Galanin, a neuropeptide, has important effects on
hormone secretion from the hypothalamus and pituitary, and may also be involved in important biological processes such as
pain, memory, and food intake. Yet, there is limited knowledge about how these processes are reflected by circulating
galanin. To study the levels and molecular forms of
galanin in the human circulation, plasma was analysed from 27 healthy subjects, 14 women and 13 men, using two extraction methods and a specific radioimmunoassay for human
galanin. After extraction on Sep Pak C-18 columns, plasma
galanin-like immunoreactivity (
galanin-LI) in the healthy men was 6.3 +/- 2.5 pmol/l (mean +/- SD, n = 12), which was higher than in the women, 4.1 +/- 1.5 pmol/l (n = 14, p = 0.010). A small increase in
galanin-LI was seen with age in the women (r = 0.54, p < 0.05) but there was no significant difference between pre- and postmenopausal women.
Galanin immunoreactivity after Sep Pak and immunoextraction correlated (r = 0.74, p < 0.001) the levels being higher after immunoextraction (p < 0.001). Gel chromatography disclosed heterogeneity of circulating
galanin-LI with the majority eluting as homologs with a molecular weight higher than synthetic human
galanin. Homologs smaller than
galanin were also found. Sep Pak C-18 extraction eliminated the majority of the higher molecular forms. In conclusion, circulating
galanin-LI was found to be higher in men and to be present mainly as molecular forms larger than synthetic
galanin.