The effects of developing perinephritic
hypertension (2-3 weeks) and a more stable period of perinephritic
hypertension (approximately 14 weeks) were examined on indexes of left ventricular (LV) diastolic function in conscious, chronically instrumented dogs. The complete period of diastole was studied using indexes of isovolumic relaxation (tau), early filling (LV +dD/dt), and stiffness (myocardial stiffness and chamber stress/diameter ratio). During developing
hypertension, increased LV end-diastolic pressure, LV end-diastolic stress, peak filling rate, myocardial stiffness, and the stress/diameter ratio increased (p less than 0.05); the time constant tau was not changed. These changes were associated with preserved baseline levels of coronary blood flow (radioactive
microspheres) but an impaired coronary
vasodilator response to
adenosine. Acute administration of
phenylephrine in the normotensive dogs caused increases in systolic and diastolic stress and resulted in increases in myocardial stiffness and in the stress/diameter ratio similar to values observed in developing
hypertension. During stable
hypertension, LV end-diastolic stress, peak filling rate, and both parameters of late-diastolic function (myocardial stiffness and stress/diameter ratio) returned toward control values, but the isovolumic relaxation time constant was increased. Quantitative histological evaluation revealed no increase in stainable connective tissue in dogs with stable
hypertension compared with control dogs, and
hydroxyproline concentration was not increased in the subendomyocardium, midmyocardium, or subepimyocardium of the dogs with chronic perinephritic
hypertension. Thus, in developing
hypertension, major alterations in diastolic function were observed that were not structurally related, since these changes 1) could be induced in normal dogs by increasing preload and afterload acutely with
phenylephrine and 2) were improved during the ensuing stable period of
hypertension.