Electrolyte handling and osmoregulatory hormones in ducks during Na+-free or Cl?-free hypertonic salt gland stimulation

Abstract

1. Domestic ducks acclimated to hypertonic saline (600 mosm·kg−1) as their only water supply received intravenous hypertonic infusions of arginine hydrochloride (830 mosm·kg−1) or sodium bicarbonate (880 mosm·kg−1). The resulting secretion by the salt glands of stoichiometrically equivalent amounts of Na+ and Cl− produced hypo- or hypernatremia associated with opposite changes in plasma chloride concentration. 2. The imbalances of sodium were internally compensated for to some extent by shrinkage or expansion of the apparent volume of sodium distribution. These adjustments indicate active osmoregulatory control of sodium distribution between extra- and intra- or trans-cellular compartments. The imbalances of chloride were not internally compensated for and its apparent volume of distribution did not change. 3. The plasma concentration of arginine vasotocin (AVT) appeared to be osmotically controlled during loading with sodium bicarbonate. During infusion of arginine hydrochloride AVT plasma concentration increased in excess of what could be anticipated from the change in plasma osmolality, indicating a potentiating effect of this amino acid on AVT release. 4. The plasma concentration of angiotensin II (ANGII) appeared to be inversely related to plasma sodium concentration and to body fluid content in accordance with the macula densa hypothesis of the control of renin formation. 5. Arginine hydrochloride infusions produced concomitant increases in plasma ANGII and aldosterone. This was associated with significant reductions of the Na+/K+ ratios of both salt gland and urinary excretions.