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  • 1
    ISSN: 1432-1912
    Keywords: α-Adrenoceptor agonists ; α-Adrenoceptor antagonists ; Arterial pressure ; Nucleus tractus solitarii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of various α-adrenoceptor agonists, microinjected into the area of the nucleus tractus solitarii (NTS) at the level of the obex, on blood pressure, and the interaction between noradrenaline and some α-antagonists in the area of the NTS were investigated in anaesthetized male rats. A dose-dependent decrease in blood pressure was induced by noradrenaline. The relative potencies of the substances were adrenaline 〉 noradrenaline 〉 α-methylnor-adrenaline 〉 clonidine 〉 tyramine. In contrast, phenylephrine was ineffective. The hypotensive effect of noradrenaline, α-methylnoradrenaline and clonidine was not affected by pretreatment with 6-hydroxydopamine given intraventricularly, while the effect of tyramine was blocked by the pretreatment. Prior application of phentolamine at the same site antagonized the hypotensive response to noradrenaline. Prazosin was about 10 times less potent than yohimbine in antagonizing the noradrenaline-induced hypotension. The present data suggest that the α-adrenoceptors in the area of the NTS responsible for the decrease in blood pressure are the same type as the peripheral presynaptic α2-adrenoceptors but may be located postsynaptically. It appears that the noradrenergic neurons in the NTS can play a role in blood pressure regulation.
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  • 2
    ISSN: 1432-1912
    Keywords: Alpha1 adrenoceptors ; Alpha2 adrenoceptors ; Arterial pressure ; Nucleus tractus solitarii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The cardiovascular effects of selective alpha1 and alpha2 agonists and antagonists injected into the nucleus tractus solitarii (NTS) were studied in urethane-anesthetized rats. Methoxamine (0.3–3 μg) injected bilaterally into the NTS caused a dose-dependent increase in blood pressure and heart rate. Phenylephrine (6 μg) and an imidazolidine derivative St 587 (3 μg) similarly injected also produced an increase in blood pressure, whereas a-methylnoradrenaline and an azepine derivative B-HT 920 (1 and 3 μg) caused a decrease in blood pressure and heart rate. The pressor response to methoxamine (1 μg) was markedly inhibited by prazosin (0.3 pg) injected into the same sites or hexamethionum (25 mg/kg, i. v.). Prazosin (0.3 μg) alone injected bilaterally into the NTS did not affect the blood pressure, while yohimbine (0.1 μg) similarly injected increased the pressure. These results suggest that in the rat NTS there exist alpha1 adrenoceptors responsible for an increase in arterial pressure. The NTS alpha2 adrenoceptors seem to be involved in the tonic regulation of arterial pressure.
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  • 3
    ISSN: 1432-1912
    Keywords: Alpha adrenoceptors ; Spinal cord ; Guanabenz ; Yohimbine ; Arterial pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of intrathecal, intracisternal and intravenous injections of yohimbine (10 μg) on hypotensive and bradycardic responses to the alpha agonist guanabenz (10 μg/kg, i.v.) were studied in anesthetized rats. The depressor response to guanabenz was inhibited by intrathecal pretreatment with yohimbine, while this pretreatment did not affect the bradycardic response to guanabenz. Intracisternal pretreatment with yohimbine inhibited both cardiovascular responses to guanabenz, whereas intravenous pretreatment with yohimbine affected neither. Guanabenz (1 μg) decreased blood pressure when injected intrathecally but did not affect it when injected intravenously. These results suggest that in rats spinal alpha adrenoceptors are involved in mediation of the hypotensive action of the alpha agonist guanabenz injected systemically.
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  • 4
    ISSN: 1432-1912
    Keywords: Carotid occlusion ; Transection of the spinal cord ; 6-Hydroxydopamine ; Guanethidine ; Arterial pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Carotid occlusion evoked a pressor response in rats after transection of the spinal cord. Intraventricular pretreatment with 6-hydroxydopamine inhibited the pressor response. The pressor response to occlusion was also diminished by the intraventricular but not by the intravenous injection of guanethidine. Intravenous atropine or mecamylamine, or intraventricular captopril did not affect the pressor response. Thus, it appears that central catecholaminergic mechanisms are involved in the mediation of the pressor response to carotid occlusion.
    Type of Medium: Electronic Resource
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