Figure 1.

The icv or systemic oPRL administration initiates a daily PRL secretory rhythm. OVX rats were injected with oPRL or vehicle icv (0.15 μg) (A) or oPRL systemically (15 or 150 μg) (B) at 2200 h of d 0 (arrow). Blood samples were withdrawn during the next 2 d to determine the presence of the PRL diurnal and nocturnal surges (n = 5–11). Data are presented as mean ± sem. #, P < 0.05; ###, P < 0.001 vs. vehicle-injected group at the same time point. *, P < 0.05; **, P < 0.01; ***, P < 0.001 vs. basal PRL on 2100 h of d 1 in the same experimental group.