Increase in the rough endoplasmic reticulum in capillary endothelial cells and pericytes in hyperplastic rat thyroid glands.

Observatios were made on the rough endoplasmic reticulum (RER) of the blood capillary endothelium, pericytes, and lymphatic endothelium in the course of studies of changes occurring in the thryoid gland during the development of thyroid hyperplasia. To induce the hyperplasia, Fischer rats were fed a goitrogen (thiouracil) an a low iodine diet for various time intervals from 3-100 days. Thyroid glands were fixed by perfusion with glutaryldehyde and embedded in Epon. A noticeable increase in the RER in the capillary endothelium was seen by 3 days. This increase was very pronounced by 7 days and persisted in many cells at 100 days. The RER response was also pronounced in pericytes. In the lymphatic endothelium, however, the increase in RER was barely perceptible. These results suggest that capillary endothelium and pericytes have protein synthetic and secretory functions of an unknown nature that become strongly activated in stimulated thyroid glands.