[The role of adhesion molecules in atherosclerosis and diabetes mellitus]. / Az adhéziós molekulák szerepe atherosclerosisban és diabetes mellitusban.

Adhesion of circulating cells to the vascular endothelium is an early step in the development of atherosclerosis. Diabetic patients have a 2-4 fold increased risk for the development of atherosclerosis. Expression of adhesion molecules is increased in diabetes. These molecules may contribute to accelerated atherosclerosis in diabetes. Three main groups of adhesion molecules have been identified: integrins, selectins and members of the immunoglobulin superfamily. The modulation of expression and activity of adhesion molecules may play an important role in the prevention and treatment of atherosclerosis. This article summarises the characteristics and the role of these molecules in atherosclerosis and diabetes.

Adenosine receptors mediate a pertussis toxin-insensitive prejunctional inhibition of noradrenaline release on a papillary muscle model.

The effects of adenosine receptor agonists and antagonists on field-stimulated release of radioactivity from superfused guinea-pig papillary muscles preincubated with [3H] noradrenaline were studied. N6-cyclopentyladenosine (CPA), N6-(R-phenylisopropyl)-adenosine, and 5'-N-ethylcarboxamidoadenosine caused concentration-dependent inhibition of evoked overflow with a rank order of potency typical for interaction of the compounds with the A1-subtype of adenosine receptors. Maximum inhibition was 80%. The A1-selective antagonist 8-cyclopentyl-1,3-dipropyl-xanthine (DPCPX) induced a rightward shift of the concentration-response curve for CPA with a pA2 of 8.35. However, DPCPX per se had no effect on stimulation-evoked tritium overflow. On the other hand, in the presence of 4-nitrobenzylthioinosine (2 mumol/l) and deoxycoformycin (1 mumol/l), inhibitors of adenosine uptake and deamination, respectively, DPCPX produced a concentration-dependent increase in overflow with a pD2 of 8.1. Pretreatment of the animals with pertussis toxin caused a substantial reduction in the activity of toxin-sensitive G proteins, as indicated by a lack of [32P]ADP ribosylation in a ventricular membrane preparation. Nevertheless, the inhibitory effect of the adenosine receptor agonists on stimulus-evoked overflow remained unaffected. These results are compatible with the existence of inhibitory prejunctional adenosine receptors in guinea-pig papillary muscle, which appear to be coupled to a pertussis toxin-insensitive G protein. The role of endogenous adenosine in occupying these receptors seems minimal under basal conditions.

Presynaptic beta-adrenoceptors in guinea pig papillary muscle: evidence for adrenaline-mediated positive feedback on noradrenergic transmission.

Guinea pig papillary muscles were preincubated in the presence of 5 x 10(-9) mol/L unlabeled noradrenaline or adrenaline then incubated with (3H)-noradrenaline and superfused. Electrical field stimulation with 180 pulses delivered at 1 or 3 Hz was used to induce overflow of radioactivity. Comparison of the effects of preexposure of the tissue to adrenaline or noradrenaline revealed that adrenaline incubation caused an enhancement of stimulation-evoked overflow of (3H)noradrenaline and a reduction of the effect of exogenously added isoprenaline. Furthermore, the selective beta 2-adrenoceptor antagonist ICI 118,551 (10(-7) mol/L), but not the selective beta 1-adrenoceptor antagonist ICI 89,406 (10(-7) mol/L), reduced electrically evoked overflow of (3H)noradrenaline in tissue preincubated with adrenaline but not in tissue preincubated with noradrenaline. The overflow-reducing effect of ICI 118.551 occurred at stimulation with 3 Hz but not at stimulation with 1 Hz. The present results support the hypothesis that noradrenergic transmission in guinea pig papillary muscle is facilitated via beta 2-adrenoceptors, and that adrenaline may serve as transmitter in this positive feedback mechanism after its incorporation into sympathetic nerves.

[Central presynaptic receptors]. / Zentrale präsynaptische Rezeptoren.

