Capillary permeability and extracellular fluid volumes in pregnancy-induced hypertension

1. Capillary permeability was determined by the disappearance rate of Evans Blue dye from plasma in healthy non-pregnant women, normal third-trimester primigravidae and primigravidae with pregnancy-induced hypertension. 2. Extracellular fluid volume was determined from the disappearance curves of injected mannitol in the same subjects and the plasma volume was measured by the Evans Blue dye dilution technique. 3. In normal pregnancy capillary permeability was not altered from that of non-pregnant subjects. Although extracellular fluid volume and plasma volume were increased in normal pregnant compared with non-pregnant women, the distribution of fluid between plasma volume and interstitial fluid volume was unaltered. 4. Women with established pregnancy-induced hypertension had a more rapid Evans Blue disappearance rate and a lower plasma volume than normal pregnant women, independent of the presence of proteinuria. Maternal plasma volume correlated positively and significantly with fetal birth weight in women with pregnancy-induced hypertension, emphasizing the important relationship between maternal plasma volume and fetal outcome. 5. The increased capillary permeability in women with pregnancy-induced hypertension was associated with a reduction in the plasma volume/interstitial fluid volume ratio but a normal extracellular fluid volume, suggesting that the reduced plasma volume did not result from sodium loss but rather from a redistribution of the total extracellular fluid volume. These changes did not differ significantly in subgroups with and without oedema.     

A cross-sectional study of basal platelet intracellular free calcium concentration in normotensive and hypertensive primigravid pregnancies

1. The intracellular free calcium concentration ([Ca2+]i) in washed human platelets was measured using the fluorescent indicator, fura-2, in a cross-sectional study of 36 normotensive, primigravid volunteers, 12 in each trimester of pregnancy and a further 12 at 6 weeks post partum. The results were compared with those obtained from 30 normal female volunteers not using oral contraception. 2. The mean basal [Ca2+]i in the platelets of the pregnant women in the first two trimesters (115.6 +/- 6.7 and 120.1 +/- 5.7 nmol/l, respectively) was not shown to differ significantly from that of normal non-pregnant volunteers (112.3 +/- 2.9 nmol/l). However, during the third trimester a significant increase in [Ca2+]i was noted (134.0 +/- 4.9 nmol/l; P less than 0.05), with a return to normal values in the post-partum period (108.2 +/- 6.1 nmol/l). 3. [Ca2+]i was also measured in the platelets of a group of 12 primigravid pregnant women in the third trimester whose pregnancies were complicated by gestational hypertension (pregnancy-induced hypertension and pre-eclampsia). A significant rise in basal [Ca2+]i was noted in the platelets of primigravidae whose pregnancies were complicated by pre-eclampsia (163.6 +/- 8.8 nmol/l) as compared with normotensive, third-trimester primigravidae (P less than 0.02). However, no correlation could be demonstrated between [Ca2+]i and systemic blood pressure.     

The effects of posture on abnormalities of forearm venous tone in women with pregnancy-induced hypertension

1. Forearm venous tone was measured in the left lateral supine position and in response to passive leg elevation in a group of women with pregnancy-induced hypertension and compared with a group of normotensive pregnant women and a group of non-pregnant women. 2. The women with pregnancy-induced hypertension were venoconstricted in the supine position compared with the normal pregnant women (P less than 0.002). There was no difference in forearm venous tone between the women with pregnancy-induced hypertension and the non-pregnant women. 3. In response to passive leg elevation the women with pregnancy-induced hypertension venodilated (P less than 0.002) whereas there was no change in forearm venous tone in the normotensive pregnant women and the non-pregnant women. There was no change in blood pressure in any of the women after 35 min of leg elevation. 4. These results demonstrate that the abnormal venous vasoconstriction that occurs in women with pregnancy-induced hypertension in the supine position is corrected by passive leg elevation, a manoeuvre which leads to an increase in central blood volume.     

Active and inactive renin in normal human plasma. Comparison between acid activation and cryoactivation.

