Control of renal handling of potassium loads in ducks with active salt glands

Domestic ducks adapted to saline of 400 mosmol/kgH2O as their only water supply received intravenous loads of 100 mM KCl for 2 h while being intravenously infused with 200 mM NaCl at 1.0 ml/min to produce simultaneous salt gland secretion and diuresis-natriuresis. K+ loading did not alter the plasma levels of the osmoregulatory hormones arginine vasotocin, angiotensin II, aldosterone, and atrial natriuretic factor but promptly evoked kaliuresis because of a rise from 17 to 155 mM in urinary K+, with a proportional decrease in urinary Na+. Continuous infusion of amiloride (0.04 mg.min.-1.kg body wt-1 iv) further enhanced diuresis and natriuresis and lowered urinary K+, but the kaliuretic response to K+ loading was only moderately reduced because of enhanced diuresis and a rise in urinary K+ from 3 to 33 mM, with a slight decrease in urinary Na+. Changes in plasma hormone levels reflected dehydration due to excessive diuresis but were not related to kaliuresis. Salt gland secretion was not affected directly by amiloride but was secondarily reduced by the induced dehydration. In amiloride-treated ducks, hyperkalemia in response to K+ loading was exaggerated relative to the modest reduction in K+ excretion and may be attributed to moderate metabolic acidosis and/or general effects of amiloride on K+ metabolism. It is concluded that none of the established osmoregulatory hormones is involved in short-term control of renal K+ handling in ducks and that distal tubular K+ excretion involving amiloride-sensitive Na+ channels is quantitatively unimportant in this avian species.