In rats, the specific activity of renal Na-K-ATPase increased by approximately 50% in one week after uninephrectomy and remained more or less constant during the next three weeks. The capacity (Jmax) of PAH influx into the renal cortical slice was sharply increased in one week after nephrectomy, but after which it returned to the control level.

In cold exposed hamsters, the specific activity of renal Na-K-ATPase did not increase until 48 days of cold exposure at which time it reached approximately 50% above the control level. On the other hand, the Jmax of PAH influx increased by about 80% in 10 days of co1d exposure and somewhat declined thereafter.

These results suggest that PAH active transport in the renal slice is not ratelimited by the activity of Na-K-ATPase under physiological conditions.