Renin Substrate Concentration Research Articles

Immunoreactive renin, prorenin, and enzymatically active renin in plasma during pregnancy and in women taking oral contraceptives.

Direct RIA of renin with monoclonal renin antibodies and indirect RIA with angiotensin I antibodies were performed in plasma of 44 pregnant women, 44 women taking an oral contraceptive (OC), and 54 normal women. The following parameters were measured: immunoreactive renin, naturally occurring enzymatically active renin (active renin), trypsin-activatable inactive renin (prorenin), PRA, and renin substrate. Immunoreactive renin (mean, 95% confidence interval) was significantly higher in pregnant women (1090; 420-2800 pg/ml; third trimester) than in normal women (248; 101-562 pg/ml; P less than 0.001) and was lower in OC-treated women (131; 41-415 pg/ml; P less than 0.001). Prorenin and active renin also were increased in pregnant women and decreased in OC-treated women. The fraction of renin that was in the active form was lower in pregnant women (4.8; 1.4-18%) than in OC-treated women (8.8; 3.0-25%; P less than 0.001) and normal women (9.1; 2.9-29%; P less than 0.001). Renin substrate was increased to comparable levels in pregnant women and OC-treated women, but PRA was increased in pregnant women and normal in OC-treated women. The maximum velocity per unit weight of renin was the same for active renal renin as for active plasma renin and trypsin-activated plasma prorenin. Maximum velocity and Km values measured in mixtures of purified active renin and renin substrate and the concentrations of active renin and renin substrate measured in whole plasma were entered into the Michaelis-Menten equation for calculating PRA. The calculated values were similar to the measured results in all three groups, indicating that PRA was determined by the molar concentrations of enzyme and substrate. Thus, we found no evidence of unknown substances in plasma interfering with the enzyme-substrate reaction. The percentage of circulating renin in the active form was much lower during pregnancy than in other conditions where the renal release of active renin is stimulated and prorenin is as high as during pregnancy. This suggests that a smaller fraction of prorenin is intrarenally converted into active renin before its release into the circulation or that a larger fraction of circulating prorenin is of extrarenal origin. The finding that PRA is normal during OC treatment suggests that the estrogen-induced increase in renin substrate is compensated for by suppressed renal release of active renin.

Renin-angiotensin system, converting-enzyme inhibition and kidney function in aging female rats.

The age-related changes in the renin-angiotensin system were investigated in normotensive 3-, 10-, 20-, and 30-mo-old female Wistar rats. Plasma renin concentration and immunofluorescent renal renin index remained constant from 3 to 10 mo, then decreased as the animals become older, whereas plasma concentration of renin substrate diminished slightly between 10 and 20 mo and plasma converting-enzyme activity was not modified with age. Acute inhibition of converting-enzyme activity by intravenous administration of 0.1 mg/100 g body wt S 9780 (the diacid form of S 9490) was followed by a 7- to 8-mmHg decrease in arterial pressure and a concomitant 10-12% increase in inulin and p-aminohippuric acid (PAH) clearance in the 10- and 20-mo-old rats. On the other hand, neither glomerular filtration rate, PAH clearance nor arterial blood pressure were affected by converting-enzyme inhibition in the 30 mo-old rats. These results indicate that the activity of the renin-angiotensin system is progressively reduced with age and suggest that angiotensin II does not play an important role in the maintenance of blood pressure and kidney hemodynamics in normotensive female senescent rats.

EXTRACTION OF PLASMA PRORENIN BY HUMAN HEART

Arterial plasma prorenin underwent 58% extraction during one passage through the coronary circulation in eleven patients undergoing myocardial metabolic studies. Active renin and renin substrate were unaffected. Changes in renin and renin substrate concentrations were not detected across the enterohepatic, femoral, or renal vascular beds. This high degree of selective extraction of prorenin by the heart accounts for its proposed half-life. Prorenin could be a cardiotropic hormone.

Changing basal and stimulated activity of the renin-angiotensin system during the second half of gestation in the anaesthetized piglet.

