Pozzi Andrea G, Lantos Carlos P, Ceballos Nora R
PRHOM-CONICET and Laboratorio de Endocrinología Comparado, Departmento de Ciencias Biológicas, Universidad de Buenos Aires, Buenos Aires, Argentina
Gen Comp Endocrinol. 2002 Mar;126(1):68-74. doi: 10.1006/gcen.2001.7770.
In amphibians, aldosterone (Aldo) is particularly important in the regulation of Na(+) exchange by skin and urinary bladder. In previous works we studied a key enzyme in Aldo biosynthesis, the 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta HSD/I), in the interrenals of Bufo arenarum. In those works a dual localization of the 3 beta HSD/I in both microsomes and mitochondria was described. The mitochondrial, but not the microsomal, enzyme prefers the immediate Aldo precursor, 3 beta-analogue of aldosterone, as substrate. In this order, the enzyme 3 beta HSD/I would be not only a key enzyme for the synthesis of Aldo but additionally, due to its microsomal and mitochondrial localization, a possible target for the regulation of Aldo biosynthesis. With this rationale in mind, we have used in vivo and in vitro approaches to study Aldo regulation. In the present investigation the levels of Aldo were determined in plasma of winter (W) and summer (S) toads subjected to different saline concentrations (0.125 and 0.15 M) or kept on wet land. Saline hyperosmotically treated toads had significantly lower levels than isoosmotically treated toads. These results are consistent with the response in mammals, in which salt loading provokes a reduction in Aldo secretion. In W toads, plasmatic corticosterone (B) concentration was higher than Aldo concentration, whereas in S toads, B/Aldo ratio approached unity. The reduction of Aldo levels after saline dehydration was due to a decline in its biosynthesis. K(m) and V(max) values for 3 beta HSD/I were calculated for mitochondrial and microsomal fractions obtained from animals acclimated to 0.15 M NaCl or kept on land. As previously described, V(max) differs between W and S toads. However, only mitochondrial V(max) changed as a consequence of saline adaptation, suggesting that the mitochondrial enzyme could be involved in the regulation of Aldo biosynthesis.
在两栖动物中，醛固酮（Aldo）在皮肤和膀胱对钠离子交换的调节中尤为重要。在之前的研究中，我们研究了Bufo arenarum肾上腺皮质组织中醛固酮生物合成的关键酶——3β-羟基类固醇脱氢酶/异构酶（3βHSD/I）。在这些研究中，描述了3βHSD/I在微粒体和线粒体中的双重定位。线粒体中的该酶（而非微粒体中的）更倾向于将醛固酮的直接前体——醛固酮的3β类似物作为底物。因此，3βHSD/I不仅是醛固酮合成的关键酶，而且由于其在微粒体和线粒体中的定位，它可能是醛固酮生物合成调节的一个靶点。基于这一理论基础，我们采用体内和体外方法来研究醛固酮的调节。在本研究中，测定了处于不同盐浓度（0.125和0.15 M）或饲养在湿地的冬季（W）和夏季（S）蟾蜍血浆中的醛固酮水平。经高渗盐处理的蟾蜍的醛固酮水平显著低于等渗处理的蟾蜍。这些结果与哺乳动物的反应一致，在哺乳动物中，盐分负荷会导致醛固酮分泌减少。在W蟾蜍中，血浆皮质酮（B）浓度高于醛固酮浓度，而在S蟾蜍中，B/Aldo比值接近1。盐脱水后醛固酮水平的降低是由于其生物合成的下降。计算了从适应0.15 M NaCl或饲养在陆地的动物获得的线粒体和微粒体部分的3βHSD/I的米氏常数（K(m)）和最大反应速度（V(max)）。如前所述，W和S蟾蜍的V(max)不同。然而，只有线粒体V(max)因盐适应而发生变化，这表明线粒体酶可能参与醛固酮生物合成的调节。
