[Effect of synthetic hypertensin II on PAH- and inulin clearance, on renal hemodynamics and on diuresis in man]

Effects of salt loading and haemodilution on the responses of perfused cat kidneys to angiotensin

1. Effects of single intra-arterial injections (0.1-1.0 mug) of angiotensin II have been observed on cat kidneys perfused with heparinized blood from heart-lung circuits.2. Angiotensin II always caused an abrupt decrease in renal plasma flow (R.P.F.) which reached maximum in 1-2 min and lasted over-all for only 3.5-4.0 min. Glomerular filtration rate (G.F.R.) usually and filtration fraction (F.F.) always increased.3. Angiotensin II caused antidiuresis provided that the kidney had not been subjected either to salt loading or to haemodilution within the preceding 3 hr. These pretreatments converted the antidiuretic action of angiotensin into a diuresis.4. Angiotensin II raised the rate of Na excretion, the urinary concentration of Na and the urinary Na/K whether anti-diuretic or diuretic.

Some contributions to the pharmacology of synthetic angiotensin

The examination of synthetic valyl-5-angiotensin II-amide in the conscious dog revealed the following:

1. Both the arterial and the central venous pressure responses exhibit tachyplylaxis when high doses of angiotensin II are administered, althoug not when medium or low doses are given. Cross-tachyphylaxis can be demonstrated between renin and angiotensin II but not between either of these and norepinephrine. These results suggest that tachyphylaxis to renin is due to tachyphylaxis to angiotensin.

2. Angiotensin II and norepinephrine provoke a dose-dependent increase in central venous pressure. The threshold dose is about 10 times higher than that necessary for the effect on arterial pressure. In doses eliciting the same increase of arterial blood pressure, norepinephrine is about twice as active on the venous pressure as angiotensin II.

3. Anesthesia and atropinization both reduce or abolish the effect of angiotensin II as well as that of norepinephrine on the venous pressure, indicating the reflex nature of the underlying mechanism.

4. In endotoxin hypotension, the pressor response to angiotensin II and to norepinephrine is diminished, and the venous pressure response becomes gradually depressed until it is completely abolished.

5. During hemorrhagic hypotension, the response to angiotensin II may be retained or even enhanced and is less likely to have an adverse effect on the myocardium than norepinephrine.

Evaluation of the pressor, cardiac, and renal hemodynamic properties of angiotensin II in man

These data demonstrate that in normal subjects angiotensin II is 10 times as potent as norepinephrine, which it resembles hemodynamically. An increase in the systolic pressure is associated with significant increase in diastolic pressure, increase in venous pressure, decrease in heart rate, slight decrease in cardiac output with striking increase in total peripheral resistance, decrease in renal blood flow, decreased glomerular filtration rate, increase in filtration fraction, arid slight decrease in urinary volume.

Preliminary studies of patients in shock suggest that angiotensin II is two or three times as potent as norepinephrine. Continuous administration is not associated with the development of resistance or tachyphylaxis, nor does sloughing of tissues occur when there is leakage outside the vein.

Effects of subpressor doses of angiotensin II on renal hemodynamics in relation to blood pressure

The renal hemodynamic response to subpressor doses of angiotensin II (AII; 0.1 and 0.5 ng/min/kg) was investigated in untreated 49-year-old men (n = 50) representing a wide blood pressure range. Renal blood flow, renal vascular resistance (RVR), glomerular filtration rate (GFR), filtration fraction (FF), plasma renin activity (PRA), plasma AII, plasma aldosterone, and the urinary excretion of sodium and norepinephrine were studied. The higher the initial blood pressure the greater was the increase in RVR in response to AII infusion (p less than 0.002), indicating an increased renal vascular reactivity with increase in initial blood pressure. The AII infusion gave a significant rise in RVR in both the borderline and hypertensive group, but gave no increase in RVR in the normotensive group, implying an enhanced sensitivity of the renal vasculature in the borderline and hypertensive group. The increase in RVR was greater in the hypertensive than in the borderline group, i.e., the hypertensives had a steeper dose-response curve than the borderline group, which points to the presence of structural vascular changes in the renal vessels in the hypertensives. The increase in RVR in response to AII was positively correlated to sodium intake and plasma aldosterone concentration, indicating that these two factors might modulate the renal vascular reactivity. These factors could, however, only partly explain that RVR increased more the higher the initial blood pressure. Thus, the results indicate that there is an increased reactivity of the renal vascular bed to AII in essential hypertension. The increased reactivity seems to be mediated through an increased sensitivity of the renal vasculature to AII in mild essential hypertension and also through the presence of structural vascular changes in established hypertension. These factors may lead to a reduced excretion of sodium and water and may therefore be of importance in the development and progression of essential hypertension.

