterial pressure or mean systemic arterial pressure were observed after Albunex^R injections during treatment with indomethacin (10 mg kg^-1+ 5 mgkg^-1 h-1 i.v., n= 6) or the thromboxane A2 receptor antagonist HN-11500 (10 mg kg^-1+ 5 mg kg^-1 h^-l i.v., n= 3). No Doppler enhancement could be detected in a carotid artery following injection of 0.12 ml kg^-1 Albunex^R during indomethacin treatment. In five rabbits, Albunex^R caused Doppler enhancement in a carotid artery, and 0.48 ml kg^-1 did not affect mean pulmonary arterial pressure or other haemodynamic parameters in five rabbits or in three cynomolgus monkeys. The pressure response in pigs may be explained by release of thromboxane A2 from the pulmonary intravascular macrophages during phagocytosis of the microspheres. This response to Albunex^R was totally absent in rabbits and monkeys.     

Flecainide blocks the stimulatory effect of veratridine on slowly adapting pulmonary stretch receptors in anaesthetized rabbits without changing lung mechanics

We examined the responses of slowly adapting pulmonary stretch receptors (PSRs), total lung resistance (R_L) and dynamic lung compliance (C_dyn) to administered veratridine before and after pretreatment with atropine or flecainide in anaesthetized, artificially ventilated rabbits with bilateral vagotomy. Administration of veratridine (10 and 30 μg kg^-1) caused vigorous stimulation of PSRs, resulting in a tonic discharge of receptors during both inflation and deflation, but did not significantly alter either R_L or C_dyn. The veratridine-induced PSR stimulation became more prominent, as the dose of this alkaloid was increased. Pretreatment with atropine (1 or 2 mg kg^-1) had no significant effect on the excitatory response of PSRs to veratridine. The veratridine induced PSR stimulation was inhibited by treatment with flecainide (1, 2 and 3 mg kg^-1), a sodium channel blocker, and this inhibition was dose-dependent. These results suggest that activation of PSRs following veratridine administration probably related to the increased influx of sodium ions into the receptive terminals but does not depend upon bronchoconstriction.     

Abnormal distributions of callosal commissural and corticothalamic neurons in the cerebral neocortex of Shaking Rat Kawasaki

It is generally believed that haloperidol exerts its motor side effects and therapeutic effects mainly by antagonizing dopamine D(2) receptors in the striatum and the nucleus accumbens, respectively. Several neurotransmitters/modulators, including glutamate, acetylcholine, adenosine and histamine, affect dopaminergic activity in these centers. We have recently shown that N-methyl-D-aspartate receptor-mediated modulation of haloperidol-induced c-fos expression differs in functionally specific regions of the striatum and the nucleus accumbens. In the present study, the entire striatum and the nucleus accumbens were comprehensively examined for the pattern of modulation of haloperidol-induced c-fos expression by adenosine A(2), histamine H(3) and muscarinic receptor antagonists.Blockade of muscarinic and H(3) receptors resulted in a profound suppression of haloperidol-induced c-fos expression in the dorsolateral part of the striatum. In addition, the H(3) receptor antagonist suppressed the effects of haloperidol in the ventrolateral aspect of the striatum and the rostral parts of the medial striatum. Muscarinic receptor antagonists suppressed haloperidol-induced c-fos expression throughout the shell and in the mid-level of the core of the nucleus accumbens while A(2) and H(3) receptor antagonists did not.We found that the muscarinic and H(3) receptor antagonists suppress the induction of c-fos by haloperidol in the dorsolateral aspect of the striatum, an area implicated in the development of extrapyramidal motor symptoms following chronic haloperidol treatment. By contrast, haloperidol-induced c-fos expression in the nucleus accumbens, an area implicated in the therapeutic effects of haloperidol, was suppressed by the muscarinic receptor antagonist, but not by the H(3) receptor antagonist. Therefore we conclude that H(3) receptor modulation may provide a useful therapeutic target in future efforts to minimize neuroleptic-induced motor side effects.     

Simultaneous presence of cAMP and cGMP exert a co-ordinated inhibitory effect on the agonist-evoked Ca2+ signal in pancreatic acinar cells

