Heber D, Marshall J C, Odell W D
Am J Physiol. 1978 Aug;235(2):E227-30. doi: 10.1152/ajpendo.1978.235.2.E227.
Utilizing biologically active 125I-labeled gonadotropin-releasing hormone (125I-GnRH), specific binding with two affinites [KA (high) = 3.2 x 10(8) M-1, KA (low) = 10(5) M-1] were identified in membrane preparations derived from the 10,800 x g pellet of rat pituitary. GnRH-specific low affinity sites (KA - 10(5) M-1) were identified in liver, spleen, renal cortex, lung, testis, ovary, and cardiac muscle. Hypothalamic tissue demonstrated both high- and low-affinity binding. When 125I-GnRH was bound and dissociated, the labeled GnRH retained fully ability to rebind to fresh membrane preparations. That is, binding was not associated with loss of biological activity of GnRH. However, when unbound 125I-GnRH was exposed to the membrane fraction of liver, almost all receptor binding activity disappeared. The presence of low-affinity binding sites in peripheral tissues raises several possibilities: 1) they act as a simple reservoir mediating metabolic clearance of GnRH; 2) they represent enzyme binding sites involved in degradation of GnRH; 3) they mediate peripheral actions of GnRH; or 4) they are simply a cellular membrane constituent unrelated to target actions of GnRH.
利用具有生物活性的125I标记促性腺激素释放激素（125I-GnRH），在源自大鼠垂体10,800×g沉淀的膜制剂中鉴定出具有两种亲和力的特异性结合[KA（高）= 3.2×10(8) M-1，KA（低）= 10(5) M-1]。在肝脏、脾脏、肾皮质、肺、睾丸、卵巢和心肌中鉴定出GnRH特异性低亲和力位点（KA - 10(5) M-1）。下丘脑组织表现出高亲和力和低亲和力结合。当125I-GnRH结合并解离时，标记的GnRH保留了与新鲜膜制剂重新结合的完全能力。也就是说，结合与GnRH生物活性的丧失无关。然而，当未结合的125I-GnRH暴露于肝脏的膜部分时，几乎所有受体结合活性都消失了。外周组织中低亲和力结合位点的存在提出了几种可能性：1）它们作为介导GnRH代谢清除的简单储存库；2）它们代表参与GnRH降解的酶结合位点；3）它们介导GnRH的外周作用；或4）它们仅仅是与GnRH靶作用无关的细胞膜成分。
