Inhibition of goby posterior intestinal NaCl absorption by natriuretic peptides and by cardiac extracts

Natriuretic peptides abolish active Na⁺ and Cl^- absorption across the posterior intestine of the euryhaline goby Gillichthys mirabilis. Inhibition by eel and human natriuretic peptides is dose-dependent with the following sequence of potencies based on experimentally determined ID₅₀ values for inhibition of short-circuit current; eel ventricular natriuretic peptide (78 nmol · l^-1), eel atrial natriuretic peptide (156 nmol · l^-1), human brain natriuretic peptide (326 nmol · l^-1), human α atrial natriuretic peptide (1.05 μmol · l^-1, and eel C-type natriuretic peptide (75 μmol · l^-1). Natriuretic peptides also significantly increase transcellular conductance. The observed sequence of natriuretic peptide potencies is suggestive of cellular mediation of GC-A-type NP-R₁ receptors in this tissue; as expected for guanylyl-cyclase-coupled NP-R₁ receptors, cyclic GMP mimics the action of natriuretic peptides on the goby intestine. Crude aqueous extracts of goby atrium and ventricle inhibited short circuit current and increased tissue conductance in a dose-dependent manner. Ventricular extract was more potent than atrial extract on both a per organ and per milligram basis.