Experiments on two different inhibitory presynaptic receptor systems are presented. 1. Superfused and electrically stimulated brain slices are a widely used experimental model to study the release of noradrenaline and its modulation by inhibitory alpha-2 adrenoceptors. By using a minisuperfusion chamber we succeeded in studying the simplest case of autoinhibition, i.e. the release of transmitter induced by a single pulse and two consecutive pulses, respectively. When electrical stimulation is performed using a single pulse, no autoinhibition is possible, whereas following stimulation with two pulses the transmitter released by the first pulse will inhibit the effect of the second pulse. By systemically varying the time interval between the two pulses the minimal time requirement for development of autoinhibition was determined to be 100 ms. Short pulse trains of high frequency such as 4 pulses within 30 ms circumvent autoinhibition and cause inhibition-free release by each applied pulse. The release of transmitter evoked in this way is not only free from autoinhibition but, in addition, easily measurable, which makes this method of stimulation very suitable for analyses at presynaptic receptors. By using this approach it became possible, for the first time, to determine dissociation constants of antagonists and agonists at the central presynaptic alpha-2 adrenoceptor without the distortion introduced by autoinhibition occurring during release. 2. There is a substantial body of evidence for a role of medullary serotonergic nerve cells in the regulation of blood pressure and heart rate. It is hypothesized that the serotonergic neurons project to the thoracic spinal cord exerting a tonic excitatory influence on presynaptic sympathetic neurons of the intermediolateral cell column. Experiments were performed in pentobarbital anaesthetized rats to reduce this excitatory tone by activating inhibitory autoreceptors which are located on the perikarya and dendrites on the serotonergic cells and which have been shown to belong to the 5-HT1A subtype. Local stereotactic injection of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) caused a decrease in mean arterial blood pressure (MAP) and heart rate (HR). The effects were blocked by pretreatment of the animals with the 5-HT1A antagonist spiroxatrine. Moreover, neurochemical lesioning of serotonergic neurons by intracisternal injection of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) abolished the effects of 8-OH-DPAT. Bilateral intraspinal injection of 5,7-DHT, which interrupts the medullo-spinal serotonergic pathway, markedly attenuated the effects of local intramedullary injection of 8-OH-DPAT.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypotensive effects of 8-hydroxy-2-(di-n-propylamino)tetralin and 5-methylurapidil following stereotaxic microinjection into the ventral medulla of the rat.

1. The effects of the 5-HT1a receptor agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methylurapidil (5-MU) on blood pressure and heart rate were investigated in the anaesthetized normotensive rat after local injection into the ventral medulla (medial part of the area of the B1/B3 cell group). 2. Both 8-OH-DPAT and 5-MU, decreased arterial blood pressure and heart rate. Local injection of the alpha 1-adrenoceptor antagonist prazosin did not affect cardiovascular parameters. 3. Subcutaneous injection of the 5-HT1a receptor antagonists spiroxatrine or spiperone inhibited the cardiovascular response to 8-OH-DPAT and 5-MU. 4. Histological examination showed the injection sites which were associated with cardiovascular responses to the agonists to be contained within the medial part of the area of the B1/B3 cell group, corresponding to the region of the nucleus raphe magnus and pallidus. Injections of agonists into adjacent areas had no effect on blood pressure or heart rate. 5. The results support the hypothesis that activation of somatodendritic 5-HT1a autoreceptors located on 5-hydroxytryptaminergic neurones in the ventral medulla of the rat results in a decrease in blood pressure and heart rate. The region of the B1/B3 cell group is suggested as a possible site for the hypotensive action of 5-HT1a receptor agonists.

Influence of urapidil and 8-OH-DPAT on brain 5-HT turnover and blood pressure in rats.

The effects of urapidil, of the selective 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and of the alpha 2-adrenoceptor agonist clonidine on the in vivo rate of synthesis of 5-hydroxytryptamine (5-HT) were determined in rat brain cortex and hypothalamus. Urapidil (10 mg/kg), 8-OH-DPAT (0.3 mg/kg) or clonidine (0.3 mg/kg; all drugs i.p.) caused significant reductions in 5-HT synthesis rate. Pretreatment with the selective 5-HT1A receptor antagonist spiroxatrine (SPX; 1 mg/kg s.c.) or the nonselective 5-HT1 receptor antagonist metitepine (1 mg/kg i.p.) abolished the effects of urapidil and 8-OH-DPAT, but not of clonidine. The effects of urapidil and 8-OH-DPAT on mean arterial blood pressure (MAP) and heart rate (HR) of pentobarbital-anesthetized, normotensive rats were measured following stereotaxic microinjection into the B1/B3 cell region of the ventral medulla. The mean percentage decreases induced by urapidil (3 micrograms) and 8-OH-DPAT (0.2 micrograms) amounted to (MAP/HR) -13%/-6% and -19%/-25%, respectively. The following pretreatments markedly attenuated or prevented the effects of intramedullary injections of urapidil or 8-OH-DPAT: (a) SPX (1 mg/kg s.c., 60 min): (b) intracisternal injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT; 0.2 mg; 7-10 days); (c) bilateral injection of 5,7-DHT at the cervical level of the spinal cord (each side 5 micrograms; 7-10 days). The present results are compatible with an action of urapidil as agonist at central 5-HT1A receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of pA2 values at presynaptic alpha 2-autoreceptors in rabbit and rat brain cortex in the absence of autoinhibition.

