RESUMEN
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.
Asunto(s)
3-Hidroxiesteroide Deshidrogenasas/metabolismo , Aldosterona/biosíntesis , Bufo arenarum/metabolismo , Riñón/enzimología , Cloruro de Sodio/farmacología , 3-Hidroxiesteroide Deshidrogenasas/fisiología , Aclimatación/fisiología , Aldosterona/sangre , Animales , Bufo arenarum/fisiología , Corticosterona/biosíntesis , Corticosterona/sangre , Riñón/metabolismo , Riñón/fisiología , Masculino , Microsomas/enzimología , Microsomas/metabolismo , Microsomas/fisiología , Mitocondrias/enzimología , Mitocondrias/metabolismo , Mitocondrias/fisiología , Estaciones del Año , Cloruro de Sodio/metabolismoRESUMEN
The human corpus luteum (CL) undergoes a dynamic cycle of differentiation, steroid hormone production and regression during the course of non-fertile cycles. In humans and other primates, luteal steroidogenesis is absolutely dependent on pituitary-derived LH. However, changes in LH and LH receptor expression do not explain the marked decline in progesterone production at the end of the luteal phase. Changes in the level of the steroidogenic acute regulatory protein (StAR), a gene whose expression is controlled by LH most likely account for the cyclic pattern of progesterone production. During the mid-to-late luteal phase of a fertile cycle, chorionic gonadotropin (hCG) rescues the CL, overcoming the actions of the factors inducing luteolysis. Although the agents causing regression of the CL in a non-fertile cycle are not yet known, intra-luteal growth factors and cytokines that modify the action of LH probably contribute to the reduction of StAR expression and the subsequent fall in progesterone production.