Abstract
The role of plasma free fatty acids (FFA) in the transport of fatty acids from host tissues to Ehrlich ascites carcinoma in mice was studied. [9,10-(3)H] Palmitate complexed to mouse serum (albumin) was injected either intraperitoneally or intravenously into unanesthetized tumor-bearing mice. The incorporation of radioactivity into tumor extracellular fluid FFA, tumor cell FFA, neutral lipid, phospholipid, water-soluble material in cells and fluid, plasma FFA, host carcass total lipid fatty acids, and water-soluble (i.e., nonlipid) material was measured. In addition, the quantity of fatty acid in each of the above lipid fractions was determined. The data were analyzed by multicompartmental analysis (SAAM) using a digital computer, and fractional rate constants of FA movement within and out of the host-tumor system were calculated. These rate constants and pool size measurements were used to estimate the corresponding fluxes. Although FFA in the tumor's extracellular fluid were replaced rapidly, almost none of the newly formed fluid FFA was derived from plasma FFA. Moreover, the transfer of FFA from the tumor extracellular fluid FFA to plasma FFA was virtually negligible. We suggest that the net amount of FFA required to replace the fluid FFA utilized for tumor energy and growth may be derived from direct transfer of FFA from host tissues to the ascitic fluid and that plasma FFA is not an intermediate in this transport process. The transport of FFA from the host to tumor cell lipids through the tumor extracellular fluid was about 26-fold greater than that required to account for net lipid accumulation during growth.
Highlights
The role of plasma free fatty acids (FFA) in the transport of fatty acids from host tissues to Ehrlich ascites carcinoma in mice was studied. [9,10-3H]Palmitate complexed to mouse serum was injected either intraperitoneally or intravenously into unanesthetized tumor-bearing mice
Because the transfer of FFA from the circulation to the peritoneal fluid was almost negligible (0.007 m o l e of FFA/min/40 g mouse compared with 1.51 pmoles of FFA/min/40 g mouse transferred to the host tissues), we considered the possibility that our observations were due to an artifact linked to the nature of the albumin-palmitate complex that was used [22]
Since plasma FFA complexed to albumin is known to be the primary intermediate in the transport of FA through the blood from the host’s fat depots to other tissues such as muscle and liver, one might assume [3] that plasma FFA is the major source of the FFA that continuously flow into the tumor’s interstitial fluid
Summary
The role of plasma free fatty acids (FFA) in the transport of fatty acids from host tissues to Ehrlich ascites carcinoma in mice was studied. [9,10-3H]Palmitate complexed to mouse serum (albumin) was injected either intraperitoneally or intravenously into unanesthetized tumor-bearing mice. A rapid incorporation of labeled fatty acids into the tumor cell lipid occurs in both of these circumstances; this need not indicate a net inward movement of FA, because the extent of simultaneous efflux of unlabeled FA from the tumor lipids is not known. In this connection it is known that the tumor cells are capable of releasing FFA at a significant rate under specified in vitro conditions [5]. 30 Quai de I’Ecole de MCdecine, 1211 GenCve, Switzerland
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