Somatostatin-Like Immunoreactivity in Mammalian Thyroid Glands: Contents and Partial Characterization

Somatostatin (SRIF)-like immunoreactivity (SLI) in the thyroid glands of human and several animal species were compared, and the SLI peptides were characterized chromatographically and immunologically. All specimens were extracted with 2 M acetic acid, and the SLI content determined by RIA. The SLI concentrations in guinea pigs [34.3 ± (SE) 4.8 ng/mg protein] and rabbits (9.4 ± 0.8 ng/mg protein) were much greater than those in other mammals: dogs, rats, mice, and humans. On gel filtration of extracts of the guinea pig, rabbit and dog thyroids, the major peak of SLI (1.6 K SLI) coeluted with synthetic SRIF-14 (S-14). Two other forms of SLI (“big” SLI and 3 K SLI) were also detected, although their relative proportions to total SLI were small (2.3 to 8.2%). The 3 K SLI and 1.6 K SLI from guinea pig and rabbit thyroids contained peptides coeluting with synthetic SRIF-28 (S-28) and S-14, respectively, on reverse-phase high performance liquid chromatography. The dilution curves of the two molecular forms of S...