Knepel W, Gerhards C. Stimulation by melittin of adrenocorticotropin and beta-endorphin release from rat adenohypophysis in vitro.
PROSTAGLANDINS 1987;
33:479-90. [PMID:
3033749 DOI:
10.1016/0090-6980(87)90027-x]
[Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effect of melittin on the release of adrenocorticotropin (ACTH) and beta-endorphin from the corticotropic cells of the rat adenohypophysis was examined in vitro. Anterior pituitary quarters were perifused or incubated in vitro and ACTH- (ACTH-IR) or beta-endorphin-like immunoreactivity (beta-End-IR) in the medium was measured by radioimmunoassays. Melittin stimulated ACTH-IR and beta-End-IR release. This effect was rapid in onset, reversible, and concentration-related (50-5000 ng/ml) and depended on the presence of calcium ions in the incubation medium. Melittin also elevated the tissue content of unesterified 3H-arachidonic acid that had previously been incorporated into lipids. Purported phospholipase A2 inhibitors, mepacrine (up to 1 mM), dexamethasone (0.5 mg/kg in vivo, 50 nM in vitro), or p-bromophenacylbromide (100 microM), did not decrease the melittin (500 ng/ml) - induced beta-End-IR release, although mepacrine and dexamethasone may have inhibited phospholipase A2 activity as indicated by an inhibition of melittin-evoked prostaglandin E2 formation. After stimulation by melittin (500 ng/ml), beta-End-IR release was not affected by the cyclooxygenase inhibitor indomethacin (up to 140 microM), whereas nordihydroguaiaretic acid (100 microM), a lipoxygenase inhibitor, or BW755C (250 microM), an inhibitor of both cyclooxygenase and lipoxygenase, abolished melittin-induced hormone secretion. We conclude that melittin generates a signal in the corticotropic cells of the rat adenohypophysis which induces hormone secretion by exocytosis. This signal may be unrelated to the activation by melittin of phospholipase A2.
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