ENDOGENOUSLY PRODUCED PROSTANOIDS STIMULATE CALCIUM REABSORPTION IN THE RABBIT CORTICAL COLLECTING SYSTEM

1. The influence of endogenously produced prostanoids on active transe pithelial Ca2+ transport and cAMP formation was investigated in immuno dissected rabbit kidney connecting and cortical collecting tubule cell s grown to confluency on permeable supports. 2. The cyclo-oxygenase in hibitor indomethacin dose-dependently (IC50 = 18 nM) reduced the net a pical-to-basolateral Ca2+ transport by 57%. Inhibition was reversed in medium obtained from monolayers incubated in the absence of indometha cin. 3. HPLC analysis following incubation with C-14-labelled arachido nic acid revealed the presence of a wide variety of radiolabelled pros tanoids in both the apical and basolateral media. These findings are c ompatible with the endogenous production and subsequent release of sti mulatory prostanoids. 4. The inhibitory action of indomethacin was rev ersed by the addition of the prostanoids PGE(1), PGE(2) and PGA(2), bu t not PGD(2), PGF(2 alpha), the stable PGI(2) analogue cicaprost or th e thromboxane A(2) mimetic U-46619. PGE(2) stimulated transepithelial Ca2+ transport dose dependently (EC(50) = 3 nM), irrespective of the c ompartment to which it was added. The stimulatory effect of PGE(2) was paralleled by increased cAMP formation, suggesting the apical and bas olateral presence of stimulatory prostanoid receptors EP(2) and/or EP( 4). 5. Sulprostone, an analogue selective for EP(1) and EP(3) receptor s, inhibited transepithelial Ca2+ transport in indomethacin-treated mo nolayers only when applied basolaterally, suggesting the exclusive pre sence of inhibitory EP receptors on the basolateral membrane. 6. The p ercentage by which parathyroid hormone and arginine vasopressin increa sed both transepithelial Ca2+ transport and cAMP formation mras dramat ically increased in indomethacin-inhibited cells as compared with cont rol cells, demonstrating that indomethacin unmasks the actions of thes e hormones to their full extent.