Peptides with high intrinsic activity to release
growth hormone from pituitary cells in tissue cultures were isolated from two different human pancreatic
tumors that had caused
acromegaly. Homogeneous
peptides were obtained after gel filtration and two steps of reverse-phase high-performance liquid chromatography. From one
tumor a 44-residue
peptide (human pancreas
growth hormone releasing factor,
hpGRF-44) was isolated, together with two shorter fragments of reduced bioactivity having 40 and 37
amino acid residues (hpGRF-40, hpGRF-37). In contrast, the other
tumor contained only one form of GRF which proved to be identical to
hpGRF-40. These hpGRFs are indistinguishable from partially purified preparations of hypothalamic
growth hormone releasing factor of human, porcine and murine origins with respect to
biological activity and are very similar in their physicochemical properties (molecular weight, retention behavior on reverse-phase HPLC, absence of sulfhydryl groups). One of the pancreatic
tumors also contained two forms of immunoreactive
somatostatin. One form, after isolation and partial microsequencing, was identified as
somatostatin-14 with a structure identical to that of the
peptide found in other species. The second form has tentatively been identified as
somatostatin-28 on the basis of chromatographic behavior.