Immunolocalization of laminin, heparan-sulfate proteoglycan, entactin, and type IV collagen in the rat anterior pituitary. I. An in vivo study.

The distribution of three components of basement membranes (BM): heparan-sulfate proteoglycan (HSPG), entactin (ENT), and type IV collagen (Coll. IV), was studied in the adult rat anterior pituitary and compared to the distribution of laminin (LAM) described in an earlier report (Vila-Porcile et al., 1987, J. Histochem. Cytochem., 35, 287). Several immunocytochemical methods were applied at both light and electron microscope levels. The three components were detected in all the pituitary BM and in endothelial and perivascular connective cells, as previously observed for LAM. In contrast to the prominent labeling previously observed for LAM within epithelial cells, however, only a faint immunoreaction could be detected for the other components, with nonetheless a discrete signal for Coll. IV. These findings indicate that 1) the four studied components are present in all the BM of the rat anterior pituitary; 2) pituitary endocrine cells contain LAM, and to a lesser extent Coll. IV, and thus could participate to the elaboration of the BM; and 3) the presence of the four components in non-epithelial cells also suggests their cooperation in BM building. The questions of the turnover and intracellular pathways of each of these components were addressed but remain unanswered.