Altered Renin-Angiotensin-Aldosterone Relationships in Normal Renin Essential Hypertension

Transcription

1 67 Altered Renin-Angiotensin-Aldosterone Relationships in Normal Renin Essential Hypertension THOMAS J. MOORE, GORDON H. WILLIAMS, ROBERT G. DLUHY, SAMUEL Z. BAVLI, THEP HIMATHONGKAM, AND MARTIN GREENFIELD SUMMARY Aldosterone responsiveness to angiotensin II (A II) was evaluated in 64 subjects with "normal renin" hypertension. Plasma aldosterone (PA) and plasma renin activity (PRA) levels were determined with the subjects supine and after 2 72 hours in the upright position while they were in metabolic balance on a meq of sodium/0 meq of potassium diet. The increment in PA between supine and upright postures divided by the increment in PRA () was used as an estimate of adrenal sensitivity to A II. Under identical conditions, the ratio in normal controls was >3.8. Although 52 of the hypertensive subjects had normal, 2 had low. Supine PA and PRA were similar in both groups, but the upright PA was lower (4 vs. 69 ng/dl) and the upright PRA higher (. vs. 7 ng/ml per hr) in the group with the subnormal. The low ratios indirectly suggest subnormal aldosterone responsiveness to A II. To test this hypothesis directly, A II was infused into 9 of the 64 subjects (0.,0.3,.0, and 3.0 ng/kg per min). PA and A II levels were measured before and 20 and 30 min after each dose was begun. Blood pressure was monitored at 2-min intervals. In 4 hypertensives with normal, PA rose significantly during the 0.3,.0, and 3.0 ng/kg per min doses. In five subjects with low, PA did not rise significantly at any dose of A II. Plasma A II levels and blood pressure rose comparably in both groups. These data demonstrate that, in the sodium-depleted state, some "normal renin" hypertensive subjects have decreased aldosterone but normal pressor responsiveness to angiotensin II. SUBJECTS WITH "normal renin" hypertension were originally thought to be a homogenous group with normal renin-angiotensin-aldosterone (RAA) interrelationships. '"* There is now, however, a growing body of data suggesting that the RAA axis is abnormal even in "normal renin" subjects. 5 " Recently, Kisch et al. 2 reported that normal renin hypertensives on high sodium intakes had greater aldosterone responsiveness to infused angiotensin II than did normotensive controls on similar diets. Since it has been shown that sodium depletion increases adrenal glomerulosa responsiveness to angiotensin II, 3 ~ S it could be hypothesized that sodium depleting the hypertensive subjects before infusing angiotensin might magnify the adrenal hyperresponsiveness described by Kisch et al. 2 Thus, it could be demonstrated whether increased adrenal responsiveness to angiotensin II was common to all or just a subgroup of normal renin hypertensives. The present study was performed to characterize the From the Endocrinology-Hypertension Unit, Peter Bent Brigham Hospital and the Department of Medicine, Harvard Medical School, Boston, Massachusetts. These investigations were supported in part by the John A. Hartford Foundation, Grant 9893, and by National Institutes of Health Grants 5-ROI-HL682, -ROI-HL8882, S-FR2-AM0629, and -F32- HL0544. The clinical studies were carried out at the Clinical Research Center of the Peter Bent Brigham Hospital supported by Grant 8-MOI-FR-3 from the Division of Research Resources, National Institutes of Health. Address for reprints: Gordon H. Williams, M.D., Peter Bent Brigham Hospital, 72 Huntington Avenue, Boston, Massachusetts 025. A preliminary report of these findings was presented at the Second International Symposium on the Epidemiology of Hypertension, September 974, Chicago, Illinois and at the American Heart Association 49th Scientific Session, November 976, Miami, Florida. Received October 5, 976; accepted for publication December 30, 976. adrenal's response to angiotensin II in sodium-depleted normal renin hypertensive subjects. Two methods of assessing adrenal responsiveness were employed: () the adrenal response to endogenous angiotensin stimulation was determined by relating the incremental response of plasma aldosterone to upright posture to the increment in plasma renin activity; (2) exogenous angiotensin II was infused intravenously in graded doses. Rather than finding an enhanced adrenal response, many of the hypertensive subjects demonstrated subnormal adrenal responsiveness to angiotensin II. Methods Sixty-four patients with normal renin essential hypertension (47 males, 7 females) were studied at the Clinical Research Center of the Peter Bent Brigham Hospital and their responses compared with normotensive controls (six males, five females) studied under identical conditions. The age range of the normal subjects was (mean of 28 years). Responses in some of these normal subjects have been reported previously. 6 The criteria for inclusion of hypertensive subjects in the study were as follows: outpatient supine diastolic blood pressure greater than 90 mm mercury determined on three different occasions and documented evidence of hypertension for at least 6 months before the study. All antihypertensive medications were discontinued at least 2 weeks prior to admission. The subjects were fed an isocaloric diet of meq of sodium/0 meq of potassium. Daily 24-hour urine samples were analyzed for sodium, potassium, and creatinine. Subjects with primary aldosteronism, pheochromocytoma, renal vascular disease, and Cushing's syndrome were ex-

