Endobronchial lipoma, an extremely rare benign tumour of the lung, mimicking asthma bronchiale.

Endobronchial lipomas are extremely rare benign tumours of the lung. Their clinical presentation mimics that of obstructive lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), leading to a delay in diagnosis and errors in treatment. Therefore, making precise diagnosis may be challenging. We report a case of a 63-year-old man with paroxysmal attacks of dyspnea, non-productive cough, and wheezing, initially suspect for adult onset asthma, but with a final diagnosis of endobronchial lipoma.

How invasive aspergillosis may have a beneficial effect after single lung transplantation.

We report the case of a 52-year-old female, who received a left single lung transplantation for end-stage smoking-induced emphysema in 1997. During the last 4 years, she experienced a progressive decline in FEV1, which we attributed to the development of bronchiolitis obliterans syndrome, stage 2. In 2007 she experienced an invasive aspergillosis of the native lung upper lobe, which resolved after 3 months of adequate treatment with voriconazole. After resolution of the infection, both FVC (forced vital capacity) and FEV1 became surprisingly better, due to fibrosis of the affected lobe, compatible with infection-induced volume reduction of the native lung.

Altered Na(+)-channel function as an in vitro model of the ischemic penumbra: action of lubeluzole and other neuroprotective drugs.

Veratridine blocks Na(+)-channel inactivation and causes a persistant Na(+)-influx. Exposure of hippocampal slices to 10 microM veratridine led to a failure of synaptic transmission, repetitive spreading depression (SD)-like depolarizations of increasing duration, loss of Ca(+)-homeostasis, a large reduction of membrane potential, spongious edema and metabolic failure. Normalization of the amplitude of the negative DC shift evoked by high K+ ACSF 80 min after veratridine exposure was taken as the primary endpoint for neuroprotection. Compounds whose mechanisms of action includes Na(+)-channel modulation were neuroprotective (IC50-values in microM): tetrodotoxin 0.017, verapamil 1.18, riluzole 1.95, lamotrigine > or = 10, and diphenylhydantoin 16.1. Both NMDA (MK-801 and PH) and non-NMDA (NBQX) excitatory amino acid antagonists were inactive, as were NOS-synthesis inhibitor (nitro-L-arginine and L-NAME) Ca(2+)-channel blockers (cadmium, nimodipine) and a K(+)-channel blocker (TEA). Lubeluzole significantly delayed in time before the slices became epileptic, postponed the first SD-like depolarization, allowed the slices to better recover their membrane potential after a larger number of SD-like DC depolarizations, preserved Ca2+ and energy homeostasis, and prevented the neurotoxic effects of veratridine (IC50-value 0.54 microM). A concentration of lubeluzole, which was 40 x higher than its IC50-value for neuroprotection against veratridine, had no effect on repetitive Na(+)-dependent action potentials induced by depolarizing current in normal ACSF. The ability of lubeluzole to prevent the pathological consequences of excessive Na(+)-influx, without altering normal Na(+)- channel function may be of benefit in stroke.

In vitro and in vivo receptor binding and effects on monoamine turnover in rat brain regions of the novel antipsychotics risperidone and ocaperidone.

