Marked differences between pigmented and albino rabbits in the concentration of clindamycin in iris and choroid-retina.

The concentrations of clindamycin were significantly higher in iris and choroid-retina or pigmented rabbits than in those of albino rabbits after subconjunctival injection. Equilibrium dialysis experiments showed no affinity of clindamycin for synthetic melanin or for collagenase digests of pigmented tissues. In contrast, strips of iris and choroid-retina took up clindamycin rapidly from solution, achieving concentrations substantially higher than those in the medium. Uptake by tissue strips was not influenced by temperature (4 C vs. 37 C), cyanide, or ouabain. However, N-ethylmaleimide, which reacts with sulfhydryl groups, decreased the tissue-to-medium ratios by about 50% for both albino and pigmented choroid-retina. Even in the presence of this inhibitor, the ratio for pigmented tissues remained higher than that for albino specimens. These findings suggest the existence of one, or possibly two, mechanisms of energy-independent accumulation of clindamycin by pigmented ocular tissues: one may relate to protein sulfhydryl bonds that are present in both breeds; the other may involve the pigmentation apparatus.