Prostaglandins as Mediators of Acidification in the Urinary Bladder of Bufo marinus

Experiments were performed to determine whether prostaglandins (PG) play a role in H⁺ and NH₄ ⁺ excretion in the urinary bladder of Bufo marinus. Ten paired hemibladders from normal toads were mounted in chambers. One was control and the other hemibladder received PGE 2 in the serosal medium (10^-5 M). H⁺ excretion was measured by change in pH in the mucosal fluid and reported in units of nmol (100 mg tissue)^-1 (min)^-1. NH₄ ⁺ excretion was measured colorimetrically and reported in the same units. The control group H⁺ excretion was 8.4 ± 1.67, while the experimental group was 16.3 ± 2.64 (P < 0.01). The NH₄ ⁺ excretion in the experimental and control group was not significantly different. Bladders from toads in a 48-hr NH₄ ⁺Cl acidosis (metabolic) did not demonstrate this response to PGE 2 (P > 0.30). Toads were put in metabolic acidosis by gavaging with 10 ml of 120 mM NH₄ ⁺Cl 3 × day for 2 days. In another experiment, we measured levels of PG in bladders from control (N) and animals placed in metabolic acidosis (MA). Bladders were removed from the respective toad, homogenized, extracted, and PG separated using high-pressure liquid chromatography and quantified against PG standards. The results are reported in ng (mg tissue)^-1. PGE 2 fraction in N was 1.09 ± 0.14 and in MA was 3.21 ± 0.63 (P < 0.01). PGF_1α, F_2α and I 2 were not significantly different in N and MA toads. Bladders were also removed from N and MA toads, and incubated in Ringer's solution containing [³H]arachidonic acid (0.2 μCi/ml) at 25°C for 2 hr. Bladders were then extracted for PG and the extracts separated by thin layer chromatography. PG were identified using standards and autoradiography, scraped from plates, and counted in a scintillation detector. The results are reported in cpm/mg tissue × hr ± SEM. In MA toads, PG6-keto-F_1α = 1964 ± 342, PGF_2α = 1016 ± 228, and PGE 2 = 904 ± 188; in N animals PG6-keto-F_1α = 625 ± 280, PGF_2α = 364 ± 85, and PGE 2 = 404 ± 104; (P < 0.01, <0.025, <0.05, respectively). We conclude that PGE 2 may be an important mediator of H⁺ excretion in toad urinary bladder and that endogenous PGE 2 levels are increased in response to MA.