Somatostatin-like immunoreactivity in mammalian thyroid glands: contents and partial characterization.

ABSTRACT

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 SLI, i.e. 3 K SLI and 1.6 K SLI, were parallel to the displacement curves of S-28 and S-14 in the SRIF RIA. It is concluded 1) that the thyroid contents of SLI varied greatly from species to species, with the highest content being found in guinea pig thyroids; 2) that in guinea pigs, rabbits, and dogs, the predominant form of thyroid SLI is 1.6 K SLI; and 3) that the 3 K SLI and 1.6 K SLI peptides from guinea pig and rabbit thyroids are immunologically and chromatographically indistinguishable from S-28 and S-14, respectively.