Centre for Integrated Systems Biology and Medicine, Department of Surgery, The University of Nottingham Medical School, Queen's Medical Centre, Clifton Boulevard, Nottingham, UK.
Br J Pharmacol. 2010 Aug;160(7):1727-40. doi: 10.1111/j.1476-5381.2010.00842.x.
We have investigated the distribution of alpha-adrenoceptors in sheep internal anal sphincter (IAS), as a model for the human tissue, and evaluated various imidazoline derivatives for potential treatment of faecal incontinence.
Saturation and competition binding with (3)H-prazosin and (3)H-RX821002 were used to confirm the presence and density of alpha-adrenoceptors in sheep IAS, and the affinity of imidazoline compounds at these receptors. A combination of in vitro receptor autoradiography and immunohistochemistry was used to investigate the regional distribution of binding sites. Contractile activity of imidazoline-based compounds on sheep IAS was assessed by isometric tension recording.
Saturation binding confirmed the presence of both alpha(1)- and alpha(2)-adrenoceptors, and subsequent characterization with sub-type-selective agents, identified them as alpha(1A)- and alpha(2D)-adrenoceptor sub-types. Autoradiographic studies with (3)H-prazosin showed a positive association of alpha(1)-adrenoceptors with immunohistochemically identified smooth muscle fibres. Anti-alpha(1)-adrenoceptor immunohistochemistry revealed similar distributions of the receptor in sheep and human IAS. The imidazoline compounds caused concentration-dependent contractions of the anal sphincter, but the maximum responses were less than those elicited by l-erythro-methoxamine, a standard non-imidazoline alpha(1)-adrenoceptor agonist. Prazosin (selective alpha(1)-adrenoceptor antagonist) significantly reduced the magnitude of contraction to l-erythro-methoxamine at the highest concentration used. Both prazosin and RX811059 (a selective alpha(2)-adrenoceptor antagonist) reduced the potency (pEC(50)) of clonidine.
This study shows that both alpha(1)- and alpha(2)-adrenoceptors are expressed in the sheep IAS, and contribute (perhaps synergistically) to contractions elicited by various imidazoline derivatives. These agents may prove useful in the treatment of faecal incontinence.
我们研究了绵羊肛门内括约肌（IAS）中α-肾上腺素受体的分布，将其作为人类组织的模型，并评估了各种咪唑啉衍生物治疗粪便失禁的潜力。
使用（3）H-哌唑嗪和（3）H-RX821002 进行饱和和竞争结合，以确认绵羊 IAS 中α-肾上腺素受体的存在和密度，以及咪唑啉化合物在这些受体上的亲和力。结合体外受体放射自显影和免疫组织化学，研究结合部位的区域分布。通过等长张力记录评估基于咪唑啉的化合物对绵羊 IAS 的收缩活性。
饱和结合证实了α（1）-和α（2）-肾上腺素受体的存在，随后用亚型选择性试剂进行特征鉴定，将其鉴定为α（1A）-和α（2D）-肾上腺素受体亚型。用（3）H-哌唑嗪进行放射自显影研究表明，α（1）-肾上腺素受体与免疫组织化学鉴定的平滑肌纤维呈阳性相关。抗α（1）-肾上腺素受体免疫组织化学显示绵羊和人 IAS 中受体的分布相似。咪唑啉化合物引起肛门括约肌的浓度依赖性收缩，但最大反应小于 l-erythro-methoxamine 引起的反应，l-erythro-methoxamine 是一种标准的非咪唑啉α（1）-肾上腺素受体激动剂。在使用的最高浓度下，哌唑嗪（选择性α（1）-肾上腺素受体拮抗剂）显著降低了 l-erythro-methoxamine 引起的收缩幅度。哌唑嗪和 RX811059（一种选择性α（2）-肾上腺素受体拮抗剂）均降低了可乐定的效力（pEC（50））。
本研究表明，绵羊 IAS 中表达了α（1）-和α（2）-肾上腺素受体，并且（可能协同）对各种咪唑啉衍生物引起的收缩做出贡献。这些药物可能在治疗粪便失禁方面有用。
