[Comparative assessment of the specific activity of several thyrotropin-releasing-hormone analogs].

A study was made of the effect of replacement of the second and third amino acid residues of the thyrotropin-releasing hormone on the manifestation of the specific biological activity assessed by the radioimmune method of determination of the thyrotropic hormone in rats. Replacement of histidine by alanine caused a 100-fold and by phenylalanine - a 10-fold reduction of the activity. Glycine analogue proved to be inactive. The biological activity of TRH analogue (Glu-Phe-Pro CH3) was only 10 times less in comparison with the activity of the standard. The second double modified analogue of this hormone (Glu-Gly-Ser NH2) was incapable of influencing the release of the thyrotropic hormone by the hypophysis.