ANGIOTENSINOGEN, PRORENIN, AND RENIN ARE CO-LOCALIZED IN THE SECRETORY GRANULES OF ALL GLANDULAR CELLS OF THE RAT ANTERIOR-PITUITARY - AN IMMUNOULTRASTRUCTURAL STUDY

In addition to the circulating renin-angiotensin system (RAS), a local system has been postulated in the anterior pituitary because immunode tection of its components in various mammalian species. However, diffe rent cell types appear to be involved in different species, and there is no general consensus on the subcellular localization of prorenin, r enin and angiotensinogen. In this ultrastructural study, we investigat ed and quantified the presence of these components using double or tri ple immunogold labeling methods, in all the immunologically identified glandular cell types of the rat anterior pituitary. In contrast to pr evious reports, all these components were identified not only in lacto tropes and gonadotropes but also in somatotropes, corticotropes, and t hyrotropes. The highest levels were detected in lactotropes and gonado tropes, and renin gave the greatest signal. Angiotensinogen, prorenin, and renin were co-localized in the secretory granules of all rat pitu itary glandular cell types. The simultaneous detection of the substrat e (angiotensinogen) and both its specific cleavage enzyme and its proe nzyme within the same granule suggests intragranular processing of thi s component. Moreover, the localization of these three constituents in the secretory granules also suggests that, in the rat anterior pituit ary, they follow the regulated secretory pathway.