Potassium Adaptation Is Impaired in Hypophysectomized Rats

K + homeostasis is critical for normal cardiovascular and neuromuscular function. The kidneys have a remarkable capacity to regulate K + excretion to match K + intake. This so‐called “K + adaptation” is critical for chronic K + balance. We recently showed that K + adaptation can occur without altering plasma K + or aldosterone level and that gut sensing of K + intake enhances renal K + excretion independent of plasma K + or aldosterone. We propose that K + adaptation is mediated by an afferent neural pathway from the gut and secretion of a humoral factor(s) by the pituitary. To test this hypothesis, we examined whether K + adaptation is impaired in hypophysectomized (HS) rats. Normal and HS rats (n=4 each) were initially fed on a control diet (1% K + ) for 3 days and subsequently on a low K + diet (0.33% K + ). Animals were individually housed and had free access to food only at night (6 PM–8 AM). Renal K + excretion was determined for the absorptive (6 PM–8 AM) and the postabsorptive (8 AM–6 PM) periods. In normal rats, reducing K + intake to 1/3 of control profoundly decreased both absorptive and postabsorptive K + excretion. In HS rats, while absorptive K + excretion decreased similarly, postabsorptive K + excretion decreased in time courses much slower than those in normal rats (Figure). In conclusion, K + adaptation was impaired in HS rats, supporting the hypothesis that the pituitary is involved in K + adaptation. (supported by NIDDK)