Effect of salt acclimatisation on 3ƒÒ-hydroxysteroid dehydrogenase activity in the interrenal of Bufo arenarum

POZZI AG; LANTOS CP; CEBALLOS N

GENERAL AND COMPARATIVE ENDOCRINOLOGY

Elsevier

Lugar: Londres; Año: 2002 vol. 126 p. 68 - 74

0016-6480

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
-hydroxysteroid dehydrogenase/isomerase (3
HSD/I), in the interrenals of Bufo arenarum. In those works a dual localization of the 3
HSD/I in both microsomes and mitochondria was described. The mitochondrial, but not the microsomal, enzyme prefers the immediate Aldo precursor, 3-analogue of aldosterone, as ubstrate. In this order, the enzyme 3
HSD/I would be not only a key enzyme for the synthesis of Aldo but dditionally, 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. Km and Vmax values for 3
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, Vmax differs betweenWand 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. exchange by skin and urinary bladder. In previous works we studied a key enzyme in Aldo biosynthesis, the 3
-hydroxysteroid dehydrogenase/isomerase (3
HSD/I), in the interrenals of Bufo arenarum. In those works a dual localization of the 3
HSD/I in both microsomes and mitochondria was described. The mitochondrial, but not the microsomal, enzyme prefers the immediate Aldo precursor, 3-analogue of aldosterone, as ubstrate. In this order, the enzyme 3
HSD/I would be not only a key enzyme for the synthesis of Aldo but dditionally, 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. Km and Vmax values for 3
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, Vmax differs betweenWand 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.