Abstract: Abstract Objective：To investigate the growth inhibitory effect of OGF and the opioid antagonist naloxone on MCF-7 human breast carcinoma cells. Methods：Cell counting、MTT essays and cell cycle distribution analysis by flow cytometry were used to detect the inhibiting growth effect of OGF on MCF- 7 cells. Results: Cell counting showed that the cell concentration reduced markedly in OGF group than other groups（P<0.01）. No difference was found between naloxone and control groups（P>0.05）. MTT essays indicated that the inhibiting rate of cell growth of OGF group was significantly higher than that in naloxone and OGF/naloxone groups (P<0.01). There was no significant difference among naloxone, OGF/ naloxone and control groups（P>0.05）. Flow cytometry results showed that PI was lower in OGF group than in other groups（P<0.01）, and no significant difference was found between naloxone and control groups（P>0.05）.Conclusions: OGF could inhibit the growth of MCF-7 cells in vitro and the growth inhibitory effect of OGF can be blocked by naloxone. The cell cycle was obstructed by OGF in G0/G1 phase.

Key words: OGF, OGFr, MCF-7 human breast carcinoma cells, receptor, growth factor, cell cycle