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. Inhi bition by eel and human natriuretic peptides is dose-dependent with th e following sequence of potencies based on experimentally determined I D50 values for inhibition of short-circuit current: eel ventricular na triuretic peptide (78 nmol . 1(-1)), eel atrial natriuretic peptide (1 56 nmol . 1(-1)), human brain natriuretic peptide (326 nmol . 1(-1)), human alpha atrial natriuretic peptide (1.05 mu mol . 1(-1)), and eel C-type natriuretic peptide (75 mu mol . 1(-1)). Natriuretic peptides a lso significantly increase transcellular conductance. The observed seq uence of natriuretic peptide potencies is suggestive of cellular media tion by GC-A-type NP-R(1) receptors in this tissue, as expected for gu anylyl-cyclase-coupled NP-R(1) 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 incr eased tissue conductance in a dose-dependent manner. Ventricular extra ct was more potent than atrial extract on both a pei organ and per mil ligram basis.