Control of sensitivity to agonists in smooth muscle
Başlık:
Control of sensitivity to agonists in smooth muscle
Yazar:
Corbett, Alistair David, author.
ISBN:
9780438053731
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (224 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 76-08C.
Advisors: David Pollock.
Özet:
1) The aim of the study was to investigate some of the factors which influence the sensitivity of smooth muscle, particularly those factors involved in the development of subsensitivity. Emphasis was placed upon an examination of the general hypothesis that the sensitivity of an effector is inversely related to the amount of transmitter to which it is exposed. 2) Two smooth muscle preparations were used, the rat anococcygeus muscle and the rat femoral artery. 3) It was confirmed that in the anococcygeus different types of supersensitivity occur. Deviation supersensitivity was produced by cocaine, desmethylimipramine, dextroamphetamine and 6 -hydroxy- dopamine. In addition, reserpine produced nondeviation supersensitivity and thyroidectomy increased the maximum responses to both noradrenaline and carbachol without affecting the position of the dose - % response curves. Reserpine and thyroidectomy also produced supersensitivity in arterial smooth muscle. 4) Various treatments which were designed to increase the amount of transmitter in the biophase failed to reduce the sensitivity of the anococcygeus. These treatments involved the use of neuronal uptake blockers and, direct and indirect sympathomimetics. The acute and chronic administration of the a - adrenoceptor aganist oxymetazoline however, did reduce the sensitivity of the anococcygeus. These effects are discussed. 5) Desensitization was readily produced in vitro, by the acute administration of noradrenaline to both the anococcygeus and to arteries. 6) The difference between the ease with which desensitization occurs in vitro and the difficulty in producing subsensitivity in vivo, suggests that factors operating in vivo, perhaps hormonal factors, prevent the development of subsensitivity. Other possible influences include the feedback system which would tend to decrease the amount of transmitter released into the biophase, and perhaps also limited neuronal activity to the effector. 7) Supersensitivity produced by altering hormone levels could be reduced by direct sympathomimetic drugs in the anococcygeus but not in the femoral artery. On the other hand, supersensitivity produced by transmitter deprivation could be reduced by sympathomimetic drugs in the femoral artery but not in the anococcygeus. This provides at least partial support for the general hypothesis that transmitter concentration determines effector sensitivity, 8) Adrenocorticotrophic hormone reduced the sensitivity in both the anococcygeus muscle and the vascular smooth muscle. This action was mediated via the adrenals and seemed to involve corticosteroids which casts doubts on the role of corticosteroids in the genesis of the increased maximum response supersensitivity. It also highlights the contribution of hormones to the regulation of autonomic neuroeffector sensitivity. 9) Increasing the calcium in the bathing Krebs solution prevented or abolished the desensitization produced in the anococcygeus muscle by acute noradrenaline suggesting that the desensitization was produced by the exhaustion of a calcium store. A large dose of noradrenaline in vitro, increased the binding of calcium in the anococcygeus muscle but carbachol had no effect. None of the animal treatments examined affected calcium binding in the anococcygeus. 10) These results suggest that there exists in smooth muscle a dynamic range of sensitivity within which the tissue sensitivity may be altered. In addition to the amount of transmitter, the hormonal background is important in determining the position of the sensitivity within this spectrum.
Notlar:
School code: 0547
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(684472.1) | 684472-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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