Pharmacokinetics of intravascularly administered (65)Zinc in channel catfish (Ictalurus punctatus)

Comparison was made of the pharmacokinetics of the radioisotope (65)Zinc (Z n-65) in blood, plasma, and whole body of adult channel catfish (Ictalurus punctatus) following intravascular (iv) administration. A two-compartment m odel described the pharmacokinetics of Zn-65 in plasma and blood during the first 40 days following iv administration, but was unable to describe the longterm disposition of Zn-65. Whole-body counting revealed that approximat ely half of the Zn-65 dose was sequestered in a slowly exchangeable pool wi th a half-life of 1.5 years. Greater than 99% of the circulating Zn-65 was bound to plasma proteins, whereas there was less than 1% binding to red blo od cells. Synthesis of the results for channel catfish and existing data in other species indicates three phases in the pharmacokinetics of zinc. The first phase consists of initial distribution outside the vascular system to kidney, liver, and other organs (alpha phase in blood and plasma; t(1/2) o f 4 to 5 h). The second phase involves distribution from organs to a slowly exchangeable zinc pool, likely consisting of bone (beta phase in blood and plasma; alpha phase in whole body; t(1/2) of 4 to 20 days). The third phas e appears to involve a slow turnover of sequestered zinc (t(1/2) greater th an 1 year). Blood sampling or short-term whole-body measurements will under estimate the persistence of zinc in fish, thus prolonged sampling and measu rement of whole-body concentrations are necessary to characterize the pharm acokinetics of zinc. (C) 2000 Academic Press.