Plasma renin activity after allogenic kidney transplantation in man

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.

[Change in renin activity and blood pressure in the dog autologous kidney transplant model with modified HTK solution]

Investigations of changes in activity of renin and blood pressure after reperfusion of the kidney transplant using HTK solution were carried out by means of an autologous, heterotopic model of kidney transplantation applied to dogs. Duration of cold ischemia was 48 h. According to variations in the composition of the HTK perfusion solution three test groups were set up. During the first 20 min after recirculation in each test group the renal venous and arterial renin activities were measured. Parallel to renin activity, the arterial blood pressure was recorded. During the first few minutes following recirculation of the kidney transplant the renin levels in the venous blood of the kidney were higher in test group 1 (HTK solution, perfusion height 120 cm) than in either of the other two, showing a median maximal increase of 195 ng/ml.h. In test group 2 the maximal venous renin concentration fell to 145 ng/ml.h, while graphs take a more uniform course. Test group 3 (HTK/tryptophan) differed from the others in having further improved renin values. After the 7.5 min of observation normal venous renin concentrations were measured following earlier values for maximal increase between 23.1 ng/ml.h and 120 ng/ml.h (median 61.5 ng/ml.h). The best reperfusion of the kidney was observed in the tryptophan group, albeit without any recognizable positive effects on the other renal functions. Initially low renin values do not necessarily correlate with a smooth postoperative renal function and vice versa. Initial renin values cannot provide a secure basis for predicting instant as well as long-term postoperative functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-renal-transplant hypertension. Urine volume, free water clearance and plasma concentrations of arginine vasopressin, angiotensin II and aldosterone before and after oral water loading in hypertensive and normotensive renal transplant recipients

Urine volume (V), free water clearance (CH2O) and plasma concentrations of arginine vasopressin (AVP), angiotensin II (A II) and aldosterone (Aldo) were determined before and three times during the first 5 h after an oral water load of 20 ml/kg body wt in 19 patients with post-renal-transplant hypertension (group I), in 13 normotensive renal transplant recipients (group II) and in 20 control subjects (group III). Both V and CH2O increased significantly in all groups, but considerably less in groups I and II than in group III. When CH2O was related to glomerular filtration rate no differences existed between patients and control subjects. Basal AVP was the same in groups I (3.3 pmol/l, median) and II (3.0 pmol/l), but significantly (p less than 0.01) higher than in group III (1.9 pmol/l). Basal A II was significantly (p less than 0.01) elevated in group I (18 pmol/l) when compared to both groups II (10 pmol/l) and III (11 pmol/l), and the level was independent of the presence of native kidneys. Basal Aldo was the same in all groups. During loading, AVP was reduced in all groups, A II was almost unchanged, and Aldo was increased in groups I and II and reduced in group III depending on alterations in serum potassium. Thus urinary diluting ability is reduced in renal transplant recipients due to a reduced glomerular filtration rate. The enhanced A II in hypertensive renal transplant recipients gives further evidence for the point of view that hypertension is angiotensin-dependent in most of these patients.

Modification of the normal postural changes in plasma renin activity by the application of positive pressure to the legs

In six normal male subjects plasma renin activity (PRA) rose progressively on standing over a 2 hour period. PRA fell to basal levels after a further 2 hours of recumbency. The rate of rise of PRA on standing was largely abolised following the application of an anti-gravity ('G') suit. Continuous monitoring of blood pressure (BP) heart rate (HR) and packed cell volume (PCV) suggest that it is the fall in effective blood volume which elicits the stimuli to renin release during changes in posture.

Renin stimulation by passive tilting: the influence of an anti-gravity suit on postural changes in plasma renin activity, plasma noradrenaline concentration and kidney function in normal man

Plasma renin activity (PRA), plasma noradrenaline concentration, heart rate, blood pressure, and clearances of para-aminohippurate and inulin were measured in twelve normal subjects (clearances in only three subjects) before and after 40 min of 60 degrees upright tilting. The tilting experiments were repeated after inflation of an anti-gravity suit to 60 mmHg on the lower extremities. Inflation of the anti-gravity suit caused an abolition of the postural PRA increase, a marked reduction of the postural increases in plasma noradrenaline and heart rate, and elimination of the decreases in pulse pressure, inulin and para-aminohippurate clearances and sodium excretion. The results suggest a decisive role of the sympathetic nervous system for postural renin increase, probably mainly activated by stretch receptors in the low-pressure cardiopulmoanry area.

The significance of body sodium content in hypertension following renal transplantation: exchangeable sodium and plasma renin concentration before and after renal transplantation

The purpose of the present study was to determine the importance of body sodium content in hypertension following renal transplantation using measurements of exchangeablesodium (NaE) before and after transplantation. Plasma renin concentration (PRC) was also investigated. In the present study the necessity of a reference for expressing NaE values was eliminated because the subjects investigated acted as their own controls. The study included fourteen recipients, of whom seven were normotensive with an average blood pressure (BP) of 136/84 mmHg and seven were hypertensive with an average BP of 182/113 mmHg after renal transplantation. In the hypertensive NaE increased significantly (mean 22%) in contrast to an insignificant decrease in NaE in the normotensives (mean, -5%). The change in NaE was positively correlated to the mean BP after renal transplantation (p = 0.69, n = 14, P less than 0.02). BP and NaE were not correlated to prednisone dosages. PRC was normal in all the hypertensives. The results strongly suggest that sodium accumulation in the body, which is not prednisone-dependent, is involved in the pathogenesis in post-transplant hypertension.

Control of renin release: a review of experimental evidence and clinical implications

Present knowledge of the mechanisms regulating release of renin is reviewed with particular emphasis on neural factors. Evidence is given for a direct effect of renal innervation on beta adrenergic receptors in juxtaglomerular cells, and for the involvement of reflex release of renin in conditions such as tilting and acute salt depletion. Participation of neural and nonneural mechanisms of control is also shown to occur in other conditions, such as aortic constriction and hemorrhage. The view is held that neural sympathetic factors might explain some of the renin disturbances found in essential hypertension. First, in patients with high renin hypertension part of the hypertension is renin-dependent, and these pressor levels of renin seem to be neurally induced since they can commonly be suppressed by beta adrenoreceptor blocking agents. Second, the hypothesis is presented that patients with low renin hypertension, at least those who have no volume disturbance, have a blunted sympathetic control of renin release. Therefore a sufficiently precise test of sympathetic activity, and possibly of body fluid volumes, should be associated with renin profiles for a better understanding of the pathophysiology of arterial hypertension and as a better guide to therapeutic management. Indeed, most of the available antihypertensive drugs act on sympathetic activity, body fluid volume or renin, and this multifaceted profile would provide more rational guidelines for treatment.

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.