Diurnal responsiveness to apomorphine.

Many parkinsonian patients respond to L-dopa better in the morning than at other times. To explore the possibility that this phenomenon represents diurnal fluctuations in dopaminergic receptor responsiveness, we compared the effects of subcutaneously administered apomorphine during "off" periods in the mornings and afternoons in nine fluctuating patients. The duration of response and area under the time-response curve, but not the magnitude of improvement, were dose responsive. Response durations to the same dose administered in the morning and afternoon were similar, although at threshold doses three subjects responded only to the afternoon dose. These observations suggest there is no large diurnal change in striatal dopaminergic responsiveness.