DISPARATE HYDRATION OF ADIPOSE AND LEAN TISSUE REQUIRE A NEW MODEL FOR BODY-WATER DISTRIBUTION IN MAN

[A new experimental look at the water phase of adipose tissue was given in relation to obesity as a disease state.] The intracellular and extracellular fluid spaces in adipose tissue were determined by 3H2O, 82Br-, and 35SO4 = uptake and by appropriate chemical methods in surgical biopsy material from 16 patients undergoing elective laparatomy. Total water space for adipose tissue was 14 .+-. 1.4%; extracellular component was 11 .+-. 1.1% in mesenteric and subcutaneous depots. Use of these adipose tissue hydration constants, combined with measurements of total body water (TBW), extracellular water (ECW), total body K and experimentally derived age-specific constants for lean body K content permits development of a 4 compartment model for body water which considers intracellular and extracellular components separately for adipose (AT) and adipose-free (AFM) tissue masses. This model has the form TBW = 0.14 (AT) + x(AFM), and ECW = 0.11 (AT) + y(AFM) where x is the total hydration and y the extracellular hydration of the adipose-free mass. The equations can be solved for the ECW and ICW of the adipose-free mass, defined by its K content. In 4 normal subjects, x was measured as 0.80 .+-. 0.032, and y as 0.24 .+-. 0.017. The adipose free mass, compared with adipose tissue, has approximately 6 times the total water and twice the extracellular water content per unit weight.