Use of bioimpedance spectroscopy to estimate body water distribution in rats fed high dietary sulfur amino acids

The effect of dietary sulfur amino acids on bioelectric properties was stud ied in rats by using bioimpedance spectroscopy. Weanling rats were assigned to one of 12 groups in a factorially arranged experiment with dietary vari ables of supplemental sulfur amino acid (none, 10 g DL-methionine/kg or 10 g DL-homocystine/kg), pyridoxine hydrochloride (0 or 7.5 mg/kg) and nickel (0 or 1 mg/kg). After 9 wk of feeding, 20-h urine specimens were collected from food-deprived rats for measurements of creatinine, and then bioimpedan ce was measured with multifrequency (Hydra ECF/ICF 4200) and single-frequen cy (RJL Systems model 101) analyzers. Urinary creatinine excretion was meas ured by intracellular water (ICW), total body solid and urinary volume (R-2 = 0.675). Extracellular water (ECW) did not add significantly to the model . Rats fed methionine had significantly lower total body water, ICW and ECW than rats fed no supplemental sulfur amino acid. Rats fed homocystine had significantly lower ECW and a significantly higher ratio of ICW to ECW. Rat s fed methionine or homocystine had significantly lower capacitance correct ed for body length and ICW than those fed no supplemental sulfur amino acid s. These results suggest that dietary homocystine changes the distribution of body water and that sulfur amino acids can affect membrane porosity and/ or membrane thickness.