Colloid osmotic pressure of the subcapsular interstitial fluid of rat kidneys during hydropenia and volume expansion.

Abstract

To determine the colloid osmotic pressure of subcapsular interstitial fluid in rat kidneys two different methods were used. Collection of subcapsular fluid with glass pipettes or implanted microcatheters and subsequent protein analysis resulted in a protein concentration of 1.8g%±0.6 and 2.0g%±0.8, respectively. Lymph protein concentration was not significantly different from that of subcapsular fluid samples. During extracellular volume expansion both subcapsular and lymph protein concentration fell to 0.42g%±0.23 and 0.7g%±0.5. Application of anin vivo oncometric method resulted in an effective oncotic pressure about twice that estimated from protein determinations. Using average values for intratubular and intracapillary oncotic and hydrostatic pressures a tubulo-interstitial net driving force of 20 mm Hg and an interstitial-capillary net driving force of 13 mm Hg is estimated in hydropenic animals. During volume expansion net transtubular pressure gradient is reduced to about 60–70% of control while the transcapillary gradient is virtually unchanged.