Concentrations of components of the renin-angiotensin system were studied in eighty anaesthetized pig fetuses aged between 57 and 112 d of gestation (term = 114 +/- 1 d). Plasma renin concentration rose from a mean value of 3.2 +/- 0.4 ng X ml-1 X h-1 (mean +/- S.E.M.) at 57 d to 17.5 +/- 2.7 ng X ml-1 X h-1 at 93 d of gestation and thereafter declined to 5.0 +/- 1.6 ng X ml-1 X h-1 just prior to term. There was no distinct pattern of change in plasma renin substrate concentrations during gestation; the concentration near term (0.33 +/- 0.10 micrograms X ml-1) was not different from that at 57 d (0.50 +/- 0.18 micrograms X ml-1) or that at 93 d (0.31 +/- 0.08 micrograms X ml-1) of gestation. Plasma angiotensin II concentrations increased from 33 (log10 (mean +/- S.E.M.) = 1.554 +/- 0.050) pg X ml-1 at 60 d to 232 (2.365 +/- 0.225) pg X ml-1 at 105 d of gestation, after which it decreased to 50 (1.699 +/- 0.100) pg X ml-1 in 20-d-old neonatal piglets. Haemorrhage of 10-20% estimated blood volume produced no consistent changes in plasma renin substrate concentrations, and inconsistent changes in renin and angiotensin II concentrations at 85-90 d of gestation, but a consistent increase in both renin and angiotensin II concentrations thereafter. These results indicate that the components of the renin-angiotensin system are present in the circulation of the pig fetus, and that their responses to stimuli develop during the second half of gestation.

Effect of age on the renin-angiotensin-aldosterone system in normal subjects: simultaneous measurement of active and inactive renin, renin substrate, and aldosterone in plasma.

To investigate the effect of aging on the renin-angiotensin-aldosterone system, plasma renin substrate concentrations (PRSC); plasma total, active, and inactive renin concentrations (TRC, ARC, and IRC); PRA; and plasma aldosterone concentrations (PAC) were measured simultaneously in 60 normal subjects, 18-84 yr old. PRSC was measured by the addition of excess human renal renin. ARC and TRC after trypsin activation were measured by adding sheep renin substrate; IRC was calculated by subtracting ARC from TRC. The active renin ratio was calculated as follows: ARC/TRC X 100%. PRA and PAC were measured by RIA. There were no significant changes in PRSC, TRC, IRC, and PRA to PAC ratio with aging. Both ARC and active renin ratio fell significantly with aging (r = 0.46 and P less than 0.01; and r = 0.54 and P less than 0.01, respectively). PRA and PAC also tended to decrease with aging (r = 0.35 and P less than 0.01; and r = 0.59 and P less than 0.01, respectively). A significant positive correlation was found between PRA and ARC (r = 0.72; P less than 0.001). PRA was also correlated with PAC. In conclusion, the age-related decrease in PRA is not due to the change in PRSC, but is mainly due to the fall in ARC. Decreased conversion of inactive to active renin might be responsible in part for the reduced ARC in the elderly.

Renin-angiotensin mechanisms in oral contraceptive hypertension in conscious rats.

Rats were placed on powdered chow containing either no additives (controls), mestranol (a synthetic estrogen), norethynodrel (a synthetic progestin), or both mestranol and norethynodrel. After 6 mo on these diets, catheters were placed in the carotid artery and jugular vein of each rat. An arterial blood sample was obtained for plasma renin activity (PRA), plasma renin concentration (PRC), and plasma renin substrate concentration (PRS). Mean arterial pressure was measured in each rat. The angiotensin II (ANG II) antagonist, [Sar1-Ile8]ANG II, was infused intravenously for 30 min while blood pressure was recorded. Rats treated with mestranol and/or norethynodrel had PRA and PRC values that were not different from the control rats; however, mestranol-treated rats and rats treated with mestranol plus norethynodrel had PRS values that were substantially (P less than 0.01) higher than the controls. Arterial pressures in rats treated with mestranol and with mestranol plus norethynodrel were significantly (P less than 0.01) elevated when compared with the controls and with the rats treated with norethynodrel alone. Infusion of the ANG II antagonist failed to alter arterial pressure in any of the groups of rats. These results indicated that, in the steroid combination found in the oral contraceptive Enovid, it is the estrogenic component that results in hypertension in this rat model. Also this study found no evidence that ANG II plays a role in maintaining the elevated arterial pressure following long-term treatment with mestranol in rats.

Multiple defects in the renin-angiotensin system in alloxan-diabetic kidney.

