Peripheral plasma renin activity in renal-homotransplant recipients

The renin-aldosterone system and renal hemodynamics in patients with posttransplant hypertension

Plasma renin concentration (PRC), plasma aldosterone concentration (PAC), renal plasma flow (RPF) and glomerular filtration rate (GFR) have been studied in 19 patients who had received a renal allotransplant. Group 1 consisted of 7 normotensive and group 2 of 12 hypertensive patients. Bilateral nephrectomy was performed in all patients; all were on a fixed daily sodium intake, and no antihypertensive agents were given. No significant differences were found between the groups in age, time after transplantation or dosages of prednisone. PRC and PAC were normal in all but one patient in group 1 and two in group 2. In these three patients a slight elevation of PRC was measured. After one hour in the erect position, a significant increase was measured in PAC, but not in PRC in both groups. After 6 days on a 10 mEq sodium diet, PRC and PAC increased significantly in both groups. After a further 6 days on the diet plus 150 mEq sodium daily, significant decreases in PRC and PAC were measured in both groups. No differences were detected in PRC or PAC between groups 1 and 2 either before or after the two dietary periods. RPF was significantly lower in the hypertensive group, whereas no significant difference was found in GFR between the groups. No significant relationship could be demonstrated between blood pressure (BP) and PRC or PAC, and PRC and PAC were not correlated to each other. RPF was significantly correlated to mean BP and PRC in the normotensive group but not in the hypertensive. It is concluded that PRC and PAC are normal in most patients with posttransplant hypertension, whereas the RPF is decreased. It is suggested that an abnormal regulation of renin secretion plays a role in the sustained elevation of BP after renal allotransplantation.

Plasma renin, plasma aldosterone and exchangeable sodium in normotensive and hypertensive kidney transplant recipients with and without transplant renal artery stenosis

Blood pressure (BP), plasma renin concentration (PRC), plasma aldosterone concentration (PAC) and exchangeable sodium (ES) were studied in 19 kidney recipients on different fixed levels of sodium intake after successful kidney transplantation. The following groups of kidney recipients were investigated: group 1: 7 normotensives, group 2:7 hypertensives without transplant renal artery stenosis (TRAS), group 3:5 hypertensives with angiographically verified TRAS. Hypertension in the recipients without TRAS (group 2) was characterized by a positive correlation between BP and ES and a normal response of PRC and PAC to a fixed low (10 mEQ/day) and high (150 mEq/day) sodium intake. In contrast, hypertension in the recipients with TRAS (group 3) was characterized by a normal or varyingly increased PRC on a liberal sodium intake and a reduced response of PRC to sodium restriction, whereas PAC did not differ from the other groups of recipients. In one recipient in group 3 who underwent surgical correction for TRAS, PRC and PAC decreased before operation during sodium restriction, but BP remained high until after operation, when it normalized simultaneously with a decrease in ES. The results indicate that sodium retention is involved in the pathogenesis of posttransplant hypertension and suggest that an increased activity of the renin--angiotensin system is counterbalanced by an accumulation of sodium in TRAS.

Extrarenal prorenin and renin in anephric patients

Active renin was detected in 6 of 7 anephric patients (mean value: 0.72 +/- 0.27 microU/ml, n = 7; normals: 19.7 +/- 2.4 microU/ml, n = 10), using an assay method without intrinsic acid- or cryoactivation. Prorenin, measured as the difference between plasma renin concentration (PRC) before and after acid-activation in vitro, was present in considerable amounts in all patients (32.4 +/- 3.5 microU/ml; normals: 80.7 +/- 9.7 microU/ml). PRC after cryoactivation at--5 degrees C during 1 week was insignificantly lower than after acid-activation in the patients. There was a linear correlation between PRC after either activation procedure (p less than 0.01). Supine or upright posture did not influence active or inactive renin in the anephric subjects. Our studies show that low but significant levels of active renin and a considerable amount of prorenin are detectable in anephric patients. The data suggest that prorenin in normal subjects in a significant proportion is of extrarenal origin. Orthostasis has no effect on extrarenal active or inactive renin.

