Effect of estrogen on the expression of a cell-surface antigen associated with rat anterior pituitary somatotrophs

Abstract

The long-term in vivo effect of diethylstilbestrol (DES) on the expression of a cell-surface antigen associated with the anterior pituitary somatotroph was studied in two strains of female rats using double immunofluorescence techniques. Mab WHC-1, a recently generated and characterized monoclonal antibody, was used to detect the antigen associated with somatotrophs, whereas rabbit anti-rat prolactin (rPRL) and anti-human growth hormone (hGH) antisera were used to identify mammotrophs and somatotrophs, respectively. In F344 rats, Mab WHC-1-positive cells increased from 13.8 ± 0.5% of total pituitary cells in normal anterior pituitaries to 34.2 ± 4.0% in DES-induced pituitary tumors. The number of mammotrophs also increased significantly from 58.0 ± 3.2% in controls to 75.9 ± 2.2% in tumors. On the other hand, somatotrophs decreased significantly in number following ovariectomy (OVX) and DES implantation (19.7 ± 0.5% vs. 6.1 ± 1.2%). Based on double immunofluorescence, the percentage of Mab WHC-1-positive cells, which were somatotrophs, decreased from 85.5 ± 2.7% in normal controls to 6.7 ± 1.5% in DES-induced tumors. On the other hand, the percentage of Mab WHC-1-positive cells which were mammotrophs increased significantly from 14.0 ± 1.4% to 86.1 ± 1.8% following OVX and DES implantation. A similar change was found in the number of somatotrophs and mammotrophs following the same treatment in Sprague-Dawley (SD) rats which did not develop pituitary tumors. In contrast to F344 rats, the number of Mab WHC-1-positive cells in SD rats decreased significantly from 32.4 ± 2.8% in sham-operated controls to 19.3 ± 2.9% in OVX + DES-implanted rats. Significant strain differences were found in the relative population of Mab WHC-1-positive cells, somatotrophs and mammotrophs. The results indicate a shift in the expression of Mab WHC-1-defined cell-surface antigens from the majority of somatotrophs to an increasing number of mammotrophs following long-term treatment of estrogen.