ARs multiply, in response to weight training/increased muscle mass and therefore probably in response to AAS also, this was often called "AR upregulation" when it was talked about in the 90s by 'gurus' like Duchaine.
Not sure what you mean by saturation or down-regulation. I mean you become more sensitive to AAS when not using them or using lower amounts, but what you would call that technically? People are using technical terms here usually to describe a phenomenon that probably involves a very large number of factors.