Risperidone and ocaperidone are new benzisoxazol antipsychotics with particularly beneficial effects in schizophrenia. We report a comprehensive study on the in vitro and in vivo receptor binding profile of the new compounds, compared with haloperidol, and on the drug effects on monoamine and metabolite levels in various brain areas. The in vitro receptor binding and monoamine uptake inhibition profiles, comprising 29 receptors and four monoamine uptake systems, revealed that ocaperidone and risperidone bound primarily, and with the highest affinity thus far reported, to serotonin 5HT2 receptors (Ki values of 0.14 and 0.12 nM, respectively). Further, the drugs bound at nanomolar concentrations to the following receptors (Ki values, in nM, for ocaperidone and risperidone, respectively): alpha 1-adrenergic (0.46 and 0.81), dopamine D2 (0.75 and 3.0), histamine H1 (1.6 and 2.1), and alpha 2-adrenergic (5.4 and 7.3). In contrast, haloperidol showed nanomolar affinity for D2 receptors (1.55) and haloperidol-sensitive sigma sites (0.84) only. The in vitro binding affinity of ocaperidone, risperidone, and haloperidol for D2 receptors was exactly the same when measured in membranes from rat striatum, nucleus accumbens, tuberculum olfactorium, and human kidney cells expressing the cloned human D2 receptor (long form). In vivo binding in rats, using intravenous administration of [3H]spiperone, revealed very potent occupation by ocaperidone and risperidone of 5HT2 receptors in the frontal cortex (ED50 of 0.04-0.03 mg/kg); in this respect, they were 6, 30, and 100 times more potent than ritanserin, haloperidol, and clozapine, respectively. Ocaperidone occupied D2 receptors in the striatum and the nucleus accumbens with similar potency as did haloperidol (ED50 of 0.14-0.16 mg/kg). Risperidone revealed biphasic inhibition curves in the latter brain areas, indicating that [3H] spiperone labeled both 5HT2 receptors (occupied by risperidone at less than 0.04 mg/kg) and D2 receptors (risperidone ED50 of approximately 1 mg/kg). In the tuberculum olfactorium, 5HT2 and D2 receptors were also distinguished with risperidone. The ED50 values for occupation of the latter were for ocaperidone and risperidone 2 times lower and for haloperidol 2 times higher than in the striatum. Ocaperidone, risperidone, and haloperidol readily increased the levels of the dopamine metabolites 3,4-dihydroxybenzene acetic acid and homovanillic acid in the striatum, the nucleus accumbens, the tuberculum olfactorium, and, to some extent, the frontal cortex. Dose-response curve shapes were markedly different; with ocaperidone maximal levels were reached at 0.16 mg/kg and maintained to 10 mg/kg; with risperidone the levels tended to increase continuously up to 10 mg/kg. Haloperidol produced dome-shaped curves (maximum at 0.16-0.63 mg/kg).(ABSTRACT TRUNCATED AT 400 WORDS)

Catabolism of high energy phosphates during long-term cold storage of donor hearts: effects of extra- and intracellular fluid-type cardioplegic solutions and calcium channel blockers.

Dog hearts were harvested and stored cold (0.5 degree C) for 24-hours. Cardiac arrest was induced by means of low-sodium and calcium-free cardioplegic (n = 6) or hyperkalemic cardioplegic (n = 6) solution. Nifedipine (2 micrograms/gm estimated heart weight) was added to each cardioplegic solution in two additional groups (n = 6 each). High energy phosphates (creatine phosphate and adenosine triphosphate) and catabolites (adenosine diphosphate and monophosphate, adenosine, inosine, hypoxanthine, xanthine) were determined in the myocardium before and during 24 hours of cold storage. With use of the standard hyperkalemic cardioplegic solution, breakdown of high energy phosphates was less pronounced than after the use of a low sodium, calcium-free solution: after 24 hours of cold storage myocardial ATP content was 57% of control versus 32% (p less than 0.05). The addition of nifedipine to the hyperkalemic cardioplegic solution delayed ATP breakdown during the first hours of cold storage: at 5 hours of preservation the myocardial ATP level was significantly higher (p less than 0.05) than in hearts preserved without nifedipine. Addition of nifedipine to the low-sodium, calcium-free solution did not influence catabolism of high energy phosphates significantly. It is concluded that preservation of high energy phosphates during long-term cold storage of donor hearts can be best achieved by simultaneous myocardial metabolic blockade at two specific sites: at the "fast" sodium-potassium channels by hyperkalemic depolarization and at the "slow" channels by means of calcium channel blockers.

Differences in high-energy phosphate catabolism between the rat and the dog in a heart preservation model.

