Effect of Prostaglandins on the Water and Sodium Transport across the Urinary Bladder of the Toad
1976 Volume 18 Issue 12 Pages 757-768
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1976 Volume 18 Issue 12 Pages 757-768
This study was undertaken to clarify the mechanism of the effect of the prostaglandins on the water and sodium transport across the toad urinary bladder. 10-7M PGE1 alone did not induce any significant change in osmotic water flow. However, the same dosis of PGE1 inhibited the osmotic water flow responses induced by vasopressin and theophylline but not inhibited those by cyclic-AMP in the toad bladder. PGE1, PGF1α, PGA1, PGE2, PGF2α, PGA2, PGB1 and PGB2 were also observed to inhibit the vasopressin-induced osmotic water flow in the following order, PGE1>PGF1×>PGA1≥PGE2≥PGF2α>PGA2>PGB1>PGB2. 7.0×10-7M PGE1 markedly stimulated the short-circuit current, and this stimulation was further potentiated by theophylline. But little effect was observed by other prostaglandins, although at higher concentrations the short-circuit current was stimulated (PGE1>PGA1>PGE2>PGF1α). 10-6M to 10-4M PGE1 alone could enhance osmotic water flow. This response was potentiated by theophylline. Furthermore, the inhibitory effect of PGEI on the vasopressin-induced water flow was observed under both experimental conditions at low and high concentrations of PGE1. Thus, the effect of PGEI on the water and sodium transport may probably be caused by the action on the two different adenyl cyclases. Three different actions of PGE1 on the water and sodium transport were analysed by the doseresponse curves. The values of ED50 of PGE1 to inhibit water flow, to stimulate sodium transport and water flow, were 7.9×10-9M, 2.5×10-7M and 7.6×10-6M, respectively. The dose-response curve of the former was different from the latter two. This result suggested that two differeent adenylcyclase-systems would be present in the toad bladder. The following hypotheses were derived from the present findings. Two different adenylcyclase-systems are present in the toad bladder : i.e., one cyclic-AMP pool controls water flow and the other controls sodium transport. PGE1 would inhibit the former and stimulate the latter. The stimulation of water flow by PGE1 may be mediated by cyclic-AMP which would spill over from the cyclic-AMP pool responsible for the sodium transport to the pool responsible for the water flow.
