Fig. 5. Sequential addition of Anoga-DH₄₄ and Anoga-DH₃₁ to the same batch of tubules demonstrates that only the latter has pronounced natriuretic activity. Fluid secretion and urine Na⁺ and K⁺ concentrations were measured over 30 min intervals under control conditions and after the addition of 1 µmol l^–1 Anoga-DH₄₄ alone and in combination with 1 µmol l^–1 Anoga-DH₃₁. Bars represent the means + S.E.M. for five tubules. Anoga-DH₄₄ stimulates fluid secretion (open bars) without affecting the [Na⁺]:[K⁺] ratio (solid bars) of the secreted urine, which increases dramatically after the addition of Anoga-DH₃₁ along with a further acceleration of urine flow. Identical letters indicate values that do not differ significantly (P>0.05).