Regulation of urea permeability in frog urinary bladder by prostaglandin E2

The present study was performed to investigate the role of prostaglandin E-2 (PGE(2)) in the regulation of urea transport in the frog urinary bladder, which is known to occur via a specialized arginine-vasotocin(AVT-) regulated urea transporter. The bladders isolated from Rana temporaria L. were filled with amphibian Ringer solution containing 370 Bq/ml (0.01 muCi/ml) of [C-14]urea, and urea permeability (P-urea) was determined by sampling the serosal and mucosal bathing medium at 30-min intervals for measurement of radioactivity. It was found that, from the serosal side, PGE(2) (10 nM to 1 muM) caused a dose-dependent increase in P-urea [(7.2 +/- 1.8) X 10(-6) cm/s in the presence of 0.5 muM PGE2 versus (1.0 +/- 0.2) X 10(-6) cm/s in control, n = 9, P < 0.001]. As in response to AVT, the PGE(2)-induced P-urea reached a maximum in 1-1.5 h after the agonist was added. The stimulatory effects of PGE2 and AVT applied together 7 were not additive. PGE2-induced urea transport was strongly inhibited by nearly 75% in the presence of mucosal or serosal phloretin (10(-4) M). P-urea was enhanced up to (4.7 +/- 0.8) X 10(-6) cm/s (n = 12, P < 0.001) by butaprost (5 X 10(-6) M), a selective EP2 receptor agonist, while sulprostone (EP1/EP3 agonist, 10-6 M) caused no changes in P-urea, PGE(2) dose-dependently increased the content of cAMP in mucosal epithelial cells (control: 18.0 +/- 1.8; 10(-6) M PGE(2): 74.2 +/- 9.3 pmol cAMP/mg protein per 30 rnin, n=7, P < 0.001). Phorbol esters did not alter PGE(2)-induced P-urea whereas H-89 (20 muM), a protein kinase A inhibitor, reduced it by 45.1 +/- 9.9% (n = 5, P < 0.05). PGE(2) did not change the AVT-stimulated P-urea measured in isoosmotic conditions, but inhibited the last one in the presence of a serosa-to-mucosa osmotic gradient. The data obtained show that, in the frog urinary bladder, PGE2 is a stimulator of phloretin-inhibitable urea transport. Its effect seems to be mediated by EP2 receptor-coupled generation of intracellular cAMP.