Adrenomedullin is a potent vasodilatory peptide that increases cAMP in a number of different systems including rat mesangial cells. Since mesangial cells play a significant role in glomerular matrix production, we evaluated the effects and molecular mechanisms of adrenomedullin action on hyaluronic acid release, an important extracellular matrix component. Adrenomedullin increased hyaluronic acid release in mesangial cells in a concentration-dependent manner. Forskolin, an adenylate cyclase activator, and dibutyryl-cAMP, a cell permeable cAMP analog, also increased hyaluronic acid release significantly. Adrenomedullin-stimulated hyaluronic acid release was inhibited by the adrenomedullin receptor antagonist, adrenomedullin-(22-52). Inhibition of protein kinase A with H89 [[N-[2-(( p-Bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, hydrochloride)]], a potent protein kinase A inhibitor did not affect adrenomedullin-stimulated hyaluronic acid release; however, H89 [[N-[2-(( p-Bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, hydrochloride]] inhibited forskolin- and dibutyryl-cAMP-induced hyaluronic acid production. In addition, SB203580 [[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-im idazole), a P38 mitogen-activated protein kinase (P38 MAPK) inhibitor attenuated adrenomedullin-, forskolin-, and dibutyryl-cAMP-stimulated hyaluronic acid release. Hyaluronic acid release induced by adrenomedullin, forskolin and dbcAMP was also inhibited by wortmannin [[1S-(1alpha, 6balpha, 9abeta, 11alpha, 11bbeta)]-11-(Acetyloxy)-1, 6b, 7, 8, 9a, 10, 11, 11b-octahydro-1-(methoxymethyl)-9a, 11b-dimethyl-3H-furo[4, 3, 2-de]indeno[4, 5-h]-2-benzopyran-3, 6, 9-trione]. We conclude that adrenomedullin, forskolin and dbcAMP cause an increase in hyaluronic acid release in rat mesangial cells through a pathway that involves activation of wortmannin-sensitive kinase and P38 MAPK. Although cAMP stimulation and protein kinase A activation can induce hyaluronic acid release. adrenomedullin-stimulated hyaluronic acid release appears to be independent of protein kinase A activation. These data provide the first demonstration of the involvement of P38 MAPK- and wortmannin-sensitive kinase pathways in the stimulation of hyaluronic acid production by rat mesangial cells.