Inactive renin in human plasma is converted to active renin in vitro by acid activation or by cryoactivation. Renin activity was measured at pH 5.5 and renin concentration at pH 7.4. The plasma renin activity before and after cryo-treatment is termed active (APRA) and total (TPRA) plasma renin activity; the plasma renin concentration before and after acid treatment active (APRC) and total (TPRC) plasma renin concentration. In this study we demonstrated that in normal subjects the proportion of active to total renin after cryo-treatment averaged 61%, which was significantly (p less than 0.001) higher than the mean percentage active renin of 34 found with the acid activation procedure. Plasma angiotensin II correlated significantly with APRA, TPRA, TPRC and plasma angiotensin I (PA I), but not with inactive renin, which suggests that inactive renin does not produce angiotensin II in vivo. Cold treatment after acid activation and acid treatment after cryoactivation did not provoke a significant change in the measured renin concentration. Our data support the view that acidification of the plasma activates more than does cryo-treatment, and that inactive renin does not contribute to plasma angiotensin II.     

The renin-aldosterone system in exaggerated natriuresis of essential hypertension

1. The effect of intravenous loading with 500 ml of sodium chloride solution (50 g/l) on plasma renin concentration, plasma aldosterone concentration, urinary sodium excretion and mean blood pressure was studied in 15 young patients with mild essential hypertension and 10 healthy normotensive control subjects. 2. Plasma renin concentration and plasma aldosterone concentration were suppressed to the same degree during loading in both the hypertensive and normotensive groups. Urinary sodium excretion was significantly higher in the hypertensive patients than in the normotensive subjects. Mean blood pressure increased slightly in both groups. 3. Plasma renin concentration and plasma aldosterone concentration were significantly correlated in both groups before sodium loading. The increase in urinary sodium excretion was significantly correlated to the suppression of plasma aldosterone concentration in the hypertensive, but not in the normotensive, group. No correlation was found between changes in urinary sodium excretion and changes in plasma renin concentration or mean blood pressure. 4. The results indicate that the suppressibility of the renin-aldosterone system by hyperosmotic sodium chloride solution is normal in young patients with mild essential hypertension. It is suggested that the changes in plasma aldosterone concentration induced by sodium loading might be involved in the regulation of exaggerated natriuresis in essential hypertension.     

Evidence for activation of circulating inactive renin by the human kidney.

1. In eight patients with essential hypertension (EHT) and six patients with renovascular hypertension (RVHT) peripheral venous enzymatically active and inactive renin values were followed after acute stimulation of renin release by the vasodilating agent diazoxide (300 mg intravenously). Active renin rose during the first hour after diazoxide and remained high during the following 15 h, but inactive renin fell during the first hour and rose thereafter. Peripheral venous active and inactive renin were not different from arterial values both before and after diazoxide. 2. Sixteen patients with EHT received propranolol, 80 mg, four times a day. Six of them had a first injection of diazoxide the day before propranolol was started and a second one after 10--14 days of propranolol treatment. Peripheral vein active renin was lowered by propranolol, but inactive renin was raised. Both the diazoxide-induced rapid rise of active renin and the fall of inactive renin observed in untreated patients were absent during treatment with propranolol. 3. In four patients with EHT and seven patients with RVHT renal vein sampling was performed before and 30 min after diazoxide. Increased release of active renin from kidneys that were not markedly contracted was associated with a fall of the renal vein to peripheral vein ratio of inactive renin to a value less than one. 4. It is concluded that under certain circumstances stimulated release of active renin is associated with removal of inactive renin from the circulation by the kidney. This may in fact be due to intrarenal transformation of circulating inactive renin into its active counterpart. The findings suggest that a beta-adrenoreceptor might be involved in this activation process.     

Serum digoxin-like substances in pregnancy-induced hypertension

1. Endogenous digoxin-like immunoreactivity (EDLI) was measured in the serum of 85 normotensive pregnant (NTP) women and 77 women with pregnancy-induced hypertension (PIH) by a radioimmunoassay (New England Nuclear). All women were in the third trimester. 2. EDLI, which was undetectable in serum from non-pregnant women, was present in NTP and PIH and was significantly higher in PIH. EDLI correlated with gestational age in NTP, but not in PIH. 3. Ouabain-sensitive Na+ transport was estimated in normal peripheral blood leucocytes after incubation with sera from 50 NTP and 42 PIH women. Significant inhibition of active Na+ transport occurred only with the serum of hypertensive patients without proteinuria. 4. EDLI did not correlate with the effect of the sera on active Na+ transport. The radioimmunoassay therefore provides a poor index of Na+ transport inhibitory activity in PIH.     

