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  • 1
    Electronic Resource
    Electronic Resource
    Regulation of α1-adrenoceptors in the cerebral cortex of the rat by thyroid hormones (1981)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 316 (1981), S. 45-50 
    Details
    ISSN: 1432-1912
    Keywords: Rat cerebral cortex ; α1-Adrenoceptor ; [3H]-WB4101 binding ; Hyperthyroidism ; Hypothyroidism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of thyroid hormones on the concentration and properties of α1-adrenoceptors in a crude membrane fraction obtained from the rat cerebral cortex was investigated using the [3H]-WB 4101 binding assay. Animals were made hypothyroid by feeding 6-propyl-2-thiouracil for 8 weeks. Hyperthyroidism was induced by triiodothyronine injections (50 μg/100 g body weight) for 9 days. 1. The binding of [3H]-WB 4101 was saturable and of high affinity in controls as well as in hyper- and hypothyroid animals. The maximal number of binding sites (B max), which amounted to 95 fmol/mg protein in control animals, was increased by 27% in cortical membranes from hyperthyroid rats and reduced by 23% in the hypothyroid group. 2. The reduction in [3H]-WB 4101 binding due to 6-propyl-2-thiouracil feeding was reversible by triiodothyronine treatment. 3. Dissociation constants (K D) calculated from saturation experiments (0.25 nM) or kinetic data (0.21 nM) remained unchanged in altered thyroid states. 4. Inhibition of [3H]-WB 4101 binding by adrenergic agonists and antagonists revealed no differences between euthyroid and hypothyroid animals. The higher affinity of prazosin to the binding sites compared with yohimbine indicated that [3H]-WB 4101 predominantly labeled α1-adrenoceptors. It is concluded that thyroid hormones regulate the number of α1-adrenoceptors in membranes of the rat cerebral cortex, leaving their affinities unchanged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00507226
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  • 2
    Electronic Resource
    Electronic Resource
    Facilitating interaction between rauwolscine and angiotensin in the mesenteric artery of the rabbit (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 326 (1984), S. 273-277 
    Details
    ISSN: 1432-1912
    Keywords: Rauwolscine ; Angiotensin ; Postsynaptic facilitation ; Rabbit mesenteric artery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The interaction between rauwolscine and angiotensin II was investigated in the isolated mesenteric artery of the rabbit. Rauwolscine, known as an antagonist at α2-adrenoceptors, did not induce contraction itself but interacted with angiotensin to produce a facilitated response of the vascular tissue. In the presence of rauwolscine, the contractile response of the tissue to angiotensin was markedly enhanced. The degree of facilitation appeared to be dependent on the rauwolscine concentration used rather than that of angiotensin. Moreover, rauwolscine induced a concentration-dependent increase in tension (pD2=6.8) in the presence of even subcontractile concentrations of angiotensin (10−10 mol/l). This effect was not attributable to an indirect action involving presynaptic catecholamines, as revealed by the use of tissue strips from animals pretreated with reserpine or after chemical sympathectomy. Furthermore, an interaction via the prostaglandin system was excluded by negative results obtained with indomethacin. The ‘agonistic effect’ of rauwolscine was significantly attenuated by phentolamine (α1/α2) but not by prazosin (α1) or phenoxybenzamine when applied for only a short time. The α2-antagonist BDF 6143 behaved like rauwolscine whereas the α1-antagonist corynanthine, a stereoisomer of rauwolscine, did not. The results indicate that the ‘rauwolscine effect’ is mediated by a receptor with α2-characteristics. In general, angiotensin appears to interfere with some process which determines the expression of a drug's intrinsic effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00505330
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of cyclooxygenase inhibitors and of lithium on the positive inotropic effect mediated by α1-adrenoceptors in guinea-pig left atrium (1987)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 336 (1987), S. 403-408 
    Details
    ISSN: 1432-1912
