Peripheral and renal venous plasma renin concentration in hypertensive patients with unilateral renal or renovascular disease

Renin-dependent hypertension in patients with unilateral kidney disease not caused by renal artery stenosis

The practical value of renin secretion studies in hypertension associated with unilateral kidney disease, other than renal artery stenosis, has not been documented. This study, comprising 19 patients of this kind, disclosed three who had an abnormal renin secretion from the diseased kidney. The level of peripheral renin under basal conditions, and the change from this level as a result of provocation of renin secretion, were used to evaluate the importance of an arteriovenous renin gradient in the diseased kidney. The three patients were the only ones to become normotensive when the diseased kidney was removed in seven of the cases studied. When nephrectomy is considered in severe hypertension with unilateral kidney disease, there is a place for renin secretion studies, but a screening procedure is advisable. Measuring peripheral renin under basal conditions and after provocation of renin secretion, should reveal whether the renin-angiotensin system might be playing a part in maintaining the high BP. The finding of diminishing kidney function in many of the patients, despite good BP control, emphasizes the importance of sparing kidney function whenever possible.

Reduced spontaneous baroreceptor sensitivity in patients with renovascular hypertension

OBJECTIVE

Sympathetic nerve activity is increased in hypertensive patients with renal artery stenosis. Less is known about cardiac vagal function in these patients before and after renal angioplasty. The aim of the present study was to investigate cardiac baroreceptor reflex sensitivity together with total body noradrenaline (NA) spillover in hypertensive patients with renal artery stenosis before, and in some patients, 1 year after renal angioplasty.

MATERIAL AND METHODS

Spontaneous baroreceptor reflex sensitivity and total body noradrenaline (NA) spillover were measured in patients with renovascular hypertension before intervention (n = 18), patients being cured/improved 1 year after renal angioplasty (n = 5) and age-matched healthy subjects (n = 25).

RESULTS

Hypertensive patients with renal artery stenosis had higher total body NA spillover (4630 +/- 619 versus 3132 +/- 210 pmol/min, P < 0.05) and reduced cardiac baroreceptor reflex sensitivity (6.1 +/- 1.0 versus 10.7 +/- 1.0 ms/mmHg, P < 0.01) compared with healthy subjects. Similar results were obtained (before intervention) in a subgroup of patients (n = 9) with renovascular hypertension defined as cured/improved 1 year following renal angioplasty. Baroreceptor reflex sensitivity improved after renal angioplasty in a subset of patients showing good blood pressure control 1 year after intervention (6.4 +/- 0.7 to 9.4 +/- 1.7 ms/mmHg, P < 0.05).

CONCLUSIONS

Patients with renovascular hypertension showed reduced cardiac baroreceptor reflex sensitivity and increased noradrenergic activity, which to some extent was reversed 1 year following successful renal angioplasty.

Differentiated response of the sympathetic nervous system to angiotensin-converting enzyme inhibition in hypertension

Hypertension with renal artery stenosis is associated with both an activated renin-angiotensin system and elevated sympathetic activity. Therefore, in this condition it may be favorable to use a therapeutic modality that does not reflexly increase heart rate, renin secretion, and sympathetic nervous activity. The purpose of the present study was to assess overall, renal, and muscle sympathetic activity after short-term administration of an angiotensin-converting enzyme inhibitor (enalaprilat) and a nonspecific vasodilator (dihydralazine) to hypertensive patients with renal artery stenosis. Forty-eight patients undergoing a clinical investigation for renovascular hypertension were included in the study. An isotope dilution technique for assessing norepinephrine spillover was used to estimate overall and bilateral renal sympathetic nerve activity. In 11 patients simultaneous intraneural recordings of efferent muscle sympathetic nerve activity were performed. Thirty minutes after dihydralazine administration, mean arterial pressure fell by 15%, whereas plasma angiotensin II, muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover increased (P<0.05 for all). In contrast, after enalaprilat administration a fall in arterial pressure similar to that for dihydralazine was followed by decreased angiotensin II levels and unchanged muscle sympathetic nerve activity, heart rate, and total body norepinephrine spillover, whereas renal norepinephrine spillover increased by 44% (P<0.05). Acute blood pressure reduction by an angiotensin-converting enzyme inhibitor provokes a differentiated sympathetic response in patients with hypertension and renal artery stenosis, inasmuch that overall and muscle sympathetic reflex activation are blunted, whereas the reflex renal sympathetic response to blood pressure reduction is preserved.

