Schoeffter P, Pérez J, Langenegger D, Schüpbach E, Bobirnac I, Lübbert H, Bruns C, Hoyer D
SANDOZ Pharma Ltd, Basel, Switzerland.
Eur J Pharmacol. 1995 Mar 15;289(1):163-73. doi: 10.1016/0922-4106(95)90180-9.
Somatostatin (SRIF) SS-1 binding sites were initially defined in radioligand binding studies performed in rat brain cerebral cortex membranes using [125I]204-090 (a radiolabelled Tyr3 analogue of SMS 201-995, octreotide). SRIF-1 recognition sites were defined in binding studies performed with [125I]MK 678 (seglitide). Both SS-1 and SRIF-1 sites were characterized by their high affinity for SRIF-14, SRIF-28 and for cyclic peptides such as octreotide and seglitide, in marked contrast to SS-2 and SRIF-2 sites which have very low affinity for these synthetic SRIF analogues. In the present study, SS-1 and SRIF-1 radioligand binding studies were performed in rat cortex membranes and compared to results obtained in cloned Chinese hamster ovary cells expressing human SSTR-2 receptors using [125I]204-090 and/or [125I]MK-678. The rank orders of affinity of a variety of SRIF analogues and synthetic peptides for SS-1/SRIF-1 binding sites and recombinant SSTR-2 receptors were very similar and correlated highly significantly (r = 0.94-0.99); by contrast, correlation between SS-1 and SSTR-5 (r = 0.44) or SSTR-3 binding (r = 0.07) was not significant. Autoradiographic studies were performed in rat brain using both radioligands [125I]204-090 and [125I]MK-678 and compared with the distribution of SSTR-2 receptor mRNA determined using in situ hybridization. A clear overlap was observed between the distribution of SSTR-2 mRNA and binding sites labelled with both radioligands. SSTR-2 receptor-mediated inhibition of forskolin-stimulated adenylate cyclase in Chinese hamster ovary cells by a variety of SRIF analogues and short synthetic peptides displayed a rank order of potency highly similar to their rank order of affinity at SS-1/SRIF-1 binding sites. It is concluded that SS-1 and SRIF-1 binding sites respectively labelled with [125I]204-090 and [125I]MK 678, both display the pharmacological profile of SSTR-2 receptors, that the distribution of [125I]204-090 and [125I]MK-678 binding sites in rat brain is superimposable and largely comparable to that of SSTR-2 mRNA expression. It is also shown that neither [125I]204-090 nor [125I]MK-678 label SSTR-3 or SSTR-5 receptors in rat brain. Finally, it is demonstrated that SSTR-2 receptors can very efficiently couple to adenylate cyclase activity in an inhibitory manner.
生长抑素（SRIF）SS - 1结合位点最初是在使用[125I]204 - 090（SMS 201 - 995、奥曲肽的放射性标记酪氨酸3类似物）对大鼠脑皮质膜进行的放射性配体结合研究中确定的。SRIF - 1识别位点是在用[125I]MK 678（司美格鲁肽）进行的结合研究中确定的。SS - 1和SRIF - 1位点的特征是它们对SRIF - 14、SRIF - 28以及环肽如奥曲肽和司美格鲁肽具有高亲和力，这与对这些合成SRIF类似物亲和力非常低的SS - 2和SRIF - 2位点形成显著对比。在本研究中，在大鼠皮质膜中进行了SS - 1和SRIF - 1放射性配体结合研究，并与使用[125I]204 - 090和/或[125I]MK - 678在表达人SSTR - 2受体的克隆中国仓鼠卵巢细胞中获得的结果进行了比较。多种SRIF类似物和合成肽对SS - 1/SRIF - 1结合位点和重组SSTR - 2受体的亲和力排序非常相似，且相关性非常显著（r = 0.94 - 0.99）；相比之下，SS - 1与SSTR - 5（r = 0.44）或SSTR - 3结合（r = 0.07）之间的相关性不显著。使用放射性配体[125I]MK - 678和[125I]204 - 090在大鼠脑中进行了放射自显影研究，并与使用原位杂交测定的SSTR - 2受体mRNA分布进行了比较。在SSTR - 2 mRNA分布与两种放射性配体标记的结合位点之间观察到明显重叠。多种SRIF类似物和短合成肽对中国仓鼠卵巢细胞中福斯高林刺激的腺苷酸环化酶的SSTR - 2受体介导的抑制作用，其效价排序与其在SS - 1/SRIF - 1结合位点的亲和力排序高度相似。得出的结论是，分别用[125I]204 - 090和[125I]MK 678标记的SS - 1和SRIF - 1结合位点均显示出SSTR - 2受体的药理学特征，[125I]204 - 090和[125I]MK - 678结合位点在大鼠脑中的分布是重叠的，并且在很大程度上与SSTR - 2 mRNA表达的分布相当。还表明，[125I]204 - 090和[125I]MK - 678在大鼠脑中均不标记SSTR - 3或SSTR - 5受体。最后，证明了SSTR - 2受体可以非常有效地以抑制方式与腺苷酸环化酶活性偶联。
