Synthesis and Release of Luteinizing Hormone by Rat Anterior Pituitary Cells: Effects of Cytochalasins B and D*

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Abstract
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 .mu.M) or cytochalasin D (CD; 1 and 10 .mu.M). 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 < 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 .mu.M) nor CD (10 .mu.M) 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 < 0.01) GnRH-stimulated [3H]LH in the medium and total system (LH glycosylation). CB reduced (P < 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 .mu.M) increased (P < 0.01), while CD (10 .mu.M) decreased (P < 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 the 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.