Differential Actions of Arachidonic Acid and Melittin on Luteinizing Hormone Release and Synthesis

Abstract

We studied the actions of arachidonic acid (AA) on luteinizing hormone (LH) release versus synthesis (translation or glycosylation) by cultured rat anterior pituitary cells. Monolayer cells were incubated for 3-4 h with secretagogues (AA, melittin, gonadotropin-releasing hormone; GnRH) which either increase endogenous AA levels or release AA. LH translation and glycosylation were monitored by measuring the incorporation of [14C]alanine and [3H]glucosamine, respectively, into total (cell plus medium) immunoprecipitable LH. Immunoreactive (IR) LH was measured by radioimmunoassay. Nonlytic doses of AA increased (p less than 0.01) IR-LH release without increasing total [3H]glucosamine-LH, [14C]alanine-LH, or [3H]glucosamine-protein. AA either had no effect or slightly increased (p less than 0.05) [3H]glucosamine uptake, but decreased (p less than 0.01) [14C]alanine uptake and incorporation into total [14C]alanine protein. AA at 250 microM lysed cells, thus increasing medium IR-LH and decreasing (p less than 0.01) [3H]glucosamine and [14C]alanine uptake and incorporation into total LH and protein. Melittin, which releases AA by activating phospholipase A2 (245 and 490 nM), increased medium IR-LH (p less than 0.01) without affecting any other parameter measured. GnRH at 1 nM enhanced (p less than 0.01) both LH (IR-LH, [3H]glucosamine-LH and [14C]alanine-LH) release and total [3H]glucosamine-LH, but had no effect on total [14C]alanine-LH. In summary, AA and melittin at doses which stimulated LH release did not stimulate either LH glycosylation or translation. This suggests that increased LH release by nonspecific secretagogues is not necessarily accompanied by increased LH glycosylation or translation.