Concentrations of ATP and creatine phosphate were measured in rat and dog hearts preserved either by cold storage (procedure A) or by continuous hypothermic perfusion (procedure B). In procedure A (3 dogs, 4 rats) the hearts were normothermically excised without cardioplegia and were stored in 0.9% NaCl at 0.5 degrees C; in procedure B (6 dogs, 21 rats) hypothermic cardioplegic arrest was performed, and then the hearts were retrogradely perfused through the aorta for 24 hours with use of an oxygenated Bretschneider cardioplegic solution at 2 degrees to 4 degrees C. Whole rat hearts were frozen using Wollenberger clamps at desired times during the preservation period; transmural needle biopsy specimens were sampled from dog hearts. In control nonpreserved hearts, the ATP and creatine phosphate were as follows (mean +/- SD): 26.7 +/- 4.1 and 27.1 +/- 10.3 mumol/gm dry weight, respectively (dog hearts), and 23.1 +/- 2.1 and 34.2 +/- 12.1 mumol/gm dry weight, respectively (rat hearts). With procedure A, ATP decreased by 36% in dog hearts and by 64% in rat hearts during the first hour of storage. By 24 hours, only 6% of the ATP remained in the dog hearts and 1% in the rat hearts. Creatine phosphate decreased by 85% (dog hearts) and by 93% (rat hearts) during the first hour of storage. The ATP and creatine phosphate values observed in rat hearts after 1 hour of procedure A preservation were significantly lower than in dog hearts (p less than 0.05). With procedure B, cardioplegic arrest by itself did not alter high-energy phosphate concentrations in dog or rat hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptamine and arachidonic acid metabolites modulate extensive platelet activation induced by collagen in cats in vivo.

1. The pathways contributing to the platelet adhesion/aggregation reaction elicited by collagen microfibrils, administered to cats in vivo, were analysed. 2. The intra-aortic infusion of collagen (100 micrograms kg-1 in 1 min) caused an extensive activation of platelets, as evidenced by the time-dependent drop of free platelet numbers in whole blood, and the increases of 5-hydroxyindoles (5-HI), 5-hydroxytryptamine (5-HT) and thromboxane B2 (TXB2) levels in plasma, prepared from effluent venous blood sampled from the inferior caval vein. 3. 5-HT2 receptor blockade with ketanserin (0.63 mg kg-1 i.v., 10 min) and cyclo-oxygenase inhibition with aspirin (10 mg kg-1 i.v., 10 min) slightly attenuated the peak reduction of free platelets in whole blood in response to collagen without affecting changes in plasma 5-HI. Aspirin, but not ketanserin, reduced the collagen-induced changes in plasma TXB2, prostaglandin E2 (PGE2) and 6K-PGF1 alpha. 4. Dual TXA2 synthetase inhibition/TXA2-prostaglandin endoperoxide receptor antagonism with ridogrel (5 mg kg-1 i.v., 10 min) halved the drop in free platelets, reduced the release of platelet 5-HI, inhibited the increase in plasma TXB2 and elevated that of 6K-PGF1 alpha and PGE2 in response to collagen. 5. Combined treatment with ketanserin and aspirin reduced the collagen-induced drop of free platelets and the release of platelet 5-HI to a similar extent as ridogrel alone; plasma prostanoids were affected as with aspirin alone. 6. Combined administration of ketanserin and ridogrel virtually eliminated the collagen-induced platelet adhesion/aggregation response and release of 5-HI; prostanoids were affected as with ridogrel alone. 6. Combined administration of ketanserin and ridogrel virtually eliminated the collagen-induced platelet adhesion/aggregation response and release of 5-HI; prostanoids were affected as with ridogrel alone. 7. The results indicate that the interplay between 5-HT and arachidonic acid metabolites is causally involved in the platelet reaction to activation induced by collagen in cats in vivo.

Biochemical and functional effects of nucleoside transport inhibition in the isolated cat heart.

With increasing periods of normothermic ischemia, increasing amounts of mainly inosine and hypoxanthine are released in reperfusates of isolated working cat hearts. Nucleoside transport inhibition (soluflazine; 1 x 10(-7) M) markedly reduces the total release, but increases the release of adenosine. Tissue levels of adenine nucleotides are reduced by 50% after 32 min of ischemia with an almost equivalent, parallel, rise in inosine and hypoxanthine. Subsequent reperfusion leads to a complete removal of the catabolites and a restoration of the energy charge, but not to any recovery of the sum of nucleotides. Nucleoside transport inhibition has no effect on the changes in the nucleotides, but induces a marked accumulation of adenosine during ischemia and prevents the rapid escape of the nucleosides--not of hypoxanthine--upon reperfusion. Cardiac function markedly deteriorates after 20 and 32 min of ischemia. Transport inhibition completely prevents the decrease in cardiac output and pressure-rate product without any effect on normoxic performance. It is suggested that the prolonged presence of adenosine and of inosine may exert a protective effect.

