Renal handling of amino acids in 5/6-nephrectomized rats: Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone under amino acid load

In anaesthetized adult female rats, the renal amino acid handling was measu red six days after 5/6 nephrectomy (5/6NX). The distinct rise in blood urea nitrogen as well as the significant reduction in urine flow and GFR indica te an impairment of kidney function. In principle, in 5/6NX rats amino acid plasma concentrations were comparable to those of control animals with two intact kidneys, whereas the fractional excretions (FEAA) of most endogenou s amino acids measured were significantly enhanced. After bolus injection o f leucine or taurine (each 20 mg/100 g b.wt.) or glutamine (90 mg/100 g b.w t.), dissolved in 2 ml normal saline per 100 g b.wt., the FEAA of both the amino acids administered and the endogenous amino acids increased as a sign of overloaded amino acid reabsorption capacity. This effect was more prono unced in 5/6NX rats than in controls. As early as one hour after amino acid load, plasma concentrations and FEAA returned to baseline values of 5/6NX rats. A pretreatment with triiodothyronine (20 mu g/100 g b.wt.) or dexamet hasone (60 mu g/100 g b.wt.), both given intraperitoneally once daily for 3 days, stimulated the renal amino acid transport capacity in 5/6NX rats: th e increase in FEAA after amino acid load was significantly lower compared t o non-pretreatred animals. This stimulation could be shown for the bolus am ino acids and the endogenous amino acids and was more distinct in 5/6NX rat s than in controls with two intact kidneys.