An attempt was made to determine pA2 values of antagonists at the presynaptic, release-inhibiting alpha 2-autoreceptors of rabbit and rat brain cortex under conditions when there was very little released noradrenaline in the autoreceptor biophase and, hence, pA2 values were not distorted by endogenous autoinhibition. Cortex slices were preincubated with 3H-noradrenaline and then superfused and stimulated by trains of 4 pulses delivered at 100 Hz or, in a few cases, by trains of 36 pulses at 3 Hz. The alpha-adrenoceptor agonists clonidine, noradrenaline, and alpha-methylnoradrenaline concentration-dependently decreased the stimulation-evoked overflow of tritium. The alpha-adrenoceptor antagonists yohimbine, rauwolscine and idazoxan did not increase the overflow of tritium elicited by 4 pulses/100 Hz in rabbit brain slices and increased it only slightly in rat brain slices. In contrast, the antagonists increased markedly the overflow at 36 pulses/3 Hz. All antagonists caused parallel shifts to the right of the concentration-response curves of clonidine, noradrenaline, and alpha-methylnoradrenaline. pA2 values were calculated either from linear regression of log [agonist concentration ratio - 1] on log [antagonist concentration] or from sigmoid curve fitting. The slopes of the linear regression lines were close to unity, and the pA2 values calculated by the two methods agreed well. There was no consistent preferential antagonism of any antagonist to any agonist. pA2 values determined with stimulation by 4 pulses/100 Hz were by 0.53-0.80 log units higher than those determined with stimulation by 36 pulses/3 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for beta 2-adrenoceptor-mediated facilitation of 3H-noradrenaline release from isolated guinea pig papillary muscles.

The effects of beta-adrenoceptor agonists and antagonists on field-stimulated release of radioactivity from superfused guinea pig papillary muscles preincubated with 3H-noradrenaline were studied. Stimulation-evoked overflow of tritium was abolished in the absence of Ca2+ or the presence of tetrodotoxin. Isoprenaline (1 mumol/L) caused a slight facilitation of evoked overflow, whereas phentolamine (1 mumol/L) exerted a strong facilitatory action. However, when phentolamine (1 mumol/L) was present throughout superfusion, isoprenaline and the selective beta 2-adrenoceptor agonist, zinterol, caused concentration-dependent increases (half-maximal effects at 1 nmol/L). The effects of the agonists were inversely related to stimulation frequency. Furthermore, the concentration-response curve of isoprenaline was shifted to the right by the selective beta 2-adrenoceptor antagonist, ICI 118,551, but not by the selective beta 1-adrenoceptor antagonist, ICI 89,406. Schild-plot analysis revealed competitive antagonism and a pA2 value of 9.04 for ICI 118,551. Both ICI 118,551 and ICI 89,406, as well as beta-adrenoceptor antagonists with intrinsic sympathomimetic activity (pindolol and celiprolol; 1 mumol/L), had no effect on stimulation-evoked overflow of tritium (phentolamine present). It is concluded that guinea pig papillary muscles are endowed with prejunctional beta 2 adrenoceptors facilitating impulse-evoked noradrenaline release. The facilitation is markedly promoted by blockade of prejunctional alpha adrenoceptors.

Effects of urapidil on catecholamine turnover and release in the central nervous system of the rat.

