Huhtaniemi I T, Rajaniemi H J, Catt K J
J Reprod Fertil. 1986 Sep;78(1):73-82. doi: 10.1530/jrf.0.0780073.
The properties of hCG binding to LH receptors of the neonatal (5-day-old) rat testis were analysed and compared with those of the adult testis. The equilibrium association constants (Ka) of hCG-binding were similar at both ages, 2-4 X 10(10) M-1. In contrast, kinetic binding studies revealed that the association and dissociation rate constants of hCG binding were more rapid in the neonatal testis. Likewise, it was observed that the progression from loose (easily dissociable) to tight (non-dissociable) binding was less complete in the young than in the adult testis. Autoradiography of 125I-labelled hCG binding to interstitial cell suspensions at the two ages showed that the gonadotrophin binding per Leydig cell was about 50% lower in the neonatal testis. Conversely, since the surface area of adult Leydig cells was about 4-fold larger, the receptor density appeared to be higher in the neonatal Leydig cells. The rapid recovery of LH receptors after hCG stimulation, typical of the neonatal cells, was due to rapid replenishment of binding in the cells initially occupied by the injected hormone, rather than to an hCG-induced increase of Leydig cell number. Finally, in-vivo experiments with cycloheximide revealed that the rapid recovery of LH receptors was dependent on protein synthesis. These differences in the kinetics of neonatal testicular LH receptor turnover may be involved in the unique functional features of the fetal-neonatal growth phase of rat testicular Leydig cells.
分析了人绒毛膜促性腺激素（hCG）与新生（5日龄）大鼠睾丸LH受体结合的特性，并与成年睾丸进行了比较。两个年龄段hCG结合的平衡缔合常数（Ka）相似，为2 - 4×10¹⁰ M⁻¹。相比之下，动力学结合研究表明，hCG在新生睾丸中的结合和解离速率常数更快。同样，观察到从松散（易于解离）到紧密（不可解离）结合的过程在幼年睾丸中不如成年睾丸中完整。对两个年龄段125I标记的hCG与间质细胞悬液结合的放射自显影显示，新生睾丸中每个睾丸间质细胞的促性腺激素结合量约低50%。相反，由于成年睾丸间质细胞的表面积大约大4倍，新生睾丸间质细胞中的受体密度似乎更高。hCG刺激后LH受体的快速恢复是新生细胞的典型特征，这是由于最初被注射激素占据的细胞中结合的快速补充，而不是由于hCG诱导的睾丸间质细胞数量增加。最后，用环己酰亚胺进行的体内实验表明，LH受体的快速恢复依赖于蛋白质合成。新生睾丸LH受体周转动力学的这些差异可能与大鼠睾丸间质细胞胎儿 - 新生儿生长阶段的独特功能特征有关。