Increased cardiovascular mortality in hypertensive patients with renal artery stenosis. Relation to sympathetic activation, renal function and treatment regimens

BACKGROUND

Previous studies in hypertensive patients with renovascular disease have shown both elevated sympathetic nerve activity and increased cardiovascular mortality.

OBJECTIVE

The aim of the present study was to assess long-term survival in hypertensive patients with renal artery stenosis in relation to sympathetic activation, renal function and treatment regimens.

SUBJECTS AND METHODS

A total of 169 consecutive patients aged 54 +/- 1 years with hypertension underwent a clinical investigation for renovascular hypertension including renal angiography and measurement of bilateral renal renin secretion. In 107 of these patients, arterial plasma concentrations of noradrenaline were measured. The mean follow-up time was 7.1 +/- 0.3 years and survival data were available in all patients up to May 1997. For comparison, healthy age-matched normotensive controls were examined.

RESULTS

Arterial noradrenaline concentrations were threefold elevated in hypertensive patients with renal artery stenosis compared to healthy controls (P < 0.01). During the follow-up time, 44 patients died. Cardiovascular mortality accounted for 75% of all deaths. The risk ratio for overall mortality in hypertensive patients with renal artery stenosis compared to the normal population of Sweden, matched for age, was 3.3 (2.4-4.4), whereas the risk ratio for cardiovascular mortality was 5.7 (3.9-8.0). The arterial plasma concentration of noradrenaline was 3.11 +/- 0.30 pmol/ml in patients who died compared to 3.84 +/- 0.26 pmol/ml in survivors. Reduced renal function and age were independent predictors of death. Survival did not differ between patients undergoing intervention with either renal angioplasty or surgical reconstruction for renal artery stenosis and patients not undergoing intervention.

CONCLUSIONS

Although sympathetic nerve activity is elevated in hypertensive patients with renal artery stenosis, our results do not suggest that this adrenergic over-activity is directly linked to the observed high cardiovascular mortality. Mortality in hypertensive patients with renovascular disease remains high whether an interventional treatment is performed or not, possibly due to the concomitant coronary disease.

Increased sympathetic nerve activity in renovascular hypertension

BACKGROUND

Increased sympathetic nerve activity may contribute to the progression of renovascular hypertension. Because previous results have been inconclusive, we investigated whether renovascular hypertensives show increased total and regional sympathetic nerve activity.

METHODS AND RESULTS

Sixty-five patients underwent renal angiography and measurements of plasma renin activity and angiotensin II in conjunction with estimation of sympathetic nerve activity by means of radiotracer dilution and intraneural recordings of muscle sympathetic nerve activity (MSNA). Age-matched healthy subjects (n=15) were examined for comparison. Total body norepinephrine (NE) spillover, an index of overall sympathetic nerve activity, was increased by 100% and MSNA by 60% in the hypertensive patients compared with healthy subjects (P<0.01 for both). A subgroup of 24 patients with well-defined renovascular hypertension (cured or improved hypertension after renal angioplasty) showed similar increases in total body NE spillover compared with the group at large. Patients with arterial plasma renin activity and angiotensin II levels above median had higher values for total body NE spillover than patients below median (P<0.01).

CONCLUSIONS

This study unequivocally demonstrates elevated sympathetic nerve activity in patients with renovascular hypertension. The adrenergic overactivity may contribute to the blood pressure elevation and perhaps also to the high cardiovascular mortality in renovascular hypertension.

The etiology of hypertension in nonrenovascular unilateral renal disease--two cases of renin induced hypertension in congenital renal dysplasia

We report two cases of severe hypertension and unilateral renal dysplasia. No renal artery stenosis and no other urogenital malformations were found. In both cases we found substantially enhanced secretion of renin from the dysplastic kidney. After nephrectomy both patients obtained a distinctive and permanent reduction or normalization of blood pressure. In the two cases reported, regional renin release induced by ischemia is a very likely etiological factor.