Ketanserin reduces a particular monoamine pool in peripheral tissues.

The effect of ketanserin and tetrabenazine treatment on monoamine and metabolite levels in central and peripheral tissues was investigated in young and senescent male Wistar and spontaneously hypertensive Okamota rats. Control animals showed significantly higher brain monoamine levels and 3 and 5.5 times higher dopamine levels in the vas deferens of the senescent and hypertensive rats, as compared with young normotensive rats. Ketanserin (20 mg/kg) produced an average of 20% reduction of brain monoamines without changing metabolite levels. In the vas deferens, dopamine was reduced by 85% and norepinephrine by 30%. In cardiovascular tissues, norepinephrine was 40% to 50% decreased and in the spleen norepinephrine was 60% and 5-hydroxytryptamine 30% reduced. Ketanserin (5 mg/kg) had only a marked effect on dopamine in the vas deferens and on norepinephrine in the portal vein. Tetrabenazine at 20 mg/kg produced complete depletion of the monoamine and 3-methoxytyramine levels in the brain with a concomitant rise in acid metabolites. In peripheral tissues, amine levels were reduced by 55% to 80%; dopamine in the vas deferens was 93% decreased. Tetrabenazine (5 mg/kg) still had marked effects in all tissues. The drug effects were the same in the three types of rats and the effects did not markedly change with chronic treatment up to 20 days. It is hypothesized that at least two different mechanisms are involved in monoamine depletion, 1) the classically proposed inhibition of uptake of monoamines in the storage vesicles, a property of tetrabenazine not shared by ketanserin in vivo and 2) triggering of the release of monoamines from a ketanserin-sensitive pool, which is relatively more important in peripheral tissues than in the brain. The latter process is probably mediated by previously identified ketanserin-binding release sites on nerve terminals and platelets. The ketanserin-sensitive monoamine pools in peripheral tissues may have a role in cardiovascular pathologies.

Measurement of microsomal ATPase activities: a comparison between the inorganic phosphate-release assay and the NADH-coupled enzyme assay.

The specific activity of the Mg2+-ATPase and the (Ca2+ + Mg2+)-ATPase has been measured in a microsomal fraction from pig antral smooth muscle with the phosphate-release assay and the NADH-coupled enzyme assay, and the release of inorganic phosphate as a function of time is compared with the concomitant production of ADP. Both assays are found to overestimate the true Mg2+-ATPase activity. The adenylate kinase inhibitor P1,P5-di(adenosine-5'-)pentaphosphate (Ap5A) reduces the specific activity of the Mg2+-ATPase measured in the NADH-coupled enzyme assay to about half of its original value; however, it does not affect the specific activity of the Mg2+-ATPase in the Pi-release assay. The considerable overestimation of the Mg2+-ATPase activity in the NADH-coupled enzyme assay results from a combined action of an ATP pyrophosphatase (ATP in equilibrium AMP + PPi) and adenylate kinase activity contaminating the microsomes. The adenylate kinase activity in the microsomes catalyses the conversion of AMP formed by the ATP pyrophosphatase together with ATP into two ADP's. Also the phosphate-release assay is prone to an overestimation artefact because an inorganic pyrophosphatase will degrade the pyrophosphate and thus lead to additional Pi-production. Measurements of AMP and NAD+ production by HPLC confirmed our proposed reaction scheme. The same (Ca2+ + Mg2+)-ATPase activity is found in both assays, because the (Ca2+ + Mg2+)-ATPase activity is calculated from the difference in ATPase activity in the presence and absence of Ca2+, so that as a consequence the interfering activities are automatically subtracted.

Identification of nonserotonergic [3H]ketanserin binding sites associated with nerve terminals in rat brain and with platelets; relation with release of biogenic amine metabolites induced by ketanserin- and tetrabenazine-like drugs.

