BIOLOGICAL ACTIONS OF ATRIAL-NATRIURETIC-FACTOR IN FLATFISH

Flounder adapted to seawater were chronically cannulated and received a single i.v. injection of either saline (control) or 10-mu-g/kg b.w. of human ANF. Compared to controls, ANF significantly reduced (p < 0.001) mean arterial blood pressure; full recovery was evident after 4 hours. Blood samples taken at intervals after saline or ANF injection showed that ANF caused a marked increase of 33.7-mu-g/100 ml in plasma cortisol concentration (p < 0.001) 5 hours post injection. The rate of recovery of Na-22 in seawater after a single i.v. injection of 14 x 10(6) cpm/kg Na-22Cl was significantly increased (p < 0.01) following ANF injection compared to controls suggesting that ANF stimulates Na+ efflux. This observation was confirmed in plaice and dab. The steroidogenic action of ANF and its ability to promote Na+ efflux are discussed in relation to its potential osmoregulatory role in teleost fish.