Journal of Animal Science, Vol 73, Issue 7 2050-2053, Copyright © 1995 by American Society of Animal Science

JOURNAL ARTICLE

Accumulation of the beta-agonist clenbuterol by pigmented tissues in rat eye and hair of veal calves

I. Dursch, H. H. Meyer and H. Karg
Institut fur Physiologie des Forschungszentrums fur Milch und Lebensmittel Weihenstephan, Technische Universitat Munchen, Freising, Germany.

Two independent experiments were carried out to determine whether Clenbuterol is accumulated by pigmented tissues. In the first experiment, unpigmented and pigmented rats were injected two times with 5 micrograms of Clenbuterol subcutaneously and the eyes were analyzed after 63 h of withdrawal by enzyme immunoassay. Only pigmented rat eyes showed a clear accumulation of Clenbuterol (68.1 to 81.5 ng/g), whereas the eyes of unpigmented treated rats demonstrated levels similar to the negative controls (< .27 ng/g). In the second experiment, two Holstein-Friesian calves were fed with .8 microgram of Clenbuterol/kg BW two times a day (therapeutic dose) in milk replacer and black and white hair was collected separately before, during, and after the treatment. The hair was analyzed with an enzyme immunoassay that provided blanks less than 1.0 ng/g and a mean recovery of 67%. This experiment showed an accumulation of Clenbuterol in both sets of hair, but a definitely higher accumulation of Clenbuterol in black (pigmented) hair than in white hair. The black/white quotient amounted to approximately 50 at 1 wk after treatment. Results of these experiments favor the use of the eye as well as the hair for residue analysis but in case of hair, variation of pigmentation in different animals must be considered.