Repeated administration of pergolide to rats attenuates the acute elevation of serum corticosterone by pergolide.

A single injection (0.3 mg/kg IP) of pergolide mesylate, a dopamine agonist, increased serum corticosterone concentration several-fold in rats. This increase did not occur or was greatly diminished in rats that had received four previous daily injections of pergolide. The non-responsiveness to pergolide persisted at the second day after the last of 4 daily injections of pergolide, but by the third and fourth days the rats were again responsive to pergolide in terms of serum corticosterone elevation. The lowering of dopamine metabolites (3,4-dihydroxyphenylacetic acid and homovanillic acid) by pergolide occurred in pergolide-pretreated rats to the same extent as in control rats. Serum corticosterone concentration in pergolide-pretreated rats was elevated normally by a serotonin agonist, quipazine. Since the pituitary-adrenocortical system can be activated in pergolide-pretreated rats (indicated by the normal response to quipazine), the insensitivity to pergolide may be due to decreased responsiveness of central dopamine receptors mediating corticosterone elevation by pergolide.