Gonadectomy induces laminin biosynthesis and basement membrane assembly in anterior pituitary glands of adult rats

Role of laminin on prolactin and gonadotrophin release from anterior pituitaries of male rats

The effect of rat laminin on the release of prolactin (PRL), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from anterior pituitaries of adult male rats was studied in vitro. Laminin had a bidirectional effect on basal release of PRL, being stimulatory at 10(-12)M and inhibitory at 10(-9) and 10(-8)M. LH release was only stimulated by the 10(-12)M concentration and no changes in FSH release were observed. Laminin did not modify the stimulatory action of thyrotropin-releasing hormone (TRH) nor luteinizing hormone releasing hormone (LHRH), but the response of FSH to LHRH was inhibited with a maximal effect at 10(-10)M. To assess its physiological role, the effect of a rabbit antibody to laminin on the release of PRL, LH and FSH was also studied. IgG anti-laminin at 2 x 10(-7)M had a highly significant stimulatory effect on PRL release after 3 and 5 hr of incubation, as compared to IgG from normal rabbit serum and medium alone used as controls. No changes on the release of LH and FSH were detected. These results suggest that laminin plays a physiologically significant inhibitory role on PRL release at the pituitary level in vitro.

Immunoelectron microscopic localization of laminin in rat ovarian follicles

We studied the immunohistochemical and ultrastructural distribution of laminin in ovaries of immature and mature rats. When sections from 1-8-week-old rat ovaries were labeled directly with conjugates of affinity purified anti-laminin IgG-horseradish peroxidase (HRP), the antibodies bound to all ovarian basement membranes including those surrounding follicles in different stages of maturation. In addition, intracellular labeling was seen in granulosa and theca cells of follicles undergoing rapid development (preantral and antral stages) and in basement membrane-like structures of the Call-Exner bodies. Intracellular laminin was generally not detected, however, in any cells of primordial or atretic follicles. Tissue processed for immunoelectron microscopy 1 hour after the intravenous injection of anti-laminin IgG-HRP showed binding of antibody in linear patterns along endothelial and follicular epithelial basement membranes. Discontinuous strands of laminin-positive, extracellular matrices were also seen between theca cells of all follicles. In addition, injected anti-laminin IgG labeled perisinusoidal basement membranes located within corpora luteae and patches of basement membrane material between granulosa lutein cells. When ovaries were examined 5 d after the intravenous injections of anti-laminin IgG-HRP, uneven or segmented labeling was found in subepithelial basement membranes surrounding developing follicles. Our results therefore indicate that granulosa and theca cells participate directly in basement membrane laminin biosynthesis and suggest that this new laminin is spliced into existing basement membranes during follicular growth.

Reconstituted basement membrane influences prolactin, LH, and FSH secretion from adult and fetal adenohypophyseal cells in vitro

These investigations tested the hypothesis that secretion of prolactin (PRL), LH, and FSH in vitro is influenced by the substratum on which adult or fetal adenohypophyseal cells are cultured. Adenohypophyses were removed from adult male Golden Syrian hamsters and from fetal hamsters on day 16 of gestation. The glands were dissociated and cultured in a 1:1 mixture of Dulbecco's Modified Eagle's Medium (DMEM) and Ham's F-12 medium containing 10% fetal bovine serum (FBS), 25 mM Hepes, and antibiotics. The cells were cultured on three substrata: glass, laminin, and the reconstituted basement membrane of the Engelbreth-Holm-Swarm (EHS) tumor (Matrigel). Medium was collected and replaced every 48 h for 14-22 days. Concentrations of PRL, LH, and FSH in medium were measured by RIA. The substratum influenced hormone secretion. PRL concentrations were elevated in cultures of adult cells on Matrigel in each of four experiments. Adenohypophyseal cells on Matrigel maintained a rounded shape longer than cells on glass or laminin. In studies using fetal adenohypophyseal cells, PRL concentrations were elevated significantly in medium from cultures on Matrigel at and after 2 days as were concentrations of LH and FSH after 6 days. Additional experiments showed that the higher PRL concentrations in medium surrounding adult cells plated on Matrigel were not due to the release of soluble factors from Matrigel, differential cell attachment on Matrigel, the differential presence of adenohypophyseal fibroblasts, nor differential rates of cell proliferation. The results show that Matrigel maintains the secretion of PRL from adult adenohypophyseal cells in vitro more effectively than glass or laminin substrata and support the hypothesis that cell-matrix interactions mediate the observed differences. The results also show that in long-term cultures (14-22 days), fetal adenohypophyseal cells secrete significantly more PRL, LH, and FSH on Matrigel than they secrete when cultured on glass or laminin. Thus, Matrigel influences the function and possibly the maturation of adenohypophyseal cells in vitro. Furthermore, although laminin is the most abundant component in Matrigel, the effects of Matrigel on lactotrophs and gonadotrophs in vitro are probably not attributable solely to its laminin content.

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.

Development of kidney tubular basement membranes

Although some progress has been made in recent years, there are truly large gaps in our basic knowledge on how the TBM is assembled during development. Some of the new evidence presented here indicates that both the tubular epithelium and interstitial fibroblasts participate in TBM protein biosynthesis during nephrogenesis. In addition, newly assembled segments of TBM are spliced or inserted into existing TBM during tubule expansion and elongation. A similar splicing mechanism has been described previously in the GBM, endocrine organs, and intestinal villi, and this mechanism therefore probably represents a fundamental process of basement membrane formation. A major unresolved question at present, however, is how this mechanism operates at the molecular level. Does the newly formed basement membrane contain identical components as that already present? Since an enzymatic process is likely occurring in the insertion of new matrix into old, which enzymes are involved? What is the cellular origin of these enzymes and which matrix component(s) is their substrate? Even more fundamental yet unanswered questions have to do with the mechanisms of epithelial induction, basement membrane gene activation, and tubular morphogenesis. Once the basement membrane is fully formed at the completion of nephrogenesis, what controls basement membrane turnover and how does this operate? Clearly, much additional research is necessary to address these questions. This work is needed, however, before we can fully understand the important roles basement membranes play in normal development as well as in disease.