@ David, thanks for the hint. I allready saw that, but i would rather work with an Graph object (if that's possible).
@ Sam, yes that would make sense, my code looks like this:
example = RandomGraph[{50, 500}, DirectedEdges -> True,
EdgeStyle -> Gray,
GraphLayout -> Automatic,
VertexLabels -> Table[i -> Placed[i, Center], {i, 50}]]