Hormone receptors and apoptotic factors of regressing mammary tumors in primiparous OFA hr/hr rats.

MASELLI, M.; SASSO, C.; CAMPO VERDE ARBOCCO, F.; SEMINO, S.; LOPEZ-FONTANA, C.; CARON, R.W.

Mendoza

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2012

SAIB

We aimed to study the mechanisms involved in the pregnancy/lactation-induced regression of mammary tumors in primiparous rats. Female OFA hr/hr rats were treated per os with the carcinogen (15 mg/rat of DMBA at 55 days of age) and divided into two groups: nulliparous (Nul, n=24) and primiparous (PL, n=17). Latency, incidence and progression of tumors (growth or regression) were determined. At sacrifice, tumors were removed for histological studies and for qPCR of hormone receptors: estrogens (ER?¿, ER?À), progesterone (PR, PRB) and prolactin (PRLR), and apoptosis related genes: Bax and Bcl-2. Statistical analysis was performed by Student t test and Fisher?Ls exact test. Tumor incidence was similar between groups, but latency was significantly lower (p<0.01) in PL group. PL rats showed the highest rate of tumors regressing during the experiment (p<0.05) and their tumors had higher count of apoptotic bodies (p<0.05). The mitotic/apoptotic ratio was significantly lower in the regressing tumors (p<0.05). No differences in the expression of ER?¿ and ER?À between groups were found, but tumors from PL rats showed lower expression of PR, PRB and PRLR (p<0.05) and the Bax/Bcl-2 ratio tended to be increased. The results so far suggest that apoptosis could be one of the mechanisms involved in the higher rate of regression observed in PL rats, probably related to changes in PRL and P pathways.