Norepinephrine overflow and renin pattern of the individual kidney in patients with unilateral renal artery stenosis

This study was performed to determine divided renal efferent sympathetic nerve activity from kidneys in seven patients with renin-positive, unilateral renal artery stenosis before and 30 minutes after an acute intravenous dose of 1.25 mg enalaprilat. Renal norepinephrine release was calculated from split renal plasma flow, venoarterial plasma concentration gradients across the kidney, and the fractional extraction of tritiated norepinephrine. All patients had unilateral renin secretion, the affected kidney increasing its plasma renin activity gradient 1.7-fold, whereas no statistically significant change was noted on the contralateral side in response to enalaprilat. Total norepinephrine release to plasma and norepinephrine plasma clearance (assessed by isotope dilution) were similar before and after administration of enalaprilat (approximately 400 ng/min and 1.0 l/min), despite a 26% fall in mean arterial pressure (from 125 mm Hg, p less than 0.01). Heart rate remained unchanged. After enalaprilat, norepinephrine venoarterial difference increased in the renin-secreting kidney (from 264 to 396, SED = 57 pg/ml, p less than 0.05), whereas it increased only slightly in the contralateral kidney (from 149 to 256, SED = 72 pg/ml, NS). Tritiated norepinephrine extraction fell approximately 25% (p less than 0.01) in both kidneys. Thus, renal norepinephrine spillover increased from 49 to 62, SED = 9 ng/min (NS) and from 81 to 129, SED = 17 ng/min (p less than 0.05) from the affected and the contralateral kidney, respectively. Hence, in this relatively small study in patients with renovascular hypertension, no evidence for increased renal nerve activity could be observed in the affected kidney, despite its marked renin production.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute vascular fluid volume expansion on erythrocyte sodium transport in essential hypertension

Evidence exists that volume expansion is associated with the appearance of a circulating sodium transport inhibitor. We have evaluated intra-arterial blood pressure (BP), central venous pressure (CVP), plasma renin activity (PRA), intraerythrocyte sodium content, erythrocyte sodium influx and rate constant of sodium efflux in 10 untreated primary hypertensive men (WHO stages I and II). The investigations were done during baseline conditions and after rapid intravenous infusion of 1 litre of saline (0.9% NaCl solution) over 15-20 min. Volume expansion caused an increase in CVP by 6.0 +/- 0.5 cmH2O (p less than 0.01), while BP only exhibited a slight increase. No significant changes in intraerythrocyte sodium content, sodium influx, sodium efflux rate constant or PRA were found after volume expansion compared to baseline. All patients with low normal PRA experienced a decrease in sodium efflux rate constant after volume expansion. We found a positive correlation between baseline PRA and change in sodium efflux rate constant after volume expansion (r = 0.62, p less than 0.05). At baseline the relationship between PRA and intraerythrocyte sodium content nearly reached statistical significance (r = 0.63, p = 0.054). These results may indicate that acute volume expansion influences the release of a circulating factor, modulating sodium transport in low-renin hypertension.

Plasma noradrenaline and dopamine in renin-mediated hypertension

Noradrenaline (NA) and dopamine (DA) have opposite effects on the kidney; NA causes vasoconstriction and increased sodium reabsorption while DA promotes vasodilation and natriuresis. In 15 patients investigated for renin-mediated hypertension measurements of plasma renin activity (PRA), NA and DA concentrations were made in arterial and renal venous blood from both kidneys before and after acute stimulation of renin release by i.v. dihydralazine. Nine patients had unilateral renin secretion and were classified as renin-positive, while the remaining six patients were renin-negative. Renin-positive patients had higher arterial and renal venous PRA, NA and DA levels than the negative ones. In the renin-positive group V-A differences for NA and DA were present on both sides despite unilateral secretion of renin. NA but not DA levels were higher in the renin-secreting kidney, which can partly be explained by the reduced plasma flow to the involved kidney. After dihydralazine the arterial NA and DA rose similarly in renin-positive and renin-negative patients, while PRA rose only in the renin-positive cases. In the renin-positive patients where stimulation of renin secretion caused a marked increase of the PRA gradient on the affected side only, renal gradients for NA and DA increased bilaterally. The increase in DA was more pronounced than that of NA yielding a rise in DA/NA ratio on the affected side. Arterial PRA was positively correlated to the plasma concentrations of NA and DA. V-A differences for PRA and NA or DA were positively correlated on the involved renin-secreting side. In summary, patients with renin-dependent hypertension have elevated plasma NA and DA concentrations. Stimulation of renin release by dihydralazine increases the DA/NA ratio in arterial and renal venous blood indicating release of 'precursor dopamine' from noradrenergic fibres and/or activation of dopaminergic nerves. There seems to be a relationship between renal nerve activity and renin release in renin-dependent hypertension.

