Osmolality and volume factors in salt gland control of pekin ducks after adaptation to chronic salt loading

Abstract

Pekin ducks were adapted to permanent osmotic stress by rearing them on a NaCl solution of increasing concentration up to 2% as drinking water. Their salt and water balance was compared with that of non-adapted ducks maintained on tap water. Amounts and osmolalities of salt gland secretion and cloacal discharges, plasma osmolality and electrolytes were measured during stepwise osmotic loading by intravenous infusion of NaCl solution of about 740 mosm·kg−1, at rates of 0.25, 0.45 and 0.65 ml·min−1. Before loading, the plasma osmolality of the adapted ducks was about 22 mosm·kg−1 higher than in non-adapted animals. The initial step of loading induced salt gland secretion in the adapted ducks after an average rise of plasma osmolality of 3.6 mosm·kg−1 and in the non-adapted animals after a rise of 7.8 mosm·kg−1. The method of osmotic loading enabled both groups of animals to balance their water input and output. However, only the adapted ducks were able to balance NaCl input and output, predominantly by salt gland secretion, thus maintaining a stable plasma osmolality. The nonadapted ducks retained 42% of the salt load which resulted in a rise of plasma osmolality of 49 mosm·kg−1, more salt being excreted by the kidneys than by the salt glands.