Different hemodynamic response after acute diuresis in the normotensive and hypertensive state

Acute diuresis is considered to alter the hemodynamic responses in the hypertensive state by reducing cardiac preload, mainly due to venodilation. To investigate the magnitude of this event, normotensive and two kidney-one clip hypertensive rats have been subjected to similar plasma volume restrictions by i.v. injection of 0.5 ml of furosemide (1 mg/100 g b.wt.). Two other groups of normotensive and hypertensive rats were subjected to 0.5 ml of 5% dextrose solution injection and served as controls. Mean arterial blood pressure and heart rate did not change after furosemide injection in either the normotensive or the renovascular hypertensive group. Alternatively, cardiac output of the hypertensive rats receiving furosemide injection was significantly lower by 39.9% and total peripheral resistance was significantly higher by 48.4% when compared to hypertensive rats receiving dextrose solution injection, whereas there was no difference concerning these indices in normotensive rats after the same interventions. Due to redistribution of regional blood flow, the coronary, cerebral and renal circulations of the hypertensive rats after furosemide injection have been protected. It is concluded that i.v. injection of furosemide, by decreasing cardiac preload, mainly due to venodilation, reduces cardiac output of renin-dependent hypertensive animals, whereas mean arterial blood pressure and heart rate remain unaltered. Redistribution of blood flow to vital organs prevented a further deterioration of the cardiovascular system.