    Keywords: Cyclooxygenase inhibitors ; Lithium ; Alpha1-adrenoceptors ; Inotropic action ; Guinea-pig atrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In experiments on the isolated guinea-pig left atrium we tried to get more information about the intracellular signal transmission of the alpha1-adrenoceptor. We were able to demonstrate that the cyclooxygenase inhibitors indometacin and acetylsalicylic acid enhance the positive inotropic effect of relatively low phenylephrine concentrations at an extracellular calcium concentration of 1.22 mmol/l. Preincubation with prazosin as well as an increased calcium concentration of 2.5 mmol/l abolished this effect. These observations led us to suppose that an elevated level of receptor-generated arachidonic acid, whose degradation is inhibited by the cyclooxygenasen inhibitors, caused the increased contractility by releasing more calcium from the sarcoplasmic reticulum. Under these conditions also lithium caused a distinct enhancement of the positive inotropic effect evoked by alpha, -adrenergic agonists, probably by inhibiting the degradation of the second messenger inositol trisphosphate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00164873
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  • 4
    Electronic Resource
    Electronic Resource
    Enhancement of noradrenaline release from rat cerebral cortex by neuroleptic drugs (1980)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 315 (1980), S. 103-109 
    Details
    ISSN: 1432-1912
    Keywords: Neuroleptic drugs ; Noradrenaline release ; Noradrenaline uptake ; Presynaptic α-adrenoceptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of different neurolepitc drugs (levomepromazine, haloperidol, thioridazine, clozapine and sulpiride) on (−)-3H-noradrenaline uptake and release by parieto-occipital slices of the rat cerebral cortex was investigated. 1. All neuroleptic drugs tested increased the 3H-efflux from electrically stimulated cortical slices preincubated in (−)-3H-noradrenaline already at 1 μM, clozapine was the most potent compound followed by haloperidol, thioridazine, levomepromazine and sulpiride. The enhanced 3H-efflux due to field stimulation was found at concentrations, which did not increase the basal 3H-efflux. Only haloperidol raised the basal 3H-efflux at 1 μM. 2. All neuroleptic drugs failed to inhibit (−)-3H-noradrenaline (10−7M) accumulation by cortical slices at 1 μM. Sulpiride was inactive in concentrations up to 100 μM. Clozapine again proved to be most potent at 10–100 μM. 3. Clozapine was able to enhance the stimulated transmitter overflow when noradrenaline uptake was already blocked by cocaine thus indicating a different mode of action. 4. Clozapine and levomepromazine antagonized the presynaptic α-adrenergic effect of clonidine. 5. The antidepressant drug amitriptyline increased the transmitter efflux at the same concentrations and to a similar extent as neuroleptic agents. It is concluded that neuroleptics enhance the stimulation induced noradrenaline release mainly by acting on presynaptic α-adrenoceptors. The effect of clozapine, however, includes a noradrenaline uptake inhibition. These findings may explain the increased noradrenaline turnover produced by neuroleptic drugs and the weak antidepressant action of low potent neuroleptics as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00499252
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of removing the endothelial cells on the reactivity of rat aortic segments to different α-adrenoceptor agonists (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 328 (1984), S. 160-163 
    Details
    ISSN: 1432-1912
    Keywords: Endothelium ; Rat aorta ; Reactivity α-Adrenoceptor agonists
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The influence of removing the endothelial cells on the α-receptor-mediated contractile response in segments of rat aorta was investigated using agonists with a range of affinity for α1 and α2. The preferential α1 were methoxamine, cirazoline, ST 587, and Sgd 101/75 and the preferential α2 were B-HT 920, clonidine, and guanfacine. When the endothelium was intact, the intrinsic activity (compared to noradrenaline) varied widely (0.0–0.7) for both groups of agonists. After removal of the endothelium the intrinsic activity was increased in each case to that of noradrenaline, or close to it. Furthermore, an increase in potency was obtained for each agonist, although to different degrees. No correlation, however, was found between the selectivity of the agonists and the degree of enhancement caused by the removal of the endothelium, in terms of either the intrinsic activity or the potency. Moreover, the use of the selective α2 antagonist rauwolscine on intact tissues did not mimic the effect of removing the endothelium. Therefore, the α-receptors of the endothelium could not be classified as either of the α1 or α2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00512066
