To study the effects of changed synthesis on intracellular transport of secretory
proteins, an
acute phase response was induced in rats. The synthesis and secretion of
haptoglobin,
complement C3,
transferrin and
albumin were then investigated by pulse labeling with [3H]
leucine. Maximal increase in the syntheses of the positive
acute phase proteins was observed after 24 h, amounting to an increase of nine, three and twofold for
haptoglobin, C3 and
transferrin, respectively. The synthesis of
albumin decreased to a minimum after 48 h, reaching approximately one fourth of normal synthesis. The time courses for transit through rough endoplasmic reticulum and for secretion were determined after 36 h, and were found to be roughly unchanged for all four
proteins despite the different changes in synthesis. The fraction of
haptoglobin associated with the microsomal membrane was reduced during the
acute phase response, but there was no significant change in membrane association as a function of time after labeling with [3H]
leucine. It is concluded that the altered
protein synthesis during an
acute phase response in vivo has little effect on the time course of secretion of the
proteins studied. Furthermore, the basal mechanisms for intracellular transport appear relatively unchanged during this condition.