Renal concentrating ability in obesity. Effect of modified fasting and the supplementation of T3, sodium chloride and carbohydrate.
The renal concentrating ability (RCA) was studied in 30 obese subjects before and after modified fasting (MF) and T3 supplementation, and during hypocaloric-carbohydrate refeeding. We also studied the effect of sodium supplementation on the RCA during MF. Modified fasting induced a low T3-high rT3 state ("sick euthyroid"). During T3-supplementation plasma T3 levels increased but were in the normal range for normal weight controls. Plasma sodium, potassium, and calcium remained within the normal range during all study periods. After MF (14 days) the mean maximal urinary osmolality was significantly lower compared to prefast values both after dehydration alone (706 +/- 12 mosm/kg H2O v 975 +/- 14, P less than 0.001) and after dehydration plus sc vasopressin administration (676 +/- 19 v 899 +/- 17, P less than 0.001). After 14 days MF followed by 14 days MF + T3-supplementation plasma urea, urinary urea excretion, and the creatinine clearance were significantly greater than after MF alone as was the RCA (764 +/- 15 v 652 +/- 25, P less than 0.002). Sodium chloride supplementation increased RCA (P less than 0.02) but no additive effect of T3 and sodium chloride supplementation was observed. Severe dietary salt restriction induced a significant decline in RCA (P less than 0.005). Refeeding with carbohydrate increased plasma T3 from 79.9 +/- 7.7 to 97 +/- 7.5 ng/100 mL (NS) and decreased plasma rT3 from 0.33 +/- 0.02 to 0.27 +/- 0.02 ng/mL, (P less than 0.02); no significant change in RCA was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
D000328:Adult; D003404:Creatinine / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D005215:Fasting; D005260:Female; D006801:Humans; D007671:Kidney Concentrating Ability / Q000187:drug effects; D008297:Male; D009584:Nitrogen / Q000652:urine; D009765:Obesity / Q000097:blood / Q000178:diet therapy / Q000652:urine*; D011188:Potassium / Q000097:blood; D012964:Sodium / Q000097:blood; D012965:Sodium Chloride / Q000494:pharmacology*; D013960:Thyroid Function Tests; D014284:Triiodothyronine / Q000097:blood / Q000494:pharmacology*; D014508:Urea / Q000097:blood
D004040:Dietary Carbohydrates; D014284:Triiodothyronine; D012965:Sodium Chloride; D014508:Urea; D012964:Sodium; D003404:Creatinine; D009584:Nitrogen; D011188:Potassium