Dipyridamole may be used safely in patients with ischaemic heart disease

It is thought that up to 50% of patients with cerebrovascular disease will have concurrent ischaemic heart disease. Dipyridamole co-formulated with aspirin has been shown to increase the relative reduction in risk of second stroke in patients with prior stroke/transient ischaemic attack beyond that obtaining with aspirin alone. We have sought to resolve the question of whether dipyridamole treatment increases the risk of cardiac adverse events in patients with co-existing ischaemic heart disease. The published literature, periodic safety update reports, the randomised controlled trials of antiplatelet agents in stroke prevention and those including dipyridamole in cardiovascular indications, have been reviewed and analysed. The early reports of serious adverse cardiac effect attributable to dipyridamole occurred in patients with severe coronary artery disease using dipyridamole as a stress test adjunct to cardiac imaging. The randomised controlled trials databases show no evidence of mortality and only isolated cases of significant cardiac morbidity attributable to dipyridamole at recommended oral doses in patients with ischaemic heart disease. We conclude that patients with cerebrovascular and mild to moderate concomitant ischaemic heart disease may be treated safely with dipyridamole for the secondary prevention of stroke.

In vivo pharmacology of BIIR 561 CL, a novel combined antagonist of AMPA receptors and voltage-dependent Na(+) channels

Glutamate receptors of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype and voltage-gated Na(+) channels are associated with diseases of the central nervous system characterized by neuronal over-excitation as in epilepsy or cerebral ischaemia. In animal models, AMPA receptor antagonists and Na(+) channel blockers provide protection in these conditions. Dimethyl-[2-[2-(3-phenyl-[1,2,4]oxadiazol-5-yl)-phenoxyl]-ethyl]-amine hydrochloride (BIIR 561 CL) combines both, AMPA receptor - and Na(+) channel blocking properties in one molecule. Here, BIIR 561 CL was investigated in vivo. BIIR 561 CL protected mice against AMPA-induced toxicity with an ED(50) value of 4.5 mg kg(-1) following subcutaneous (s.c.) administration. A 0.1% solution of BIIR 561 CL provided local anaesthesia in the corneal reflex test in rabbits. In mice, the compound prevented tonic seizures in the maximal electroshock (MES) model with an ED(50) value of 3.0 mg kg(-1) s.c. In amygdala-kindled rats, BIIR 561 CL inhibited seizures at doses of 3 and 11 mg kg(-1) following intraperitoneal (i.p.) injection. The data show that the combination of blocking AMPA receptor- and voltage-gated Na(+) channels in one molecule induces effective protection in animal models of neuronal over-excitation.

The AMPA receptor/Na(+) channel blocker BIIR 561 CL is protective in a model of global cerebral ischaemia

In this study, we investigated whether the novel neuroprotective compound dimethyl-[2-[2-(3-phenyl-[1,2,4]oxadiazol-5-yl)-phenoxy]-ethyl]-amine hydrochloride, BIIR 561 CL, a combined non-competitive antagonist of AMPA receptors and blocker of voltage-gated Na+ channels, is protective in a rat model of severe global ischaemia. BIIR 561 CL administered immediately after 10 min of ischaemia (occlusion of both carotid arteries plus reduction of arterial blood pressure to 38-40 mm Hg) significantly reduced hippocampal damage at 4 x 26.8 mg/kg (subcutaneous injections). The competitive AMPA receptor antagonist 2,3-dihydro-6-nitro-7-sulfamoyl-benz(F)quinoxaline, NBQX, was used as a reference compound and was protective at 3x30 mg/kg (intraperitoneal and/or subcutaneous administration). BIIR 561 CL significantly reduced the ischaemia-induced premature mortality from 33.6% in the controls to 14.3%, whereas NBQX treatment had no statistically significant effect.Thus, BIIR 561 CL could be shown to reduce hippocampal damage and premature mortality in a model of severe global ischaemia. A compound with these properties might be an interesting candidate for the treatment of disorders related to global cerebral ischaemia in man.

