JOHNSON, Keven R*; OLSON, Kenneth R; Notre Dame: Natriuretic peptide expression in saltwater and hemorrhaged rainbow trout

Natriuretic peptides (NPs) have been implicated in osmoregulation in the euryhaline Japanese eel (Anguilla japonica), but their function in the euryhaline rainbow trout (Oncorhynchus mykiss) has yet to be determined. We found mRNA expression of the NP family (ANP, BNP, CNP, VNP) in freshwater (FW) trout to be predominantly cardiovascular. As determined by RT-PCR and northern blotting, trout ANP, VNP, and BNP are expressed in the atria and ventricle, while the major site of CNP expression is the brain. We also found CNP transcripts in the efferent branchial artery (EBA), celiacomesenteric artery (CMA), the anterior cardinal vein (ACV), skeletal muscle and to a lesser extent, the atrium. NP expression was not found in the gills, esophagus, stomach, anterior intestine, posterior intestine, head kidney, posterior kidney, and a tail fin clipping (negative control). Saltwater (SW; 1,000 mosm) and acute hemorrhage (35% blood volume) resulted in marked NP transcriptional changes. As determined by Northern blotting, SW adaptation significantly (p< 0.05) reduced expression of atrial ANP (0.35 +/- 0.15 fold; n=4), ventricular VNP (0.4 +/- 0.13 fold; n=4), and ventricular BNP (0.42 +/- 0.11 fold; n=4). In contrast, brain CNP expression was significantly increased (1.13 +/- 0.05 fold n=4). Hemorrhage reduced transcription of atrial ANP and ventricular VNP (0.78 +/- 0.65 fold and 0.81 +/- 0.73 fold, respectively), whereas brain CNP mRNA levels were not significantly affected. These studies show that ANP, BNP, and VNP are elevated in the hyperosmotic FW trout and depressed in the hypoosmotic SW trout, whereas CNP expression exhibits the opposite behavior. In the FW hemorrhaged trout ANP, BNP, and VNP expression are again volume responsive; acute volume depletion reducing expression as compared to normovolemic trout, while CNP is unaffected. Supported by NSF Grant No. IBN 0235223