Synthesis, transport, and secretion of plasma proteins by the livers of control and Streptococcus pneumoniae-infected rats

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Abstract
The synthesis, intracellular transport, and secretion of plasma proteins by the liver was studied in both control and Streptococcus pneumoniae-infected rats. Rats were injected with [3H]leucine; at various time intervals, the components of the intracellular secretory system were isolated. The isolation and partial characterization of rough microsomes, smooth microsomes, and Golgi from both control and infected animals are described. After infection, the specific activity of the label in the homogenate and in all isolated cell fractions was significantly increased. In both control and infected animals, the kinetics of labeling suggested that the secretory pathway of the newly synthesized protein was from the rough endoplasmic reticulum to the smooth endoplasmic reticulum to the Golgi and finally to the circulation. Even though infected animals synthesized, transported, and secreted significantly more plasma protein, infection did not significantly alter the secretion time (time between injection of isotope and appearance of labeled protein in the circulation). It is concluded that, after S. pneumoniae infection, the liver still maintains its capability to perform the basic functions of protein synthesis, intracellular transport, and secretion and that newly synthesized plasma protein follows the same intracellular pathway in both control and S. pneumoniae-infected rats.