In mammalian striatal tissue and cat platelets, [3H]ketanserin labels besides serotonin-S2 receptors nonserotonergic saturable binding sites. The sites have been distinguished and characterized in [3H]ketanserin binding assays by selective inhibition with tetrabenazine (Ki = 4 nM), a monoamine depleting agent. In rats, the nonserotonergic ketanserin sites were enriched in the striatum (KD = 12.4 +/- 0.3 nM, maximal number of binding sites = 53.2 +/- 11.8 fmol/mg of tissue at pH 7.7, 37 degrees C) and nucleus accumbens. The sites were decreased by 65 to 78% after 6-hydroxydopamine lesions, suggesting an association with dopaminergic nerve terminals. In in vitro superfusion experiments using [3H]dopamine, [3H]norepinephrine and [3H]serotonin loaded rat brain tissue and [3H]serotonin loaded human platelets, 5 min superfusion with 10(-6) M ketanserin, tetrabenazine and reserpine caused instantaneously a marked increase in tritium efflux. The effect was attenuated by the monoamine oxidase inhibitor, pargyline, in brain slices but not in platelets. High-performance liquid chromatography analysis of endogenous catecholamines, serotonin and metabolites in superfusates from striatal slices revealed that stimulation with these drugs provoked mainly release of 3,4-dihydroxybenzeneacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid. Potencies of a series of ketanserin derivatives, benzoquinolizine derivatives and a variety of drugs affecting neurotransmission were assessed in the in vitro release test using [3H]dopamine loaded striatal slices, and in [3H]ketanserin binding assays to nonserotonergic sites in the striatum and to serotonin-S2 receptors in brain tissue. Activities of drugs in the release test correlated strongly with their binding affinities for nonserotonergic ketanserin sites (rs = 0.83, n = 30, P less than .001). High potency in the latter two tests was confined to few close structural congeners of ketanserin and tetrabenazine. Distinct structural activity relationships for interaction with nonserotonergic ketanserin sites and serotonin-S2 receptors were found. It was concluded that nonserotonergic ketanserin sites mediate release of oxidated metabolites of biogenic amines from nerve endings and of serotonin from platelets. Hence release of biogenic amine metabolites or of cytoplasmic amines is probably not a mere diffusion process but involves specific membranous molecules. Unlike tetrabenazine, ketanserin caused no obvious depletion of central catecholamine and indoleamine stores. Implications of these findings for the mechanism of action of the drugs are discussed.

Formation and release of purine catabolites during hypoperfusion, anoxia, and ischemia.

To answer some of the as yet unresolved questions about the formation, metabolism, and release of purine catabolites in hypoxic myocardium, we compared their release from isolated rabbit hearts during hypoperfusion, anoxia, and after ischemia, with and without nucleoside-transport inhibition. Results provide evidence to suggest the following. Besides the supply-to-demand ratio for O2, other factors may affect the formation of adenosine. The myocyte is the major source of purine catabolites. Adenosine is not produced within the myocyte. Once in the interstitium, adenosine is (largely) taken up in the endothelial cells, where it is catabolized to inosine and hypoxanthine and released that way into the lumen. Some of the adenosine can reach the lumen unchanged through clefts. Nucleoside transport inhibition prevents the escape through the endothelial cells and thus the formation and release of inosine and hypoxanthine. As a consequence, more adenosine will accumulate in the interstitium and more will reach the lumen through the clefts. The pathway, as proposed, explains the long known paradox of increased extracellular levels of adenosine after inhibition of nucleoside transport.

Serotonin-induced alterations in inositol phospholipid metabolism in human platelets.

When human platelets were incubated for 5 min with [32P]orthophosphate and then stimulated with serotonin, the 32P content of phosphatidylinositol (PI) increased within seconds, compared with the control. The 32P content of phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) only slightly increased during the first minute after addition of serotonin and became more apparent on prolonged stimulation. These changes were not caused by serotonin-induced change in the specific activity of ATP. Using inorganic phosphate determination for the chemical quantification of different inositol phospholipid pools, we found that the platelet PI content remained nearly constant; the amount of PIP increased while that of PIP2 decreased. When the platelets were first prelabeled for 80 min with [32P]orthophosphate, the changes in 32P-labeled inositol phospholipids after addition of serotonin were similar to their changes in mass. When the platelet inositol phospholipids were labeled with myo-[2-3H]inositol, serotonin induced an increase in [3H]inositol phosphates. From these data, it is concluded in addition to the earlier-reported effects on phospholipid metabolism (de Chaffoy de Courcelles, D. et al. (1985) J. Biol. Chem. 260, 7603-7608) that serotonin induces: a very rapid formation of PI; and alterations in inositol phospholipid interconversion that cannot be explained solely as a resynthesis process of PIP2.

