Synthesis and release of luteinizing hormone by rat anterior pituitary cells: effects of cytochalasins B and D.
We determined the role of microfilaments in regulating LH synthesis (translation or glycosylation) and release from cultured rat anterior pituitary cells under basal and GnRH-stimulated conditions. Cells were pretreated for 2 h with microfilament-disrupting drugs, cytochalasin B (CB; 2 and 20 microM) or cytochalasin D (CD; 1 and 10 microM). LH synthesis and release were measured after 4 h of incubation with or without 1 nM GnRH and drugs. LH translation and glycosylation were monitored by measuring the incorporation of [14C]alanine and [3H]glucosamine, respectively, into total (cell and medium) immunoprecipitable LH. Immunoreactive LH (IRLH) in medium and cells was measured by RIA. GnRH at 1 nM significantly (P less than 0.01) increased the release of IRLH and total [3H]LH (glycosylation), but had no effect on total [14C]LH (translation), uptake, or incorporation of precursors into total protein. Neither CB (2 and 20 microM) nor CD (10 microM) altered basal or GnRH-stimulated IRHL release. Neither drug altered basal medium concentrations of [3H]LH or [14C]LH. In contrast, both CB and CD reduced (P less than 0.01) GnRH-stimulated [3H]LH in the medium and total system (LH glycosylation). CB reduced (P less than 0.01) [3H]glucosamine uptake, total [3H]protein synthesis, and basal level of total [3H]LH, while CD had no effects on these parameters. Thus, CD exerted a more specific inhibitory effect on GnRH-stimulated LH glycosylation than CB. CB (2 and 20 microM) increased (P less than 0.01), while CD (10 microM) decreased (P less than 0.01) [14C]alanine uptake, total [14C]LH, and [14C]protein under both basal and GnRH-stimulated conditions. These results demonstrated that while the cytochalasins did not inhibit either basal or GnRH-stimulated IRLH release, they did inhibit GnRH-stimulated LH glycosylation, although the effect of CB was due partially to reduced [3H]glucosamine uptake. Integrity of microfilaments appears to be important for GnRH-enhanced LH glycosylation, but not for GnRH-enhanced LH release.
D008841:Actin Cytoskeleton / Q000502:physiology; D000818:Animals; D001692:Biological Transport; D003571:Cytochalasin B / Q000494:pharmacology*; D015638:Cytochalasin D; D003572:Cytochalasins / Q000494:pharmacology*; D005260:Female; D005944:Glucosamine / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000096:biosynthesis* / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects
D003572:Cytochalasins; D015638:Cytochalasin D; D007987:Gonadotropin-Releasing Hormone; D003571:Cytochalasin B; D007986:Luteinizing Hormone; D005944:Glucosamine