Calcium-dependent stimulation of renal medullary prostaglandin synthesis by furosemide.

The present study examined the actions of furosemide and other "loop" diuretics on immunoreactive prostaglandin E (iPGE) and [14C]arachidonate (AA) release in vitro in incubates of slices from rat and dog outer or inner medulla. The loop diuretics furosemide, ethacrynic acid, bumetanide and 3-benzylamino-4-phenylthio-5-sulfamoylbenzoic acid all significantly increased [14C]AA and iPGE release (1.5- to 4-fold) into the media of rat outer and inner medulla and dog outer medullary slice incubates. By contrast, equimolar concentrations of chlorothiazide and hydrochlorothiazide were without effects on these parameters. Stimulation of [14C]AA or iPGE by furosemide was abolished by exclusion of Ca++ from the incubation media or by addition of verapamil to complete media, but was not altered by exclusion of Na+. Ca++-free media or verapamil also abolished the increases in [14C]AA and iPGE induced by ionophore A23187. By contrast, these incubation conditions did not influence the iPGE responses to hypertonic mannitol or exogenous AA. The presence of Ca++-responsive acyl hydrolase activity was demonstrated in the microsomal fraction from rat outer medulla. However, this activity was not altered by addition of furosemide to the subcellular fraction in the presence or absence of Ca++. Thus, furosemide and other loop diuretics stimulate renal medullary iPGE synthesis in vitro, and may do so through Ca++-mediated or dependent enhancement of the release of AA.