Rapid renal potassium adaptation in rats.

The possibility that renal K adaptation, defined as the increased capacity to excrete an intravenous K load, can occur within hours of intake of a normal K ration was examined in fed and fasted rats. Rats maintained on a 12-h light-dark cycle were fed either a standard diet (fed rats) or had food removed before the onset of the dark phase to prevent the early dark phase ingestion (fasted rats). Four hours into the dark phase, fed and fasted rats were infused intravenously with 0.143 M KCl, while control fed and fasted rats did not receive any KCl. The initial urinary K excretion rate (UKV, 5.67 +/- 0.47 in K-loaded fed rats were greater than the UKV (3.13 +/- 0.45 mu eq/min) and PK (3.24 +/- 0.1 meq/l) in K-loaded fasted rats. After the acute KCl infusion (100 min), the UKV increased similarly in both fed and fasted rats, while the magnitude of the increase in PK in fasted rats was twice that in fed rats. Consequently, the delta UKV/delta PK was greater in fed rats (3.83 mj eq/min per meq/l) than in fasted rats (2.14 mu eq/min per meq/l). During the KCl infusion for any level of PK, the UKV was greater in fed rats than in fasted rats. This relationship was not altered by concurrent infusion of potassium canrenoate or somatostatin. These results indicate that within 3-6 h after an oral K intake, the renal excretion of an acute intravenous K load is enhanced.(ABSTRACT TRUNCATED AT 250 WORDS)