Early effects of uninephrectomy on K homeostasis in unanesthetized rats

Mechanisms underlying the change in K excretion (UKV) during the first 6 days after uninephrectomy (UNX) were examined in unanesthetized rats. Arterial plasma K concentrations (P-K) were 0.55 meq/l above control values at 12 and 24 h after UNX but were not significantly different 36-72 h after UNX. To determine if there was an increased sensitivity of the distal K secretory mechanism to increases in P-K, an intragastric KCl infusion was given. The Delta UKV/Delta P-K per kidney values were in the following order: 6-day UNX > 2-day UNX > control. In the normal rats, an acute increase of 0.5 meq/l in P-K increased UKV by an amount approximating 25% of the increase in UKV observed 12-24 h after UNX. Amiloride, administered 48 h after UNX, increased Na excretion per kidney and decreased UKV per kidney approximately twice as much in UNX as in control groups. Thus an adaptive increase of amiloride-inhibitable K secretion occurred within 2 days of UNX and continued to increase thereafter. This K adaptation may have been induced by transient increases in P-K.