[Lipolytic effects of a synthetic tetradecapeptide, corresponding to 31-44 amino acid sequence of human somatotropin].

A synthetic tetradecapeptide 31--44 developed a fast lipolytic effect in rats and rabbits in vivo and in vitro. The concentration of plasma fatty acid was maximal after 30 min following the injection and came down to the initial level after 60--120 min. The effect was prolonged when the tetradecapeptide was injected in the form of Zn-suspension. Both in rats and rabbits the in vivo lipolytic effect of native somatotropin was pronounced only after a 2-hr latency. Actinomycin D and cycloheximide did not prevent the lipolytic effect of the tetradecapeptide in isolated adipose tissue; however, this effect was not exerted in the absence of Ca2+. The hexapeptide fragment of tetradecapeptide was inactive in rats in vivo, but had a slight effect an isolated rat adipose tissue when taken at high doses. Thus, the lipolytic effect of the tetradecapeptide requires Ca2+ and is more pronounced in rabbits than in rats. Contrary to somatotropin, the effect of tetradecapeptide is fast and independent of RNA and protein synthesis. These data and previously shown tetradecapeptide lipolytic effect on isolated human adipose tissue suggest that the tetradecapeptide possesses structural features required for the lipolytic effect of the whole hormone.