AJP - Renal Physiology, Vol 247, Issue 4 596-F601, Copyright © 1984 by American Physiological Society
Renal handling of phosphate during acute respiratory acidosis and alkalosis in the rat
A. Haramati and D. Nienhuis
Clearance experiments were performed in acutely thyroparathyroidectomized
rats to evaluate the renal handling of phosphate during respiratory
acidosis (R ACID) and alkalosis (R ALK) in rats fed either a normal (0.7%)
or low (0.07%) phosphate diet for 4 days. Different acid-base states were
achieved by varying the mixture of carbon dioxide in the inspired air. Each
group received graded infusions of phosphate to control for differences in
plasma phosphate (PPi) and to determine the maximum transport capacity of
phosphate reabsorption (TmPi/GFR). In rats fed a normal phosphate diet, PPi
and the fractional excretion of phosphate (FEPi) were significantly greater
in R ACID than in R ALK. However, there were no differences between R ACID
and R ALK when FEPi was evaluated as a function of the PPi, and values for
TmPi/GFR during R ACID were not different from those during R ALK. In rats
fed low phosphate diet, PPi during R ACID was significantly greater than
during R ALK, yet FEPi was less than 1% in all groups due to an adaptive
increase in TmPi/GFR. Further, the TmPi/GFR was similar irrespective of the
acid-base state. We conclude that acute respiratory acid-base changes do
not alter the intrinsic capacity of the kidney to reabsorb phosphate.
