Atrial natriuretic factor controls salt gland secretion in the Pekin duck (Anas platyrhynchos) through interaction with high affinity receptors.

Marine birds possess supraorbital salt-secreting glands in addition to the kidneys as osmoregulatory organs to excrete a strongly hypertonic salt solution of mainly NaCl. Atrial natriuretic factor (ANF)-like peptides could be demonstrated immunocytochemically in duck atria, but not in the salt glands. To elucidate the putative role of bird-specific ANF (cANF) in the control of salt gland function, conscious saltwater-acclimated Pekin ducks received 15 pmol/min.kg BW cANF for 10 min at two states of salt gland activity. During steady state diuresis and salt gland secretion induced by systemic infusion of 1.0 ml/min isotonic Krebs-Ringer solution, cANF applied iv enhanced the secretion rate from 0.20 to 0.29 ml/min and the osmolality of secretion from 870 to 920 mosmol/kg. At threshold conditions of salt gland activity, cANF infused intracarotideally stimulated the secretion rate from 0.07 to 0.15 ml/min at elevated osmolality of 760 compared to 480 mosmol/kg. Mean arterial pressure and heart rate remained unchanged. Receptor autoradiography with [125I]Bolton-Hunter-cANF as ligand demonstrated specific binding sites throughout the salt gland tissue of both freshwater and saltwater ducks. Scatchard analysis using an enriched membrane fraction revealed high affinity (Kd = 0.9 nM) binding sites of 270 fmol/mg protein density. Displacement studies with unlabeled cANF and human ANF showed comparable Ki values for both peptides in freshwater and saltwater ducks. The combined results indicate an important role for cANF in the control of avian salt gland function.