The effects of vertebral artery injections of an enkephalin analogue, (D-Met2,Pro5)-enkephalinamide, on somatosympathetic reflexes.

The present study was initiated to test the effects of intravertebral arterial injection of an enkephalin analogue (D-Met2,Pro5)-enkephalinamide on somatosympathetic responses to myelinated A afferent and to unmyelinated C afferent stimulation (A- and C-reflex, respectively). In anesthetized cats, 0.5 mg/kg administered directly into the vertebral artery, the artery supplying most of the cat brain stem and upper cervical spinal cord, depressed both the A- and C-reflex (to 66 and 64% of control, respectively) while intravenous or carotid arterial injections did not have any effect on these reflexes. It is suggested that intravertebral arterial administration may be a useful method of restricting the effective sites of delivery of biologically active compounds to areas of the brain supplied by this artery.