Endocrine and neurochemical effects of (+)-PHNO, a dopamine D2 agonist

The naphthoxazine compound, (+)-PHNO, is a dopamine D2 receptor agonist which acts within the central nervous system. The effects of this drug on serum concentrations of corticosterone and prolactin and on brain concentrations of catecholamines and some of their metabolites were determined in male rats. Administration of (+)-PHNO in doses ranging from 3-300 micrograms/kg i.p. resulted in increased serum corticosterone, decreased serum prolactin and decreased concentrations of the dopamine metabolites, DOPAC and HVA, in the brain. At the higher doses of (+)-PHNO, concentrations of MHPG sulfate in the brain stem were increased and hypothalamic epinephrine concentrations were decreased. Pretreatment with centrally acting dopamine antagonists (spiperone or haloperidol) prevented the (+)-PHNO-induced changes in serum corticosterone, prolactin and brain catecholamines. In contrast, pretreatment with halopemide, a dopamine antagonist which penetrates poorly into the brain, was unable to block the effects of (+)-PHNO on serum corticosterone and brain catecholamines. These data show that (+)-PHNO, a dopamine agonist structurally unrelated to other dopamine agonists, acts centrally to affect serum corticosterone and brain catecholamines.