Characterization of the anticonvulsant and neuroprotectant BIIR 561 CL in vitro: effects on native and recombinant alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors

BIIR 561 CL is a novel blocker of AMPA receptors and voltage-dependent sodium channels. In this study we further describe the effects of BIIR 561 CL on AMPA receptor-mediated membrane currents in rodent neurons, as well as in cells expressing recombinant human GluR1/2 receptors in more detail. BIIR 561 CL suppressed responses to kainate in neuronal cultures from rat cortex with an IC50 of 9.8 microM. Similar effects were observed using acutely dissociated neurons from the CA1 region of rat hippocampus (IC50 = 9.5 microM). Inhibition of kainate responses by BIIR 561 CL was prevented by preapplication of GYKI 53655, suggesting that both non-competitive inhibitors bind to a common site of the receptor. The effect of 10 microM BIIR 561 CL on kainate-induced currents was dependent on extracellular pH, with more pronounced block (84.1%) under acidic conditions (pHextern=6.4), compared to only 30.1% at a pHextern of 8.4. Thus, it can be hypothesized that BIIR 561 CL inhibits AMPA receptors in ischaemic brain regions more effectively than in healthy tissue. BIIR 561 CL inhibited responses to 1 mM glutamate in cells expressing recombinant human GluR1/2 receptors with similar potency, as compared to kainate responses in rat neurons (IC50=17.3 microM). The reference compound NBQX had an IC50 of 25.2 nM. None of the two compounds affected the glutamate-induced receptor desensitization at any tested concentration. The block by BIIR 561 CL was not use-dependent and had fast on- and off-kinetics (tauon=6.8 s; tauoff=1.3 s in hGluR1/2 receptors with 30 microM BIIR 561 CL). Thus, BIIR 561 CL can be anticipated to have a promising profile for the treatment of neurological disorders like brain ischaemia and head trauma.

BIIR 561 CL: a novel combined antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and voltage-dependent sodium channels with anticonvulsive and neuroprotective properties

Antagonists of glutamate receptors of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype, as well as of voltage-gated sodium channels, exhibit anticonvulsive and neuroprotective properties in vivo. One can postulate that a compound that combines both principles might be useful for the treatment of disorders of the central nervous system, like focal or global ischemia. Here, we present data on the effects of dimethyl-(2-[2-(3-phenyl-[1,2, 4]oxadiazol-5-yl)-phenoxy]ethyl)-amine hydrochloride (BIIR 561 CL) on neuronal AMPA receptors and voltage-dependent sodium channels. BIIR 561 CL inhibited AMPA receptor-mediated membrane currents in cultured cortical neurons with an IC50 value of 8.5 microM. The inhibition was noncompetitive. In a cortical wedge preparation, BIIR 561 CL reduced AMPA-induced depolarizations with an IC50 value of 10.8 microM. In addition to the effects on the glutamatergic system, BIIR 561 CL inhibited binding of radiolabeled batrachotoxin to rat brain synaptosomal membranes with a Ki value of 1.2 microM. The compound reduced sodium currents in voltage-clamped cortical neurons with an IC50 value of 5.2 microM and inhibited the veratridine-induced release of glutamate from rat brain slices with an IC50 value of 2.3 microM. Thus, BIIR 561 CL inhibited AMPA receptors and voltage-gated sodium channels in a variety of preparations. BIIR 561 CL suppressed tonic seizures in a maximum electroshock model in mice with an ED50 value of 2.8 mg/kg after s.c. administration. In a model of focal ischemia in mice, i.p. administration of 6 or 60 mg/kg BIIR 561 CL reduced the area of the infarcted cortical surface. These data show that BIIR 561 CL is a combined antagonist of AMPA receptors and voltage-gated sodium channels with promising anticonvulsive and neuroprotective properties.

