Melanotropic drugs and retinal functions. II. Effects of phenothiazine and rifampicin on the sheep ERG

Selective effects of retinal dopamine depletion on partial ischemia-induced electroretinographic hyperresponses in rabbits

The interaction of retinal dopamine depletion and partial ischemia on the a- and b-wave amplitudes and implicit times of the electroretinogram was examined in adult pigmented rabbits. Seven days after 6-hydroxydopamine treatment, which resulted in a depletion of the amine, partial retinal ischemia was induced by raising the intraocular pressure. As expected, moderate elevation of intraocular pressure produced increases in both a- and b-wave amplitudes. Amplitude hyperresponses were significantly reduced in dopamine-depleted retinas. These reductions were more prominent with relatively lower intensities. However, response delays were not shortened but lengthened by 6-hydroxydopamine pretreatment. Together, these results point to a selective role of dopamine in partial retinal ischemia induced by moderate elevation of intraocular pressure in rabbits.

Electroretinographic effects induced in humans by psychopharmacologic agents

We studied the effects of single doses of different dopamine agonists and antagonists on the electroretinogram of a group of healthy volunteers. The results demonstrated significant b-wave amplitude changes after drug administration, suggesting that electroretinograms can be employed to evaluate the effects on retinal dopaminergic activity induced by psychotropic drugs and that the study of the electroretinographic effects of psychopharmacologic agents can provide new insights into the relationship between retinal dopaminergic mechanisms and the electroretinogram b-wave origin.

The ocular distribution of bunolol in the eyes of albino and pigmented rabbits

The ocular administration of a 50 microL instillation of bunolol hydrochloride, a beta 1- and beta 2- adrenoceptor blocking agent, resulted in significantly higher drug levels in the choroid/retina, iris, and ciliary body of pigmented rabbits compared with albino rabbits following topical administration. The concentrations in these tissues also persisted longer in the pigmented rabbits' eyes. However, no statistically significant differences in tissue levels were observed in the cornea or conjunctiva. The results of this study support the previously reported finding with timolol which showed longer retention of the drug in the iris, ciliary, choroid, and retina of pigmented rabbits than albinos.

Studies of the mechanism of chloroquine binding to synthetic DOPA-melanin

In order to elucidate the mechanism of drugs binding to melanin, effects of pH, ionic strength and organic solvent on the interaction of chloroquine with synthetic dopa-melanin were studied. The results indicate that electrostatic, hydrophobic and van der Waals' forces participate in the formation of the chloroquine-melanin complex. Binding analysis by the Scatchard method showed that two classes of binding sites take part in the complex formation: strong binding sites with the association constant k1 approximately to 10(5) and weak binding sites with K2 approximately 10(4). Experiments with chemically modified melanin yielded some information about binding sites of this biopolymer. The obtained results suggest that strong binding involves both hydrophobic interaction and electrostatic attraction between the protonated ring system of chloroquine and the ortho-semiquinone groups of melanin. However, the weakly reacting sites can be identified as ionic bonds between protonated aliphatic nitrogen of chloroquine molecule and carboxyl groups of melanin. Van der Waals' forces occurring at the conjunctions of the aromatic rings of the drug and the aromatic indole-nuclei of the melanin probably take part in the weak binding too.