Beta-Endorphin-like peptides in autopsy pituitaries from adults, neonates and foetuses.

Abstract

Abstract. The presence of β-endorphin in human pituitary was studied using radioimmunoassay, opiate receptor binding assay and different chromatographic methods. Adult human pituitaries were found to contain 291 ± 59 μg/g β-endorphin immunoreactivity, of which 15–45% eluted like β-endorphin in Sephadex G-75 gel filtration. The yield of β-endorphin immunoreactivity was found to be dependent of the extraction method used, but the relative proportion of the different immunoreactive components (proopiomelanocortin, β-lipotrophin and β-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 β-endorphin immunoreactivity or the β-lipotrophin/β-endorphin ratio in the acid extracts of human pituitaries. Repeated freezing and thawing was found to cause a progressive loss of extractable β-endorphin immunoreactivity so that the smaller molecular weight material (β-endorphin) disappeared more rapidly than the higher molecular weight material (β-lipotrophin). Pituitaries from neonates and foetuses were found to contain proportionally more β-endorphin than pituitaries from adults (β-lipotrophin/β-endorphin ratio was 2.76 ± 0.43 in adults, 0.93 ± 0.11 in neonates and 0.47 ± 0.09 in foetuses). β-endorphin-like material from gel filtration was found to separate into two components on SP-Sephadex C-25 cation exchange chromatography. The more basic of these eluted identically with synthetic human β-endorphin in reversed phase HPLC, displaced tracer parallelly both in radioimmunoassay and opiate receptor binding assay and had a receptor binding potency not significantly different from that of synthetic β-endorphin. The less basic component has a smaller molecular weight than β-endorphin and represents a formerly unrecognized human pituitary endorphin-like peptide. The results suggest that β-endorphin is a naturally occurring peptide in human pituitary.