Compensation of muscarinic bronchial effects of talsaclidine by concomitant sympathetic activation in guinea pigs

The aim of the present investigation was to determine the reasons why the muscarinic receptor agonist talsaclidine (WAL 2014 FU, 1-azabicyclo[2.2.2] octane,3-(2-propynyloxy)-, (R)-,(E)-2-butenedioate) is devoid of bronchospastic effects in anaesthetized guinea pigs but causes contracture in isolated tracheal muscle from this species. Effects on airway resistance were assessed with a modified Konzett-Rossler method in guinea pigs anaesthetized with urethane. Intravenous injection of 1-64 mg/kg talsaclidine did not cause substantial bronchospasm in control animals. After blockade of beta-adrenoceptors, the muscarinic receptor agonist induced dose-dependent bronchospasm which could be blocked by atropine. In despinalized animals and in animals with spinal transection, talsaclidine was bronchospastic but ED50 values were higher and maximal effects were smaller than in intact animals after beta-adrenoceptor blockade. In adrenalectomized guinea pigs, talsaclidine was nearly as bronchospastic as after blockade of beta-adrenoceptors. In contrast, the muscarinic ganglion stimulant McN-A-343, 4-(m-chlorophenylcarbamoyloxy)-2-butyn-trimethyl-ammonium chloride, (2-32 mg/kg i.v.), which has a muscarinic receptor profile similar to that of talsaclidine, i.e., full muscarinic agonism and highest affinity at muscarinic M1 receptors, partial agonism at muscarinic M3 receptors, but in contrast to talsaclidine does not penetrate the blood-brain barrier, caused dose-dependent bronchospasm in control animals. These results indicate that talsaclidine has bronchospastic potential which, however, does not become evident in vivo because of functional antagonism via beta-adrenoceptors resulting from concomitant activation of the sympathetic nervous system in general and the adrenals in particular. It can be concluded that the unique profile of action of talsaclidine is due to partial agonism at bronchial muscarinic M3 receptors, a prerequisite for susceptibility to functional antagonism, and to its ability to penetrate the blood-brain barrier readily and to induce sympathetic activation as a result of full agonism at peripheral ganglionic and adrenal as well as central muscarinic M1 receptors.

Hypotensive and bradycardic effects of talipexole (B-HT 920) in anaesthetized rabbits are antagonized by metoclopramide but not by yohimbine

The interactions of talipexole (B-HT 920) and clonidine with selective alpha-adrenoceptor antagonists, yohimbine (alpha 2) and prazosin (alpha 1), as well as with dopamine receptor antagonists, metoclopramide (D2), domperidone (D2) and SCH23,390 (D1) were investigated in anaesthetized rabbits after i.v. administration. Both talipexole (0.03-0.1 mg/kg) and clonidine (0.01-0.03 mg/kg) dose-dependently induced hypotension and bradycardia. Talipexole had a shorter duration of action. The hypotensive effect of the alpha 2-adrenoceptor and D2 agonist talipexole (0.03 mg/kg) was antagonized by pretreatment with metoclopramide (3 mg/kg) or domperidone (0.3-3 mg/kg), but not with yohimbine (3 mg/kg), prazosin (0.1 mg/kg) or SCH23,390 (1 mg/kg). Its bradycardic effect was antagonized only by metoclopramide (3 mg/kg). The hypotensive and bradycardic effects of clonidine (0.03 mg/kg) were most effectively antagonized by yohimbine (0.3-3 mg/kg). These findings indicate that in anaesthetized rabbits after i.v. administration, talipexole may lower blood pressure by peripheral, and heart rate by central, dopamine D2 agonism.

Neuroendocrine and side effect profile of pramipexole, a new dopamine receptor agonist, in humans

The effects and tolerability of pramipexole, a new dopamine D2-receptor agonist, on prolactin, human growth hormone, thyrotropin, cortisol, and corticotropin levels were investigated in a randomized, double-blind, crossover study in 12 healthy volunteers. Single oral doses of 0.1, 0.2, and 0.3 mg pramipexole and placebo were studied over a period of 24 hours. Pramipexole decreased serum prolactin levels in a dose-dependent manner, with a maximum effect after 2 to 4 hours. Serum levels of human growth hormone were dose-dependently increased; however, this effect was only significant 2 hours after drug administration. Furthermore, a slight increase in serum cortisol levels and a slight decrease in serum thyrotropin levels was observed. Our findings show for the first time pharmacodynamic effects of pramipexole after single oral doses in healthy volunteers. The compound was well tolerated and showed an endocrine profile similar to other dopamine D2-agonists.

