Midwall left ventricular performance in salt-loaded Dahl rats: effect of AT1 angiotensin II inhibition

OBJECTIVEThe relationship between left ventricular midwall shortening and circumferential end-systolic stress was studied in Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats after 6–8 weeks of an 8% Na diet with or without losartan, an AT1 angiotensin II receptor antagonist. MATERIALS AND METHODSLosartan was given in drinking water to 13 Dahl S and 13 Dahl R rats, while 14 control Dahl S and 14 control Dahl R rats were given tap water, for 8 weeks. The endpoint was the last blood pressure and echocardiographic examination after 8 weeks or before death for rats which did not survive the entire period. Tail blood pressure was measured in awake animals and two-dimensional guided M-mode echocardiography was used. RESULTSThe left ventricular midwall shortening-circumferential end-systolic stress relationship in 45 normotensive Wistar rats was used to calculate the ratio of observed to predicted left ventricular midwall fractional shortening. At the endpoint, afterload-independent midwall shortening was higher in Dahl S rats on losartan or tap water, and in Dahl R rats on losartan than in weight-matched normotensive Wistar rats (all P