Osmotic and volume control of diuresis in conscious ducks (Anas platyrhynchos)

Summary In conscious Pekin ducks made diuretic either by infusing hyposmotic glucose solution or isosmotic saline, osmotic and volume effects on renal water excretion were investigated. As in mammals, antidiuresis mediated by enhanced release of antidiuretic hormone was induced by increasing carotid blood osmolality while a decrease augmented diuresis, indicating cerebral osmotic control of renal water excretion in birds.In contrast to the situation in mammals, a sensitive diuretic response to isosmotic volume expansion, corresponding to 1% of the extracellular volume, can be demonstrated, with intracarotid and intravenous application of the isosmotic saline infusion having identical effects.Volume loading with isosmotic saline produced a greater diuretic response than loading with the same amount of autologous blood, thereby indicating a major contribution of volume changes in the interstitial compartment to the control of renal water excretion. This corresponds to the importance of the interstitial fluid compartment for the control of salt gland activity in this species.Abbreviations AVP arginine vasopressin - ECF extracellular fluid - i.c., i.v. intracarotid, intravenous - ECFV ECF volume