Atrial natriuretic factor and salt adaptation in the teleost fish Gila atraria

It is unknown whether atrial natriuretic factor (ANF) is a mediator of environmental salt tolerance in euryhaline teleost fish. This was investigated in anesthetized Gila atraria, a euryhaline teleost native to springs of pleistocene Lake Bonneville. Plasma levels of immunoreactive (ir) ANF [using anti-human ANF-(99-126) antibodies] in fish obtained from a "fresh water" spring were significantly lower (146 +/- 27) than those in fish obtained from a "1% NaCl" spring (347 +/- 21 pg/ml, P less than 0.01). Electron micrographs of fish atrial and ventricular cardiocytes demonstrated many perinuclear granules, which closely resembled ANF-containing secretory granules seen in mammalian atriocytes. Fish heart extract contained ANF-like material of 3 kDa, which caused a marked diuresis and natriuresis in rats. In a second study, fish from a 1% NaCl spring were kept in tanks. One-third of the fish were maintained in 1% NaCl and one-third each were either adapted to fresh- or high-salt water. After 12 days, plasma irANF levels in 1% NaCl fish were 343 +/- 55, in fresh water fish 213 +/- 20 and in high-NaCl fish 691 +/- 79 pg/ml. These values differed significantly from each other (P less than 0.01). There was a close correlation between plasma irANF levels and both environmental and internal salt concentration. These data suggest that piscine ANF is an as yet unrecognized mediator of salt tolerance in this teleost and that ANF in these animals closely resembles mammalian ANF.