The patterns of peripheral plasma renin concentration in the early post-renal-transplant period

Serial determinations of peripheral plasma renin concentration (PRC) were performed in 11 kidney transplant recipients during the early post-transplant period. In 5 recipients with late onset of graft function, PRC values were increased during the anuric phase and, subsequently, PRC values declined in every during restoration of graft function. In 4 recipients with an acute renal allograft reaction, PRC values were increased at the onset of the allograft reaction in 3 with hypertension whereas PRC values were normal in one normotensive recipient. Subsequently, PRC normalized in the hypertensives coincident with increasing body weights. In 2 recipients with an uncomplicated course and with a normal graft function immediately after transplantation and throughout the study period, PRC values were constantly normal. The results indicate that acute anuria in the early phase after kidney transplantation is associated with an increased release of renin. The results also suggest that an increased activity of the renin-angiotensin system may be counterbalanced by sodium and fluid retention in hypertension following an acute renal allograft reaction.

Interrelationships among thiazide diuretics and calcium, magnesium, sodium, and potassium balance in normal and hypertensive man

The benzothiadiazide diuretics are known to cause magnesium and potassium wasting and retention of calcium and uric acid. The effect of magnesium replacement on diuretic-induced changes in sodium, potassium, calcium, and magnesium balance, weight, and blood pressure was studied in 12 normal subjects and 13 hypertensive patients to determine whether oral magnesium would reduce thiazide-induced kaliuresis. The groups differed in their response to diuresis in that the normotensive subjects did not show a fall in blood pressure (despite an equivalent weight loss), returned to a state of sodium balance earlier, and developed a greater net negative potassium balance over 12 days of diuretic therapy. Both groups displayed calcium and uric acid retention and magnesium wasting during diuretic therapy. The addition of oral magnesium replacement during diuretic therapy had no effect on any measured values beyond that seen in subjects who took diuretics without magnesium replacement. Thus, magnesium replacement did not reduce urinary potassium loss. However, urinary calcium losses increased when magnesium was given to subjects who were not receiving diuretics. The data provide the first report that small doses of oral magnesium enhance calcium excretion in hypertensive subjects.

Post-transplant hypertension. Normoreninemic severe hypertension treated by bilateral nephrectomies

In a nineteen-year-old male in whom severe and protracted hypertension developed after a successful renal transplantation, the removal of the diseased kidneys resulted in restoration of normal blood pressure. Prenephrectomy blood samples obtained from the venous drainage of all three renal veins demonstrated no evidence for excessive renin secretion, nor was a significant difference in renin activity found between any two kidneys. It is postulated that the patient may be a clinical variant of the experimental form of renal hypertension with normoreninemia. Alternatively, the remnant kidneys may be implicated to produce a nonrenin pressor substance.

beta-adrenergic blockade in essential hypertension: reduced renin release despite renal vasoconstriction

The acute effects of small doses of intravenous propranolol on renin release and on circulatory dynamics were studied at the time of renal arteriography in 12 persons with essential hypertension. All of the subjects had a normal peripheral renin response to chronic sodium depletion and all had normal renal function. Seven subjects received a 10-mEq sodium diet. At the time of arteriography, arterial blood pressure, pulse rate, cardiac output, renal blood flow, and arterial and renal venous renin activity were measured before and 6-20 minutes after the intravenous administration of propranolol (9-18 mjg/kg). Average renin secretion rate in the salt-depleted subjects fell from 367 +/- 80 (SEM) U/ml per 100 g/min to 122 +/- 51 U/ml per 100 g (P=0.03) and renal plasma flow fell from 189 to 155 ml/min per 100 g (P = 0.018). We also found that in the salt-loaded subjects, renal plasma flow fell from 213 to 184 ml/min per 100 g (P = 0.025), whereas renin secretion did not change significantly in either group. We conclude that propranolol rapidly blocks renin release despite circulatory changes which ordinarily constitute a stimulus for renin secretion, i.e., renal vasoconstriction and reduced renal blood flow.

