Distribution of active and inactive forms of endorphins in rat pituitary and brain.

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Abstract
The recent isolation and identification of .alpha.-N-acetyl forms of the C-fragment of lipotropin (.beta.-endorphin, residues of 61-91) and the C''-Fragment (residues 61-87) has led to a study of their distribution in the pituitary and brain of the rat. Regions were mapped by the method of immunofluorescent staining and the reactive peptides were determined by immunoassay after extraction, gel filtration and ion exchange chromatography. The major immunoreactive peptides in both lobes of the pituitary were C''-Fragment and N-acetyl C''-Fragment, which are weakly active or inactive as opiates; the C-Fragment and its N-acetyl derivative represented minor components. In the rat the circulating endorphins released from pituitary would have little morphinomimetic activity. The same 4 immunoreactive peptides were observed in rat brain. In the hippocampus the C''-Fragment was the principal component; in the midbrain there was more C-Fragment but C''-Fragment predominated; in the hypothalamus the C-Fragment was the major peptide, almost to the exclusion of the other peptides. The processing of lipotropin is under differential control in anatomically distinct regions of the CNS. The processing of lipotropin in the hypothalamus is directed specifically to the production of lipotropin C-Fragment.