Binding of ractopamine HCl to ocular tissues of cattle and turkeys in vivo and to melanin in vitro1,2

Abstract

Experiments were conducted to determine the total residues remaining in ocular tissues of cattle and turkeys after oral administration of [14C]ractopamine HCl. Twelve cattle were intraruminally dosed with 0.9 mg x kg(-1) x d(-1) of [14C]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 [14C]ractopamine HCl (0.33, 1.02, and 1.36 mg x kg(-1) x d(-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 <0.09 to 0.17 ppm for treatment groups 2 and 3, respectively. The propensities of ractopamine and synthetic ractopamine metabolites to bind to melanin were studied in vitro using radiolabeled ligands with centrifugal filtration to separate melanin from unbound ligand. In vitro studies showed that [14C]ractopamine HCl binds to melanin rapidly and was displaced from melanin by other beta-agonists. Glucuronidation of ractopamine, which produced the major biotransformation product of ractopamine in all species studied to date, prevented binding to melanin. These studies demonstrate that the propensity for the in vivo binding of ractopamine HCl to pigmented ocular tissues is less than that reported for clenbuterol.

Residues of Ractopamine and Identification of its Glucuronide Metabolites in Plasma, Urine, and Tissues of Cattle

“…Ractopamine residues in plasma and urine of cattle (mean ± SE, n = 3) fed 0.67 mg/kg body weight of ractopamine for 28 days not surprising to find high ractopamine residue concentrations in lung tissues because ractopamine is a β-agonist in the same category as salbutamol, which is used for the treatment of human asthma. The three tissues with the greatest concentration of residual ractopamine in this study included the eyes, which was inconsistent with previously reported results (15,16). Smith et al (16) demonstrated that the propensity for binding of ractopamine to melanin is weaker than that of clenbuterol and ractopamine was undetectable in whole-eye homogenates from cattle dosed with 0.9 mg/kg per day for 7 days.…”

Nitrofuran antibiotic metabolites detected at parts per million concentrations in retina of pigs—a new matrix for enhanced monitoring of nitrofuran abuse

“…9 Other b-agonists such as ractopamine do not accumulate to the same extent. 10 The pigment melanin has been identified as the site of binding of drugs in pigmented ocular tissues. 11 Melanin is found in the iris, ciliary body and the retinal and choroid layers of the eye in addition to hair, skin and certain regions of the brain.…”

Plasmonic biosensors for food control

“…Pseudomonas aeruginosa, a foodborne pathogen, was detected using SEF technique where (R)-4-(anthracen-9-yl)-6-(naphthalen-1-yl)-1,6-dihydropyrimidine-2-amine (ANDPA) as fluorescence probe and glucose stabilized silver nanoparticles (Glu-AgNPs) in various food samples including milk, orange juice and sugarcane (Ellairaja, Krithiga, Ponmariappan, & Vasantha, 2017). Due to their specificity, immunosensors could be used in the agrifood sector for monitoring different types of molecules from pesticides (Miyake et al, 2019), bacterial and fungal toxins (Commission, 2006, p. 364;Mayer, Färber, & Geisen, 2003;Organization & Cancer, 1993;Park, Kim, Kim, & Ko, 2014;Patel, 2004;Squire, 1981), drug traces (Elliott et al, 1998;Lu et al, 2012;Smith, Ehrenfried, Dalidowicz, & Turberg, 2002), and allergens (Ashley et al, 2017;Pollet et al, 2011;Rebe Raz, Liu, Norde, & Bremer, 2010;Tomassetti et al, 2013;Yman, Eriksson, Johansson, & Hellens, 2006). SPR biosensors can detect a specific biomarker of a pathogen even in a fmol range (Bhunia, 2008;Rasooly & Herold, 2006;Vidic et al, 2013).…”