Unfortunately the API does not provide a way to trigger the gesture programmatically nor does it provide public access to the targets and selectors of the UIGestureRecognizer.
However, if you are wanting to do this for unit tests, you could get access to the targets and selectors by doing the following:
NSArray *targets = [panGesture valueForKey:@"_targets"];
NSArray *actions = [panGesture valueForKey:@"_actions"];
You can then loop through those arrays and call the action on the target:
[target performSelector:selector withObject:panGesture];