AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 1 129-R134, Copyright © 1993 by American Physiological Society
Effects of furosemide or acetazolamide infusion on renal handling of lithium: a micropuncture study in rats
R. Fransen, W. H. Boer, P. Boer, E. J. Dorhout Mees and H. A. Koomans
Department of Nephrology and Hypertension, University Hospital, Utrecht, The Netherlands.
Renal lithium (Li) handling was studied by micropuncture at the late
proximal (LPT) and early distal (EDT) tubules in control rats and rats
infused with furosemide (FUR) or acetazolamide (ACTZ). In control rats, the
tubular fluid-to-plasma Li concentration ratio [(T/P)Li] at the LPT
exceeded unity (1.05 +/- 0.02, P < 0.05). Some 25% of the filtered load
(FL) of Li and water was reabsorbed in proportion between the LPT and the
EDT, and consequently the (T/P)Li at the EDT (1.03 +/- 0.03) did not
change. FUR inhibited Li reabsorption in the proximal convoluted tubules
(PCT), by approximately 7% of the FL. Reabsorption of Li and water in the
loop segment was also inhibited, virtually in proportion, by approximately
10% of the FL. These data suggest that FUR-sensitive Li reabsorption in the
loop mainly takes place in the pars recta. However, a small increase in the
(T/P)Li at the EDT (to 1.10 +/- 0.01) suggested inhibition of some Li
transport (approximately 2% of the filtered load of Li) without water, most
likely in the thick ascending limb (TAL). In the PCT, ACTZ reduced Li
reabsorption by approximately 16% of its FL. Although it is likely that
ACTZ also inhibited the pars recta, net Li reabsorption in the loop was not
reduced. This suggests that TAL Li reabsorption can compensate for
increased delivery.(ABSTRACT TRUNCATED AT 250 WORDS)
