The separation of neuropeptides by high performance liquid chromatography and its application to the analysis of peptides in the rat pituitary neurointermediate lobe (author's transl)

Abstract

High performance liquid chromatography (HPLC) was used for the separation of many neuropeptides. Chromatography was carried out using a Hitachi Model 638 high performance liquid chromatograph. Peptides and samples from tissue dissolved in an aqueous buffer were injected into a stainless-steel column (4 X 250mm) packed with Hitachi #3053 (octadecylsilane). The aqueous buffer consisted of NaH2PO4 and H3PO4. After a loading phase (0% organic solvent) of 1 min, the peptides were sequentially eluted at room temperature using a gradient of organic solvent (acetonitrile or methanol, 0-60%). The eluted polypeptides were detected by UV absorbance at 220nm, and then they were collected for subsequent bio and radioimmunoassay using a fraction collector. The gradient of methanol or acetonitrile in 0.02M NaH2PO4, 0.1% H2PO4 was useful for separating small molecular peptides. The gradient of acetonitrile in 0.05-0.1M NaH2PO4, 0.1% H2PO4 was useful for separating many neuropeptides including ACTH related peptides. Retention times of chromatographed polypeptides showed good reproducibility. Good reproducibility was also found in peak areas of these peptides. A linear relationship was observed between the doses of peptides and their peak areas. The extracts of rat pituitary neurointermediate lobe showed several peaks of UV absorbance on PHLC; some of them coincided with AVP, oxytocin, alph-MSH, CLIP and beta-endorphin but others were unidentified. AVP immunoreactivity showed one peak which coincided with the AVP peak of UV absorbance, but ACTH immunoreactivity showed 5-6 peaks. Thus, many polypeptides were well separated using HPLC by changing the eluting condition. The simplicity, speed, good reproducibility and good quality of the separations render this technique suitable for purification and quantitative analysis of neuropeptides, and the combination of HPLC, radioimmunoassay and bioassay gives very fine analysis of neuropeptides.