Single-pass gill extraction and tissue distribution of atrial natriuretic peptide in trout

A new method is described in the present experiments to quantify atrial natriuretic peptide (125I-ANP) extraction from plasma in a single transit through the gill vasculature of an unanesthetized trout. Tissue distribution of 125I relative to an inert extracellular space marker, 58Co-EDTA, was also measured 1 h after injection of 125I-ANP. Single-pass extraction of 125I-ANP by the gill was 60% in control fish; it fell to 18% in fish previously injected with saline and became negative (relative to 58Co-EDTA) after treatment with the clearance (C-type) receptor inhibitor SC 46542. Approximately 90% of a 125I-ANP bolus injected into control trout is removed from the circulation within 2 min. 125I concentration in gill tissue was nearly seven times greater than that predicted by the 58Co-EDTA space. 125I was also concentrated in brain (2X), gallbladder, gastrointestinal tract, and eye (all 1X). SC 46542 decreased gill 125I binding from seven times to one times the 58Co-EDTA space and increased 125I accumulation in heart, kidney, fat, and skeletal muscle. Extraction of 125I-ANP by the isolated perfused gill was 53%, similar to that observed in vivo. These results show that the gill is a major site for ANP removal from trout plasma and that C-type receptors are predominant in this process.