The actions of urapidil, prazosin, idazoxan, and haloperidol on the turnover of noradrenaline in the hypothalamus and dopamine in the nucleus accumbens of the rat were investigated using changes in the ratios of 3-methoxy-4-hydroxyphenyl-glycol/noradrenaline (MHPG/NA) and 3,4-dihydroxyphenylacetic acid/dopamine (DOPAC/DA), respectively, as measures for drug-induced effects. Urapidil (2.5-30 mg kg-1 i.v.) increased the ratios of MHPG/NA and DOPAC/DA. Its effects on NA turnover were maximal at 60 min (160% of control at 30 mg kg-1), and on DA turnover at 30 min (138% of control at 30 mg kg-1). Prazosin (0.5-2.5 mg kg-1 i.v.) had no effect, but the high dose of 5 mg kg-1 i.v. significantly increased the ratio of MHPG/NA in the hypothalamus. Idazoxan (2-50 mg kg-1 i.v.) and haloperidol (0.02-0.5 mg kg-1 i.v.) selectively enhanced turnover of NA and DA, respectively. In experiments on field-stimulated overflow of tritium from slices of hypothalamus and nucleus accumbens labelled with [3H]NA or [3H]DA, respectively, urapidil (1 mumol L-1) facilitated the evoked responses in both regions. Prazosin (0.1 mumol L-1) had no effect in either of the two areas. Idazoxan (0.1 mumol L-1) increased stimulated overflow of [3H]NA from the hypothalamus but not of [3H]DA from the nucleus accumbens. Conversely, haloperidol (0.1 mumol L-1) greatly enhanced evoked overflow of [3H]DA but not of [3H]NA. From the present results it is concluded that urapidil has an antagonistic effect at central alpha 2-adrenoceptors and also a weak antagonistic action at central dopamine D2-receptors.

Presynaptic autoinhibition of central noradrenaline release in vitro: operational characteristics and effects of drugs acting at alpha-2 adrenoceptors in the presence of uptake inhibition.

Functional characteristics of autoinhibition of central noradrenaline release were studied in the presence of uptake inhibition. Slices of rat cerebral cortex were incubated with [3H]noradrenaline, superfused and field-stimulated with 1 to 16 monophasic rectangular pulses at frequencies of 0.02 to 40 Hz. 1) Substances acting at presynaptic alpha-2 adrenoceptors were identified as antagonists, agonists or partial agonists by comparing their effects on 3H-overflow evoked by a single pulse or by two consecutive pulses at 1 Hz. 2) When 1 to 16 pulses were delivered at 0.02, 0.08, 0.3 and 1 Hz to stimulate outflow of tritium, a frequency-dependent suppression of responses to the second and the following pulses was observed. In the presence of the alpha-2 adrenoceptor antagonist idazoxan (10(-6) M), comparable amounts of tritium were released by the first stimulus and each of the following stimuli at 0.02 Hz. In contrast, at 0.08, 0.3 and 1 Hz the amount of 3H-overflow evoked by the first pulse was not reached in response to the following pulses. Clonidine (10(-6) M) diminished markedly the response to the first as well as to the following stimuli, irrespective of the frequency of stimulation. 3) Using two consecutive pulses delivered with decreasing pulse intervals, an apparent reduction or complete abolition of autoinhibition was observed at intervals of less than 100 msec, indicated by reduction or loss of the facilitatory effects of alpha-2 adrenoceptor antagonists. The present results provide detailed insights in operational characteristics of alpha-2 adrenoceptor-mediated autoinhibition and the effects of drugs on this regulatory mechism.

Evidence against a functional link between noradrenaline uptake mechanisms and presynaptic alpha-2 adrenoceptors.

Slices prepared from rat cerebral cortex were labelled with 3H-noradrenaline and superfused. Electrical field stimulation was carried out 15 min (S1) and 45 min (S2) after the start of collection of 5-min samples using 4 pulses delivered at 100 Hz. Drugs acting at alpha 2-adrenoceptors were added 20 min before S2, and their effects were evaluated using the S2/S1-ratio. The alpha 2-adrenoceptor antagonists idazoxan (1 mumol/l) and rauwolscine (1 mumol/l) failed to increase stimulation-evoked overflow of radioactivity in the absence or presence of the noradrenaline reuptake inhibitor desipramine (1 mumol/l). This indicates that the duration of electrical stimulation was too short to allow development of alpha 2-adrenoceptor-mediated autoinhibition by released noradrenaline. The effect of clonidine (3-1000 nmol/l) on stimulation-evoked overflow of radioactivity was tested in the absence and presence of three different reuptake inhibitors (desipramine, 1 mumol/l; maprotiline, 1 mumol/l; cocaine, 10 mumol/l). The analysis yielded identical concentration-response curves under all conditions. These results argue against an action of inhibitors of neuronal reuptake of noradrenaline at the presynaptic alpha 2-adrenoceptor and against the concept of a functional link between uptake site and receptor.