Objective To investigate whether extracellular signal-regulated kinase （ERK1/2） was involved in changes of vascular smooth muscle cell （VSMC） under hypertension.Methods Two-kidney one clip Wistar hypertensive rats （WHR） were sacrificed and their right kidneys were harvested 4 weeks after surgery.The spontaneously hypertensive rats （SHR） were divided into 4

8

and 16 weeks old groups （SHR4w

SHR8w

and SHR16w）

respectively.The control group were sham operated age-matched Wistar rats.Immunohistochemical technique and Western blotting were applied to study ERK1/2 protein expression in VSMC of the renal vascular trees in WHR

SHR

and control rats.Results Blood pressure in two-kidney one clip WHR obviously increased at one week after surgery

and reached to 198.00±33.00 mm Hg at the end of experiment

significantly higher than that in the control rats （P<0.01）.Blood pressure in SHR4w （108.00±11.25 mm Hg） was similar to that in the controls.However

it rose to 122.25±21.75 mm Hg in SHR8w

and even up to 201.75±18.00 mm Hg in SHR16w

which were significantly higher than that of both the SHR4w and the controls （P<0.01）.The rate and degree of glomerular fibrosis in WHR were significantly higher than controls （P<0.05）.Hyaline degeneration of the afferent arterioles was found in WHR.In contrast

either fibrosis of glomerulus or hyaline degeneration of the arterioles or protein casts was not observed in SHR4w

SHR8w

and SHR16w.Immunohistochemical staining results showed expression of ERK1 was similar to that of ERK2.The positive rates of ERK2 staining in VSMC of afferent arterioles

interlobular

interlobar

and arcuate arteries in two-kidney one clip WHR were significantly higher （7.09%±1.75%

14.57%±4.58%

29.44%±7.35%

and 13.63%±3.85%

respectively） than that of the controls（P<0.01）.The positive rates of ERK2 staining in VSMC at afferent arterioles

interlobular

interlobar

and arcuate arteries in SHR16w were significantly higher （12.09%±1.40%

24.17%±6.92%

32.44%±4.05%

and 18.61%±3.35%

respectively） than that of the controls （P<0.01）

too.The expression of ERK1/2 protein of kidney in WHR and SHR16w was significantly higher than that in the controls by Western blotting assay （P<0.01）.Conclusion Extracellular signal transduction system are highly expressed in kidney VSMC of two-kidney one clip WHR and SHR.Phospho-ERK1/2 may play an important role in VSMC hypertrophy and hyperplasia under hypertension.