Iso-renin of extrarenal origin. "The tissue angiotensinogenase systems"

Enzymes, similar to kidney renin, are present in extrarenal tissue of most mammals; they hydrolyze angiotensinogen to form angiotensin I. We suggest that these enzymes be called angiotensinogenases. Angiotensinogenase concentrations in extrarenal tissue can exceed those in the kidney. The enzyme has been obtained in pure crystalline form. Angiotensinogenases are part of a complex enzyme system which leads to local production of angiotensin. Results indicating a biologic role of the angiotensinogenase system in brain, adrenal gland, uterus and tissue culture are discussed.

Hypertension due to renal artery stenosis in transplanted kidneys

Hypertension appeared to be related to stenosis of the hypogastricrenal artery system in 5 patients among 153 recipients of renal allografts. Renin assay and arteriography were crucial in the comprehensive evaluation of patients whose hypertension was not clearly related to rejection or excessive sodium intake. Hypereninemia was persistent in 4 of the 5 patients. Stenoses of the transplant renal arteries in three patients were caused by extensive intimal plaque formation. In one patient, periarterial fibrosis caused reduction of flow; 180 degrees torsion of the anastomosis resulted in stenosis in the fifth patient. Surgical correction is difficult and may be facilitated by a transabdominal approach. Vein bypass is probably preferable to patch angioplasty for intimal lesions. Following operation, hypertension was ameliorated and function improved in all patients. Rejection, which has been suggested as one of the causes of intimal plaque formation, ultimately led to the loss of the transplant in one patient. Function is normal in two patients; two patients have evidence of chronic rejection. No effort should be spared to evaluate this special group of patients whose transplant function can predictably be prolonged by decisive surgical management.

The aetiology of hypertension after renal transplantation in man

The renin-angiotensin-aldosterone system was studied in renal allograft patients, 70 per cent of whom were hypertensive.

Plasma-renin levels were found to be normal, and a normal increase was observed when patients were changed from the supine to the erect posture (P<0.01). However, aldosterone-secretion rates were found to be approximately four times normal, and a positive correlation between these values and diastolic blood-pressure was observed (r = 0-5, P = 0-05). In patients with intact kidneys a highly significant correlation between plasma-renin activity and aldosterone-secretion rate was observed (r = 0.8, P>0.05), but this normal correlation was not apparent in the patients with transplanted kidneys (r = 0.1, P>0.5). Thus the aldosterone-secretion rates in these patients was not under the control of the renin-angiotensin system.

Concurrent studies in adrenalectomized patients showed that they also had elevated aldosteronesecretion rates, and the injection of 14C-labelled cortisone acetate showed that they were capable of converting this steroid into aldosterone or an aldosterone-like metabolite. It is suggested that the hypertension seen after renal transplantation is related to the conversion of prednisone to a mineralocorticoid.

Further support for this hypothesis was obtained from studies in patients who had their therapy changed from daily prednisone to alternate-day methylprednisolone. They were found to secrete less aldosterone and all the patients became normotensive following this régime (P >0.1). In addition, patients treated with an aldosterone antagonist, spironolactone, showed a prompt decrease in blood-pressure.

It is concluded that the denervated transplanted kidney is able to maintain normal blood-pressure homeostasis in man, and that hypertension Seen after renal allografting is largely due to the therapy with immunosuppressive steroids.

