[Heterogeneity of immunoreactive calcitonin in the plasma of patients with bone marrow cancer].

Plasma from patients with medullary carcinoma containing very high levels of immunoreactive calcitonin were fractionated by filtration on Sephadex gel. In all cases the elution gave four immunoreactive fractions. Two of these fractions correspond to the volume of elution of the monomere and of the dimere of human calcitonin. The two other fractions emerge at an elution volume corresponding to much higher molecular weights. After stimulation of calcitonin secretion in vivo, by dynamic tests, the fractions corresponding to the monomere and dimere increase more strongly than the two other fractions. Preliminary studies of secretion, in vitro, of calcitonin by medullary carcinoma tissue, show the presence in the incubate of four immunoreactive forms having the same elution characteristics as those found in the plasma. The significance of these results is discussed.