Optimization of a high-performance liquid chromatographic method for the determination of nucleosides and their catabolites. Application to cat and rabbit heart perfusates.

A high-performance liquid chromatographic method is described for the separation of nucleosides and related compounds in a single isocratic run. The separation of a standard mixture of at least thirteen compounds is achieved within 15 min on a new type of reversed-phase column 25 cm long, filled with 5-micron particles of Select B. Pre-treatment of the silica particles before silanization has given this type of reversed-phase material unique characteristics for basic and acidic compounds. Chromatograms are shown to compare the effectiveness of the Select B column for the separation of nucleosides with that of other C18 and C8 phases. The separation is achieved with 0.3 M ammonium dihydrogen phosphate (pH 4.00) and a mixture of methanol, acetonitrile and tetrahydrofuran. Detection is carried out with a variable-wavelength UV detector at 254 nm. Sample preparation and the influence of the organic solvents, pH and buffer concentration are described. To illustrate the applicability of the method, representative chromatograms are shown of perfusates of Langendorff preparations and the working hearts of cats and rabbits. Remarkable differences were obtained before and after ischaemia and before and after treatment with a nucleoside transport inhibitor. Baseline separation of cytosine, orotic acid, cytidine, uracil, uric acid, hypoxanthine, xanthine, inosine, guanosine, xanthosine, allopurinol, thymine and adenosine was achieved. The detection limit for these compounds was less than 1 ng per injection.

Changes in creatine phosphate, inorganic phosphate, and the purine pattern in dog hearts with time of coronary artery occlusion and effect thereon of mioflazine, a nucleoside transport inhibitor.

A detailed analysis was made of the changes in canine myocardium, with time of occlusion, in several important metabolites such as creatine phosphate and adenosine triphosphate (luminometry), inorganic phosphate (spectrophotometry), and most of the purines and nicotinamide adenine dinucleotide (high performance liquid chromatography). Within 1 min there was a significant reduction in creatine phosphate and a significant increase in inorganic phosphate, adenosine diphosphate, and adenosine monophosphate. A decrease in adenosine triphosphate became apparent after 4 min, concomitant with a progressive rise in the nucleosides, which reached almost 50% of the total purines after 64 min of occlusion. The formation of hypoxanthine was detectable in 50% only of all animals, suggesting a lack of active nucleoside phosphorylase in the others. Nicotinamide adenine dinucleotide, although decreasing slightly, was by far the most constant of all variables measured during at least 30 min of ischaemia. Therefore, this component is suggested to be a useful internal standard, thus minimising analytical and biological variations. Mioflazine, a potent nucleoside transport inhibitor (I50 3 X 10(-8) mol X litre-1), when given orally at 2.5 mg X kg-1, did not affect any of the changes with the exception of the nucleosides, where the drug completely inverts the adenosine to inosine ratio. The contribution of adenosine to the total nucleosides changed from 20% in the controls to 80% with treatment during at least 16 min of occlusion, there being no overlap between the groups. It is concluded therefore that adenosine is not deaminated in the cell where it is produced. It is not yet clear how this notable effect of mioflazine could be linked to its remarkable protective effect against ischaemia.

Oral pretreatment with mioflazine completely changes the pattern and remarkably prolongs the accumulation of nucleosides in ischemic and reperfused myocardium.

In dog myocardium, the changes in the levels of creatine phosphate, inorganic phosphate, ATP, ADP, AMP, adenosine and inosine with 8 min of ischemia and subsequent reperfusion for 2, 4, 8, 16 and 32 min have been followed. Creatine phosphate and inorganic phosphate recovered completely within a few minutes as did the energy charge. However, total nucleotides remained depressed, the decrease being compensated for by the increase in inosine levels during ischemia. There was a rapid removal of the latter with reperfusion. Low oral doses of mioflazine (2.5 mg X kg-1), given 2.5 h before LAD occlusion, did not affect the pattern of changes seen in control animals, except for the nucleosides. The drug induced a complete reversal of the adenosine to inosine ratio during ischemia and a remarkable prolongation of the accumulation within the tissue of mainly adenosine during early reperfusion and inosine afterwards. Assuming that the main action of mioflazine is through inhibition of nucleoside transport, the present results provide interesting information about the mechanism of release, metabolism and final washout of adenosine.