Variations in arterial blood pressure after kidney transplantation. Relation to renal function, plasma renin activity, and the dose of prednisone

The course of hypertension within the first 2 months after kidney transplantation was correlated with renal function, plasma renin activity (PRA), and the daily maintenance dose of prednisone in 18 homograft recipients. During acute rejection blood pressure (BP) closely correlated with PRA. Patients with normal homograft function showed an increase in BP early after transplantation which in most returned to normal 3–8 weeks later. In the latter group no correlation could be found between the level of BP and PRA, however the BP correlated closely with the dose of prednisone. These observations suggest that during acute rejection the increase in BP may at least partly be mediated by a renal pressor mechanism, whereas with normal renal function the high dose of glucocorticoids may play an important role in the development of hypertension.

Changes of blood pressure, renin, and angiotensin after bilateral nephrectomy in patients with chronic renal failure

Circulating levels of renin, angiotensin I, and angiotensin II were increased in six patients with chronic renal failure and hypertension uncontrolled by dialysis and hypotensive drugs. Lower and often normal levels were found in 10 patients whose blood pressure was controlled by dialysis treatment. For a variety of reasons all patients were subjected to bilateral nephrectomy. The logarithm of the decrease in plasma concentrations of renin and angiotensin II was significantly related to the fall of blood pressure after operation. Plasma renin concentration correlated significantly with blood angiotensin I concentration and with plasma angiotensin II in samples taken before and after nephrectomy. Renin, angiotensin I, and angiotensin II were measurable in samples of blood taken 48 hours or more after the operation.

Hypertension following cadaveric renal transplantation

The incidence and aetiology of hypertension following cadaveric-donor renal transplantation have been investigated in twenty-four patients. Initially, the diastolic blood pressure was persistently above 100 mmHg in 52% of the patients. By 1 month after renal transplantation the incidence had fallen to 17% but it then increased rapidly, so that by 5 months 83% had hypertension.

Changes in blood pressure correlated poorly with changes in the dose of prednisone, extracellular fluid volume, exchangeable sodium, creatinine clearance and haemoglobin.

The recipient's original diseased kidneys were removed after transplantation in seven patients. The blood pressure fell to normal levels in three, remained unchanged in two and became easier to control with antihypertensive drugs in the other two patients. Measurements of plasma renin concentration were of no value in predicting the response to recipient nephrectomy.

Renal blood flow and renin activity in renal venous blood in essential hypertension

The intrarenal distribution of blood flow measured by the 133 xenon washout method and the renin activity of renal venous blood were determined in 16 patients with early essential hypertension. None of the patients had evidence of systemic disease except for the elevation in blood pressure (> 150/100 mm Hg). Fifteen of the subjects received a controlled sodium diet during 7 to 9 days before study, at the time of renal angiography. An inverse relationship was noted between the cortical component of the renal blood flow and renin activity of renal venous blood (r = 0.64, P < 0.02). Renin secretion rates were also calculated in 12 patients confirming the inverse relationship between cortical distribution of blood flow and renin secretion (r = 0.763, P < 0.01). The cortical renal blood flow in 10 patients on a low salt intake was 79.6% ± 2.6 (SE) of the total renal blood flow. The cortical blood flow in five patients on a high salt diet was 87.6% ± 1.9 (SE); the statistical difference between the two groups is significant ( P < 0.05). A direct relationship was noted between cortical blood flow and the logarithm of the 24-hour urinary sodium excretion from the day preceding the study (r = 0.54, P < 0.05). Renin secretion rate and renin in renal venous blood were directly correlated (r = 0.813, P < 0.01). Changes in corticomedullary distribution of flow were inversely related to the changes in cortical distribution. The degree of reduction of cortical renal blood flow correlated with the degree of increase in renin secretion and in renin activity in renal venous blood. Our data are compatible with reduced cortical renal blood flow mediating renin release or vice versa. Either mechanism would result in more efficient conservation of salt and water by the kidney.

