Following PAGE of trout pituitary extracts three bioactive peaks of MSH were detected. These peaks labelled A, B and C had Rf values of 0.55-0.65, 0.7-0.85 and 0.9-1 respectively. Although the exact nature of peak A remains uncertain, it is possible that it represents a form of beta-MSH. Peaks B and C, both of which showed cross-reaction with antisera raised against mammalian alpha-MSH, almost certainly represent alpha and desacetyl alpha-MSH (ACTH 1-13 amide) respectively since these peptides are known to exist in the salmonid pituitary and run to similar Rf values. These three bioactive peaks were also extracted from flounder pituitaries, while in the lamprey a single bioactive molecule with an Rf value 0.6-0.7 was found to be present. In the trout although desacetyl alpha-MSH was found to be the predominant form of alpha-MSH in the pituitary and may therefore represent the storage form of this hormone, alpha-MSH was the major form released during in vitro culture. It is therefore likely that the plasma titres of immunoreactive alpha-MSH (im alpha-MSH) measured in trout and eel represented alpha-MSH alone, although the presence of desacetyl alpha-MSH in such samples cannot be excluded. Direct radioimmunoassay (RIA) of trout plasma samples was not possible since the presence of a plasma interfering factor(s) (IF) resulted in apparent loss of added alpha-MSH. This IF exerted a greater effect in black-adapted trout plasma and some indication of a similar factor(s) in flounder plasma was seen; there was little evidence for its existence in the eel. A plasma extraction technique which utilised ODS-porasil was developed and plasma titres of im alpha-MSH in trout and eels kept on black and white backgrounds were determined. In both species, black-adaptation was found to be associated with elevated levels of im alpha-MSH relative to those seen in white- adapted individuals. Pituitary and plasma levels of im alpha-MSH seen in trout obtained from two sources showed marked differences, indicating that the balance between hormone synthesis and release can vary in fish of the same species.
|Date of Award||1982|