Fig. 5. Impaired secretory function at lactation. (A,B) Paraffin wax-embedded sections from mammary glands harvested on the date of birth were stained with Hematoxylin and Eosin. Scale bar: 50 µm. In comparison with wild-type (A), glands lacking Hif1 (B) contained fewer alveoli, which were less differentiated. (C,D) Glands were also harvested at mid-lactation from weaned dams, allowing milk (indicated by yellow stars) to fill the gland. Scale bar: 50 µm). In wild-type mice (C), the accumulation of milk fully distended the alveoli, and a relatively small volume of adipose tissue was present. By contrast, in the Hif1a^–/– glands (D), accumulation of milk was minimal, large lipid droplets remained trapped within the epithelial cells (white arrow), and large areas of adipose tissue were visible. (E) Wet weight (±s.e.m.) of frozen inguinal glands harvested from lactating dams. (F) Representative growth curve of litters nursing wild-type (black circles) and Hif1a^–/– dams (gray circles). Pronounced defects in pup weight gain were observed by day 3 of lactation that persisted until mid-lactation.