Transcapillary extravasation rate of albumin in rat skeletal muscle. Effect of motor activity.

Transcapillary extravasation of albumin in hindlimb and neck skeletal muscle of rats was determined as extravascular plasma equivalent volumes (I-HSAev), 1-168 h after a single intravenous injection of radiolabelled human serum albumin (I-HSA). One experimental group was immobilized in pentobarbital anaesthesia for the first 8 h after injection of I-HSA. With longer extravasation periods, the rats then woke up and moved freely. In the other experimental group, injections were made in ether anaesthesia allowing the rats to move freely within 10 min after injection. One hour after injection, I-HSAev in the immobilized group averaged 1.5 10(-3) ml g-1 in neck and hindlimb muscle. In the mobile group, I-HSAev was two to three times higher than in the immobilized rats up to 12 h in both muscle groups (P less than 0.05). At 24 h and later I-HSAev was similar in mobile and immobile rats (P greater than 0.05). The I-HSAev increased up to 48 h, levelling off at about 0.06 and 0.08 ml g-1 in hindlimb and neck skeletal muscle, respectively. Corresponding interstitial albumin concentration, calculated from steady-state I-HSAev and interstitial fluid volume (51Cr-EDTA space), averaged 48% and 34% of plasma albumin concentration, respectively.