BIG ATRIAL-NATRIURETIC-PEPTIDE - INVESTIGATION ON SPECIFIC HORMONE-BINDING PROTEINS

We reported previously that the incubation of radioiodinated 1-28 huma n ANP ([I-125]alpha-hANP) for 24 h at 4 degrees C in plasma resulted i n a partial conversion to large molecular weight forms of ANP (big ANP ) To clarify whether binding of hANP to plasmaproteins is involved, th e specificity, sensitivity and saturability of the binding were checke d. The results obtained at 4 degrees C do not support the existence of ANP-binding proteins in plasma since none of the predicted requisites was fulfilled. Moreover we checked for temperature dependence of poss ible specific binding by repeating the same experimental steps at phys iological temperature. Although at 37 degrees C there was enhanced bin ding with respect to that obtained at 4 degrees C, the results further demonstrate that human plasma does not contain specific ANP-binding p rotein. In conclusion the present data indicate that big ANP is not pr otein-bound but is an aggregated form. The question remains as to its possible physiopathological role in vivo.