Multiple sites for interaction of prostaglandin and vasopressin in toad urinary bladder

Abstract

The interaction of vasopressin with prostaglandins were examined in the toad bladder by determining water flows, cAMP levels, and cAMP-dependent protein kinase activity. Both water flow and activation of cAMP-kinase in response to vasopressin were enhanced after prostaglandin inhibition, consistent with inhibition of vasopressin-induced cAMP generation by endogenous prostaglandins. On the other hand exogeneous PGE stimulated cAMP generation. PGE1 (10(-7) M) alone did not increase water flow but activated kinase more than vasopressin only. Addition of PGE1 (10(-7) M) and vasopressin inhibited water flow as compared with vasopressin along but increased the kinase ratio above that with vasopressin only. PGE2 (10(-5) M) increased the cAMP content and kinase ratio even more than vasopressin but again resulted in no water flow. Addition of vasopressin and PGE2 (10(-5) M) increased water flow but did not alter cAMP content or the kinase ratio compared with PGE2 alone. Similar results were obtained with PGE1. Accordingly, prostaglandin dissociates cAMP levels and kinase ratio from the hydroosmotic response, suggesting that PGE2 inhibits steps distal to cAMP. Consistent with this, in bladders pretreated with naproxen or meclofenamate, PGE2 (10(-8) to 10(-6) M) inhibited the response to submaximal doses of cAMP (5 mM) or 8-bromo-cAMP (0.03 mM). Furthermore, pretreatment with naproxen significantly enhanced the response to cAMP (5 mM). These studies provide evidence for vasopressin-PGE interaction at the site of cAMP generation and also at a step(s) unrelated to cAMP generation.

Role of inhibitory and stimulative effects of prostaglandins on vasopressin-stimulated osmotic water flow in the toad bladder.

“…Compared to the endogenous generation of PGE2, 10 -5 M of PGE2 used by SCHOLONDORFF et al (1981) to demonstrate the dissociation of cyclic AMP levels and kinase ratio from the hydro-osmotic response in the toad bladder, is extremely high, and may not be a physiological concentration. They found that low doses of PGE2, such as 10 -' and 10 -8 M, have no effect on 5 mM cyclic AMP-stimulated water flow, but could find no dose-dependent inhibitory effect at concentrations from 10-9 to 106 M. In the present study, PGE2 significantly inhibited the cyclic AMP-stimulated water flow at 10-9 to 10-6 M, but no dose-dependency could be observed, showing agreement of our results with those of SCHLONDORFF et al (1981) in regard to the effects of low doses of PGE2 on cyclic AMP action. Figure 1 shows different half maximum activation doses of indomethacin on vasopressin-and cyclic AMP-stimulated water flow and indicates endogenous Vol.…”

“…That PGH2 has an effect at 10-' M indicates PGE2 physiologically inhibits vasopressin action while PGF2a has merely a pharmacological effect. SCHLONDORFF et al (1981) found PGE2, with or without vasopressin, to have an effect on water flow, cyclic AMP generation and cyclic AMP-dependent protein kinase activity in the toad bladder. They reported that 10 -5 M PGE2 increased cyclic AMP content and kinase ratio even more than vasopressin but had no effect on the rate of water flow, and that 5 mU/ml vasopressin and 10 -5 M PGE2 when added together, increased the water flow but had no effect on cyclic AMP content or the kinase ratio compared to that of PGE2 when administered alone.…”

“…However, SHLONDORFF et al (1981) observed that PGE2 inhibited cyclic AMP-stimulated water flow when the bladders were pretreated with prostaglandin synthesis inhibitors, but had no effect on water flow (ORLOFF et al, 1965;FLORES and SHARP, 1972;ALBERT and HANDLER, 1974). SCHLONDORFF et al (1981) suggest that PGE2 interferes with the stimulation of water flow at both "post cyclic AMP" and "pre cyclic AMP" sites, but they have not clarified at which of these two sites PGE2 exerts its effects against vasopressin under physiological conditions. Thromboxane B2 (TXB2) has been shown in several reports to enhance vasopressin-stimulated water flow (BURCH et al, 1979;BISORDI et al, 1980;BURCH and HALUSHKA, 1982).…”

Inhibition of vasopressin-stimulated water flow in toad bladder by phorbol myristate acetate, dioctanoylglycerol, and RHC-80267. Evidence for modulation of action of vasopressin by protein kinase C.

“…Transport studies were performed in bladder sacs from female Dominican toads by use of techniques that we have previously reported in detail (4,13,14). Measurement of basal water flow began 15 min after addition of experimental agent to the serosal bath.…”

“…The heat-inactivated aliquots of the original homogenate prepared as outlined above were centrifuged at 900 g for 30 min. The supernate was removed and cAMP levels were measured directly in duplicate by radioimmunoassay (Collaborative Research Inc., Waltham MA) as we have previously reported (13,16). The pellet was resuspended in 0.1 N NaOH for determination of protein.…”