Abstract
The possible existence of binding protein for TRH was studied in rat serum. Synthetic TRH was incubated in rat serum and extracted in 90% methanol for measurement of tripeptide by RIA. The amount of TRH in serum at 37 C decreased progressively with incubation time, while that of tripeptide, which was incubated in serum at 60 C, significantly decreased 5 min after incubation, but TRH concentration afterward remained unchanged until 60 min. The concentration of TRH, which was incubated in serum at 37 C for 30 min, did not differ from that which was successively incubated at 60 C for 60 min. An elution pattern of TRH incubated in serum on a Sephadex G-25 was similar to that of authentic tripeptide, and this elution profile was not changed by heating at 60 C. An isoelectric focusing analysis of TRH incubated in serum showed a single peak of pI 8.2 which was not distinguished from the authentic peptide and was not changed by heating. These data indicate that TRH-degradation in rat serum is not dependent on its binding protein.
