Endogenous as well as exogenous hormonal modulation of lectin binding sites in normal and neoplastic tissue of rat mammary gland.

Free and sialic acid conjugated binding sites for the lectin from Arachis hypogaea (peanut agglutinin, PNA) have been histochemically demonstrated in normal rat mammary tissue and in N-nitrosomethylurea (NMU) induced mammary tumors of rats. The lectin binding sites were predominantly associated with secretory activities of the normal and neoplastic breast tissue (secretory PNA binding sites). In normal breast tissue and in NMU induced mammary tumors the expression of secretory PNA binding sites was reduced after ovariectomy and by the antiestrogen tamoxifen. Estrogen stimulated the formation of free and sialic acid conjugated PNA binding sites in the presence of prolactin. In rat mammary tumors the estrogen induced formation of PNA binding sites was accompanied by an increase of the progesterone receptor concentration in the tumors. Comparative lectinhistochemical, morphological, and biochemical studies on NMU induced rat mammary tumors revealed that the expression of secretory PNA binding sites was associated with a good histologic differentiation and the presence of steroidhormone receptors. Endocrine therapeutic studies showed that tumors responding to therapy possessed higher amounts of secretory PNA binding sites than unresponsive tumors. Therefore secretory PNA binding sites represent a useful histochemical marker for hormone dependence in NMU induced mammary tumors.