The present article indicates that dopamine and/or its agonists induce biph
asic dose-response relationships for numerous endpoints. These include loco
motion, pain sensitivity, blood pressure, prolactin secretion, oxytocin rel
ease, heart rate, memory, and neuronal adenylate cyclase activity. Biphasic
responses were reported predominantly with male Sprague-Dawley rats, but a
lso with mice, dogs, monkeys, and humans. Regardless of the model or endpoi
nt the maximum changes from the control were always modest being within the
10 to 80% range. The range of stimulatory responses was quite variable, ex
tending from slightly greater than a factor of 10 for the endpoints such as
memory, pain-vocalization, and diastolic blood pressure to the lob range f
or prolactin release and the 10(8) range for oxytocin release. Mechanistic
studies suggested that the stimulatory and inhibitory effects of dopamine a
re mediated by different receptors or receptor subtypes having opposite act
ions and different ligand affinities.