ROLE OF GUANYLYL CYCLASE RECEPTORS FOR CNP IN SALT SECRETION BY SHARKRECTAL GLAND

The role of C-type natriuretic peptide (CNP) and its guanylyl cyclase- linked receptors in mediating salt secretion by the rectal gland of th e spiny dogfish shark (Squalus acanthias) was investigated using HS-14 2-1, a competitive inhibitor of the binding of natriuretic peptides to their guanylyl cyclase receptors. CNP binds to receptors and activate s guanylyl cyclase in rectal gland membranes in a way that is inhibite d by HS-142-1. Guanylyl cyclase activation in rectal gland membranes i s far more sensitive to CNP than to atrial natriuretic peptide, wherea s the reverse is true for membranes derived from mammalian (rabbit) re nal collecting duct cells. HS-142-1 inhibited the stimulatory effect o f CNP on ouabain-inhibitable oxygen consumption by rectal gland tubule s. In explanted rectal glands continuously perfused with blood from in tact donor sharks, HS-142-1 inhibited the increase in salt secretion n ormally provoked by infusing isotonic saline solutions into the donor animal. These results strongly support the view that CNP released into the systemic circulation in response to volume expansion mediates the secretion of chloride by the rectal gland via receptors linked to gua nylyl cyclase.