Distribution and metabolism patterns of plasma 7S- and β-NGF in the adult male rat

Abstract There is a great deal of controversy on the existence of NGF in body fluids and tissues. To date it remains unknown whether this peptide accumulates preferentially at significant levels in different organs. Thus we undertook the evaluation of kinetic parameters of the disappearance of blood of 125 I-7S-NGF and 125 I-β-NGF after intravenous injection in male adult rats. Our results indicate that the plasma half-life of 125 I-7S-NGF is approximately twice as long as for 125 I-β-NGF (respectively 61.7 ± 11.7 min and 36.3 ± 2.2 min) while the distribution volume is not significantly different between both peptides. Furthermore, the uptake of radioactive NGF by different tissues seems very low as shown by 125 I-7S-NGF and 1 25I-β-NGF content of the sampled organs compared to the plasma concentration at the same time. These results indicate that the tissue uptake of circulating 7S and β-NGF is very low in the adult rat. Thus in these animals NGF did not cross the blood-brain barrier and did not accumulate in peripheral organs which are known to contain subsequent amounts of this peptide. This lack of deposition might be due to a binding with plasma proteins (probably α2-macroglobulin).