Assay of dopamine and its metabolites in human and rat retina

Human and rat retina dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured after various delays in enucleation and freezing of the eyes. Human eyes were enucleated 45 min to 4 h after death, kept at 4 degrees C and frozen at -70 degrees C from 1.5 to 15 h after enucleation. In human retina, maximal DA concentration (4.85 ng/mg prot.) was obtained from eyes enucleated with a delay of 1 h and frozen with a delay of 2 h. After longer delays, DA concentrations decreased. Retinas of humans who died during the night had lower DA retina concentrations compared to those who died during daytime. Rats were decapitated and the eyes enucleated within 5 min or with a delay up to 8 h before freezing at -70 degrees C or kept at 4 degrees C for 5 min to 12 h before being frozen at -70 degrees C. Delays in enucleation of the rat eyes markedly decreased DA retinal concentrations with a minimal value reached as soon as 2 h after death. However, when the rat eyes were kept at 4 degrees C the minimal value was obtained after a longer period of time (about 7 h). Our results thus show that time of death and delays in enucleation and freezing significantly influence DA and its metabolite concentrations in retinas of rats and humans.