Different effects of three aldosterone treatments on plasma aldosterone and salt intake

Adrenalectomized male rats received a nominal dose of 47.6 micrograms/day aldosterone for 14 days by daily injections, osmotic minipumps, or controlled-release pellets. Plasma aldosterone concentrations were barely detectable (< 20 pg/ml) 24 h after rats received aldosterone by injection, remained constant at 200 pg/ml in rats with osmotic minipumps, and dropped from > 500 to 75 pg/ml during the first week after implantation of controlled-release pellets. For the most part, the effects of the different treatments on NaCl intake were related to their effects on plasma aldosterone levels according to a U-shaped function. However, NaCl intake was dissociated from plasma aldosterone levels when treatment first began or was discontinued. NaCl intake may be a function of the amount of aldosterone delivered but not necessarily plasma aldosterone concentration.