The effect of neuropeptides kyotorphin and neokyotorphin on proliferation of cultured brown preadipocytes

Stimulation of DNA and protein synthesis in brown preadipocytes by 1 mu M neokyotorphin in serum-containing media was comparable with the effect of 1 mu M norepinephrine. In serum-free medium a decrease and a shift of the maximal effect to lower concentration of neokyotorphin were observed, Kyotorphin had no effect on cell proliferation in either medium; however, 0.01-1 mu M kyotorphin inhibited the cell proliferation stimulated by 1 mu M norepinephrine. Norepinephrine and both peptides stimulated comparable Ca2+ rise in freshly isolated brown preadipocytes. The effects of neokyotorphin and norepinephrine were additive, whereas 0.03-0.3 mu M kyotorphin blocked the action of 3 mu M norepinephrine. The peptides did not affect the cAMP level in non-stimulated or norepinephrine-stimulated cultured cells, The effects of the peptides on the brown fat cell cultures indicate that peripheral tissue cells contain receptors for these neuropeptides. (C) 1997 Federation of European Biochemical Societies.