Urate excretion in old age.

Serum urate levels were marginally higher in 11 nonbacteriuric elderly men (5.1 +/- 1.8 mg%) than in 24 nonbacteriuric women (3.9 +/- 1.6 mg%) of the same age. Bacteriuric elderly subjects (6 men, 7 women) had lower levels, these being closely similar in the two sexes (3.4 and 3.6 mg%, respectively). Significant reductions of CIn, Ccreat, and TMPAH were observed for bacteriuric men, but not for bacteriuric women. Further, the CUrate:CIn ratio was higher in bacteriuric men and in women, bacteriuric or not, and was not depressed during the TMPAH periods. Increased daily intake of protein from 60 to 75 g was associated with higher serum urate levels in a larger group of subjects. We conclude that: (1) women, even at the age of 80 have a lower serum urate, related to a higher CUrate; (2) bacteriuria increases the ratio CUrate:CIn, particularly in men; (3) secretory mechanisms for urate differ from those of p-aminohippurate in the human, and (4) dietary protein overrides the effect of bacteriuria on serum urate without affecting the male:female ratio.

Renal effects of lithium administration in rats: alterations in water and electrolyte metabolism and the response to vasopressin and cyclic-adenosine monophosphate during prolonged administration.

Lithium (Li+) chloride, 2 to 3 mEq. per kilogram of body weight, was administered intraperitoneally to normal Wistar rats daily for 4 to 66 days. This resulted in a marked reduction in urine osmolality (Uosm.) and increase in the excretion of water, Na+, K+, uric acid, and phosphate. The excretion of uric acid and potassium was a direct function of UNaV. The magnitude of depression in urine osmolality was significantly related to the rate of excretion of lithium in the urine, suggesting that the change in water reabsorption is dependent on the presence of the ion in the luminal side of the tubule. During 2 per cent saline diuresis, Li+-treated rats achieved less fractional free water reabsorption (TcH2O/GFR times 100) at any level of fractional osmolar clearance (Cosm./GFR times 100) than normal rats. On the other hand, during 0.225 per cent saline diuresis, fractional free water clearance (CH2O/GFR times 100) was normal over a wide range of fractional urine flow (V/GFR times 100), indicating intact function of the ascending limb of the loop of Henle. The intravenous infusion of vasopressin (VP) or dibutyryl cyclic-adenosine monophosphate (dcAMP) to Li+-treated rats resulted in a modest rise in Uosm. and a reduction in V/GFR times 100 and CH2O/GFR times 100. Although the response to VP appeared earlier than that to dibutyryl cyclic-AMP, the magnitude of the changes in Uosm., V/GFR times 100, and CH2O/GFR times 100 was eventually the same with both substances. Comparison between normal and Li+-treated rats revealed that the response to both VP and dibutyryl cyclic-AMP was blunted, albeit to a greater extent in the former. Inhibition by Li+ of adenylate cyclase will only partially explain the present data. Impairment in the release of endogenous VP or a block distal to the formation of cyclic-AMP must have played a role. In view of a normal diluting capacity and the increase in the excretion of phosphate and uric acid, it is suggested that Li+, when administered chronically in the present doses, inhibits proximal tubular reabsorption.