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of long term treatment with atypical neuroleptic drugs on beta adrenoceptor binding in rat cerebral cortex and myocardium (1982)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 321 (1982), S. 271-275 
    Details
    ISSN: 1432-1912
    Keywords: Neuroleptic drugs ; β-Adrenoceptors ; 3H-Dihydroalprenolol binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Several neuroleptic drugs enhance the release and the turnover of noradrenaline in the central nervous system and in peripheral organs. The present study demonstrates the effect of long term treatment (18 days) with atypical neuroleptic drugs (clozapine, thioridazine, and sulpiride) on β-adrenoceptor density in the cerebral cortex and in the myocardium of rats. 1. Clozapine and thioridazine significantly reduced the number of 3H-dihydroalprenolol (DHA)-binding sites by 24 and 21%, respectively, in a crude cortical membrane fraction, and by 28 and 24% in myocardial membranes. 2. Sulpiride failed to alter the maximal number of binding sites in the cortex and in the myocardium. 3. The affinity of 3H-DHA to its binding sites remained unchanged by treatment with neuroleptic drugs. 4. Desipramine, which is known to reduce cerebral β-adrenoceptors during chronic administration, was tested as reference compound. It proved to be more effective in this regard than clozapine and thioridazine in the cortex, but failed to reduce 3H-DHA binding in the myocardium. 5. Acute treatment with desipramine, clozapine, and thioridazine had no effect on 3H-DHA binding in the cerebral cortex. The decrease in β-adrenoceptor density after long term treatment with neuroleptics may be ascribed to an increased concentration of noradrenaline at the receptor site due to antagonism at presynaptic α2-adrenoceptors and inhibition of noradrenaline reuptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00498512
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of hypo- and hyperthyroidism on plasma catecholamines in pithed rats (1981)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 317 (1981), S. 159-164 
    Details
    ISSN: 1432-1912
    Keywords: Pithed rat ; Hypothyroidism ; Hyperthyroidism ; Plasma catecholamines ; Circulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Altered thyroid states are known to produce profound changes in sympathetic mechanisms. The influence of thyroid hormones on plasma catecholamines, adrenal catecholamines and on circulatory parameters were studied in pithed rats. Animals were made hypothyroid by feeding 6-propyl-2-thiouracil for 6 weeks. Hyperthyroidism was induced by triiodothyronine injections (0.5 mg/kg body weight) for 7 days. 1. The basal heart rate was decreased in hypothyroidism and accelerated in hyperthyroidism. Basal diastolic blood pressure was reduced in both dysthyroid states. 2. Electrical stimulation of autonomic outflow from the spinal cord induced tachycardia and increased diastolic blood pressure. The increase in heart rate due to electrical stimulation was reduced in hypo- and hyperthyroidism. In hyperthyroid animals this may be due to the already accelerated basal heart rate. The initial rise in diastolic blood pressure was decreased in the hypothyroid and increased in the hyperthyroid state. 3. Basal adrenaline plasma levels were higher than control values in hypothyroidism and unaltered in hyperthyroidism. Basal noradrenaline levels were not significantly influenced by either thyroid state. 4. The increase in plasma noradrenaline during electrical stimulation was enhanced in hyperthyroid animals and remained unaltered by hypothyroidism. 5. The increase in plasma adrenaline during electrical stimulation was significantly changed in both dysthyroid states. Hyperthyroidism reduced the initial peak of adrenaline release. Hypothyroidism raised plasma adrenaline in the steady state after sustained stimulation. 6. Elevated basal and stimulated adrenaline plasma levels corresponded to an increased adrenaline content and enhanced phenylethanolamine-N-methyltransferase activity in adrenal glands of hypothyroid rats. The significant influence of thyroid hormones on plasma catecholamines seems to contribute but cannot explain completely the circulatory changes in hypo- and hyperthyroidism. The role of additional factors such as receptor changes and central nervous mechanisms is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00500073