The control of aldosterone secretion and its relationship to the diagnosis of hyperaldosteronism

Current concepts of the control of aldosterone secretion in man have been reviewed with particular reference to the role of the kidney. On the basis of these concepts, it is concluded that hyperaldosteronism is most conveniently diagnosed by repeated estimation of plasma potassium, which is usually persistently or intermittently reduced in this disease. Occasional cases fail to show hypokalaemia. Distinction between primary and secondary hyperaldosteronism is made by means of measurement of plasma renin concentration. Subnormal values are usually obtained in the first instance and supranormal values in the second.

Plasma renin activity in end-stage kidney disease

Plasma renin activity, fluid and electrolyte balance, and hemodynamic conditions were measured in seven hypertensive patients with end-stage renal disease before and after five exchanges of peritoneal dialytic fluids which removed large amounts of water and sodium, sodium but little water, and little water and sodium, respectively. The subjects had normal plasma renin activity, severe anemia, high cardiac output, high total peripheral resistance, and elevated blood volume. Plasma renin activity rose with large losses of sodium and water but changed slightly when large amounts of sodium with little water or small amounts of sodium and water were removed. Plasma renin activity prior to dialysis did not correlate with mean arterial pressure, blood volume, cardiac index, total peripheral resistance, or serum sodium concentration. Change in plasma renin activity with dialysis correlated inversely with change in mean arterial pressure, water balance, and change in cardiac output, and directly with change in total peripheral resistance and change in serum sodium concentration. There was no correlation with change in blood volume or sodium balance.

Effects of saline loading on the renin, erythropoietin, and blood pressure responses to canine renal allotransplantation

Serial determinations of plasma erythropoietin and renin activities and mean arterial blood pressure were done in five dogs before and after renal allotransplantation. Throughout the experiment, the animals were given 154 mEq of NaCl per day, starting 1 week before transplantation. No immunosuppressive therapy was given. Onset of immunological rejection was determined by daily measurement of endogenous creatinine clearance. Arterial pressure and plasma erythropoietin concentration increased markedly at the time of rejection, with the curves for the two variables closely paralleling each odier in all animals. Serial determinations of plasma volume done in two of the dogs did not show any significant change at the time when hypertension appeared. Plasma renin activities remained very low throughout the experiments, indicating that even with the vascular lesions of rejection renin release is still subject to normal control mechanisms. It is concluded that elevated plasma renin activity is not an essential causal factor of the hypertension which occurs with renal allograft rejection. Since it is possible to suppress renin release without substantially inhibiting erythropoietin release, different stimuli appear to cause release of these substances.

Studies on the role of angiotensin in experimental renovascular hypertension: an immunologic approach

The role of angiotensin in three forms of experimental hypertension was assessed in rats. First, the acute blood pressure response to injected angiotensin amide and angiotensin acid was determined. Rats made hypertensive with deoxycorticosterone and saline showed exaggerated responses; rats made hypertensive by clipping one renal artery showed depressed responses; and rats made hypertensive by clipping one renal artery and contralateral nephrectomy showed normal responsivity to angiotensin amide but depressed responsivity to angiotensin acid. These findings suggested that different mechanisms may be involved in the three types of hypertension studied. To assess the role of angiotensin in these hypertensive rats the blood pressure response, the presence of antibodies determined by radioimmune techniques, and the degree of refractoriness to injected angiotensin after immunization with angiotensin were studied. None of six rats made hypertensive by deoxycorticosterone and saline, and none of five mock immunized rats with renal hypertension of both types had a fall in blood pressure. By contrast, of the 20 rats with both types of renal hypertension in which antibody determinations were made, 11 had developed a significant antibody titer, of which seven showed a significant reduction in blood pressure at the time of antibody determination, and three of the remaining four had a significant blood pressure reduction earlier in their course. None of the nine renal hypertensive rats without demonstrable antibodies had a reduced blood pressure at the time of antibody determination, and only one had an earlier reduction in blood pressure. The renal hypertensive rats were all refractory to injected angiotensin after immunization. These results suggest a primary role for angiotensin in both forms of renal hypertension.