CONCENTRATIONS OF THYMULIN IN UNEXTRACTED SERUM FROM PIGS, SHEEP AND CATTLE AS MEASURED BY ELISA

These studies were conducted to develop an ELISA for measurement of th ymulin concentrations in unextracted blood serum (or plasma) from dome stic animal species (pigs, sheep and cows). This assay was quite varia ble (intraassay C.V. of 13.3 and 6.4% at 12.6 and 50.5 pg/mL arid inte rassay C.V. of 24.2%). Serial dilutions of serum from these species pr oduced inhibition curves parallel to the reference standard, suggestin g that there were no substances in serum causing non-specific interfer ence in the assay. In addition, none of the other thymic peptides test ed resulted in problematic displacement of thymulin binding to the ant iserum. Using this assay, it was found that somatotropin (ST) treatmen t had no effect on serum thymulin concentrations in either pigs or cow s. Chromatographic separation of thymulin activity in sheep serum show ed three peaks with approximate MW estimates of 95, 80 and 1 kDa. Seru m thymulin concentrations in a sheep injected with thymulin was cleare d from blood with a half-life (t(1/2)) of 10.3 +/- 0.6 min. Serum thym ulin concentrations increased between birth and 6 mo old in pigs. Thes e data indicate that a rapid and reliable ELISA has been developed to measure thymulin in blood of these domestic animals. This assay should be of value in the study of thymulin function and factors regulating its secretion.