Dissociation of renin and noradrenaline release in the renal circulation. Studies on patients with renal hypertension

Plasma renin activity (PRA) and noradrenaline concentration (NA) were measured in the renal veins (V) and arterial blood (A) in 30 patients investigated for renin-mediated hypertension. Both PRA and NA concentrations in arterial blood were above our reference limits and they were positively correlated. In 18 of the patients renin secretion was unilateral from the diseased side. Their renal vein NA concentration was always higher on that side, compared to the contralateral one, but there were V-A gradients for NA on both sides in all but two cases. In 15 of the patients with such lateralisation of renin secretion the changes of PRA and NA V-A gradients were determined 30-60 min after an i.v. injection of dihydralazine. Both PRA and NA increased more markedly in the renal vein on the affected side where the estimated renal plasma flow was lower than on the contralateral side. The NA gradients increased less than the PRA gradients when changes on the renin secreting side were compared in patients with proven increase of renin secretion. We conclude that patients with renal hypertension have a high sympathetic nervous activity as evidenced by increased plasma NA concentrations and (V-A) gradients for NA on both sides. The release of NA into the renal circulation in renin mediated hypertension is thus not invariably accompanied by renin release. The higher renal vein NA concentration on the involved renin secreting side is explained by reduced RPF on this side.

Treatment of renovascular hypertension by unilateral nephrectomy. A follow-up study in patients above 60 years of age

The long term results of surgical intervention in 26 elderly patients with renovascular hypertension are presented. All patients were above 60 years of age at the day of operation. The majority of the patients had atherosclerotic renovascular disease with only one case of fibromuscular dysplasia. Several patients had severe extrarenal atherosclerotic disease. The diagnosis of renovascular hypertension was based upon the results of isotope renography, renal arteriography and renal vein catheterization. All patients underwent unilateral nephrectomy. Notably, no deaths or complications occurred in relation to surgery. At the follow-up study, blood pressure was lowered and the requirement for antihypertensive drugs reduced in 86% of the patients. We conclude that unilateral nephrectomy in elderly high risk patients with renovascular hypertension is a safe and efficient procedure.

Spontaneous variations in renal vein renin activity in man

The spontaneous variations in renal vein renin activity (RVRA) and in peripheral vein renin activity (PVRA) were studied in one normotensive and nine hypertensive patients. Eight of the hypertensive patients had renal artery stenosis on one or both sides. Blood samples were drawn simultaneously from the two renal veins and from a peripheral vein every fifth or tenth minute for one hour. Plasma renin activity (PRA) was measured by radioimmunoassay. The precision of the PRA assay, expressed as coefficient of variation, was related to the PRA level. A large intra-individual variations was found in RVRA, the RVRA ratio and PVRA even in patients with unilateral renovascular hypertension. The intra-individual variation could not be explained by specimen collection error or by error of the assay procedure. The variation seems to be reflect a biological fluctuation. The clinical implication of these findings is that repeated, simultaneous collection from the two renal veins, avoidance of factors known to decrease renin secretion. and consideration of the relation between the RVRA ratio and RVRA level are of importance in the preoperative evaluation of patients with renal artery stenosis.

Rate of angiotensin II generation within the human pulmonary vascular bed

Plasma angiotensin II concentration gradients across the pulmonary vascular bed were measured during diagnostic renal venous/right heart catheterization in twenty-seven hypertensive patients with renal or renovascular disease. There was a linear correlation between the plasma angiotensin II concentration in mixed venous blood and in systemic arterial blood. The pulmonary angiotensin II production rate was measured in fourteen patients. This parameter was linearly correlated with plasma renin concentration in systemic arterial blood. The plasma clearance of angiotensin II across the systemic vascular bed varied from 0.7 to 1.71/min, i.e. within a fairly narrow range.

