Carsia R V, Scanes C G, Malamed S
Endocrinology. 1984 Dec;115(6):2464-72. doi: 10.1210/endo-115-6-2464.
Exogenous corticosterone (B), the natural glucocorticoid product of rats, suppressed endogenous B production of isolated rat adrenocortical cells induced by alpha ACTH-(1-24), [9-tryptophan (O-nitrophenylsulfenyl)]ACTH-(1-24) [( Trp (Nps)9]ACTH-(1-24], and cAMP as well as pregnenolone supported-steroidogenesis. This self-suppression occurred within 2 h. It was dependent on the concentration of exogenous B. However, self-suppression did not alter the half-maximal steroidogenic concentration (ED50) of each steroidogenic agent. In addition, exogenous B did not suppress ACTH-induced cAMP production or gross protein synthesis, as measured by leucine incorporation into bulk cellular proteins. These results with isolated cells suggested at least two mechanisms for self-suppression: 1) exogenous B inhibited steroidogenic steps in a noncompetitive manner, and/or 2) exogenous B induced B degradation. In this study we examined the effect of exogenous B on the degradation of B. Accordingly, we measured the adrenal 5 alpha-reductase activity (5 alpha RA) of cell homogenates prepared from treated cells. Isolated adrenocortical cells were incubated for 2 h with alpha ACTH-(1-24), ovine PRL (oPRL), and B. They were then homogenized and assayed for 5 alpha RA, as indicated by the disappearance of exogenous B, as shown by RIA. In addition, the percentage of exogenous tritium-labeled B [( 3H]B) converted to 5 alpha-dihydrocorticosterone (DHB), the principal reduced metabolite of B, was determined by TLC. Isolated adrenocortical cells from intact rats showed insignificant 5 alpha RA and DHB formation when incubated with or without alpha ACTH-(1-24) and with or without oPRL. However, with exogenous B, there was significant 5 alpha RA and DHB formation. oPRL plus B decreased DHB formation. The effects of B and oPRL were more demonstrable with cells from hypophysectomized rats. These cells exhibited high 5 alpha RA and DHB formation; exogenous B increased these values, whereas oPRL acutely reversed the effects of hypophysectomy and exogenous B. In other work avoiding cell homogenization, exogenous B suppressed ACTH-induced B accumulation and increased DHB formation in intact cell suspensions from intact rats and intact male domestic fowl. Furthermore, exogenous B increased the conversion of [3H] pregnenolone to DHB in intact cell suspensions from intact rats, showing that B synthesized de novo as well as exogenous B can be degraded during self-suppression. These data indicate that acute self-suppression of corticosteroidogenesis is at least partly mediated by an increase in 5 alpha RA.
外源性皮质酮（B），即大鼠的天然糖皮质激素产物，抑制了由α促肾上腺皮质激素-（1-24）、[9-色氨酸（邻硝基苯硫基）]促肾上腺皮质激素-（1-24）[（Trp（Nps）9]促肾上腺皮质激素-（1-24）以及环磷酸腺苷（cAMP）诱导的分离大鼠肾上腺皮质细胞的内源性B生成，同时孕烯醇酮支持类固醇生成。这种自我抑制在2小时内发生。它依赖于外源性B的浓度。然而，自我抑制并未改变每种类固醇生成剂的半数最大类固醇生成浓度（ED50）。此外，外源性B并未抑制促肾上腺皮质激素诱导的cAMP生成或总蛋白合成，这通过亮氨酸掺入大量细胞蛋白来测定。这些分离细胞的结果提示了至少两种自我抑制机制：1）外源性B以非竞争性方式抑制类固醇生成步骤，和/或2）外源性B诱导B降解。在本研究中，我们检测了外源性B对B降解的影响。因此，我们测量了由处理过的细胞制备的细胞匀浆的肾上腺5α-还原酶活性（5αRA）。将分离的肾上腺皮质细胞与α促肾上腺皮质激素-（1-24）、羊催乳素（oPRL）和B一起孵育2小时。然后将它们匀浆并检测5αRA，如放射免疫分析所示，外源性B的消失表明了这一点。此外，通过薄层层析法测定了外源性氚标记的B[（3H）B]转化为5α-二氢皮质酮（DHB）（B的主要还原代谢产物）的百分比。来自完整大鼠的分离肾上腺皮质细胞在与或不与α促肾上腺皮质激素-（1-24）一起孵育以及与或不与oPRL一起孵育时，显示出微不足道的5αRA和DHB形成。然而，有外源性B时，有显著的5αRA和DHB形成。oPRL加B减少了DHB形成。B和oPRL的作用在来自垂体切除大鼠的细胞中更明显。这些细胞表现出高5αRA和DHB形成；外源性B增加了这些值，而oPRL急性逆转了垂体切除和外源性B的作用。在其他避免细胞匀浆的研究中，外源性B抑制了促肾上腺皮质激素诱导的B积累，并增加了来自完整大鼠和完整雄性家鸡的完整细胞悬液中的DHB形成。此外，外源性B增加了来自完整大鼠的完整细胞悬液中[3H]孕烯醇酮向DHB的转化，表明在自我抑制过程中，新合成的B以及外源性B都可以被降解。这些数据表明，皮质类固醇生成的急性自我抑制至少部分是由5αRA的增加介导的。
