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Isoproterenol-stimulated release of beta-endorphin and related peptides from the rat pituitary neurointermediate lobe in vitro: evidence for preferential release of certain molecular forms of beta-endorphin



Isoproterenol-stimulated release of beta-endorphin and related peptides from the rat pituitary neurointermediate lobe in vitro: evidence for preferential release of certain molecular forms of beta-endorphin



Neuropeptides 17(2): 63-74



The intermediate lobe of the pituitary gland synthesizes the multifactorial precursor molecule pro-opiomelanocortin (POMC), from which, through a process of post-translational enzymatic processing, .beta.-endorphin-(1-31) (.beta.E) and a variety of Na-acetylated and C-terminally shortened forms of this peptide are generated. Using an in vitro superfusion system, the release of these endorphins from intact rat neurointermediate lobes (NILs) was investigated under basal and isoproterenol (ISO) stimulated conditions. Superfusion of NILs with the .beta.-adrenergic agonist ISO (30 min pulse) resulted in a rapid, sustained and concentration-dependent stimulation of the release of .beta.E-like immunoreactivity (.beta.E-IR) over basal as determined with an antiserum directed against the C-terminus of the .beta.E-(1-31) sequence (10-6M: +145%; 10-7M; +73%; 10-8m: +41%). The release of Na-acetylated-endorphin-like immunoreactivity (AcE-IR) was stimulated to a similar extent. These effects of ISO were antagonized by the competitive .alpha.-adrenoceptor antagonist propranolol in a concentration-dependent manner, indicating the involvement of .alpha.-adrenoceptors. The .beta.-related peptides released from the NILs under basal and ISO-stimulated conditions were further characterized, based on their retention times in a reversed-phase HPLC system and their reactivity with specific antisera recognizing respectively the midportion of .beta.E, the N-terminus of acetylated endorphines, the C-terminus of .tau.-endorphin (.beta.E-1-17); .tau.E), or the C-terminus of .alpha.-endorphin (.beta.E-(1-16); .alpha.E). In HPLC fractionated superfusates 10 peaks were resolved that reacted with the midportion .beta.E antiserum. In superfusates collected under basal conditions, three major peaks possessed chromatographical and immunological characteristics of Ac.beta.E-(1-26), Ac.beta.E-(1-27) Ac.beta.E-(1-31). In addition, a prominent peak was found eluting around the retention time of .beta.E-(1-31), that contained both acetylated and non-acetylated material. Six smaller peaks were observed, with the characteristics of .beta.E-(1-26) and .beta.E-(1-27) (these peptides were not resolved with the HPLC system used), Ac.tau.E, .tau.E, Ac.alpha.E, and des-tyrosine-.alpha.E (DT.alpha.E), respectively. In superfusates collected during superfusion of NILs with ISO (10-6M) all peaks were increased. However, those eluting as .beta.E-(1-31), .beta.E-(1-26)/.beta.E-(1-27), Ac.beta.E-(1-26) and Ac.tau.E appeared to be preferentially stimulated. The results indicate, that the NIL in vitro simulatneously releases .beta.E and a variety of highly processes .beta.E-related peptides including .tau.- and .alpha.-type endorphins. In addition, the data suggest the existence of .beta.-adrenoceptor coupled mechanisms, that govern the secretion of a preferred set of .beta.E-related peptides from the pituitary intermediate lobe cell.

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Accession: 007496495

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PMID: 2280822


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