Formation and release of nucleosides in the ischemic myocardium. Is the guinea-pig the exception?

In this study evidence is provided to suggest that nucleoside formation with hypoxia in myocardial tissue from the guinea-pig follows a different course from that in the rat, rabbit or dog. 1) After ischemia, tissue levels of adenosine remain barely detectable in the guinea-pig but rise considerably in the rat and the dog. 2) IMP, remaining almost absent in the dog, does not change in the rat but strongly increases (X 6) in the guinea-pig heart with ischemia. 3) Mioflazine, a nucleoside transport inhibitor, completely reverses the ratio adenosine/inosine in dog myocardium after 8 min of ischemia, making adenosine by far the major nucleoside. No effect could be detected in the guinea-pig. 4) In contrast with the rat and rabbit, ischemia in the guinea-pig does not lead to any considerable release of adenosine upon reperfusion. 5) In the rabbit, the presence of a nucleoside transport inhibitor completely reverses the adenosine/inosine ratio in reperfusates after ischemia. Although the release is strongly inhibited under these conditions in the guinea-pig, adenosine release remains negligible when compared with inosine. 6) Even in the presence of high concentrations of an adenosine deaminase inhibitor, inosine remains the major metabolite released upon reperfusion after ischemia, in the guinea-pig heart.

Receptor-binding properties in vitro and in vivo of ritanserin: A very potent and long acting serotonin-S2 antagonist.

In vitro and in vivo receptor-binding properties of the new serotonin antagonist, ritanserin, are reported. In in vitro binding assays, ritanserin shows high affinity binding to serotonin-S2 sites in rat frontal cortex tissue: IC50 = 0.9 nM without drug preincubation and 0.3 nM with 30-min drug preincubation; IC50 values for histamine-H1, dopamine-D2, and adrenergic-alpha 1 and -alpha 2 sites were 39-, 77-, 107-, and 166-fold higher, and at up to 1 microM, the drug did not bind to serotonin-S1 sites. In in vitro assays, ritanserin dissociated very slowly from serotonin-S2 (t1/2 = 160 min) and histamine-H1 sites (t1/2 = 77 min) and rapidly from dopamine-D2 sites (t1/2 = 11 min). Half-times of dissociation from adrenergic-alpha 1 and -alpha 2 sites were 18 and 26 min. The inhibition by ritanserin of [3H]ketanserin binding was found to be partially noncompetitive and the inhibitory potency increased with drug preincubation. Due to the slow dissociation of ritanserin from the serotonin-S2 sites, the drug cannot be displaced completely by [3H]ketanserin. In contrast, inhibition by ritanserin of [3H]haloperidol binding to dopamine-D2 sites in rat striatum was fully competitive, in agreement with the rapid dissociation of the drug from the latter sites. In ex vivo binding assays using brain areas of rats and guinea pigs treated subcutaneously with ritanserin, occupation of serotonin-S2 sites was observed at very low dosage (50% occupation at 0.08-0.1 mg/kg) and sites remained occupied during a prolonged time period (greater than 70% occupation up to 48 hr after 2.5 mg/kg ritanserin). Histamine-H1 receptor sites in guinea pig cerebellum became occupied at dosages 25-fold higher than the dosage producing occupation of frontal cortical serotonin-S2 sites. Dopamine-D2 sites in rat striatum and cortical adrenergic-alpha 1 sites became only slightly occupied (less than 20%) at higher dosages and the effect was not dose-dependent. Adrenergic-alpha 2 sites were not occupied up to doses of 160 mg/kg given subcutaneously. In vivo binding assays using [3H]spiperone confirmed the occupation of frontal cortical serotonin-S2 sites following low dosage of ritanserin and a minor occupation of striatal dopamine-D2 sites. Levels of dopamine and serotonin and their metabolites remained unchanged in brain areas of rats orally treated with ritanserin up to dosages of 40 mg/kg. At 160 mg/kg, there seemed to be a slight reduction in dopamine and serotonin content.(ABSTRACT TRUNCATED AT 400 WORDS)