The influence of anaesthetics on the increase in the water permeability of the toad bladder induced by vasopressin.

1 Single lobes of the bladder of Bufo marinus were isolated and filled with, and suspended in, oxygenated Ringer solution. The fluid in contact with the outside (serosa) of the lobes had a total osmolarity of 225 m-osmol/litre, and that bathing the inside (mucosa) of 45 m-osmol/litre.2 Osmotic water flow from mucosa to serosa was measured by weighing the lobes every 30 minutes. It was negligible unless vasopressin was added to the serosal bath. Standard concentrations of either 1.25 or 6.25 mu/ml were used to render the bladder lobes permeable to water.3 The presence in the serosal medium of pentobarbitone or thiopentone in concentrations ranging from 0.25 to 2.5 mM, or of chloralose in concentrations ranging from 0.65 to 6.5 mM, diminished the increase in water permeability induced by vasopressin.4 The three anaesthetics exerted similar inhibitory effects on the action of vasopressin from the serosal and from the mucosal surface of the bladder.5 In the presence of a constant high concentration of anaesthetic, increasing the concentration of vasopressin over three orders of magnitude led to stepwise increases of osmotic water flow out of the lobes, although at every dose level the effect of vasopressin was depressed by the anaesthetic. However, it was not completely abolished even if the concentration of vasopressin was close to threshold.6 The increase in water permeability of the bladder induced by 3',5'-adenosine monophosphate (cyclic AMP) was also depressed by the three anaesthetics.7 Possible explanations of the findings are discussed.