2 68 CIRCULATION RESEARCH VOL. 4, No. 2, AUGUST 977 eluded by rapid sequence intravenous pyelogram, urinalysis, serum creatinine, serum electrolytes, 24-hour urinary vanillylmandelic acid (VMA), metanephrines, 7-OH, and aldosterone levels, and, where clinically indicated, renal arteriogram and bilateral renal vein renin determinations. Thirty-nine per cent of the 64 subjects reported herein did have a renal angiogram which in all cases was normal. Subjects with high and low renin essential hypertension also were excluded. The normal PRA in our laboratory is ng/ml per hour (upright posture, meq of sodium diet). 7 The protocol was approved by the Human Subjects Committee of the Peter Bent Brigham Hospital and written informed consent was obtained in all cases. UPRIGHT POSTURE STUDY When subjects had achieved metabolic balance, usually on the 5th or 6th day of sodium restriction, after an overnight fast and maintenance of a supine position for at least 2 hours, two supine control samples were drawn at least 30 minutes apart and the subjects were told to walk for 272 hours. Additional blood samples were obtained after 20 and 50 minutes of upright posture. All samples were analyzed for plasma renin activity, aldosterone and cortisol, serum sodium and potassium, and, in a subpopulation of 6 subjects, angiotensin II levels. Eleven normal controls were studied in an identical fashion. ANGIOTENSIN II INFUSION On a different day, during the same hospital stay when the subjects were still in balance on a sodium-restricted intake, 9 of the previously studied hypertensive subjects were infused with angiotensin II. Adrenal and vascular responses to angiotensin II were compared to those of six normotensive controls studied under identical conditions. After an overnight fast, with the subjects in the supine position, an intravenous line was placed in each of the subject's arms (one for infusion and one for blood sampling). Control blood samples were obtained and a graded infusion of angiotensin II (Hypertensin, Ciba) was begun with a Harvard infusion pump at rates of 0., 0.3,.0, and 3.0 ng/kg per min as previously described. 2 Each dose was infused for 30 minutes and blood samples were obtained at 20 and 30 minutes at each level. All samples were analyzed for angiotensin II, aldosterone, cortisol, sodium, and potassium. Blood pressure was monitored using an indirect recording sphygmomanometer (Arteriosonde, Hoffmann-La Roche) at 2-minute intervals for a 30-minute control period and throughout the angiotensin infusion. LABORATORY PROCEDURES All blood samples were immediately centrifuged and the plasma separated and frozen until time for assay. Samples for PRA and A II levels were drawn with ethylenediaminetetraacetic acid (EDTA) as the anticoagulant; heparin was used as the anticoagulant in the samples for cortisol and aldosterone. Serum and urine sodium and potassium levels were measured by flame photometry with lithium as an internal standard. Plasma aldosterone, renin activity, and angiotensin II values were measured by radioimmunoassay techniques as previously described. 8 ' 9 The values for renin activity and angiotensin II were reported in reference to the World Health Organization Standards and , respectively. Therefore, the absolute values may differ somewhat from those reported previously from this laboratory. The results are expressed as mean ± standard error of the mean. Threshold dose during angiotensin infusion is defined as the lowest dose of angiotensin II required to produce a response significantly different from control using two way analysis of variance and P values were obtained in Dunnett's tables. 20 For other statistical analyses for parametric data Student's /-test 2 and for nonparametric data, Fisher Exact Test (FET) were used. 22 Differences are considered significant for P < 0.05 unless otherwise indicated. Results a PA fl PRA UPRIGHT POSTURE STUDY Release of endogenous renin and generation of angiotensin II were increased by upright posture. The increment in plasma renin activity between supine and upright positions (APRA) was used as an estimate of the degree of acute stimulation of the adrenal gland by angiotensin II. The plasma aldosterone increment (APA) (supine» upright) was used as a measure of the adrenal response. Thus, the ratio reflects the response of plasma aldosterone relative to changes in plasma renin. The individual ratios for the 64 hypertensives and normotensive controls are shown in Figure. All of the normal subjects had ratios greater than 3.8. In contrast, 2 of the 64 subjects with normal renin essential hypertension (20%) had ratios lower than those of any of the normotensive controls. There were no significant differences in a number of metabolic or biochemical parameters between the normal or low hypertensive subjects (Table ). Specifically, there was no diff- 0, NORMOTENSIVE (n = II)! HYPERTENSIVE (n = 64) FIGURE Comparison of normotensive and hypertensive subjects classified according to their APA I APRA ratios which represent the increment in plasma aldosterone (APA) divided by the increment in plasma renin activity (APRA) when the subjects change from the supine to the upright position ( meq Na diet).

