[Potentiation of in vitro lipolytic effect of ACTH by its fragment]

The influence of fragment ACTH 11-14 analogues with amino acid sequences H-Lys-Pro-Val-Gly-OH (fragment I) and H-Lys-Pro-Val-Gly-NH2 (fragment II), possessing structural elements, similar for certain groups of peptide hormones and kinins, on lipolytic effect of ACTH in adipose tissue and isolated epydidymal fat cells of rat, was studied. Both fragments have no effect on the lipolysis; they potentiate the ACTH-induced lipolysis 1,5--2,0 fold, but do not alter the maximal effect at concentrations 0,1--1,0 mkg/ml in tissue and fragment I--at concentrations from 0,01 to 0,1 mkg/ml in isolated fat cell system. The role of "common" fragments in hormone-receptor interactions as well as mechanism of their potentiating effect is discussed. It is assumed that the "common" fragment of ACTH--ACTH11-14--is a second, non-specific active site of hormone directly involved in secondary signal formation.