Differential release of alpha-melanophore stimulating hormone isoforms by the pituitary gland of red porgy, Pagrus pagrus.

The best known actions of the pleiotrope alpha-melanophore stimulating hormone (alpha-MSH) are skin pigment regulation and corticotrope actions in the response to chronic stress. Stress-induced and enhanced release of alpha-MSH may therefore influence skin pigmentation and stress physiology simultaneously. The release of alpha-MSH is under multiple control by hypothalamic hormones and neurotransmitters. Thyrotropin releasing hormone (TRH), corticotropin releasing hormone (CRH), melanophore concentrating hormone (MCH), and dopamine (DA) have been tested in a superfusion set up for their potential to regulate alpha-MSH release from the pituitary gland of red porgy, Pagrus pagrus, in vitro. The release of alpha-MSH was stimulated by TRH and CRH, and was inhibited by MCH and DA. During unstimulated (basal) release, mono-acetylated alpha-MSH was the dominant form. During superfusion with secretagogues, we found that independent of their inhibitory or stimulatory capacity, isoform frequency did not change. MSH-isoform ratios were similar for all the substances that were used, except that both the inhibitory and the stimulatory factors increased the percentage of di-acetylated alpha-MSH at low concentrations (10(-11)M) when compared to their effects at high concentrations (10(-7)M).