3 ALTERED A II-ALDOSTERONE RELATION IN HYPERTENSION/Moore et al. 69 TABLE Characteristics of the Hypertensive Subjects Divided According to &PA/&PRA Responses to Upright Posture Sex Race Age (yr) Serum Na (meq/liter) Serum K (meq/liter) Admission Na,, (meq/24 hr) Admission K,, (meq/24 hr) Low salt Nau (meq/24 hr)* Low salt Ku (meq/24 hr)* Weight loss (kg) (admission -» low salt balance) Admission systolic BP (mm Hg) Admission diastolic BP (mm Hg) Low salt systolic BP (mm Hg)* Low salt diastolic BP (mm Hg)* Low salt ASR (/*g/day)t Low salt PRA (supine)* (ng/ml per hr) Low salt aldosterone (supine)* (ng/dl) Low salt cortisol (supine)* Results are expressed as mean ± SEM. BP = blood pressure. * Values on day of upright posture study. t ASR = aldosterone secretory rate. Normal M, 38; F, W,48; B, 42 ± 2 44 ± 4.3 ± ± 8 5 ± ± 78 ± 3.2 ± ± 3 3 ± 2 34 ± 3 88 ± ± ± ± 2 4 ± 4 4 Low M, 9;F,3 W, 8; B, 4 48 ± 3 44 ± 4.5 ± ± 9 44 ± 3 ± 4 82 ± 6.7 ± ± 7 3 ± 5 2 ± 4 92 ± ± ± 3 8 ± 3 erence between the two groups in age, urinary electrolyte excretion either on the day of admission or on the day of study, level of blood pressure, supine plasma aldosterone, cortisol, potassium, or renin activity. However, as would be anticipated because of the method used to separate the groups, the upright plasma aldosterone level was less, while the upright plasma renin activity was greater in the subgroup with the low ratio (Fig. 2). For comparison, in the normotensive subjects, the mean supine and upright plasma renin activities were 2.7 ± 0.3 and 9.2 ± 0.8 ng/ ml/per hour and supine and upright plasma aldosterones were 24 ± 5 and 78 ± 4 ng/dl. Since one explanation for the low response could be a decrease in the generation of angiotensin II per unit of renin activity, angiotensin II levels were measured in 6 of 64 hypertensive subjects (nine with normal and seven with low ) and all of the normal subjects. The regression relationship between angiotensin II and renin activity was not significantly different between the normal controls (y = 8.x +.7) and the low APA/ APR A hypertensive subjects (y = 7.x + 5). In both subgroups of hypertensive subjects and in the normotensive controls, the plasma renin activity and angiotensin II values correlated significantly (P < 0.00). ANGIOTENSIN II INFUSION To assess more directly the adrenal responsiveness to angiotensin II and to compare adrenal and vascular responses, angiotensin II was administered intravenously to 9 (30%) of the 64 hypertensive subjects and to six normotensive controls. Fourteen hypertensive subjects had normal and five had low ratios. There were no significant biochemical or metabolic differences between the two subgroups (Table 2). Figure 3 shows the mean increment in blood pressure, angiotensin II, and aldosterone levels in response to graded infusions of angiotensin II in the two subgroups of hypertensive subjects compared to the normotensive controls. There were no significant differences in the plasma aldosterone or angiotensin II levels obtained at 20 and 30 minutes after the initiation of a particular dose of angiotensin IF; therefore, the 20- and 30-minute values have been pooled. Angiotensin II levels rose similarly in all three groups. The only difference was at the highest angiotensin II infusion rate for which the increment in angiotensin II in the low hypertensive group was significantly greater (P < 0.005; FET) than in either the normal APA/ APRA group or the normotensive controls. The latter two were not significantly different from each other. The threshold dose for blood pressure response was 0.3 ng/kg per min in the normal hypertensives and.0 ng/kg per min in the low hypertensives and normotensive controls. However, the blood pressure increments at each dose of angiotensin II were not significantly different in the three groups. A significant increment (P < 0.0) in plasma aldosterone occurred at an infusion rate of 0.3 ng/kg per min in hypertensive subjects with normal and at ng/kg per min in the normotensive controls. On the other /0ml en c PLASMA a PA fnorm A PRA ilow ALDOSTERONE O--0 ^f PLASMA RENIN ACTIVITY i SUPINE UPRIGHT FIGURE 2 Supine and upright plasma aldosterone and plasma renin activity in normal (n = 52) and low (n = 2) hypertensives ( meq Na diet; mean ± SEM). i

