EFFECT OF PROSTAGLANDIN-E2 ON AGONIST-STIMULATED CAMP ACCUMULATION IN THE DISTAL CONVOLUTED TUBULE ISOLATED FROM THE RABBIT KIDNEY

The effects of calcitonin, vasoactive intestinal peptide (VIP), parathyroid hormone (PTH) and isoprenaline on intracellular cAMP accumulation were determined in the distal tubule (DCT) microdissected from collagenase-treated rabbit kidney. In DCTb (the initial ''bright'' portion) calcitonin (10 ng/ml) elicited a highly reproducible response 203.7 +/- 19.1 fmol cAMP mm-1 4 min-1 (SE,N = 13) whereas VIP-induced cAMP accumulation was less and more variable from one experiment to another (1 muM, 97.2 +/- 17.8 fmol mm-1 4 min-1, SE, N= 12). When used in combination, these two agonists were non-additive, indicating stimulation of a single pool of cAMP in DCTb. In DCTg, (''granular'') which consists of at least two cell types, PTH (100 nM) elicited a marked, reproducible accumulation of cAMP (154.3 +/27. Of mol mm-1 4 min-1; SE, N = 5). Isoprenaline (1 muM) and VIP (1 muM) induced much smaller increases in cAMP levels 20.9 +/- 2.7 and 29.4 +/- 4.1 fmol mm-1 4 min-1 (SE, N = 5) respectively, and, when used in combination, were non-additive, demonstrating that VIP and isoprenaline are active on the same cell type. In DCTb, prostaglandin E2 (PGE2) inhibited both calcitonin- and VIP-stimulated cAMP accumulation (calcitonin 57.8 +/- 2.7% inhibition, SE, N = 16; VIP, 80.6 +/- 2.1 % inhibition, SE, N = 5). The EC50 values for calcitonin were 1.21 +/- 0.33 ng/ml and 1.83 +/- 0.25 ng/ml (SD, N = 3) in the absence and presence of PGE2 (300 nM) respectively with an IC50 for PGE2 of 26.3 +/- 6.3 nM (SE, N = 4). In contrast, no effects of PGE2 were seen in DCTg vis a vis PTH, isoprenaline or VIP. The percentage inhibition of calcitonin-stimulated cAMP accumulation by PGE2 was of the same order in the presence of isobutylmethylxanthine (an inhibitor of all types of phosphodiesterase), Ro 20-1724 (inhibitor of low-K(m) cAMP-specific phosphodiesterase) or in the absence of inhibitor. Preincubation of DCTb with pertussis toxin for up to 8 h in different experimental conditions did not relieve the inhibition by PGE2. Protein kinase C activation by phorbol ester did not attenuate calcitonin responses. These data demonstrate that the inhibition by PGE2 of cAMP production is restricted to the initial portion (DCTb) of the distal convoluted tubule and is effective on both calcitonin and VIP responses. When tested in the presence of Ro 20-1724, ionomycin, A1-adenosine, alpha2-adrenergic and muscarinic agonists were without effect on calcitonin- and PTH-stimulated cAMP accumulation in DCTb and DCTg respectively.