Compliance of the interstitial space in rats. III. Contribution of skin and skeletal muscle interstitial fluid volume to changes in total extracellular fluid volume.

The contribution to the extracellular fluid volume (ECV) from plasma volume (PV) and the total interstitial volumes contained in skin ( IFVS ) and skeletal muscle ( IFVM ) has been studied in rats over a wide range of overhydration and dehydration. ECV was measured as the two-hour distribution space for 51Cr-EDTA after nephrectomy while PV was measured with radiolabelled albumin or erythrocytes. Total interstitial volumes in skin and skeletal muscle were calculated from measurement of local interstitial volumes and the amount of skin and skeletal muscle in the rat. In control conditions ECV was on average 24.12 ml/100 g body weight. PV was 11.0% of ECV in control while IFVS and IFVM was 28.1% and 19.0% respectively. In dehydration the change in PV was 13.3% of the change in ECV, while the change in IFVS and IFVM was 30.0% and 21.0% of the change in ECV respectively. In overhydration (ECV on average 33.76 ml/100 g rat) the changes in PV, IFVS and IFVM were 7.5%, 22.1% and 17.2% of the change in ECV respectively. The regression coefficients describing the change between ECV and IFVS and IFVM were not significantly different in overhydration and dehydration while the regression coefficient between ECV and PV in overhydration was significantly less than the regression coefficient in dehydration. Thus, the fraction of ECV contained in skin and skeletal muscle is similar over the range of hydration studied. The fraction of ECV located in plasma is similar in control and dehydration, while in overhydration less of ECV is localized in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)