4 70 CIRCULATION RESEARCH VOL. 4, No. 2, AUGUST 977 TABLE 2 Characteristics of Hypertensive Subjects Who Were Infused with Angiotensin II (Divided into Two Groups According to Their &PAI&PRA Upright Posture Responses) Number of subjects Age (yr) Low salt Na,, (meq/24 hr)* Low salt!< (meq/24 hr)* Control serum Na (meq/liter) Control serum K (meq/liter) Control mean BP (mm Hg) Control angiotensin II (pg/ml) Control aldosterone (ng/dl) Control cortisol (jig/dl) Results are expressed as mean ± SEM. BP = blood pressure. * Values on the day of angiotensin infusion. Normal 4 35 ± ± 5 42 ± 4. ± 0. 3 ± 3 35 ± 4 25 ± 4 3 ± 2 Low 5 40 ± 5 2 ± 2 78 ± 7 42 ± ± 0.2 ± 6 35 ± 7 9 ± 4 5 ± 3 hand, in the hypertensive subjects with low, aldosterone level did not significantly increase even at the highest infusion rate. Furthermore, the aldosterone increment at the highest infusion rate in the low ratio subgroup (9.4 ±3.6 ng/dl) was significantly less than in either the normally responsive hypertensive subgroups (25.7 ±3.9 ng/dl; P < 0.04, FET) or in the normotensive controls (24.9 ± 7. ng/dl; P < 0.0, FET). There were no significant differences between the three groups in the plasma cortisol or serum potassium levels during the angiotensin infusion. o o o Discussion The present study demonstrates that some subjects with normal renin essential hypertension do not have a normal relationship between the various components of the RAA axis when studied in the sodium-depleted state. However, in contrast to the enhanced adrenal responsiveness found by Kisch et al. 2 in sodium-loaded hypertensives, in 2 of the 64 hypertensives in this study (20%) aldosterone responsiveness was diminished as determined by the ratio of the increment in plasma aldosterone to renin activity in the upright position. The altered adrenal responsiveness in these subjects was directly confirmed by infusing angiotensin II, with the low group responding subnormally both in terms of threshold dose and absolute aldosterone increments. It is important to note that while adrenal responses to angiotensin II were significantly different in the two hypertensive subgroups, blood pressure responses were similar. Although the state of sodium and potassium balance can influence adrenal responsiveness to angiotensin II, ^ no differences in electrolyte balance were found between the hypertensive groups. In addition, because cortisol levels were similar, it is unlikely that the aldosterone levels reflect differences in adrenocorticotropin (ACTH) secretion in the two groups. Another explanation for the difference in aldosterone levels could be an increase in the metabolic clearance rate of aldosterone in the low APA/ APRA group. This is unlikely because only decreases in aldosterone metabolic clearance rates have been reported in essential hypertensives. 23 However, because aldosterone metabolic clearance in our subjects was not assessed, such a possibility cannot be definitely excluded. It has been reported that subjects with high circulating angiotensin II levels are less sensitive to both the pressor and aldosterone-stimulating effects of infused angiotensin II. Kaplan 24 found that higher doses of angiotensin II were needed to achieve a rise in blood pressure in subjects with malignant hypertension or cirrhosis and ascites. Ames et al. 25 reported diminished blood pressure and aldosterone responses to angiotensin II in subjects with cirrhosis. These findings suggest that high angiotensin II levels per se may cause relative unresponsiveness to infused angiotensin II. It is unlikely that this phenomenon accounts for the differences found in the hypertensive population in this report for two reasons. First, the angiotensin II levels were within the normal range and identical in both hypertensive subgroups at the start of the angiotensin II infusion (35 pg/ml). Second, in the previous reports, high circulating angiotensin II levels were associated with both pressor and aldosterone hyporesponsiveness to infused angiotensin II. In the present study, the hypertensive subjects with subnormal adrenal responsiveness had normal pressor responsiveness; this suggests a more specific defect in the interaction of angiotensin II with the glomerulosa cell. It is possible that sodium depletion uncovers a subgroup PLASMA ALDOSTERONE O E 30 ^ A PA Hypertensives PLASMA ANGIOTENSIN E MEAN BLOOD PRESSURE O.I ANGIOTENSIN H INFUSED (ng/kg/min) FIGURE 3 Incremental responses of plasma aldosterone, angiotensin II, and blood pressure to graded infusions of angiotensin II in six normotensive and 9 hypertensive subjects. Al! subjects were on a meq Na diet and in the supine position (mean ± SEM).

