Urinary zinc in relation to other cations and flow during volume expansion and intravenous chlorothiazide

Abstract

Urinary excretion of zinc, sodium, potassium, and calcium was studied in anesthetized dogs under conditions of volume expansion by saline infusion and volume expansion plus chlorothiazide administration. Zinc excretion was positively correlated to the fractional water excretion, as well as to th excretion of the other cations, during volume expansion. Chlorothiazide administration during volume expansion increased the zinc, sodium, and potassium excretion without changing that of calcium. The enhanced zinc excretion during chlorothiazide diuresis was equal to that expected on the basis of the increase in fractional water excretion alone. The urinary concentration of zinc appeared inversely related to the urine flow rate, reaching a minimum below that of the plasma ultrafilterable zinc concentration. The ratio of the clearance of zinc to that of sodium was 0.28, indicating a greater degree of net reabsorption for zinc than for calcium. These findings suggest that zinc and sodium reabsorption may be inhibited to a similar degree at chlorothiazide-sensitive sites in the tubule. Furthermore, the zinc reabsorptive mechanism seems capable of lowering urinary zinc concentration below that of ultrafiltrate and appears related in some way to sodium reabsorption.

Zinc and Chronic Renal Disease

“…While urinary zinc excretion in patients with chronic renal insufficiency generally does not account for a large amount of excreted zinc, the results of several studies (1 2, 13) suggest that the urinary concentration of zinc, when normalized for reduced glomerular filtration rate, might be elevated. Losses through the urinary tract may be increased as a result of long-term courses of treatment with diuretics, which may enhance urinary zinc excretion (7); renal concentrating defects which may increase urine volumes, predisposing to increased urinary zinc losses (7) and proteinuria and amino aciduria which may increase excretion of bound zinc (24). Patients with nephrotic syndrome may exhibit inappropriately increased urinary zinc excretion in spite of significant hypozincemia (25).…”

“…First, the filtered load of zinc is somewhat less than 15 mg/day because of its extensive binding to plasma proteins. In addition, zinc is reabsorbed along the length of the nephron (7).…”