A defect in the renin-angiotensin system has been shown in diabetic patients and experimental animals, in particular with nephropathy or autonomic neuropathy. The mechanism for this low plasma renin activity (PRA) is poorly understood. In order to clarify this defect, the renin-angiotensin system was studied in alloxan-induced diabetic and age-match control mice. In diabetic animals, kidney renin activity (KRA) was significantly lower than that of the controls, while plasma renin substrate (PRS) concentration was slightly higher and PRA was normal. The amount of injected radiolabeled renin extracted by the kidney was normal, but the amount extracted by the liver was significantly decreased in diabetic animals. On the other hand, the degradation of the extracted renin by both the kidney and the liver was elevated as compared to the controls. This high degradation rate was accompanied by a slight increase in lysosomal protease activity in the kidneys. In in vivo studies, isoproterenol-induced PRA was 20-fold in control animals. In diabetics, isoproterenol-induced PRA was attenuated and rose only four- to fivefold over basal level. The angiotensin converting enzyme (ACE) activity in the kidney was significantly decreased in the diabetic state. It is concluded that there were multiple defects in the renin-angiotensin system in this diabetic model, namely, a depletion of renin storage with subsequent loss of maximal responsiveness to the adrenergic agonist in renin release, an elevation of intrarenal renin degradation together with a deficiency in ACE which would possibly lead to a decrease in intrarenal formation of angiotensin II.

Pathogenetic aspects of hypertension in Cushing's syndrome.

Abnormalities of the renin-angiotensin-aldosterone system (RAAS) were observed in hypertensive patients suffering from Cushing's syndrome. In 12 patients with different etiology of Cushing's syndrome renin substrate concentration and urinary-free cortisol, as well as the circadian rhythms of plasma cortisol, aldosterone and plasma renin activity were measured. Plasma renin substrate concentrations were found elevated in all but 1 patient, while plasma renin activity was elevated, normal or lowered. Plasma aldosterone values were found in the lower normal range. A physiological rhythm of cortisol secretion was not observed in any patient with Cushing's syndrome, while plasma aldosterone was secreted episodically mostly within the normal range. We conclude that changes of the RAAS may not be predominantly responsive for hypertension in Cushing's syndrome; other factors like circulating catecholamines are probably of greater importance for the pathogenesis of blood pressure elevation in hypercortisolemic patients.

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.

Plasma renin concentration, activity and substrate in normal children.

Plasma renin concentration (PRC), activity (PRA) and substrate concentration (PRSC) were measured in 27 males and 31 female children aged 3 days to 14.5 years (median age 10 months). No sex difference between the three parameters was found and the data were therefore combined for boys and girls. Logarithmic transformation were used for all parameters. PRC, PRA and PRSC were significantly higher in children than in adults and were negatively correlated by age or body surface area. As expected, PRA was strongly positively correlated to PRC (r = 0.98, P less than 0.001) and to PRSC ( r = 0.55, P less than 0.001). From the second order partial correlation coefficients it is concluded that PRSC and PRC in children decrease with age or body surface area, and that PRA consequently also decreases. A negative feed-back regulatory mechanism between PRSC and PRC is suggested. Because of the decline in PRSC during childhood, it is recommended to measure PRC instead of PRA and to use age related reference values.

Direct radioimmunoassay for human renin substrate and its measurement in plasma from essential hypertensive patients, diabetic patients and pregnant women.

We homogeneously purified human renin substrate from outdated bank plasma and raised antibody against it. The antibody did not cross-react with angiotensin I, angiotensin II or synthetic tetradecapeptide at concentrations of up to 160 nmol, nor did it cross-react with up to 0.2 ml of plasma from rat, rabbit or sheep. It did, however, completely cross-react with human des-angiotensin I renin substrate. A direct radioimmunoassay for human renin substrate was developed using the antibody, and the minimum detectable value of renin substrate found to be 70 pg of protein. Plasma renin substrate concentrations of normal subjects, essential hypertensive patients, diabetic patients and pregnant women were measured by direct and indirect assays. Hypertensive patients had similar concentrations of plasma renin substrate to normal subjects, whereas diabetic patients had significantly lower plasma renin substrate concentrations (p less than 0.01). The direct assay always gave a higher value than the indirect assay, and the ratios of the two assays (direct assay/indirect assay) were similar in normal subjects, hypertensive patients, diabetic patients and pregnant women.

Plasma renin substrate in the prediction of pregnancy outcome in threatened abortion.

