Turnover rate of interstitial albumin in rat skin and skeletal muscle. Effects of limb movements and motor activity.

Fractional removal rate (FRR) of radioactive-labelled human serum albumin (I-HSA) injected subcutaneously or intramuscularly was determined by external gamma-detecting equipment. Radioactivity over the injection site fell monoexponentially during registration periods up to 6 h. The FRR was calculated as the turnover rate constant of the radioactivity removal. The FRR fell into one of two ranges: in anaesthetized rats FRR was 0.02-0.03 h-1, and in awake and freely moving rats FRR was 0.08-0.11 h-1. In awake rats, FRR was similar during day and night (spontaneous motor activity is four times higher during the night). Passive limb movements at 1 Hz in anaesthesia increased FRR in skin to that in awake rats, while FRR in skeletal muscle was unchanged. Immobilization resulted in FRR similar to that in anaesthesia. Interstitial albumin mass did not change during 6 h of anaesthesia. It is concluded that the observed FRR reflects steady state changes in albumin turnover. In the awake and freely moving rats at least 3/4 of the removal of albumin is by the lymphatics. Calculated lymph flow was 10 microliters g-1 h-1 and 40 microliters g-1 h-1 in skeletal muscle and skin respectively with corresponding figures during anaesthesia of 3 microliters g-1 h-1 and 10 microliters g-1 h-1 respectively.