Active and inactive renin after captopril (SQ 14225) administration in hypertensive patients

The changes in active and inactive renin after oral administration of captopril (SQ 14225) were studied in 29 hypertensive patients. Inactive renin was calculated as plasma renin activity (PRA) after cold storage (total renin) minus PRA before cold storage (active renin). The patients were divided into 2 groups, responders and non-responders, according to the response of active renin to captopril. In 9 responders, the active renin increased markedly, while the inactive renin decreased. On the other hand, in 20 non-responders, both renin activities increased only slightly. Total renin increased markedly in responders; it increased in much smaller degree but significantly in non-responders. These data suggest that captopril promotes the conversion of inactive renin to active one and augments the renin release as a whole.     

The basal levels of active and inactive plasma renin concentration in infancy and childhood

Basal plasma renin activity, active and inactive plasma renin concentration were measured in 89 healthy recumbent children aged between 1 week and 16 years. A significant (P less than 0.001) age-related decrease for active (r = -0.60), inactive (r = -0.59) and total renin concentration (r = -0.66) was observed. After correction for the influence of age, active renin concentration correlated with plasma renin activity (r = 0.81), but not with inactive renin concentration (r = 0.18). The proportions of active and inactive renin were not related to age, and the overall percentage of inactive renin was 79%.     

Effects of furosemide and orthostasis on active and inactive renin in normal and anephric man

Abstract. We investigated active and inactive (acid-activatable) plasma renin in anephric and in normal persons. In anephric patients ( n = 15) plasma concentration of active and inactive renin was 1.15 ± 0.2 and 40.7 ± 7.1 μU/ml, respectively; angiotensin II ( n = 13) was 14.5 ± 1.9 pg/ml. Furosemide ( n = 10), 40 mg i.v., and upright posture ( n = 8) did not change active or inactive renin in the anephric state. In normal men, furosemide ( n = 9) within 15 min increased active renin from 29.9 ± 5.8 to 82.4 ± 14.8 (μ/ml ( P lt; 0.001), while inactive renin slightly but not significantly decreased from 136.3 ± 29.9 to 121.1 ± 19.2 μU/ml; orthostasis ( n = 15) within 4 h stimulated active renin ( P < 0.001) and slightly raised inactive renin ( P < 005). Both furosemide and orthostasis increased ( P < 0.001, each) the proportion of active renin in normal persons. Studies in one patient within 24 h after bilateral nephrectomy indicated half-life to be 30–60 min for active and 2–4 h for inactive renin. Thus, we detected low levels of active renin and considerable amounts of inactive renin and angiotensin II in anephric patients. Our data suggest that about 30%, of inactive renin in normal plasma is of extrarenal origin. The stimulation of active renin by furosemide and orthostasis is bound to the presence of the kidney. Our studies provide indirect evidence that both manoeuvres may stimulate the conversion of inactive to active renin within the human kidney.     

The renin-angiotensin-aldosterone system in normal 85-year-old people

Active and total plasma renin concentration, as well as plasma angiotensin II, aldosterone and renin substrate concentrations were measured in venous blood samples from 17 normal 85-year-old people at rest. No discernible sex-related differences were seen. Active plasma renin and plasma aldosterone concentrations were significantly lower in the old people compared to a group of normal 40-year-old people. Plasma angiotensin II concentration showed no decrease with increasing age. Active plasma renin concentration constituted approximately 20% of total plasma renin concentration, with a significant correlation between the two renin moieties. The values for plasma renin substrate concentration are similar to those reported for younger age groups. The lack of standardization of methods severely hampers inter-laboratory comparisons of both active plasma renin and total plasma renin concentrations.     

