Effect of salt acclimatization on 3β-hydroxysteroid dehydrogenase/isomerase activity in the interrenal of Bufo arenarum
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 3β-hydroxysteroid dehydrogenase/isomerase (3βHSD/I), in the interrenals of Bufo arenarum. In those works a du...
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| Autores principales: | , , |
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| Formato: | JOUR |
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00166480_v126_n1_p68_Pozzi |
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| Sumario: | 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 3β-hydroxysteroid dehydrogenase/isomerase (3βHSD/I), in the interrenals of Bufo arenarum. In those works a dual localization of the 3βHSD/I in both microsomes and mitochondria was described. The mitochondrial, but not the microsomal, enzyme prefers the immediate Aldo precursor, 3β-analogue of aldosterone, as substrate. In this order, the enzyme 3βHSD/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 cotticosterone (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. Km and Vmax values for 3βHSD/I were calculated for mitochondrial and microsomal fractions obtained from animals acclimated to 0.15 M NaCl or kept on land. As previously described, Vmax differs between W and S toads. However, only mitochondrial Vmax changed as a consequence of saline adaptation, suggesting that the mitochondrial enzyme could be involved in the regulation of Aldo biosynthesis. © 2002 Elsevier Science (USA). |
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