Possible aminergic mediation of MSH release and of the CNS effects of MSH and MIF-I

It is well known that the release of melanocyte-stimulating hormone (MSH) from the pituitary gland is mainly controlled by an inhibitory influence from the hypothalamus. In addition to this inhibitory control, there may also be a stimulatory influence. Most, but by no means all, of the evidence is compatible with the possibility that inhibition is mediated by dopaminergic and/or α-adrenergic receptors. Gamma-aminobutyric acid also has been shown to have an inhibitory role in some studies. β-Adrenergic receptors, serotonin, and acetylcholine may be involved in the stimulation of MSH release. Interaction of hypothalamic peptides like Pro-Leu-Gly-NH₂ (MIF-I) with biogenic amines, however, has not been excluded as a factor in the control of the release of MSH from the pituitary. Just as the evidence for the involvement of amines in the control of MSH release is somewhat puzzling and contradictory, conflicting evidence concerning their involvement in mediating the specific effects of MSH and MIF-I on the CNS remains unresolved.