Effects of KCl infusion on potassium excretion in sheep

To determine the quantitative relation of K excretion (UKV) to plasma K concentration (PK), three fasted, conscious, mature ewes were infused intravenously with 50 mmol KCl over 15, 30, and 60 min. Control experiments were without infusion. During KCl infusion PK was increased to 7.26 +/- 0.40 (15 min), 6.68 +/- 0.48 (30 min), and 5.59 +/- 0.3 meq/liter (60 min). During all three infusions the increase in UKV relative to the increase in PK was similar. The mean delta UKV/delta PK ratio was 160 +/- 30 (SD) mueq/min per meq/liter (range 102-203). On termination of each infusion PK decreased to control values, but UKV either remained elevated (60-min infusion) or first decreased and then increased (15- and 30-min infusions). The second, delayed kaliuresis began 30-45 min after initiation of KCl infusion and accelerated a return to the level of K balance of the control experiments. A plot of UKV against the corresponding period PK showed that, at a common value of PK, UKV was higher following KCl infusion when PK was dropping than during KCl infusion when PK was rising. The mechanisms responsible for this hysteresis phenomenon are not identified.