Protein synthesis in the pancreas of the rat after stimulation of secretion.

Abstract

Rats were starved for 48 hrs and stimulated to secrete by means of pilocarpine. The rate of synthesis of protein was determined both biochemically and autoradiographically by the assessment of leucine-3H incorporation during 10 min after its administration at various intervals (up to 7 hrs) after the pilocarpine stimulation. Care was taken to assess the incorporation with reference to the number of cells present, not to the total dry matter content nor to the protein content, as the latter tend to vary with the physiological state of the organ. Depletion of a pancreas filled with zymogen granules by means of pilocarpine gives rise to a transitory decrease in its rate of protein synthesis. After 1 hr the rate of synthesis reverts to the value found in fasting, unstimulated rats. Studies of pancreas slices taken from the rats after killing show that the in vitro synthetic capacity (leucine-14C) of the gland is unaffected by either fasting or stimulation. Peri-insular acini do not lose their zymogen granules upon pilocarpine stimulation as do the other acini. Yet, the rate of protein synthesis in both types of acini follows the same course after fasting and subsequent stimulation. Protein synthesized during fasting is largely lost from the gland during the next 24 hrs of continued fasting, either through catabolism or secretion. The results are discussed with a view on conflicting reports in the literature on the possibility of enhancing the rate of protein synthesis in the pancreas by stimulation of the secretion. A concept is given of a secretory cycle combined with a continuous protein synthesis at a constant rate in the cells of the rat pancreas, the cycle being divided into four phases.