Hypothalamic alpha-melanocyte-stimulating hormone (alpha-MSH) is not under dopaminergic control.

A possible dopaminergic regulation of hypothalamic proopiomelanocortin (POMC)-containing neurons has been investigated in rats by means of in vivo and in vitro approaches. Acute or 3-weeks chronic in vivo treatments with the dopaminergic agonists apomorphine (1 mg/kg: s.c.) and 2-Br-alpha-ergocriptine (2.5 mg/kg; s.c.) or the dopaminergic antagonist haloperidol (0.15-3 mg/kg; i.p.) had no significant effect on the concentration of alpha-melanocyte-stimulating hormone (alpha-MSH) in two hypothalamic regions: arcuate nucleus (AN) and dorsolateral area (DLH). In the same way, chronic administration of the dopaminergic agonists or antagonist did not induce any change in hypothalamic contents of beta-endorphin, another peptide derived from POMC. Reverse-phase high-performance liquid chromatographic analysis revealed that acetic acid extracts of AN and DLH both contained two major forms of alpha-MSH-like peptides: deacetylated alpha-MSH and authentic alpha-MSH. The ratio between these two forms was not altered after acute haloperidol treatment (3 mg/kg, i.p.). The possible effect of dopamine on the release of hypothalamic alpha-MSH was studied in vitro using perifused rat hypothalamic slices. Infusion of dopamine (10(-7)-10(-5)M) or its antagonist haloperidol (10(-5)M) had no effect on spontaneous alpha-MSH release from hypothalamic tissue. In addition, none of these drugs had any effect on potassium (50 mM)-induced alpha-MSH release. It is concluded that dopaminergic neurons are not involved in the regulation of synthesis, post-translational processing (acetylation) or release of hypothalamic alpha-MSH.