The stimulation of the pancreatic acinar cells by physiological secretagogues, such as acetycholine (ACh), activates a well-established intracellular signalling pathway, which involves the generation of Inositol 1,4,5-trisphosphate (InsP₃) and the release of Ca²⁺ from intracellular stores. Caffeine, which inhibits this agonist-evoked Ca²⁺ response reversibly and competitively also blocks the Ca²⁺ signal generated by the non-specific activation of the membrane guanine nucleotide-binding proteins (G-proteins). Removal of caffeine is associated with an increase of intracellular [Ca²⁺] ([Ca²⁺]_i) and the spatial and temporal characteristics of this Ca²⁺ signal are identical to those of the signal generated by the initial agonist stimulation. Caffeine is also a potent non-specific inhibitor of various cellular phosphodiesterases (PDE) and its inhibitory effect can be reproduced by other PDE inhibitors, chemically related (theophylline) or not (papaverine). Various protocols designed to increase the concentration of either of the major intracellular cyclic nucleotides [adenosine 3′,5′-cyclic monophosphate (cAMP) and guanosine 3′,5′-cyclic monophosphate (cGMP)] failed to reproduce the full extent of the caffeine inhibition: at maximal agonist concentration (1 μM ACh) increases of either cAMP or cGMP did not affect the Ca²⁺ signal, whereas at submaximal doses of agonist (0.1–0.3 μM ACh) they induced partial inhibition. Here we show that only the simultaneous increase of the cellular concentrations of both cyclic nucleotides (either simultaneous or sequential) are effective in mimicking the blocking effect of caffeine and other non-specific PDE inhibitors. These data indicate, thus, that, in addition to other independent intracellular effects, cAMP and cGMP can exert a co-ordinated inhibitory effect of the agonist-evoked Ca²⁺ signal in pancreatic acinar cells. Received: 25 March 1996/Accepted: 23 May 1996     

The effects of caffeine on ischemic neuronal injury as determined by magnetic resonance imaging and histopathology

The effects of caffeine on ischemic neuronal injury were determined in rats subjected to forebrain ischemia induced by bilateral carotid occlusion and controlled hypotension (50 mmHg for 10 min). High resolution (100 microns) multi-slice, multi-echo magnetic resonance images were obtained daily for three consecutive days post-operatively in sham-operated rats and in rats that received either saline vehicle (controls), a single i.v. injection of 10 mg/kg caffeine 30 min prior to an ischemic insult (acute caffeine group), or up to 90 mg/kg per day of caffeine for three consecutive weeks prior to an ischemic insult (chronic caffeine group). Rats in the control group exhibited enhanced magnetic resonance image intensity in the striatum 24 h after ischemia which increased in the striatum and also appeared in the hippocampus after 48 h, and which began to resolve in both regions by 72 h post-ischemia. Histopathological analysis of each rat following the final magnetic resonance examination showed that ischemic neuronal injury was strictly confined to the brain regions showing magnetic resonance image changes. Acute caffeine rats showed accelerated changes in the magnetic resonance images, with increased hippocampal intensity appearing at 24 h post-ischemia. Although there was magnetic resonance evidence of accelerated injury, quantitative analysis of the histopathological data at 72 h showed no significant difference in the extent of neuronal injury in any brain region between control-ischemic and acute caffeine rats. Nine out of 11 rats in the chronic caffeine group showed no magnetic resonance image changes over the three study days. Chronic caffeine rats had significantly less neuronal damage in all vulnerable brain regions than either of the other groups of ischemic rats. The accelerated ischemic injury in rats treated with an acute dose of caffeine may occur secondary to antagonism of adenosine receptors, whereas protection from ischemic injury following chronic administration of caffeine may be mediated by up-regulation of adenosine receptors.     

NMDA-receptor blockers but not NBQX,an AMPA-receptor antagonist,inhibit spreading depression in the rat brain

The effect of different glutamate-receptor antagonists on the induction of cortical spreading depression of Leao and of cortical anoxic membrane depolarization were investigated in the anaesthetized rat. Spreading depression (SD), elicited by mechanical stimulation of the cortical surface, was inhibited by the non-competitive N-methyl-d -aspartate (NMDA)-receptor blocker, (±)-5-methyl-10,11-dihydro-SH-dibenzo(a, d)-cyclo-hepten-5,10-imine maleate (dizocilpine or MK-801), (0. 30 μmol kg^-1 (0. 10 mg kg ^-1)), and the competitive NMDA-receptor antagonists; cis-4-phosphonomethyl-2-piperidine carboxylate (CGS 19755), (3.36 μmol kg^-1 (0.75 mg kg^-1)), d -(E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 40116), (1.20 μmol kg^-1 (0.25 mg kg^-1)) and its carboxylester CGP 43487, (6.30 μmol kg^-1 (1.50 mg kg^-1)). The α-amino-3-hydroxy-5-methyl-4-isoxazolepripriate (AMPA)-receptor blocker, 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F) quinoxaline (NBQX), administered as an intravenous dose of 29.76 and 89.29 μmol kg^-1 (10 & 30 mg kg^-1), which is sufficient to block seizures and protect against ischaemic brain damage, did not inhibit spreading depression. None of the drugs utilized inhibited the anoxic membrane depolarization. The data demonstrate that NMDA-receptor activation is essential for the initiation and propagation of spreading depression, while activation of AMPA-receptors is not obligatory. The observed initiation and propagation of SD, during AMPA-receptor blockade, suggest that activation of voltage-operated ion channels may contribute to release the magnesium block of the NMDA-receptor operated channel and to the initiation of SD.