Concentrations of plasma renin substrate, serum oestradiol-17 beta, human chorionic gonadotrophin, sex-hormone binding globulin and plasma renin activity were measured in 77 samples from 74 patients with uterine bleeding during the first and second trimesters of pregnancy and in a control group of 29 normal pregnant women (51 samples). Mean concentrations of these substances were lower than control values in patients with an abnormal outcome of pregnancy. In patients with a normal outcome after uterine bleeding, concentrations were mostly within the control range. Serum oestradiol-17 beta concentration was superior to the other variables in predicting fetal outcome in the whole group. In patients with a live fetus at the time of blood sampling but who subsequently aborted, serum oestradiol-17 beta concentration was mostly normal, whereas plasma renin substrate was decreased. Our results suggest that plasma renin substrate may provide additional prognostic information to that given by serum oestradiol-17 beta measurement or ultrasonography in threatened abortion.

Effects of natural oestrogen therapy on blood pressure and renin-angiotensin system in normotensive and hypertensive menopausal women.

The blood pressure level and the renin-angiotensin system were investigated in 24 menopausal women (12 normotensive and 12 hypertensive) before, during and after six months of treatment with either oestradiol or trisekvens (sequential preparation containing oestradiol, oestriol and norethisterone acetate). In the normotensive women no significant alterations in systolic or diastolic blood pressure were found during treatment for six months. In the hypertensive women systolic blood pressure fell significantly during treatment with oestradiol as well as with trisekvens, while diastolic pressure did not change. All individual variations of blood pressure were small. The plasma concentrations of renin, angiotensin II and aldosterone remained unchanged during the treatments. A statistically significant increase in plasma renin substrate concentration was observed in all groups with the exception of the normotensive women treated with oestradiol. Menopausal symptoms in hypertensive women may safely be treated with natural oestrogens on the same indications as used for normotensive women.

The effect of changes in blood gas tension upon the renin-angiotensin system of the newborn infant.

Renin and renin-substrate concentrations were measured in the paired umbilical artery and vein blood of 20 babies born by elective caesarean section, and 36 babies born vaginally. Blood pH, carbon dioxide tension and oxygen tension were measured in all samples. Babies born vaginally were significantly more acidaemic than those delivered by caesarean section. The cord artery blood also had a significantly greater carbon dioxide tension at vaginal delivery. A decrease in pH of either cord artery or vein blood, irrespective of mode of delivery, was associated with an increase in renin concentration. Renin-substrate concentration tended to be lower in the cord vein blood of acidaemic babies born vaginally, such that the ratio renin: renin-substrate concentration was negatively correlated with pH. At caesarean section the renin concentration of cord vein blood was positively correlated with carbon dioxide tension and increased dramatically at oxygen tensions less than 3kPa. This was not observed in babies born vaginally, but the cord artery substrate concentration in these infants was positively correlated with carbon dioxide tension. Thus changes in the renin-angiotensin system at birth may partly be affected by blood gas tension.

Estrogen replacement therapy by transdermal estradiol administration

To determine whether the nonoral administration of estradiol (E2) might provide physiologic replacement without alteration of hepatic function, 20 postmenopausal women were studied before and after 3 weeks of treatment with either E2-containing transdermal therapeutic systems or placebo. Twenty premenopausal women were also studied. With E2-containing systems, serum E2 and estrone levels were restored to the premenopausal range. Variable responses of the different biochemical and biologic markers of the actions of E2 were observed. The most sensitive marker was vaginal cytology, with the E2 dosage reverting the maturation index to premenopausal values. Hot flashes, measured objectively, were reduced in frequency but not abolished. Serum levels of follicle-stimulating hormone and luteinizing hormone were lowered but remained higher than the premenopausal range. No significant changes were noted in urinary calcium/creatinine and hydroxyproline/creatinine ratios, which were used as markers of bone resorption. With active systems, no significant changes were noted in the concentrations of the hepatic proteins renin substrate and thyroxine-binding globulin or in the binding capacities of cortisol-binding globulin and sex hormone-binding globulin. These results indicate that transdermal E2 administration may be used to provide estrogen replacement while exerting limited effects on hepatic function.

The renin-angiotensin-aldosterone system in fulminant hepatic failure.

