Fig. 3. Anoga-DH₄₄ has diuretic activity but does not selectively stimulate Na⁺ transport. Fluid secretion and urine Na⁺ and K⁺ concentrations were initially measured over a 30 min control period and then at 10–15 min intervals after the addition of 1 µmol l^–1 Anoga-DH₄₄ alone (first arrow) and then in combination with 1 mmol l^–1 8-bromo-cyclic AMP (second arrow). Data points show the means ± S.E.M. for five tubules. (A) Fluid secretion (solid line) is increased 3-fold by Anoga-DH₄₄, whereas the urine [Na⁺]:[K⁺] ratio (broken line) fell slightly. The addition of 8-bromo-cyclic AMP to the same batch of tubules further accelerates fluid secretion and increases the [Na⁺]:[K⁺] ratio. (B) Both Na⁺ (solid line) and K⁺ (broken line) transport are increased by Anoga-DH₄₄, whereas 8-bromo-cyclic AMP selectively stimulates the secretion of Na⁺.