Lack of Secretion of Serum Protein by Transplanted Rat Hepatomas1

In addition to studies concerning the regulation of enzyme activity and synthesis in minimal deviation hepatomas (10, 15, 16), it is of interest to investigate how the production and secre tion of serum proteins is affected by the change of normal liver to a minimal deviation hepatoma. Morphologic studies of the ultrastructure of the tumor cell (especially of the endoplasmic reticulum-Golgi apparatus system) showed no histologie evidence of secretory activity in the fast-growing Morris hepatoma 3683 (1) whereas the appearance of granules containing large Golgi com plexes in the Morris hepatoma 5123 (11) and the Reuber hepa toma H35 (17) was interpreted as a sign of secretory activity (1, 4). The studies presented in this paper were undertaken to meas ure the amount of serum protein that might be secreted by the Morris 9121 and 5123 TC and the Reuber H35 TC. The pharmacodynamics and metabolism of an i.p.-adminis tered mixture of uniformly 14C-labeled leucine, lysine, and histidine and its oxidation to I4CU2was studied. The hepatomas oxidized about the same portion of the amino acids to 14CO¡ as did the liver; furthermore, the specific activity of the tumor pro tein was comparable to that of the liver. However, no secretion of 14C-labeledprotein from the tumor into the blood stream could be detected.