Abstract: Objective To investigate the changes of prolactin (PRL) expression in lymphoid nodes of BALB/c mice treated with diethylstilbestrol (DES) in neonatal period and whether these changes differ from female mice to male ones. Methods Neonatal brood BALB/c mice whose weight discrepancies less than 5% were divided randomly into control group and DES group, and 25 pairs of female mice and 25 pairs of male mice were chosen in all. Within 24 hours after birth, mice in DES group were injected subcutaneously at cervix-backside with DES at intervals of 24 hours for 5 times, and mice in control group were injected with germ-free bean oil by the same way. Mice were killed on day 7, 21, 35, 49 and 63 after birth separately, and 5 pairs of female mice and 5 pairs of male mice were killed at each time point. The lymphoid nodes were taken out, imbedded with paraffin and sectioned serially in 5 μm. The expression of PRL in slices of lymphoid nodes was detected by immunohistochemistry technique. Results No matter in female or male mice, PRL positive cells were present in mice of both DES group and control group since day 7 until day 63 after birth. Prolactin positive cells were recognized as lymphocytes with typical morphological characteristics, and distributed in cortex and medulla. PRL expression in both groups increased in an age-dependent manner until day 35 after birth and then declined. At each the same time point, both the average absorbance (A EM>A/EM> ) and the integrate absorbance (I EM>A/EM> ) of PRL expression were higher in DES group than those in control group. In female mice, statistic differences were showed in A A on day 35 and in I A on day 21, 35 (EM>P/EM><0.001), 49 and 63 after birth between the two groups. In male mice statistic differences were showed in AEM> A/EM> on day 35 and in I EM>A/EM> on day 21 and 35 between the two groups. Conclusion In both female and male BALB/c mice PRL positive cells were present in their lymphoid nodes, and the level of PRL expression was the highest on day 35 after birth. Being reated with DES during neonatal period could lead an increased PRL expression in lymphoid nodes of BALB/c mice. The female BALB/c mice were much more sensitive to DES stimulation than male mice, and the effects of DES on female mice can continue to their adulthood at least.

Key words: Lymphoid node, Diethylstilbestrol, Prolactin, Immunohistochemistry, Neonatal BALB/c mice