Renal response to blood volume expansion in Brattleboro rats after acute treatment with vasopressin

The renal response to iso-oncotic blood volume expansion with bovine serum albumin was studied in anaesthetized homozygous Brattleboro (DI) rats after acute (1 day) pretreatment with 1 U arginine-vasopressin (AVP) compared to heterozygous controls. In AVP-treated DI (DI + AVP) rats, basal urine flow as well as urinary sodium, chloride, and potassium excretion, were not different from controls. Diuresis and kaliuresis induced by volume expansion were blunted in DI + AVP rats. However, natriuresis and chloruresis were exaggerated in DI + AVP rats. They increased faster, reached a higher maximum, but declined earlier, compared to controls. The blunted diuresis resulted in a positive volume balance by the end of the experiment in DI + AVP rats, whereas the controls showed restoration of normal balance. Significant retention of sodium and chloride was observed in controls, but not in DI + AVP rats, over the time of the experiment. DI + AVP rats lost significantly less potassium than controls during the experiment. As judged from the lithium clearance method, the exaggerated saluresis in DI + AVP rats was mainly due to a reduced proximal sodium reabsorption. Plasma immunoreactivity of atrial natriuretic peptide (ANP) rose during blood volume expansion and fell in the recovery period. It was not different between AVP-treated DI rats and controls at any time of the experiment. Inulin clearance was slightly, but not significantly, lower in DI + AVP rats and increased after blood volume expansion in DI + AVP rats only.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure lowering action and alpha-adrenolytic effect of adimolol in rats

Adimolol is a new antihypertensive agent with strong nonselective beta- and moderate alpha-adrenolytic properties. In order to elucidate whether the alpha-adrenoceptor blockade by adimolol may contribute to the blood pressure lowering action of the compound, we tested 1) the effect on heart rate and blood pressure in conscious spontaneously hypertensive rats after oral administration and 2) the influence on the pressor effect of intra-arterially injected noradrenaline in autoperfused rat hindquarters after i.v. administration. Adimolol was compared with propranolol, labetalol, prazosin and combinations of propranolol plus low-dose prazosin. In conscious spontaneously hypertensive rats, labetalol, propranolol plus low-dose prazosin and adimolol lowered blood pressure considerably in parallel with heart rate. Propranolol alone acutely lowered heart rate, but not blood pressure. Low-dose prazosin alone lowered blood pressure and heart rate only moderately. In autoperfused hindquarters, the pressor-response curve to noradrenaline was dose-dependently shifted to the left by propranolol and to the right by labetalol or prazosin. The leftward shift by propranolol could be antagonized dose-dependently by addition of low doses of prazosin. Adimolol, at doses of 0.1, 10 and 20 mg/kg, did not significantly influence the pressor-response curve to noradrenaline in this model, whereas a slight but significant shift to the left was observed with 1 mg/kg. In summary, the cardiovascular effects of adimolol in rats cannot completely be explained by beta-adrenoceptor blockade. They can be mimicked by the concomitant administration of a beta-adrenoceptor blocking and an alpha-adrenoceptor blocking agent. We conclude that the alpha-adrenolytic activity of adimolol can be demonstrated in vivo and may contribute to the blood pressure lowering action of the compound in rats.