The use of an angiotensin II antagonist (saralasin) as an adjunct during renal vein catheterization

Renal vein catheterization was performed in fifteen hypertensive patients with unilateral renal disease. Samples for measurement of plasma renin concentration were obtained from each of the two renal veins and from the femoral artery (or the inferior caval vein)-before and during saralasin infusion. Saralasin infusion induced a significant decrease in blood pressure. In ten patients with lateralization of renin secretion before infusion, saralasin induced a 2-fold increase of the renin gradient across the diseased kidney, whereas there was no significant renin gradient across the contralateral kidney neither before nor after saralasin infusion. Thus, the renal venous renin ratio (diseased/contralateral) increased from a mean value of 2.10 to 4.13. In five patients without lateralization of renin secretion prior to infusion, saralasin induced a significant increase of renin gradient across both kidneys. In consequence, evidence for lateralization did not emerge and the renal vein renin ratio remained unchanged at 1.10. In cases with lateralization of renin secretion, the use of saralasin provides confirmatory evidence for strictly unilateral renin secretion with suppression of renin output from the contralateral kidney. In patients without obvious lateralization of renin secretion before saralasin, the administration of this angiotensin II inhibitor can serve to demonstrate a potential renin for renin secretion, shared by both kidneys.

Cyclic AMP, renal function and dihydralazine-stimulated renin secretion in hypertensive patients

The concentrations of plasma cAMP and plasma renin activity were determined in arterial and renal venous plasma in nineteen patients investigated for renin-mediated hypertension. The cAMP measurements were performed in two different situations (1) under basal conditions and (2) after i.v. dihydralazine administration, a potent renin stimulation procedure. Thirteen patients had a lateralization of the renin secretion in the basal state and the administration of dihydralazine caused a further marked renin-secretion. The cAMP concentration was higher in the renal veins draining renin-positive kidneys than in the contralateral renal veins. No significant change was observed between the arterial cAMP concentration and the cAMP concentration in either of the renal veins during dihydralazine-stimulated renin secretion. There was no correlation between the cAMP extraction and the renin secretion of the individual kidneys, but the cAMP extraction correlated with the extraction ratio of PAH. These results show that cAMP values are mainly influenced by the renal function and are not related to the state of renin secretion. Increased cAMP levels in renovascular patients and urameic patients are therefore mainly due to defective elimination of the nucleotide by the kidneys.

Renal vein renin concentration in the hypertension of unilateral reflux nephropathy

Hypertension is a frequent complication of reflux nephropathy. The cause of this hypertension is unknown. Our study was undertaken to assess the possible role of the renin-angiotensin system in the hypertension associated with unilateral reflux nephropathy. We selected for study 17 normotensive and 12 hypertensive patients with strictly unilateral reflux nephropathy. There were 3 normotensive and 2 hypertensive patients with a renal vein renin ratio exceeding 1.5. Of these 3 normotensive patients 1 had evidence from divided renal function studies to suggest functional renal ischemia. No consistent evidence was obtained to support the concept that the renin-angiotensin system has a primary role in the non-malignant hypertension of unilateral reflux nephropathy.

Effects of metoprolol and propranolol on furosemide-stimulated renin release in healthy subjects

The effects of single doses of the beta1-receptor antagonist metoprolol (40 mg orally), propranolol (40 mg orally) and placebo were compared on furosemide-stimulated plasma renin activity (PRA) in seven healthy subjects. In the placebo studies, PRA increased by 0.59+/-0.18 ng x ml-1 x h-1 60 minutes after intravenous administration of 30-60 mg furosemide. After propranolol and metoprolol, the corresponding increases in PRA were significantly less pronounced amounting to 0.16+/-0.06 and 0.24+/-0.08 ng x ml-1 x h-1, respectively. The resting heart rate was reduced to the same extent after the two beta-blockers, which means that the two drugs had been given in equipotent beta1-receptor blocking doses. It is suggested that the release of renin from the kidney may partly be mediated via an adrenergic beta1-receptor.