5 ALTERED A II-ALDOSTERONE RELATION IN HYPERTENSION/Moore ei al. 7 of normal renin hypertensive subjects with a specific defect in angiotensin-aldosterone interaction. This is unlikely because the distribution of ratios in Figure suggests that there are no distinct subgroups among the hypertensive subjects but rather this group constitutes a single population with a wider range of adrenal responsiveness than in the normotensive subjects. A more likely hypothesis to explain the subjects with subnormal adrenal responsiveness is that dietary sodium content does not alter adrenal sensitivity to angiotensin II as consistently in hypertensive as in normotensive subjects. Thus, the hypertensives' adrenal responsiveness would increase less in the sodium-depleted state and reveal those individuals with low ratios (subnormal adrenal responsiveness). Conversely, sodium loading would suppress adrenal responsiveness less in the hypertensive than the normotensive subjects and reveal the adrenal hyperresponse to angiotensin II reported by Kisch 2 in his hypertensive patients. If this is the case, the present study and Kisch's findings, although seemingly contradictory, could be demonstrating the same phenomenon. In conclusion, it could be speculated that hypertensive subjects with subnormal adrenal responsiveness, in order to close their renin-angiotensin-aldosterone volume feedback loop, generate more angiotensin II even though the plasma levels are still within the normal range. Since blood pressure response to angiotensin II is normal, the net effect could be an elevated blood pressure. In support of this hypothesis is a preliminary communication which reports that some but not all patients with normal renin essential hypertension show a reduction in blood pressure when given an angiotensin I converting enzyme inhibitor 2 "; this suggests that these that these individuals have an angiotensin-mediated component to their hypertension. References. George JM, Gillespie L, Banter FC: Aldosterone secretion in hypertension. Ann Intern Med 69: , Bayard, F, Alicandri CL, Beitins IZ, Lubash GF, Kowarski A, Migeon CJ: A dynamic study of plasma renin activity and aldosterone concentration in normal and hypertensive subjects. Metabolism 20: 53-59, Buhler FR, Laragh JH, Sealey JE, Brunner HR: Plasma aldosteronerenin interrelationships in various forms of essential hypertension. Am JCardiol 32: , Mendelsohn FAO, Johnston CI, Doyle AE, Scoggins BA, Demon DA, Coghlan JP: Renin, angiotensin II, and adrenal corticosteroid relationships during sodium deprivation and angiotensin infusion in normotensive and hypertensive man. Circ Res 3: , Streeten DHP, Schletter FE, Clift GV, Stevenson CT, Dalakos TG: Studies of the renin-angiotensin-aldosterone system in patients with hypertension and in normal subjects. Am J Med 46: , Christlieb AR, Hickler RB, Lauler DP, Williams GH: Hypertension with inappropriate aldosterone stimulation. N Engl J Med 28: 28-3, Williams GH, Rose LI, Dluhy RG, McCaughn D, Jagger PI, Hickler RB, Lauler DP: Abnormal responsiveness of the renin aldosterone system to acute stimulation in patients with essential hypertension. 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J Lab Clin Med 79: , Emanuel RL, Cain JP, Williams GH: Double antibody radioimmunoassay of renin activity and angiotensin II in human peripheral plasma. J Lab Clin Med 8: , Dunnett CW: New tables for multiple comparisons with a control. Biometrics : , Snedecor GW, Cochran WG: Statistical Methods. Iowa State University Press, ed 6, 967, pp Fisher RA: Statistical Methods for Research Workers. New York, Hafner Publishing Co., ed 3, 958, pp Nowaczynski W, Kuchel O, Genest J: A decreased metabolic clearance rate of aldosterone in benign essential hypertension. J Clin Invest SO: , Kaplan NM, Silah JG: The effect of angiotensin II on the blood pressure in humans with hypertensive disease. J Clin Invest 43: , Ames RP, Borkowski AJ, Sicinski AM, Laragh JH: Prolonged infusions of angiotensin II and norepinephrine and blood pressure, electrolyte balance, and aldosterone and cortisol secretion in normal man and in cirrhosis with ascites. J Clin Invest 44: 7-86, Case DB, Wallace JM, Keim HJ, Sealey JE, Laragh JH: Exposure of angiotensin II as a pressor factor in normal renin hypertension. Abstract of the 58th Annual Meeting of The Endocrine Society, p. 6, 976