LOCALIZATION OF PHOSPHATASE ACTIVITIES IN THE RAT ANTERIOR PITUITARY GLAND

Abstract

All five known secretory cell types of the rat anterior pituitary gland display nucleoside diphosphatase (NDPase) activity throughout the endoplasmic reticulum (ER), including the nuclear envelope but not the specialized region of ER at the inner aspect of the Golgi apparatus known as GERL. The functions of the ER diphosphatase are currently unknown. However, speculations concerning its association with glucuronyl transferase may focus on the metabolic roles of the ER in pituitary cells other than those directly related to secretory protein transport. The gonadotrophs have been studied for thiamine pyrophosphatase and acid phosphatase activities as well as NDPase activity. The results suggest that the secretory granules of gonadotrophs arise from GERL and not from the inner element of the Golgi apparatus. The innermost Golgi element of this cell type shows NDPase and thiamine pyrophosphatase activities and appears to be composed, in part at least, of anastomosing tubules. Nucleoside phosphatase activity is also present at the surfaces of all five secretory cell types and between the cells and adjacent blood capillaries.