AGE-RELATED-CHANGES IN THE HORMONAL-REGUL ATION OF THE EXPRESSION OF MESSENGER-RNA OF ALPHA-ISOFORMS AND BETA-ISOFORMS OF NA, K-ATPASE AND ITS ACTIVITY IN THE RAT-KIDNEY

We studied the hormonal regulation of the expression of alpha- and bet a-mRNA isoforms of Na, K-ATPase in the kidneys of 10- and 60-day-old r ats. Adrenalectomyzed rats were injected intrapertitoneally aldosteron e (A) (5 mug/100 b.w.) alone or spironolactone (AS) (12 mg/100 b.w.) o r dexametasone (AD) (5 mug/100 b.w.) every 3 h 4 times. No expression of alpha2, alpha3 and beta2 isoforms was detectable in the two age gro ups of rats under any conditions. Both A and AD induced and increase i n mRNA abundance of alpha1 and beta1 in 10-day-old and adult rats. Age differences were revealed when A was administrated together with its antagonist S. S almost completely inhibited the effect of A in adults, whereas it has no effect on the induction of mRNA expression in young rats. The results are in agreement with the influence of A on the Na, K-ATPase activity in the crude cortex membrane fraction. These data s eem to indicate that the A induction of Na, K-ATP-pump mRNA and its ac tivity in the kindyes of 10-day-old rats may be the result of its inte raction net with mineralocroticoid, but with glucocorticold, receptors .