β-endorphin-like peptides in autopsy pituitaries from adults, neonates and foetuses

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Abstract
The presence of .beta.-endorphin in human pituitary was studied using radioimmunoassay, opiate receptor binding assay and different chromatographic methods. Adult human pituitaries contained 291 .+-. 59 .mu.g/g .beta.-endorphin immunoreactivity, of which 15-45% eluted like .beta.-endorphin in Sephadex G-75 gel filtration. The yield of .beta.-endorphin immunoreactivity depended on the extraction method used, but the relative proportion of the different immunoreactive components (proopiomelanocortin, .beta.-lipotropin and .beta.-endorphin) was approximately identical irrespective of the extraction method. No correlation was observed between the time lag from death to autopsy (within 7 days) and either the total amount of .beta.-endorphin immunoreactivity or the .beta.-lipotropin/.beta.-endorphin ratio in the acid extracts of human pituitaries. Repeated freezing and thawing caused a progressive loss of extractable .beta.-endorphin immunoreactivity so that the smaller MW material (.beta.-endorphin) disappeared more rapidly than the higher MW material (.beta.-lipotropin). Pituitaries from neonates and fetuses contained proportionally more .beta.-endorphin than pituitaries from adults (.beta.-lipotropin/.beta.-endorphin ratio was 2.76 .+-. 0.43 in adults, 0.93 .+-. 0.11 in neonates and 0.47 .+-. 0.09 in fetuses). .beta.-Endorphin-like material from gel filtration separated into 2 components on SP-Sephadex C-25 cation exchange chromatography. The more basic of these eluted identically with synthetic human .beta.-endorphin in reversed phase high performance liquid chromatography, displaced tracer parallelly both in radioimmunoassay and opiate receptor binding assay and had a receptor binding potency not significantly different from that of synthetic .beta.-endorphin. The less basic component has a smaller MW than .beta.-endorphin and represents a formerly unrecognized human pituitary endorphin-like peptide. .beta.-Endorphin apparently is a naturally occurring peptide in human pituitary.