Hemodynamic effects of an angiotensin II antagonist in rabbits with perinephritis hypertension

Role of angiotensin II in renal wrap hypertension

The role of angiotensin II in the development of renal wrap hypertension was studied in rabbits that underwent either bilateral renal cellophane wrap or sham operation. In half the rabbits, angiotensin II production was blocked by continuous administration of enalapril. Four weeks after renal wrapping, mean arterial pressure had risen by 48 +/- 5 mm Hg in untreated rabbits, but by only 25 +/- 4 mm Hg in enalapril-treated rabbits (p less than 0.01). Similar differences were also measured 6 weeks after wrapping. In untreated rabbits, plasma renin activity had increased fourfold 4 and 6 weeks after renal wrapping. There were no significant changes in blood pressure or plasma renin activity following sham operation. Compared with that in sham-operated rabbits, renal blood flow was reduced by 60% in the untreated rabbits 4 weeks after wrapping but by only 30% in the enalapril-treated wrapped rabbits (p less than 0.05). Renal vascular resistances were 5.5 +/- 1.7 mm Hg . ml-1 . min-1 and 1.2 +/- 0.1 mm Hg . min . ml-1 in the untreated wrapped and sham-operated rabbits respectively and 1.9 +/- 0.4 mm Hg . min . ml-1 and 0.8 +/- 1 mm Hg . min . ml-1 in the enalapril-treated wrapped and sham-operated rabbits. Renal wrapping did not alter filtration fraction in untreated rabbits, but markedly reduced it in enalapril-treated rabbits. These results suggest that angiotensin II had two major effects in rabbits after bilateral renal wrapping: it contributed substantially to the increase in blood pressure and caused renal vasoconstriction, primarily at a postglomerular site.

Systemic and regional haemodynamic profile of captopril in conscious rabbits with bilateral cellophane perinephritis hypertension

The radioactive microsphere technique was used to study the systemic and regional haemodynamic effects of the converting enzyme inhibitor captopril (0.1, 0.3 and 1.0 mg/kg) 10 min after intravenous administration in conscious rabbits with bilateral cellophane perinephritis hypertension, an experimental model of hypertension associated with normal plasma renin levels. Captopril lowered arterial blood pressure as a result of a dose-dependent decrease in total peripheral resistance. The fall in blood pressure was accompanied by an increase in cardiac output after the second and third dose of captopril; heart rate was not significantly altered. Captopril produced a generalized peripheral vasodilatation; the changes in vascular conductance being most pronounced in the kidneys, intestines and skin which resulted in a significant increase in blood flow to these vascular beds. The effective antihypertensive properties of captopril in this 'low plasma renin' model of hypertension and the uniform increase in vascular conductances produced by captopril, which antagonizes the generalized increase in vascular resistances that characterizes cellophane perinephritis hypertension, may indicate the involvement of an increased activity of the renin-angiotensin system, possibly in tissues, such as the vascular wall and brain, in the maintenance of the elevated blood pressure in this hypertensive form.

Hemodynamic effects of captopril in one-kidney, one clip hypertensive rabbits

Hemodynamic effects of captopril were examined in chronic one-kidney, one clip renal hypertensive rabbits and normotensive controls either in normal sodium or in sodium depletion. The mean arterial pressure (MAP) of hypertensive and normotensive rabbits in sodium depletion did not differ from that in normal sodium, while plasma renin activity (PRA) was elevated by sodium depletion. The cardiac output of sodium depleted groups decreased slightly. The increase in total peripheral resistance was greater in hypertensive than in normotensive groups. The MAP in all groups was decreased by acute administration of captopril irrespective of sodium intake. The decrease in MAP in the sodium-depleted hypertensive group was correlated with the control values of PRA, but no correlation was observed in other groups. Captopril significantly reduced the cardiac output of the sodium-depleted hypertensive group, but not of the other groups. These results show that: (1) the lowering effect of captopril on arterial pressure is not mediated only by blocking of the renin-angiotensin system, and (2) the decrease in cardiac output with captopril in sodium depleted hypertensive rabbits is an important factor in the reduction in the arterial pressure.

Systemic and regional hemodynamic characteristics of bilateral cellophane perinephritis hypertension in conscious rabbits

Using the radioactive microsphere technique, systemic and regional hemodynamic variables were measured in normotensive rabbits and in rabbits with bilateral cellophane perinephritis hypertension. An average decrease in cardiac output of 18 percent was measured in the hypertensive rabbits as a result of a reduction in stroke volume; heart rate remained unchanged. Thus, in the established phase, hypertension was maintained by the elevated total peripheral resistance. A redistribution of cardiac output was observed in the hypertensive rabbits; a significantly higher fraction was received by the brain, small intestine and heart. The weight normalized blood flow to the kidneys, spleen, skeletal muscles, bones and fat was significantly decreased while an increase in vascular resistance was observed in the hypertensive rabbits in all the organs investigated. A negative correlation existed between the weight of the left ventricle and the blood flow to the left ventricle in hypertensive rabbits, suggesting inadequate coronary perfusion as myocardial hypertrophy becomes more pronounced.

Systemic and regional haemodynamics in experimental renal hypertension in conscious rabbits

1. The radioactive microsphere method was used to measure the distribution of cardiac output, regional flows and resistances in conscious normotensive and hypertensive rabbits implanted with an electromagnetic flow probe on the ascending aorta or pulmonary artery. Hypertension was induced by wrapping one kidney with cellophane and removing the other, and studies were performed about 5 weeks later. 2. Heart rate, stroke volume, cardiac output and total renal mass were reduced in the hypertensive animals, while the weight of, and the cardiac output distribution to left ventricle and the remaining kidney were increased. 3. In renal hypertensive rabbits, the weight normalized regional blood flow was diminished in a number of tissues, including the kidney, and, except for some organs in the splanchnic area (stomach, small intestine, mesentery and pancreas) and the fat, there was a rather uniform increase in tissue vascular resistance.

Pressor responses to norepinephrine in rabbits with 3-day and 30-day renal artery stenosis. The role of angiotensin II

Pressor responses to norepinephrine (NE) infusions were examined in normal rabbits, in rabbits with renal artery stenosis of over 30 days' duration (chronic renal hypertensive rabbits), and in rabbits with renal artery stenosis of 3 days' duration (3-day clipped rabbits). The 3-day clipped rabbits did not have hypertension, but they showed the same increased pressor responses to NE as did the chronic renal hypertensive rabbits, which was about 2.5 times that of the normal rabbits. Plasma renin activity (PRA) was the same in the 3-day clipped rabbits as in the normal group, but in the chronic renal hypertensive rabbits the PRA was significantly below normal. Infusions of angiotensin II (A II) in either subpressor or pressor amounts potentiated the pressor responses to NE in normal rabbits, whereas, in 3-day clipped rabbits and chronic renal hypertensive rabbits, A II in subpressor or pressor doses did not alter the pressor responses to NE. Infusion of the A II antagonist, [1-sarcosine, 8-isoleucine]angiotensin II, did not alter the pressor responses of normal rabbits to NE, but this A II analogue completely abolished the pressor hyperresponsiveness to NE in the 3-day clipped rabbits and greatly reduced the NE hyperresponsiveness in the chronic renal hypertensive rabbits; this A II antagonist did not alter the control arterial pressure in any of the three groups of rabbits. These studies show that the increased pressor response to NE in rabbits with renal artery stenosis occurs before the onset of hypertension and thus is not merely a result of the hypertension. Also, these results provide evidence that A II plays an important role in the increased pressor responses to NE in hypertensive and prehypertensive rabbits.