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The guanylin peptides – guanylin, uroguanylin and renoguanylin (RGN) – are endogenously produced hormones in teleost fish enterocytes that are activators of guanylyl cyclase-C (GC-C) and are potent modulators of intestinal physiology, particularly in seawater teleosts. Most notably, they reverse normal net ion-absorbing mechanisms that are vital to water absorption, an important process for seawater teleost survival. The role of guanylin-peptide stimulation of the intestine remains unclear, but it is hypothesized to facilitate the removal of solids from the intestine by providing fluid to enable their removal by peristalsis. The present study used one member of this group of peptides – RGN – to provide evidence for the prominent role that protein kinase A (PKA) plays in mediating the effects of guanylin-peptide stimulation in the posterior intestine of the Gulf toadfish (Opsanus beta). Protein kinase G was found to …