Effect of melittin on renin and prostaglandin E2 release from rat renal cortical slices

1. The present experiments were designed to determine the effect of melittin on renin secretion. Melittin is a polypeptide component of bee venom which stimulates phospholipase A2 activity, thereby increasing arachidonic acid release and prostaglandin (PG) synthesis, and which inhibits protein kinase C activity. Either of these actions might be expected to stimulate renin secretion, since renin secretion is stimulated by arachidonic acid and by several PGs, and since renin secretion is inhibited by several activators of protein kinase C. 2. In rat renin cortical slices incubated at 37 degrees C in a buffered and oxygenated physiological saline solution, 0.1-10 microM-melittin produced a concentration-dependent stimulation of both prostaglandin E2 (PGE2) synthesis and renin secretion. However, melittin-stimulated renin secretion is independent of melittin-stimulated phospholipase A2 activity, arachidonic acid release, and PG synthesis, since 20 microM-quinacrine (a phospholipase A2 antagonist) and 50 microM-meclofenamate (a cyclooxygenase antagonist) antagonized basal and melittin-stimulated PGE2 synthesis but had no effects on basal or melittin-stimulated renin secretion. 3. Furthermore, melittin-stimulated renin secretion is not produced by inhibition of protein kinase C, since an activator of protein kinase C (12-O-tetradecanoylphorbol 13-acetate, TPA), enhanced rather than antagonized melittin-stimulated renin secretion. Ouabain partially antagonized, but did not completely block, melittin-stimulated renin secretion. 4. Thus, melittin-stimulated phospholipase A2 activity probably accounts for stimulated PGE2 production, but not for stimulated renin secretion. The mechanism of melittin-stimulated renin secretion is unclear; an effect on protein kinase C does not appear to be involved, and in contrast to the stimulatory effects of a variety of other substances, melittin-stimulated renin secretion is only partially antagonized by ouabain.