The relationship of the renin-angiotensin-aldosterone system to blood pressure and sodium homeostasis and to renal function was investigated serially in 12 patients with fulminant hepatic failure. The plasma concentrations of renin, angiotensin II, and aldosterone were, in most instances, markedly increased. Systolic blood pressure, which was often very low, showed a significant inverse relationship to the plasma renin concentration, suggesting that the marked stimulation of the system is a homeostatic response to hypotension. However, the plasma renin substrate concentration was markedly decreased, and the conversion of angiotensin II to inactive peptides increased, both of which may have severely limited the full 'expression' of the stimulated system. Renin and angiotensin II levels were both related to creatinine clearance, which was often reduced, but it is not clear as to which was cause and which effect. No relationship between the plasma aldosterone concentration and renal sodium excretion could be detected.

Studies on the effect of mode of delivery on the renin-angiotensin system in mother and fetus at term.

Plasma renin substrate (PRS) and renin (PRC) concentrations were measured in the paired umbilical artery and vein blood of 54 babies and in the venous blood of 23 of their mothers at vaginal delivery. Similar samples were collected from 31 babies and their mothers at elective caesarean section. Fetal renin concentrations in both umbilical artery and vein blood were markedly increased at vaginal delivery compared with values at operative delivery. Renin substrate concentration was correlated with the length of second stage of labour. Umbilical vein PRC and PRS were greater than corresponding umbilical artery values at vaginal, but not at operative delivery, suggesting that some factor associated with delivery might stimulate the placenta to produce renin and renin substrate during vaginal delivery. Maternal and umbilical concentrations of both renin and renin substrate were unrelated, supporting the view that the maternal and fetal compartments are independent. It is suggested that hyperactivity of the renin-angiotensin system may be an integral part of the marked changes in cardiovascular homeostasis which occur at birth.

Marathon run: effects on plasma renin activity, renin substrate, angiotensin converting enzyme, and cortisol.

Altogether 33 Finnish amateur runners were studied before and after a non-competitive Marathon run over the classical itinerary in Athens in 1976 (n = 8), 1977 (n = 14) and 1978 (n = 11). Plasma renin activity (PRA) rose 3-fold in all runs, whereas plasma renin substrate (RS) concentration did not change significantly. Serum angiotensin converting enzyme (ACE) activity was not changed. Serum cortisol concentration was increased 2-3 fold. The unchanged plasma RS concentration, in spite of increasing PRA, indicates that plasma RS is kept within normal limits during prolonged strenuous physical exercise. One contributing mechanism may be stimulation of RS biosynthesis by cortisol. Low PRA levels in two old runners, 65 and 83 years old, may indicate a decreased ability to respond with renin release to the stimuli of physical exercise.

An increase in high-molecular weight renin substrate associated with estrogenic hypertension

We have previously reported that estrogens have the potential to induce new forms of renin substrate in addition to elevating the major circulating form of this protein. One of these estrogen-induced forms had a molecular weight in excess of 150,000. In this study we have compared the plasma concentration of the high-molecular-weight renin substrate in normotensive women receiving estrogen therapy and women with estrogenic hypertension. A statistically significant elevation of this protein was associated with estrogenic hypertension and normotensive pregnant women at term. This form of renin substrate differed from the major form with respect to electrophoretic mobility, isoelectric point, and immunologic cross-reactivity. In addition, kinetic analysis indicated that this high-molecular-weight substrate has a significantly higher affinity for the enzyme renin than the major circulating form ( K m = 1800 ± 290 versus 3520 ± 260 ng angiotensin I equivalents/ml). These results suggest that in addition to renin substrate concentration, substrate composition may play an important role in blood pressure regulation.

Plasma renin substrate and oestrogens in normal pregnancy

Relationship between concentrations of serum oestrogens, plasma renin substrate and plasma renin activity were studied in six women throughout pregnancy. There was a significant positive correlation between serum oestradiol-17 beta and plasma renin substrate concentrations (r=0.60). Serum oestriol concentrations also correlated significantly with plasma renin substrate concentrations (r = 0.68). Correlation coefficients calculated separately for each subject throughout pregnancy were higher than those for the whole group. Also, there was much individual variation in dose-response of serum oestrogens to plasma renin substrate concentrations. There was no significant correlation between serum oestrogens and plasma renin activity. Our results support the view that oestrogens cause the increase in plasma renin substrate concentration during pregnancy, and emphasize the individual variation in response of renin substrate concentration to serum level of oestrogens.