Tissue distribution of polaprezinc in rats determined by the double tracermethod

The tissue distribution of polaprezinc (an insoluble zinc complex of L-carn osine) in rats was studied by the double tracer method using [U-C-14-histid ine]-, Zn-65-polaprezinc. The Zn-65-radioactivity was measured with an auto -gamma counter, and the C-14 containing Zn-65 was converted to an absolute count according to the calibration curve for quenching with a liquid scinti llation counter with the spill-over method. After the administration of C-1 4-, Zn-65-po- laprezinc to rats, the excretion ratio and time courses in th e tissues of the C-14-and Zn-65-radioactivity were different each other. We found that polaprezinc was metabolized as endogenous amino acid or zinc af ter dissociation in the body. The zinc concentration in plasma reached its maximum at 1 h and decreased slowly, returning to the endogenous level at 1 1 h after the administration of non-labeled polaprezinc. The concentrations of zinc in liver, kidney, testis, prostate, and cerebrum remained rather c onstant. The replacement ratios of Zn-65 to zinc in the tissues at its maxi mum percentage were 40% in plasma, 16-20% in liver, kidney, blood, and pros tate. The low replacement ratios in testis and cerebrum (2-3%) suggested th at zinc uptakes in testis and brain were regulated by the blood-testis-barr ier and blood-brain-barrier, respectively. (C) 1999 Elsevier Science B.V. A ll rights reserved.