Previous studies demonstrated that acetylated and deacetylated forms of Alpha-MSH and Beta-endorphin exist in the same neurons and pituitary cells in rat and human brain. Alpha-MSH released from the neurons may influence processes of attention, arousal and learning; Beta-endorphin released from the neurons may influence analgesia. The acetylated form of Alpha-MSH is 2-3 orders of magnitude more potent than deacetylated Alpha-MSH while the acetylated form of Beta-endrophin is 3-4 fold less potent than Beta-endorphin. Enzymes which acetylated alplha-MSH and Beta-endorphin have been identified in brain and pituitary. Among these is a general acetyltransferase (GAT) present in all organs of the rat. In addition, a specific enzyme capable of acetylating both opiate (Beta-endorphin) and melanotropic (Alpha-MSH) peptides has been identified, localized to secretory vessicles and named opiomelanotropin acetyltransferase (OMAT). OMAT activity can be induced by physiological manipulation which induces MSH synthesis. Studies of the physiology and pharmacology of Alpha-MSH in the brain have also continued. It was found that Alpha-MSH administration selectively influences visual but not auditory learning. Furthermore, a compound 4-Norleucine, 7-D-Phenylalanine-Alpha-MSH has been synthesized and been found to have identical effects on arousal as Alpha-MSH but opposite effects on learning--suggesting multiple Alpha-MSH receptors in brain. In addition, Alpha-MSH injected into the dorsomedial nucleus of the hypothalamus has been found to cause increases in heart rate. The results of these studies demonstrate that brain Alpha-MSH may be involved in a variety of different physiological functions.
NIH ExPorter
NIH ExPorter