Prostaglandin E2 and parathyroid hormone: comparisons of their actions on the rabbit proximal tubule.

Recent studies demonstrated that prostaglandin E2 (PGE2) participates in the regulation of glomerular and distal tubular function. A functional role for PGE2 on the proximal tubule has only recently been explored. Thus, we reported that PGE2 antagonizes the phosphaturic effect of PTH in the dog, which suggests that PGE2 may influence the transport functions of the mammalian proximal tubule. The present studies were designed to examine the direct effect of parathyroid hormone (PTH) and PGE2 on the fluxes of fluid (Jv) and phosphate (Jl-b PO4) in the rabbit proximal convoluted and straight tubules (PCT and PST). The activation of adenylate cyclase by the two agents was also examined. Finally, the combined effects of PTH and PGE2 on Jv and Jl-b PO4 were also studied in the PST. In the PCT, PTH (1 microgram/ml) inhibited Jv by 31% (P less than 0.05) but did not alter Jl-b PO4. PGE2 (10(-5) M) failed to act on either Jv or Jl-b PO4. In this segment, PTH stimulated adenylate cyclase but PGE2 did not. In the PST, PTH (1 microgram/ml) inhibited Jv and Jl-b PO4 by 34 and 20%, respectively (P less than 0.01). PGE2 (10(-5) M) also inhibited Jv and Jl-b PO4, by 33 and 12%, respectively (P less than 0.02). In contrast, PGF2 alpha, a related prostanoid, failed to influence these transport parameters. In the PST, PTH activated adenylate cyclase but PGE2 failed to do so. When both PTH (1 microgram/ml) and PGE2 (10(-7) M) were present simultaneously, Jv and Jl-b PO4 were comparable to that seen during control collections.(ABSTRACT TRUNCATED AT 250 WORDS)