Abstract： The role of platelet-derived growth factor (PDGF) receptor-mediated signal transduction in myocardial hypertrophy of spontaneously hypertensive rats (SHR) was investigated. The protein expressions of PDGF β receptor and extracellular signal-regulated kinase 1/2 (ERK 1/2) and the level of phosphorylated ERK 1/2 (pERK 1/2) in cardiac tissues from 4- and 12-week-old SHR and their age-matched normotensive control Wistar-Kyoto rats (WKY) were examined by Western blot analysis. The results showed that arterial systolic and diastolic blood pressure,±dp/ dtmax and the ratio of left ventricular weight to body weight were unchanged in 4-week-old SHR,while they were increased significantly in 12-week-old SHR as compared with those of age-matched WKY. There were no differences in PDGF β receptor,pERK 1/2,and ERK 1/2 between 4-week-old WKY and SHR. The expression of PDGF β receptor of 12-week-old SHR was significantly increased by 32.77% (P<0.05) as compared with that of age-matched WKY. Although the expression of ERK 1/2,the downstream signal molecule of PDGF receptor-mediated signal transduction pathway,was unchanged,the level of pERK 1/2,the active form of ERK 1/2,was increased by 19.6% (P =0.01) in 12-week-old SHR. To further elucidate the effect of PDGF β receptor on cardiomyocyte growth and the relation between PDGF β receptor and ERK 1/2 activity,[3H]leucine incorporation assay and immunoblotting analysis of pERK 1/2 were performed after cultured neonatal rat cardiomyocytes were stimulated with PDGF-BB. It was shown that [3H]leucine incorporation and pERK 1/2 level were significantly increased after PDGF-BB stimulation. These findings suggest that PDGF β receptor may play an important role in the myocardial hypertrophy of spontaneously hypertensive rats.