The objective of this study was to investigate the effects of oestrogen receptor (ER) beta activation on vascular protein synthesis and protein expression. Nuclear immunoreactivity towards ER beta was observed abundantly in vascular smooth muscle and endothelial cells of mouse aorta. No ER alpha-positive cell nuclei were observed. In aorta from ovariectomized mice, treatment with the selective ER beta agonist genistein (100 nM) for 24 h increased (3)Hleucine incorporation by about 30%. This effect was prevented by the ER blocker ICI 182780 (10 microM). Although genistein treatment stimulated protein synthesis, it caused no change in total protein determined either by the Lowry method on tissue homogenate or by densitometric scanning of protein bands (10-220 kDa) separated by SDS-PAGE. Separation of (35)Smethionine-labelled proteins by SDS-PAGE did not reveal the protein(s) stimulated by genistein. DNA synthesis was not affected by 100 nM genistein, suggesting that genistein-induced stimulation of protein synthesis is not part of a growth response. Protein expression, determined by SDS-PAGE, was similar in aorta from ER beta-knockout and wild-type mice, suggesting that expression of vascular proteins does not depend solely on a functional ER beta gene. We suggest that activation of vascular ER beta stimulates synthesis of proteins and that this response is not associated with vascular growth.