Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:This indicates that the upregulation of TGF-b1 by ANG II is enhanced in the obstructed kidney, an effect that occurs in the face of normalization of receptor expression after 3 days of UUO (48).
Category: