When is it a compulsory call ?

[Pondy]

as an example i'm sitting in the BB with J8 suited, blinds 50. 4 callers round to the button. Button raises to 150. Which means the pot is 425, and I have only got to stick in another 100. so it's offering me 4-1.

Now my question is that many books say that this is a call, infact a call with lmost any 2 cards (obviously not low ones). Is this true bearing in mind there are 5 people to act behind me, and i'm in early pos.

When is it a compulsory call, and how low can your cards be before it becomes a fold no matter what the pot odds are ( with this i mean if the pot is offering more than say 6-1 ) ?

hope this makes sense.