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

Abstract

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 PGE2 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 less than 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 PGE2 (P greater than 0.30). Toads were put in metabolic acidosis by gavaging with 10 ml of 120 mM NH4+Cl 3 x 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. PGE2 fraction in N was 1.09 +/- 0.14 and in MA was 3.21 +/- 0.63 (P less than 0.01). PGF1 alpha, F2 alpha and I2 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 microCi/ml) at 25 degrees 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 x hr +/- SEM. In MA toads, PG6-keto-F1 alpha = 1964 +/- 342, PGF2 alpha = 1016 +/- 228, and PGE2 = 904 +/- 188; in N animals PG6-keto-F1 alpha = 625 +/- 280, PGF2 alpha = 364 +/- 85, and PGE2 = 404 +/- 104; (P less than 0.01, less than 0.025, less than 0.05, respectively). We conclude that PGE2 may be an important mediator of H+ excretion in toad urinary bladder and that endogenous PGE2 levels are increased in response to MA.

Mechanism of acid-induced bone resorption

“…In both toad bladder [106,107] and rat kidney [108], prostaglandin E 2 levels have been shown to increase in response to chronic metabolic acidosis, leading to enhanced proton excretion rates. The acidosis-induced inhibition of the hydroosmotic response to vasopressin in the toad bladder is also apparently mediated by increased prostaglandin E 2 synthesis.…”

Phospholipids and Electrolyte Transport

“…These structurally different compounds produced similar effects whereas the inactive epimer of phorbol 12-myristate 13-acetate was without an effect. In toad urinary bladder, however, enhanced acidification was seen with the nonphorbol PKC activator mezerein (70). A summary of the effects of activating PKC on ion transport processes is presented in Table 111.…”

Metabolic, but not respiratory, acidosis increases bone PGE2levels and calcium release

“…In nonosseus cells, metabolic acidosis increases the levels of prostaglandins (1,34,35,41). In both toad bladder (34,35) and rat kidney (41), PGE 2 levels have been shown to increase in response to metabolic acidosis.…”

“…In the brains of newborn pigs, acidosis increases the level of prostaglandins that are associated with vasodilatation (1). An increase in prostaglandin levels by bone cells is important as prostaglandins are potent local stimulators of bone resorption and appear to mediate resorption induced by a variety of cytokines and growth factors (35,62). Goldhaber and Rabadjija (40) first demonstrated that the prostaglandin inhibitor indomethacin inhibits acid-induced, cell-mediated calcium efflux from bone, and Rabadjija et al (61) subsequently demonstrated that protons stimulate release of PGE 2 from neonatal mouse calvariae.…”

“…In both toad bladder (34,35) and rat kidney (41), PGE 2 levels have been shown to increase in response to metabolic acidosis. In the brains of newborn pigs, acidosis increases the level of prostaglandins that are associated with vasodilatation (1).…”