Effects of drugs on the formation of homovanillic acid in the rat retina.

Homovanillic acid (HVA) levels were measured in the eye and the corpus striatum of rats under normal conditions and after different drug treatments. Neuroleptic agents such as clozapine, cis-flupenthixol and haloperidol induced comparable increases in HVA levels, whereas the non-neuroleptic trans-isomer of flupenthixol was inactive in both structures. Apomorphine decreased HVA levels in the retina and the corpus striatum, while amphetamine induced a decreased HVA formation in the retina and did not change levels of HVA in the corpus striatum. Probenecid caused a similar percentage rise of HVA in both structures. Morphine and oxotremorine induced a rise in HVA levels in the corpus striatum but not in retinal samples.