Identification of epidermal growth factor mRNA-expressing cells in the mouse anterior pituitary

Epidermal growth factor (EGF) produced within the pituitary gland is associated with the growth of pituitary cells in rats. The aim of the present study was to localize EGF- and EGF receptor-expressing cells, and to clarify the involvement of EGF in DNA replication in 2-month-old male mouse pituitary cells. In situ hybridization of the pituitaries of these mice demonstrated that EGF mRNA was expressed in the anterior and intermediate lobes. Within the anterior pituitary, EGF mRNA-expressing cells were medium-sized and round, and made up 40% of the total number of secretory cells. EGF receptor mRNA was only detected in anterior pituitary cells. Forty-seven percent anterior pituitary cells expressed EGF receptor mRNA. An immunocytochemical study showed that most somatotropes and some mammotropes expressed EGF mRNA. When anterior pituitary cells were enzymatically dissociated and cultured in serum-free medium, RT-PCR demonstrated both EGF mRNA and EGF receptor mRNA expression. Treatment with EGF (1 and 10 ng/ml) for 5 days stimulated DNA replication in mammotropes and corticotropes. These results indicate that the DNA replication in mammotropes and corticotropes is regulated by the paracrine and/or autocrine activity of EGF produced at least in part by these cell types themselves.