Hypertonic serosal medium (SH) invokes a hydro-osmotic response in anuran urinary bladder similar to that induced by antidiuretic hormone (ADH) (Bentley, 1964). We have reported that the hydro-osmotic response of bladders to medium made hypertonic by addition of 100 mosmol NaCl (SH-NaCl) is reversed by noradrenaline (NA) (Hanna-Mitchell & Gebruers, 2001). Ripoche et al. (1973) reported that NA failed to reverse the hydro-osmotic response to medium made hypertonic by addition of mannitol (220 mosmol). This was interpreted as indicating that the SH-hydro-osmotic response did not depend on cAMP for its maintenance, in contrast to ADH-induced water flow.

In this study, we examined the mode of reversal by noradrenaline (50 mM) of SH-NaCl-induced water permeability increases. Rana temporaria urinary bladders from humanely killed males were used in gravimetric experiments, employing a modification of the Bentley method. Bath addition of NA was 15 min following imposition of SH-NaCl. Flux (J_w) is expressed as mean cumulative fluid loss (ml 20 min^-1), commencing 5 min post-addition of agents to the bath. Statistical analysis employed Student’s unpaired t test and results are expressed as means ± S.E.M.

Noradrenaline failed to reverse the SH-water response in the presence of 100 mM yohimbine (a specific α₂ -antagonist). Neither 100 mM prazosin (a specific α₁-antagonist) nor 100 mM propranolol (a non-specific β-antagonist) inhibited NA (Table 1).

To exclude a role for prostaglandins, bladders were incubated in indomethacin (10^-5 M) for 2 h before exposure to SH. The hydro-osmotic response was still reversed by NA (244.2 ± 40.8 ml 15 min^-1 (n = 5) compared with 521.0 ± 89.5 ml 15 min^-1 (n = 5) in control bladders, P < 0.005).

Successful RT-PCR using RNA extracted from isolated urinary bladder epithelium, resulted in a product of approximately 520 bp, suggesting that the frog α₂-receptor gene (Hunter & Elgar, 2001) is expressed in Rana temporaria bladder.

These results indicate that similar to the ADH-hydro-osmotic response, the SH-NaCl-water response is dependent on cAMP for its maintenance.

We acknowledge support of HRB, Ireland and UCC Foundation.

All procedures accord with current National guidelines.