Mendelson C, Dufau M, Catt K
J Biol Chem. 1975 Nov 25;250(22):8818-23.
Gonadotropin binding and stimulation of cyclic adenosine 3':5'-monophosphate (cyclic AMP) formation and testosterone synthesis were studied in collagenase-dispersed interstitial cells from the adult rat testis. Binding of 125I-human chorionic gonadotropin (hCG) by isolated Leydig cells was of high affinity (Ka = 10(10) M-1) and low capacity, equivalent to approximately 6000 sites/cell. The binding data were consistent with the presence of a single order of receptors, with no interaction between binding sites. Stimulation of testosterone synthesis by increasing concentrations of hCG was completely dissociated from changes in cyclic AMP formation, and maximum activation of steroidogenesis was induced by hCG concentrations which had no effect upon cyclic AMP production. Kinetic analysis of gonadotropin-induced responses in dispersed Leydig cells also showed a marked dissociation between steroidogenesis and cyclic nucleotide formation. Low concentrations of hCG caused maximum stimulation of testosterone production which was not accompanied by a rise in cyclic AMP formation at any time after addition of gonadotropin. Higher concentrations of hCG caused marked elevations of cyclic AMP at progressively earlier time intervals, but did not alter the 20 to 30 min lag period required for induction of testosterone synthesis. These observations indicated that occupancy of gonadotropin receptors occurs over a much wider range of hCG concentration than that required for maximum steroidogenesis.
对成年大鼠睾丸经胶原酶分散处理的间质细胞中促性腺激素结合以及环磷酸腺苷（cAMP）生成和睾酮合成的刺激作用进行了研究。分离的睾丸间质细胞对125I-人绒毛膜促性腺激素（hCG）的结合具有高亲和力（Ka = 10(10) M-1）和低容量，相当于约6000个位点/细胞。结合数据与单一顺序的受体存在一致，结合位点之间无相互作用。hCG浓度增加对睾酮合成的刺激与cAMP生成的变化完全分离，且hCG浓度对cAMP产生无影响时却能诱导类固醇生成的最大激活。对分散的睾丸间质细胞中促性腺激素诱导反应的动力学分析也显示类固醇生成与环核苷酸形成之间存在明显分离。低浓度的hCG在添加促性腺激素后的任何时间都能引起睾酮产生的最大刺激，而不伴有cAMP生成的增加。较高浓度的hCG在逐渐提前的时间间隔内引起cAMP的显著升高，但并未改变诱导睾酮合成所需的20至30分钟的延迟期。这些观察结果表明，促性腺激素受体的占据发生在比最大类固醇生成所需范围更宽的hCG浓度范围内。
