Podesta E J, Milani A, Steffen H, Neher R
Biochem J. 1979 May 15;180(2):355-63. doi: 10.1042/bj1800355.
Because several groups have recently questioned a mediating role for cyclic AMP in adrenocortical steroidogenesis, we analysed the problem in more detail by measuring three different cyclic AMP pools in cells isolated from decapsulated rat adrenals. Extra-cellular, total intracellular and bound intracellular cyclic AMP were determined by radioimmunoassay in comparison with corticosterone production induced by low corticotropin concentrations. The increase in extracellular and total intracellular cyclic AMP with low corticotropin concentrations was dependent on the presence of a phosphodiesterase inhibitor and short incubation times. Bound intracellular cyclic AMP was less dependent on these two parameters. In unstimulated cells cyclic AMP bound to its receptor represents only a small fraction of the total intracellular cyclic AMP. After stimulation by a concentration of corticotropin around the threshold for corticosterone production, an increase in bound cyclic AMP was observed which correlated very well with steroidogenesis both temporally and with respect to corticotropin concentration. This finding was complemented by measuring a concomitant decrease in free receptor sites. Full occupancy of the receptors was not necessary for maximal steroidogenesis. Binding kinetics of cyclic [(3)H]AMP in concentrations equivalent to the intracellular cyclic AMP concentration suggest the presence of at least three different intracellular cyclic AMP pools. These observations are in agreement with a possible role for cyclic AMP as a mediator of acute steroidogenesis induced by low corticotropin concentrations.
由于最近有几个研究小组对环磷酸腺苷(cAMP)在肾上腺皮质类固醇生成中的介导作用提出质疑,我们通过测量从摘除包膜的大鼠肾上腺分离的细胞中三种不同的环磷酸腺苷池,对该问题进行了更详细的分析。通过放射免疫测定法测定细胞外、细胞内总环磷酸腺苷和结合型细胞内环磷酸腺苷,并与低浓度促肾上腺皮质激素诱导的皮质酮生成进行比较。低浓度促肾上腺皮质激素导致的细胞外和细胞内总环磷酸腺苷增加依赖于磷酸二酯酶抑制剂的存在和短孵育时间。结合型细胞内环磷酸腺苷对这两个参数的依赖性较小。在未受刺激的细胞中,与受体结合的环磷酸腺苷仅占细胞内总环磷酸腺苷的一小部分。在受到接近皮质酮生成阈值浓度的促肾上腺皮质激素刺激后,观察到结合型环磷酸腺苷增加,其在时间上和促肾上腺皮质激素浓度方面均与类固醇生成密切相关。通过测量同时出现的游离受体位点减少,这一发现得到了补充。受体完全被占据并非最大类固醇生成所必需。与细胞内环磷酸腺苷浓度相当的[(3)H]环磷酸腺苷的结合动力学表明存在至少三种不同的细胞内环磷酸腺苷池。这些观察结果与环磷酸腺苷作为低浓度促肾上腺皮质激素诱导的急性类固醇生成的介质的可能作用一致。