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  • 8
    Electronic Resource
    Electronic Resource
    Postjunctional α-adrenoceptors in the isolated saphenous vein of the rabbit (1983)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 323 (1983), S. 328-334 
    Details
    ISSN: 1432-1912
    Keywords: Rabbit saphenous vein ; Postjunctional α-Adrenoceptors ; Angiotensin II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Experiments on the isolated saphenous vein of the rabbit have been performed in order to determine whether a coexistence of postjunctional α1- and α2-adrenoceptor subtypes can be demonstrated also under in vitro conditions. 1. Prazosin, selective for α1-receptors, and rauwolscine, selective for α2-receptors, were used to antagonize the contractile response of the agonists phenylephrine (α1), B-HT 920 (α2) and noradrenaline (α1/α2). Each of the antagonists was equipotent against all three agonists; the effect of neither antagonist fulfilled the criteria for a competitive antagonism. The preferential α1-receptor antagonist phenoxybenzamine, applied for irreversible blockade of α-receptors, reduced the effect of phenylephrine and B-HT 920 to the same degree. Thus, the results obtained with α-receptor antagonists cannot be reconciled with the coexistence of α1- and α2-receptors or the existence of only one of them. 2. Contractile responses induced by α1- and α2-receptor agonists, respectively, could be differentiated by the calcium entry blocker nitrendipine. The effect of B-HT 920 was decreased whereas that of phenylephrine was hardly affected. 3. Furthermore, we investigated the influence of angiotensin II on the effects of the α-adrenoceptor agonists as well as the antagonists. We observed firstly, that angiotensin, acting postsynaptically, potentiates the contractile response of certain α2-receptor agonists and secondly, that in the presence of angiotensin the characteristics of the receptors as revealed by B-HT920 are converted to typical α2-adrenoceptors. It is concluded that the postjunctional α2-receptors of the saphenous vein require the blood borne substance angiotensin for their expression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00512471
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  • 9
    Electronic Resource
    Electronic Resource
    B-HT 920 acts as an α 1-adrenoceptor agonist in the rabbit aorta under certain in vitro conditions (1984)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 325 (1984), S. 42-46 
    Details
    ISSN: 1432-1912
    Keywords: B-HT 920 ; Spasmogens ; Postsynaptic α-adrenoceptors ; Rabbit aorta
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have investigated the interaction of the α 2-adrenoceptor agonist B-HT 920 with the α-adrenoceptors in the rabbit aorta using various experimental conditions. In standard Krebs-Henseleit solution B-HT 920 behaved as an antagonist when tested against the α 1-agonist phenylephrine. However, it behaved as a partial agonist at α-receptors when subcontractile concentrations of various spasmogens (angiotensin II, serotonin, prostaglandin F2α ) were applied, although no change in the affinity of the receptor to B-HT 920 was observed. By means of the selective antagonists prazosin and rauwolscine it was established that B-HT 920 activated α 1-renoceptors. The same agonistic effects of B-HT 920 were obtained after pretreatment of the animal with reserpine or in the presence of ouabain. The various treatments used (except reserpine) did not influence the contractile response to phenylephrine. The contractile response to B-HT 920 was found to be highly susceptible to the calcium entry blocker nitrendipine whereas the response to phenylephrine was not. It is concluded that spasmogens modulate the responsiveness of α-receptors to certain agonists, possibly by causing a depolarization of the cell membrane and, thereby, sensitization of a mechanism involved in excitation-contraction coupling, conceivably a calcium gating mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00507052
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  • 10
    Electronic Resource
    Electronic Resource
    Über den Arterenolgehalt des Nebennierenmarks. Versuche mit Hormonkristallisaten (1949)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 206 (1949), S. 484-494 
    Details
    ISSN: 1432-1912
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245808
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