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近年用特异性竞争拮抗的药理方法,确定有两类组织胺受体,简称为H_1和H_2受体。H_1受体主要分布于支气管和肠道中。H_2受体则存在于胃的壁细胞膜上。甲氰咪胍(Cimetidine,Tagamet)是一种H_2受体拮抗剂,曾译为甲氰咪胺,其实在它的化学结构式中,只有胍基,并无胺基。概况和药理作用典型的抗组织胺药,即H_1受体拮抗剂,能抑制组织胺对平滑肌的刺激作用,但对组织胺刺激胃酸分泌的作用,却无抑制功效。此点提示人们存在另一种组织胺受体,并开始从组织胺化学结构的变异产物中,探寻另一类拮抗剂-H_2受体拮抗剂。第一批合成的H_2受体拮抗剂是甲咪硫脲(Metiamide),曾广泛应用,虽较安全,但少数可出现以粒细胞减少为主的可逆性骨髓抑制反应,而被弃置不用。甲咪硫脲的骨髓抑制可能与其分子中的硫脲基有关,而不是H_2受体被阻滞所致。为了减少副作用,1975年Brimblecombe等以氰胍基代替硫脲基合成了
In recent years, with specific competitive antagonistic pharmacological methods to identify two types of histamine receptors, referred to as H_1 and H_2 receptors. H_1 receptors are mainly found in the bronchi and intestine. H 2 receptor is present in the gastric parietal cell membrane. Cimetidine (Tagamet) is a H 2 receptor antagonist, has been translated as mecamylamine, in fact, in its chemical structure, only guanidine, and no amine. Overview and pharmacological effects Typical antihistamines, H 1 receptor antagonists, inhibit the stimulation of histamine on smooth muscle, but histamine stimulation of gastric acid secretion, but no inhibitory effect. This suggests that there is another histamine receptor present and to start looking for another antagonist, the H2 receptor antagonist, from the mutated product of the histamine amine chemical structure. The first synthetic H 2 receptor antagonist is metiamide (Metiamide), has been widely used, although safer, but a few can be neutropenic mainly reversible myelosuppression, and was abandoned. Myrmic thiourea myelosuppression may be related to its molecule thioureas, rather than H 2 receptors are blocked. In order to reduce the side effects, 1975, Brimblecombe and other thioguanidine instead of thiourea synthesis