Renal tubular handling of zinc in the dog

Clearance and stop-flow techniques, performed on anesthetized dogs, were used to obtain evidence for renal tubular reabsorption or secretion of 65Zn (administered intravenously with varying amounts of carrier ZnCl2). Ultrafilterability of plasma 65Zn was determined in vitro with Amicon CF-50A filter cones. Clearances were obtained under six conditions: antidiuresis, mannitol diuresis alone and following the infusion of chlorothiazide, citrate, cysteine, histidine. The percentage of ultrafilterability averaged, respectively, 1.15, 1.38, 0.91, 1.53, 19.90, and 11.61, while fractional zinc excretion averaged 0.046, 0.10, 0.31, 0.43, 0.78, and 0.12, respectively. Control stop-flow patterns invariably showed net Zn reabsorption in the distal nephron. Stop-flow patterns after chlorothiazide revealed significant net secretion in the far distal area in all animals. Patterns after either citrate or histidine infusion revealed significant net reabsorption in the proximal nephron. Those after cysteine were similar to the control patterns. Thus, both clearance and stop-flow experiments revealed net reabsorption as the major tubular mechanism of zinc handling, tubular secretion occurring only during chlorothiazide administration.