Figure 1.

A, Mean concentration (nanograms per milliliter ± sem) of serum PRL in lactating animals 5 d after parturition (n = 6) after the infusion of saline or OTA (1.25 or 12.5 μg/μl). Upon pup replacement, 12.5 μg/μl of OTA prevented the suckling-induced rise in PRL secretion by 20 min (two-way ANOVA, followed by Bonferroni’s test; ***, P < 0.001). B, Mean (grams ± sem) pup weight gain on d 5 and 7 of lactation after infusion of OTA on d 3. When OTA was infused on d 3 of lactation, OT receptors were still affected on d 5 as determined by a lack of gain in pup weight. By d 7, pup weight gain was significantly greater, suggesting clearance of OTA and subsequent release of milk (one-tailed paired student t test; **, P < 0.01).