ISSN:1018-1172    

DOI:10.1159/000158697

出版商:S. Karger AG    

年代:1987

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158698

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Dopamine represents 1–5% of the total catecholamine pool in sympathetically innervated tissues. A substantial proportion of this dopamine is located in vesicles, and nerve activation results in liberation of dopamine as well as noradrenaline. In certain tissues, there is neurochemical and functional evidence for the existence in addition of separate populations of dopaminergic sympathetic nerves. Some of the unsolved questions relating to the neural release of dopamine are: Is intravesicular dopamine in noradrenergic nerves a stable storage pool? Do noradrenergic nerves release dopamine and noradrenaline by identical mechanisms? What physiological roles do the sympathetic dopaminergic nerves play? What are the diagnostic and therapeutic implications of neural dopamine releas

ISSN:1018-1172    

DOI:10.1159/000158699

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

This review seeks to discuss the possible importance of monoamine oxidase (MAO) and semicarbazide-sensitive amine oxidase (SSAO) in terminating the effects of released sympathetic transmitters and in the inactivation of endogenous or administered sympathomimetic amines with particular reference to some aspects of the cardiovascular system. Use of in vitro preparations of blood vessels and of other smooth muscles, such as vas deferens and anococcygeus, has thrown light on possible roles for these deaminating enzymes, even in the inactivation of noradrenaline, while the new reversible inhibitors of MAO-A show promise as antidepressants with a reduced risk of hypertensive crises following the ingestion of tyramine-containing food. However, the role of SSAO in the inactivation of amines remains an enigma, even though much is now known of its biochemical nature. While the pharmacological responses to amine substrates can be potentiated by inhibition of SSAO, there is a suspicion that it is product rather than substrate that is more important.

ISSN:1018-1172    

DOI:10.1159/000158700

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Recently, using intracellular recording techniques, it has been shown that transmitter release from individual varicosities in sympathetic nerves occurs intermittently, and that only a single quantum of transmitter is secreted when the release process of a varicosity is activated by the nerve action potential. Here we discuss results obtained using a novel method of extracellular recording which allows simultaneous measurement of both the nerve action potential and transmitter release from postganglionic sympathetic nerve terminals. We have confirmed that release is intermittent, but the importance of this new approach is that the relationship between the nerve terminal action potential and transmitter release can be studied unambiguously for the first time. Thus, we are able to show unequivocally that: (1) intermittence is caused by a low probability of transmitter release in the invaded varicosity; (2) frequency-dependent facilitation of release is determined by the rate of arrival of the action potential and not by detectable changes in its configuration; (3) the current underlying the excitatory junction potential (EJP) is brief compared to the total duration of the EJP, and (4) clonidine may inhibit transmitter release by modifying the nerve terminal action potential. These results provide important new insights into the fundamental mechanisms involved in the physiological and pharmacological control of transmitter release from sympathetic nerves.

ISSN:1018-1172    

DOI:10.1159/000158701

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The mode of action of indirectly acting sympathomimetic amines was analysed in the rat vas deferens (preloaded with 3H-(–)-noradrenaline). When monoamine oxidase (MAO), catechol-O-methyltransferase and vesicular uptake were inhibited (i.e., when the concentration of 3H-noradrenaline in the axoplasm was high), all substrates of neuronal uptake induced a carrier-mediated outward transport of ¾noradrenaline, in strict dependence on the Km for neuronal uptake of the substrate. However, when MAO and vesicular uptake were not inhibited, some of the substrates of neuronal uptake were better releasers of 3H-noradrenaline than others; obviously, when the axoplasmic 3H-noradrenaline concentration is very low (intact vesicular uptake, intact MAO), a ‘mobilization’ of vesicular 3H-noradrenaline is a prerequisite for substantial r

ISSN:1018-1172    

DOI:10.1159/000158702

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

A survey is given of the interaction between α-adrenoceptor-triggered vasoconstriction and the influx of extracellular calcium ions. This problem was investigated by studying the influence of calcium entry blockers (CEB) on the vasoconstriction, induced by several types of α2- and α1-adrenoceptor agonists, both in vivo and in vitro. In addition, experiments were performed with the calcium entry promoter Bay K 8644. α2-Adrenoceptor-triggered vasoconstriction is invariably accompanied by an influx of extracellular calcium ions which substantially contributes to the initiation of vascular smooth muscle contraction. This concept is a very general phenomenon, which holds for a variety of α2-adrenoceptor agonists and CEB, in vivo and in vitro, and in different animal species. The α1-adrenoceptor-induced vasoconstriction appears to be caused both by the release of intracellular calcium and by the transmembranous influx of intracellular calcium. The ratio between both processes is very different, depending upon the type of α1-adrenoceptor agonist and on the experimental preparation used. It has been speculated that this ratio can be influenced by phenoxyben

ISSN:1018-1172    

DOI:10.1159/000158703

出版商:S. Karger AG    

年代:1987

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158704

出版商:S. Karger AG    

年代:1987

数据来源: Karger