The Interstitial Water Space of Tumors.

components : (a) the extracellular fluids, which include blood, interstitial fluid, and lymph (if existing in the tumor) ; and (b) the extracellular solids, consisting mainly of connective tissue proteins and mucopolysaccharides of the ground and cement substances. The components of the extracellular compartment are arranged in a structure which can be described morphologically as a frame of collagen fibers and ground substances bathed in the inter stitial fluids. These fluids are subdivided into at least 2 compartments or spaces, the vascular and the interstitial space. The separation between these 2 spaces is main tained by the vascular wall, a structure formed by endo thelial cells and by the fibers and cells of the connective tissue. A tumor can therefore be considered a 3-compart ment system (5) in which the cells constitute Compart ment 1, the vessels Compartment 3, and the space between the cellular membranes and the vascular walls Compart ment 2. The aim of this investigation was to measure the vol ume of Compartment 2, the interstitial water space. The volume of this space was calculated by the difference between the vascular and the extracellular water spaces measured simultaneously in the same specimen. The vascular space was measured with high molecular weight as previously described (8) ; the extracellular water space was evaluated by the use of DNa, UC1, and D-manmtOl 1-'4C. MATERIAlS AND METHODS Animals and tumors.†" Rats of both sexes, weighing 150†" 200 gm, were used, and were fed Purina laboratory following transplanted tumors were studied : Walker car cinoma 256, fibrosarcoma 4956, hepatoma 5123, hepatoma 3683, and Novikoff hepatoma. More information about the animals and the tumors was reported previously (7). The interstitial fluid of the tumors (TIF) was sampled by means of a micropore chamber incorporated into the neo plastic tissue as previously described (6). Surgical proce dures were performed under ether anesthesia ; plasma was obtained from heparinized animals (0.5 mg heparin/100 gm rat). Experimental procedure.†" The markers were injected via the dorsal vein of a foot in a 0.5-mi solution.