A new sensitive direct radioimmunoassay for human plasma renin and its clinical application

We developed new sensitive direct radioimmunoassay for human plasma renin. Renin was purified from Haas' preparation utilizing a pepstatin-C6-Sepharose affinity chromatography. Antiserum, prepared by immunizing rabbits with the purified renin, was used for the direct radioimmunoassay at a final dilution of 1:30,000. The antibody was specific for human renal and plasma renin, but did not cross-react with cathepsin D, trypsin, or renins of mouse, dog, and rat. Radioimmunoassay was performed by the double antibody technique using the delayed tracer addition method. In this method, a standard curve was obtained over a range from 0.2 to 8.0 ng/ml. The values from our assay correlated well with total renin activity measured as the generation rate of angiotensin I after trypsin activation (r = 0.78, p less than 0.01), but correlated weakly with active renin activity. This finding disclosed that both active and inactive renin were detected by this method. In normal participants, plasma renin concentration determined by direct radioimmunoassay was increased by standing and furosemide injection. The plasma renin concentration determined by direct radioimmunoassay of patients with essential hypertension (0.7 to 1.7 ng/ml) was not significantly different from values in normal controls (0.8 to 1.9 ng/ml). The values were higher in patients with renovascular hypertension (1.6 to 2.7 ng/ml), malignant hypertension (2.8 to 3.4 ng/ml) and Bartter's syndrome (1.8 to 2.5 ng/ml), but lower in patients with primary aldosteronism (0.4 to 0.8 ng/ml) than in normal controls. This newly developed radioimmunoassay for human renin was sensitive enough to estimate the levels of renin in plasma of patients with low renin hypertension. It provides a new tool for the understanding of the renin-angiotensin system under various clinical conditions.     

Inactive renin and aldosterone in Bartter's syndrome

Studies of plasma samples of 3 subjects with Bartter's syndrome were compared to 8 subjects with other conditions. Despite high levels of active renin initially, with low levels of inactive renin, addition of either human nephrectomized plasma or sheep substrate not only increased active renin (by at least 3-fold) but also led to the appearance of large quantities of inactive renin (10-20 times the concentration originally present, much greater than the small increase seen with other plasmas). The activated inactive renin after substrate addition possibly had a larger and more variable molecular size (42,000-48,000) than normal inactive renin (42,500-44,500). Renin substrate in Bartter's plasma was present in similar amounts and had a normal or supranormal angiotensin generation rate with exogenous human renin. Bartter's substrate had a similar molecular weight (55,000) to that found in normal human plasma. The agent in the exogenous substrate preparations causing the increase in apparent active and inactive renin was not ultrafiltrable. However, an acidification procedure that destroyed exogenous substrate also removed the renin-increasing effect. Captopril increased renin but not aldosterone, while amiloride increased aldosterone but not renin. Neither agent improved serum potassium significantly in these patients on indomethacin.     

Reexamination of the conditions for processing and storing of blood for plasma renin assay

Reexamination of conditions for processing and storing blood for plasma renin assay confirmed that plasma can be stored at -20 degrees C for at least 4 weeks without significant changes in active renin level. The active renin concentration is increased by storage at 4 degrees C because of conversion from inactive renin.     

Active, inactive and total renin concentrations in plasma of hypertensive patients

To assess the role of inactive renin in hypertensive patients, active, inactive and total renin concentrations (ARC, IRC and TRC) were measured in 37 patients with hypertension of various etiologies. Inactive renin was activated by trypsin and renin concentration was measured using an excess of sheep substrate. Mean values of ARC, IRC, TRC and active renin ratio (AR ratio = ARC/TRC) were higher in 6 cases of renovascular hypertension, and lower in 6 cases of primary aldosteronism and 1 case of idiopathic hyperaldosteronism, when compared with 59 cases of normal subjects. Between ARC and IRC, a slightly positive correlation was observed. Moreover, between ARC and TRC as well as between ARC and AR ratio, close positive correlations were observed. Exceptionally, in a case of juxtaglomerular cell tumor, AR ratio was low in spite of the extremely high value of ARC. Our data suggest that the increase in circulating active renin is due to both the enhancement of the release of renin from the kidney and the increase in the activation of inactive renin, and vice versa.     

The effect of in vitro captopril and angiotensin II on plasma renin activity

Samples of plasma from ten normotensive volunteers and ten hypertensive patients were assayed for plasma renin activity before and after the addition of either captopril or captopril and angiotensin II. The study was repeated after treating portions of the same specimens with trypsin, to activate the inactive renin component. The results indicate that inactive renin is not converted to the active form by captopril in vitro, nor does the addition of angiotensin II inactivate the active form. These data are consistent with the in vivo findings that changes in active and inactive renin occur independently under conditions of challenge by captopril or angiotensin II analogues.     