Renal hyper-responsiveness to blood volume expansion in Brattleboro rats is not related to plasma ANF immunoreactivity

1. Anaesthetized homozygous Brattleboro (DI) rats were used to study the renal response to iso-oncotic blood volume expansion. 2. With the same degree of hypervolaemia DI rats had exaggerated diuresis, natriuresis, and chloriuresis, but not kaliuresis, compared with heterozygous control rats. This increased excretion resulted in negative water balance by the end of the experiment in DI rats, whereas the controls showed restoration of normal balance. The control rats retained significant amounts of sodium and chloride, the Brattleboro rats, however, did not. 3. The lithium clearance method was used to localize the defect in sodium reabsorption. As judged from this method, there was a significantly lower sodium reabsorption in the proximal tubules as well as in the distal parts of the nephron of DI rats. 4. Plasma immunoreactivity of atrial natriuretic factor (ANF) was not different between groups before volume expansion. ANF levels rose and fell similarly in both groups during and after the iso-oncotic infusion. 5. Our results demonstrate that DI rats respond to acute hypervolaemia with an exaggerated diuresis and saluresis. The mechanism of the increased salt excretion may involve inhibition of sodium transport in the proximal tubules as well as in the distal parts of the nephron. These transport defects are not dependent on differing plasma ANF levels.

Hyperresponsiveness to atrial natriuretic factor in adult Brattleboro rats

Renal and hemodynamic effects of an intravenous infusion of atrial natriuretic factor (ANF) (8 micrograms/h) were studied in homozygous Brattleboro rats, which lack endogenous vasopressin. Heterozygous rats were used as controls. ANF-induced increases in sodium, chloride and volume excretion were higher, whereas changes in potassium excretion were lower in homozygous, as compared to heterozygous rats. The initial decrease in arterial blood pressure after ANF infusion was greater in the homozygous group, whereas there were no differential effects on heart rate. Inulin clearance, as well as clearance and fractional excretion of lithium were not significantly different between groups. The results indicate that Brattleboro rats show an exaggerated diuretic as well as saluretic response to ANF. They suggest that these effects are localized in the distal nephron and may be due to the known anatomical abnormalities in juxtamedullary nephrons of Brattleboro rats.

Severe proteinuria without impairment of sodium and volume excretion after puromycin aminonucleoside administration in rats

The effects of a single intravenous injection of 100 mg/kg puromycin aminonucleoside (PAN) on renal protein, electrolyte, and fluid excretion as well as inulin and lithium clearances in rats were investigated under basal conditions, after iso-oncotic blood volume expansion with bovine serum albumin (BSA) and during infusion of atrial natriuretic peptide (ANP). All treated rats developed severe proteinuria 7-28 days after injection. On day 17, the protein excretion of the PAN group was 1,050 +/- (SE) 118 micrograms/(min x kg body weight) compared with 42.3 +/- 3.9 micrograms/(min x kg body weight) in the control group. Hypoproteinemia, edema or ascites were not observed. The renal protein excretion increased dramatically after BSA infusion and even more during ANP infusion in the PAN group. The PAN-treated animals lost about 62% of the infused BSA during the time of the experiment. No significant changes in protein excretion were observed in the controls. Both groups had similar basal excretions of urine volume, sodium, chloride, and potassium and responded to the BSA and PAN infusions with comparable increases in these parameters. The glomerular filtration rate was slightly, but not significantly higher in the PAN group during the control periods. Increases after BSA and ANP occurred in both groups, reaching significance only in the control group. Proximal tubular function was slightly impaired in PAN-treated rats as judged from a lower increase of the fractional excretion of lithium after BSA. Mean arterial blood pressure was higher in the PAN group (136.2 +/- 2.4 vs. 127.0 +/- 2.2 mm Hg) and fell in both groups to a comparable degree after BSA infusion. A further fall in blood pressure occurred after ANP infusion. Plasma ANP immunoreactivity was not different between the groups and increased after BSA infusion. Our data demonstrate that severe glomerular lesion as indicated by proteinuria can be observed after PAN administration without impairment of distal tubular function as judged from sodium and fluid excretion, and therefore support the view that the sodium retention observed in nephrotic syndrome is due to a separate intrarenal defect rather than a consequence of protein loss.

