alpha-MSH acetylation in the pituitary gland of the sea bream (Sparus aurata L.) in response to different backgrounds, confinement and air exposure

MSH is a pituitary hormone derived by post-translational processing from PO MC and involved ill stress and background adaptation, N-terminal acetylatio n of MSH to monoacetyl alpha-MSH or diacetyl alpha-MSH increases the bioact ivity of the peptide. The aim of this study was to characterize alpha-MSH a cetylation in the sea bream (Sparus aurata L.) pituitary gland in response to the stressors air exposure and confinement, as well as in fish adapted f or 15 days to a white, gray or black background. Pituitary were purified by reversed-phase HPLC (RP-HPLC). The alpha-MSH content of fractions was meas ured rd by RIA. Immunoreactive RP-HPLC fractions were further analyzed by e lectrospray mass spectrometry and the peptide sequence determined as SYSMEH FR WGKPV-NH2. In the pituitary gland of sea bream, des-, mono- and diacetyl alpha-MSH were identified. Then plasma alpha-MSH levels were measured in s ea bream adapted Cu different backgrounds. Surprisingly, we found the highe st plasma alpha-MSH levels in white-adapted as compared with black-adapted sea bream with intermediate values for gray-adapted fish. This observation is in contrast with results that have been obtained in eel, trout or terres trial vertebrates. Next, des-, mono- and diacetyl alpha-MSH forms were meas ured in homogenates of the pituitary gland and in plasma of sea bream expos ed to air, to confinement, or to different backgrounds. Monoacetyl alpha-MS H was the predominant form in all control and experimental groups. The lowe st content of monoacetyl alpha-MSH relative to des- and diacetyl alpha-MSH was found in white-adapted fish. Levels of des- and diacetyl alpha-MSH form s were similar under all conditions. We observed that monoacetyl alpha-MSH is the most abundant isoform in the pituitary gland after background adapta tion, confinement and air exposure, in sea bream. These data indicate that the physiologically most potent isoform of alpha-MSH may vary from species to species.