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The Carboxy‐Terminal Glycopeptide of the Vasopressin Precursor in the Guinea‐Pig: Release Studies Using a Specific and Sensitive Homologous Radioimmunoassay
Author(s) -
Fairhall K. M.,
Robinson I. C. A. F.
Publication year - 1989
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/j.1365-2826.1989.tb00086.x
Subject(s) - vasopressin , guinea pig , radioimmunoassay , hypertonic saline , endocrinology , medicine , posterior pituitary , chemistry , glycopeptide , in vivo , cisterna magna , neuropeptide , biology , cerebrospinal fluid , biochemistry , pituitary gland , receptor , hormone , antibiotics , microbiology and biotechnology
The glycopeptide corresponding to the C‐terminal portion of the vasopressin precursor (CPP)has been isolated from guinea‐pig posterior pituitary glands and used to generate a specific and sensitive radioimmunoassay. The antiserum is directed to the peptide rather than sugar moieties, and detects two components in pituitary extracts: CPP itself, and a biosynthetic intermediate (NP‐CPP) containing both neurophysin and CPP sequences. Release of CPP from neurointermediate lobes incubated in vitro was stimulated five‐fold by high K + in a Ca 2+ dependent manner: in vivo studies suggest that CPP is released under conditions stimulating vasopressin release. Chronic dehydration depleted neural lobe stores of CPP in parallel with other vasopressin‐related components, and plasma levels of CPP were raised from 68±18 to 320 + 89 fmol/ml (SEM, n = 6). In anaesthetized guinea‐pigs, intraperitoneal injections of increasingamounts of hypertonic saline increased plasma levels of CPP in a graded manner compared with isotonic saline injections. Acute haemorrhage also stimulated CPP release into plasma, and the half‐time of clearance of CPP after infusion to steady state levels in guinea‐pig plasma was 24 min. Cerebrospinal fluid withdrawn from the cisterna magna also contained detectable amounts of CPP (390 + 25 fmol/ml) suggesting that CPP is released from both hypophysical and extra‐hypophysical projections. This assay may now be used to study the biosynthesis, processing and release of endogenous CPP under different physiological conditions.