AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 1 231-R238, Copyright © 1991 by American Physiological Society
Control of renal handling of potassium loads in ducks with active salt glands
E. Simon and D. A. Gray
Max-Planck-Institut fur physiologische und klinische Forschung, W.G. Kerckhoff-Institut, Bad Nauheim, Federal Republic of Germany.
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.