Effect of angiotensin on normal renal circulation determined by angiography and a dye dilution technique

Angiotensin in a dose of 0.5 to 1.0 microgran injected into the renal artery of healthy kidneys initially decreased renal blood flow and increased the appearance time and mean transit time of dye and contrast medium as examined by a dye dilution technique and angiography. The initial phase is followed by a reactive hyperemia. The increased vascular resistance is probably localized peripherally on the arterial side of the vascular tree. Optimum dose is 0.5 to 1.0 microgram angiotensin in diagnosis of renal tumours. Optimum interval between drug administration and angiography is 10 to 60 s.

Renal actions of dihydroergocristine and of phentolamine in anaesthetized cats

1. Comparison has been made of the effects of dihydroergocristine (DCS) and phentolamine mesylate (phentolamine) on cardiac and respiratory rates, systemic arterial pressure, renal clearances of creatinine (C(Cr)) and of p-amino-hippuric acid (C(PAH)) and on the secretion of Na and K, in cats under chloralose anaesthesia.2. Phentolamine antagonized vasomotor tone and the pressor effect of circulating noradrenaline to comparable extent. The extent of reduction in urine flow, C(Cr), C(PAH) and Na excretion correlated with the fall in mean arterial pressure. Innervated and denervated kidneys responded similarly. Cardiac and respiratory rates rose slightly as arterial pressure fell.3. DCS, 10 to 20 mug/kg per min, did not reduce vasomotor tone, markedly reduced the pressor effect of exogenous noradrenaline, caused bradycardia and respiratory slowing but had little or no effect on renal function.4. DCS, 30 to 40 mug/kg per min, lowered mean arterial pressure by 15-25 mm Hg, decreased C(PAH) but not C(Cr), so raising the filtration fraction and caused a small reduction in urine flow and in Na excretion. Innervated and acutely denervated kidneys responded similarly.5. DCS, 30 to 40 mug/kg per min, raised mean arterial pressure, decreased C(PAH), urine flow and Na excretion but did not alter C(Cr) in animals pretreated with full alpha-adrenergic blocking doses of phentolamine.6. DCS, 30 to 40 mug/kg per min, increased the rate of secretion of sympathetic amines from the adrenal medulla and increased the concentration of renin in renal venous blood.7. Isolated kidneys perfused at constant pressure from pump-oxygenator circuits and in saline diuresis responded to DCS (15-17 mug/120 ml. blood) by diuresis and natriuresis and by a rise in the rate of secretion of renin. Higher concentrations of DCS (125-250 mug/120 ml.) were without effect on renal function and did not influence renin secretion.8. The renal effects of full alpha-adrenergic blocking doses of DCS and of phentolamine were comparable, in the whole animal.9. The evidence indicates that the release of noradrenaline by DCS 30-40 mug/kg per min from nerve terminals supplying the juxtaglomerular apparatus may have caused the enhancement of renin secretion.

Effects of Hypertensin on Arterial Pressure, Heart Work and Cardiac Oxygen Utilization

Pharmacodynamically induced changes in left ventricular work, using an intravenous infusion of Hypertensin, were studied in intact anesthetized dogs. Coronary and systemic hemodynamics and cardiac metabolism under a combined morphine- "Dial" -urethane-pentobarbital-sodium (MDUP) anesthesia were measured during the action of the drug. The significant hemodynamic changes induced were increased mean arterial pressure and increased left ventricular work. A greater cardiac lactate utilization during the Hypertensin infusion was the only change in cardiac metabolism. The oxygen tension in left ventricular venous blood was not reduced during the action of the drug.