Binding of ractopamine HC1 to ocular tissues of cattle and turkeys in vivo and to melanin in vitro

Experiments were conducted to determine the total residues remaining in ocular tissues of cattle and turkeys after oral administration of [^sup 14^C]ractopamine HCl. Twelve cattle were intraruminally dosed with 0.9 mg*kg^sup 1*d^sup -1^ of [^sup 14^C]ractopamine HCl for 7 d. Four cattle each were slaughtered with withdrawal periods of 48, 96, and 144 h. Radioactive residues were not detectable in whole-eye homogenates from the cattle. Eight male and eight female turkeys per treatment received either 7.5, 22.5, or 30 ppm dietary [^sup 14^C]ractopamine HCl (0.33, 1.02, and 1.36 mg*kg^sup -1^*d^sup -1^; treatment groups 1, 2, and 3, respectively) for 7 d, and the birds were slaughtered with a 0-d withdrawal period. Eyes were dissected into retina/choroid/schlera (RCS), cornea/iris (CI), and aqueous humor (AH) fractions. Residues in RCS, CI, and AH of treatment 1 turkeys were not detectable. Residues in AH were < 0.02 ppm in treatment groups 2 and 3. Mean residues in RCS ranged from 0.15 to 0.26 ppm, and mean CI residues ranged from