The binding of fluorescent 4,6,8(14)-triene-3-one steroids to cyclodextrins as a model for steroid-protein interactions

The 4,6,8(14)-triene-3-one steroids, highly fluorescent in aqueous solutions, lose their fluorescence power when binding occurs to hydrophobic regions of other molecules, such as the hydrophobic cavity in the ring system of cyclodextrins. The fluorescence intensity decreases almost completely when beta- and gamma-cyclodextrins are present in the solution. Scatchard plots derived from fluorescence titrations show that one or two molecules of steroid bind to one cyclodextrin molecule with KD,F-values of about 10(-4)-10(-5) mol/liter. Temperature-jump experiments show a single relaxation process, with rate constants for the decay of the beta-cyclodextrin-steroid complexes of about 10(4)-10(5) per s. For alpha- and gamma-cyclodextrins such relaxation processes are not observed.

Fluorescence of 3-keto-steroids in aqueous solution. Probes for steroid-protein interactions

The physiologically important 3-keto-steroids are non-fluorescent or only weakly fluorescent in protic as well as in aprotic solvents. In contrast, the 4,6,8(14)-triene-3-one steroids are highly fluorescent in aqueous solution but they do not appreciably fluoresce in other solvents. Evidence is presented that the introduction of double bonds into the skeleton of the 3-keto-steroids leads to a decrease of the energy of the lowest pi-pi* state, bringing this level into the neighbourhood of the non-fluorescent n-pi* state. As a consequence, for two states of approximately the same energy, relatively small perturbations such as those due to solvent interactions, protein binding and micelle formation, will then determine whether a system will fluoresce (pi-pi* state lowest) or not (n-pi* state lowest). When the fluorescent 3-keto-steroids, having three conjugated double bonds, bind to proteins, the fluorescence intensity becomes almost zero, making these compounds useful as probes for steroid-protein interactions. This quenching of the fluorescence is explained by a decrease in energy of the n-pi* state relative to the pi-pi* state of th steroids due to hydrophobic interactions with the proteins.

Interactions of MEN 935 (adimolol), a long acting beta- and alpha-adrenolytic antihypertensive agent, with postsynaptic alpha-adrenoceptors in different isolated blood vessels--influence of angiotensin II

MEN 935 [1-(3-[3-(1-naphthoxy)-2-hydroxypropyl) amino)-3,3-dimethylpropyl)-2-benzimidazolinone-hydrochloride monohydrate, adimolol] is a long acting antihypertensive agent with beta- and alpha-adrenolytic properties. Preliminary experiments in pithed rats had led to the suggestion that the alpha-adrenolytic activity was of the alpha 2-subtype. The alpha-adrenolytic properties of MEN 935 were now tested in isolated vascular preparations of rat aorta, rabbit vena ischiadica and rabbit vena cava inferior against the selective alpha 1-adrenergic agonist phenylephrine (PE) and the selective alpha 2-adrenergic agonist B-HT 920 [2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-(4,5-d)azepine]. The experiments were performed in absence and in presence of 5 X 10(-9) mol/l angiotensin II (A II). MEN 935 antagonized contractions to phenylephrine as well as those to B-HT 920 in each vessel. A twofold shift to the right of the concentration-response curves to both agonists was obtained with concentrations between 1.9 X 10(-8) and 1.4 X 10(-5) mol/l, depending on the vessel under investigation. A II modulated the adrenolytic properties of MEN 935 in each vessel. However, irrespective of the presence or absence of A II, no pharmacologically relevant difference between antagonism against PE or B-HT 920 could be seen. In isolated vessels, MEN 935 exerts a nonselective alpha-adrenergic antagonism. In receptor binding studies in rat cerebellar cortex, MEN 935 showed a Ki of 5.2 X 10(-7) mol/l at alpha 1-adrenoceptors and a Ki of 1.3 X 10(-5) mol/l at alpha 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor

Mammalian atria contain different peptides with potent diuretic, natriuretic, smooth muscle relaxing and blood pressure lowering properties. A preprohormone of these peptides is synthetized and stored in specific granules in atrial myocytes. Different peptides have been isolated, analyzed and in vitro synthetized. Their biological activity indicates a potential role in the regulation of volume and sodium homeostasis as well as in blood pressure regulation.