Subcutaneous apomorphine increases regional cerebral blood flow in parkinsonian patients via peripheral mechanisms.

1. We have measured regional cerebral blood flow (rCBF) and motor function before and after the subcutaneous (s.c.) injection of apomorphine in parkinsonian patients deprived of their usual treatment for at least 48 h. 2. Nineteen patients, pretreated with domperidone (20 mg three times daily for 48 h), received a mean dose of 5.8 mg s.c. apomorphine. All patients switched 'on'. The mean motor score was significantly improved (‐65%, P less than 0.01) but no significant change in rCBF was observed. 3. Seven other patients, not pretreated with domperidone, received a lower dose (0.3 mg) of s.c. apomorphine. No change in motor score was observed while the mean rCBF significantly increased (+12%, P less than 0.05). 4. We conclude that s.c. apomorphine increases rCBF in parkinsonian patients. This effect is independent of the central therapeutic effects of the drug. It is mediated by the stimulation of dopaminergic receptors of the cerebral vessels. These receptors are located outside the cerebral blood brain barrier and can be considered as 'peripheral' ones.