Kinetics of Protein Synthesis and Release in the STH-Cell of the Mouse Anterior Pituitary as Revealed by Electron Microscopic Autoradiography of ³H-Amino Acids

Abstract

In order to investigate the kinetics of the synthesis and release of the secretory protein in the STH-secreting cell of the pituitary anterior lobe, studies were made using the electron microscopic autoradiography of ³H-amino acids. Each mouse received an intravenous injection of 2.8mCi of ³H-amino acids consisting of equal amounts of ³H-leucine, ³H-tyrosine, ³H-lysine, ³H-histidine and ³H-glycine. The animal was sacrificed at 3, 5, 15 and 30min, 1, 2, 4, 8 and 24hrs after the injection.
Although the whole silver grains are very few 3min after the injection, half of the grains are recognized over the r-ER (47.1%); the Golgi apparatus already shows a few grains (5.9%). Total silver grains over the STH-cell increase in number with the lapse of time; the ratio of the grain number over the r-ER to the total grains over the whole cell decreases gradually, while the ratio of the grain number over the Golgi apparatus increases to reach a peak about 30min after the injection (40.1%) and then decreases gradually.
The ratio of the number of labelled granules to that of total granules increases slowly until 24hrs after the injection (3min:0%, 5min:0.8%, 30min:3.9%, 2hrs:5.0%, 8hrs: 8.0%, 24hrs:12.3%).
It is concluded that the turnover in synthesis and release of exportable protein in the mouse STH-cell is very slow as compared with that of the thyroid and parathyroid cell.