Glucocorticoid regulation of vasopressin gene expression in the rat brain.

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It is well known that glucocorticoid hormone (GC) has effects on the release and production of vasopressin (AVP). However, it is yet uncertain whether GC affects AVP gene expression in vivo. The current study was undertaken to investigate changes in hypothalamic vasopressin (AVP) mRNA in response to GC under dehydration and to RU 486, a glucocorticoid receptor antagonist, under water loaded states. [Methods] Experiments were carried out in male Spraue-Dawley rats. In GC studies, dexamethasone tablets (0.5mg) were implanted subcutaneously 5 and 2 days before the experiment. Effects of 3 days of dehydration were also studied. RU 486(20mg/kg) was administered subcutaneouly 2 days and 1 day before and on the day of the experiment and 20ml/kg/hr of water was given oraly for 5 hrs. The hypothalamus was used to determine AVP mRNA by northern blot analysis with a rat AVP cDNA probe or RT-PCR methods. [Results and conclusion] In the GC group, plasma osmolality (Posm) and AVP mRNA increased under the euhydrated state, but AVP mRNA under defydration decreased compared with the control. In both dehydrated growps, increases in Posm were comparable. In the RU 486 group, plasma AVP and AVP mRNA were increased with decreased Posm. Water load decreased Posm further, but did not change plasma AVP and AVP mRNA in RU486-treated rats. From these results, it is concluded that GC stimulated the AVP gene expression under the euhydrated state, but attenuated it under the dehydrated state. On the other hand, RU 486 itself stimulated AVP gene expression, which was not affected by the hypoosmolality.