Inactive plasma renin exhibits sex difference in mice

1. The plasma concentration of inactive renin was two- to three-fold higher in male than in female mice independently of whether mice of strains with low (BALB/c) or high (Theiller) content of active renin in the submandibular salivary glands were studied. 2. Removal of the submandibular glands did not affect the high plasma concentration of inactive renin in male mice. 3. Inactive plasma renin decreased over several days after castration of normal and sialoadenectomized male mice to the same levels as those found in normal female mice. 4. Treatment of these castrated male mice with testosterone increased and normalized inactive plasma renin independently of whether the submandibular glands had been previously removed or not. 5. Testosterone treatment of sialoadenectomized female mice increased inactive renin to the same levels as those found in normal male mice. 6. Our findings suggest that the sex difference in inactive plasma renin in mice may be explained by an increased secretion of inactive renin in male mice stimulated by androgens. 7. Since we have recently found that inactive plasma renin in male mice is mainly of renal origin, this increased secretion is most likely located to the kidneys.     

Platelet intracellular free calcium concentration in normotensive and hypertensive pregnancies in the human

1. Basal and stimulated platelet intracellular free calcium concentrations were measured in non-pregnant women and in third trimester patients who were either normotensive or who had pregnancy-induced hypertension or pre-eclampsia. There were 15 subjects in each group. 2. A trend for a reduction of the maximal response of platelet calcium levels to stimulation by 5-hydroxytryptamine was seen in pregnant groups compared with nonpregnant subjects, but this was significant only in pre-eclampsia. 3. No significant differences in basal or adenosine 5'-pyrophosphate-stimulated levels of platelet intracellular free calcium concentration were observed between the four groups. 4. These results illustrate that basal platelet calcium levels are unchanged in hypertension of pregnancy. Alterations in basal platelet calcium levels may not be involved in the platelet activation that is a feature of pre-eclampsia.     

Enzymatic activity of renin in plasma of normal and uraemic subjects

Plasma renin reactivity (PRR) is the rate of angiotensin I production after addition of renin to plasma, minus endogenous renin activity. PRR is increased in plasma of patients with renal failure compared with that of normal subjects. The present study was carried out to determine if increased PRR in uraemic plasma is related to differences of endogenous active or inactive renin, endogenous renin substrate, or pH of the incubation in vitro. PRR in plasma of ten uraemic patients was greater (P less than 0.02) than that in plasma of ten normal subjects in incubations carried out at pH 7.4 and 5.7. Increased PRR was not accounted for by differences of endogenous active and inactive renin activity. After addition of renin, renin concentration (measured by direct radioimmunoassay) did not differ in normal and uraemic plasma. Renin substrate concentration, measured both indirectly and by direct radioimmunoassay, also did not differ in normal and uraemic plasma. Increased PRR in uraemic plasma is not related to alterations of renin or renin substrate concentrations. These observations are consistent with our earlier hypothesis that there is a deficiency of a renin inhibitor in uraemic plasma.     

Exchangeable sodium in Goldblatt one-kidney one-clip hypertension in the rat

Exchangeable sodium (NaE), plasma active renin concentration and blood pressure were measured in rats with a sole remaining kidney before and after the development of hypertension induced by clipping of the single renal artery and again after unclipping. Control observations were made in sham-clipped and sham-unclipped uninephrectomized rats. Renal artery clipping caused hypertension and expansion of NaE, the latter being sustained throughout the 6 weeks during which the renal artery was constricted. Hypertension in the clipped rats was progressive over 6 weeks, whereas the expansion of NaE was not; thus the two measurements were not significantly correlated. Two rats which remained normotensive after clipping did not show expansion of NaE. Plasma active renin was elevated in comparison with the sham-clipped controls on the day after clipping, but not thereafter. Unclipping in hypertensive rats was followed by a return of NaE and blood pressure to control values. Both the sustained expansion of NaE and the transient rise in active renin probably contribute to the development of hypertension in this model, but neither alone nor together do they provide a full satisfactory explanation.