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 2.8 mCi 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 30 min, 1, 2, 4, 8 and 24 hrs after the injection. Although the whole silver grains are very few 3 min 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 30 min 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 24 hrs after the injection (3 min: 0%, 5 min: 0.8%, 30 min: 3.9%, 2 hrs: 5.0%, 8 hrs: 8.0%, 24 hrs: 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.