Response of the Kallikrein-Kinin and

Renin-Angiotensin Systems

to Saline Infusion and Upright Posture

PATRICK Y. WONG,RICHARDC. TALAMO, GORDONH. WILLIAMS, andROBERTW. COLMAN

From the Thorndike Memorial Laboratory, Harvard Medical Unit, Boston CityHospital, Endocrine-Metabolic Unit, Peter Bent Brigham Hospital, Children'sService and Hematology Unit, Massachusetts General Hospital, and theDepartments of Medicine and Pediatrics, Harvard Medical School,Boston, Alassachusetts 02118

A B STRACT The possibility that bradykinin, a po-tent vasodilator, might be a physiological antagonist ofthe renin-angiotensin system was investigated. 11 nor-man subjects, ranging in age from 21 to 33 yr werestudied. Seven of the subjects were given a 10 meqsodium, 100 meq potassium, 2,500 ml isocaloric diet.After metabolic balance was achieved, they were in-fused with either 1 liter of 5% glucose over 2 h or 2liters of 0.9,% saline over 4 h. During the infusions,plasma renin activity (PRA), angiotensin II (A II),prekallikrein, bradvkinin, and aldosterone levels werefrequently determined. Plasmna prekallikrein and kalli-krein inhibitor did not change during the infusion ofeither glucose or saline. In subjects receiving saline,plasma bradykinin fell from 3.9+1.5 (SEM) ng/ml at0 min to 0.93±0.2 at 30 min and 0.95±0.3 at 120 min.These changes paralleled the decrease in PRA overthe same period (7.9±1.3 ng/ml-l/h to 5.6±0.8 at 30min and 3.5±0.7 at 120 min). Similarly, A II fell from113±12 pg/ml to 62±10 and 48+5, respectively, at30 and 120 min. In contrast, the control group infusedwvith glucose showed no change in bradykinin, A II,or PRA.

Another four subjects were given a constant 200meq sodium/100 meq potassium isocaloric diet. After

Dr. Wong's present address is Department of Medicine,Albany Medical College, Albany, N. Y. 12208; Dr. Ta-lamo's present address is Department of Pediatrics, JohnsHopkins Hospital, Baltimore, Md. 21205; Dr. Colman'spresent address is Hospital of the University of Pennsyl-vania, 3400 Spruce Street, Philadelphia, Pa.

Received for publication, 1 February 1974 and in revisedformst 19 Augtust 1974.

metabolic balance was achieved, they were kept supineand fasting overnight. At 9 a.m. they assumed an up-right position and began walking a fixed distance (200ft) at a normal rate (3-4 ft/s). Plasma prekallikreinand kallikrein inhibitor did not change during the pos-ture study. The plasma bradvkinin rose from a baseline of 0.54+0.01 (SEM\) ng/ml to 0.96±0.13 at 20min, 0.77±0.18 at 60 min, and 0.96±0.07 at 120 min.These changes parallel the increase in PRA over thesame period (1.65±0.33 ng/ml/h to 3.6+0.85 at 20 min,5.3±0.9 at 60 min, and 5.35+0.55 at 120 min). Like-wise, the A II rose from 32.5±1.82 pg/ml to 50.8±3.6at 20 minm 54.3+3.2 at 60 min, and 61.3±5.9 at 120 min.

Thus, in sodium-depleted individuals, saline infusionlroduces a rapid fall of plasma bradykinin at a ratesimilar to that observed for A II and PRA. Converselyin sodium-loaded individuals, assumption of uprightposture leads to a parallel rise in A II, PRA, andbradvkinin. These studies indicate that there is a closecorrelation of bradvkinin levels with renin activity andangiotensin IJ, in both acute sodium loading and as-sumption of upright posture, suggesting that these twosystems may be physiologically interrelated.

INTRODUCTIONAngiotensin is the most potent endogenous vasocon-strictor agent identified (1). Its role in the maintenanceof normal blood pressure and in the pathogenesis ofhypertension, however, is disputed (2-4). For ex-ample, in normal individuals sodium depletion, whileassociated with high levels of circulating angiotensin

The Journal of Clinical Investigation Volume 55 April 1975-691-698 691

II (A II),' is not correlated with consistent increases inblood pressure (2). Moreover, in several hyperten-tive disorders, plasma renin and/or angiotensin con-centrations have been normal (5, 6). Finally, the ad-ministration of an antibody to A II to hypertensiveanimals does not necessarily correct the hypertension(7-9).

Conversely, there is also evidence suggesting thatangiotensin in the sodium-depleted state does contributeto the maintenance of a normal or elevated blood pres-sure. Several studies support this concept. When acompetitive inhibitor of A II was given to the sodium-depleted dog, a decrease in blood pressure occurred,while no such effect was produced in the sodium-loaded state (10). Similarly, in the one-kidney Gold-blatt-hypertensive rat, a competitive antagonist of A IIproduced a fall in blood pressure only when the animalswere sodium-restricted (11). One possible explanationfor the differing results in these studies is that addi-tional vasoactive substance(s) may be important inregulatory blood pressure. Both in vitro and in vivostudies suggest that bradykinin is the most potent mam-malian vasodilator known (12).

A serendipitous observation of a normotensive pa-tient with renal artery stenosis and elevated bradykininand A II levels (unpublished observation) promptedus to investigate the physiological interrelationships be-tween the renin-angiotensin and kallikrein-kinin sys-tems. Since is has been previously shown that therenin-angiotensin system is rapidly suppressed by salineinfusion (13) and activated by upright posture, thepresent study examines whether the kallikrein-kininsystem is equally responsive.

METHODSSelcction of subjects. 11 normal subjects (four men and

seven women), ranging in age from 21 to 33 yr, werestudied in the clinical research centers of either the PeterBent Brigham Hospital or the Thorndike Memorial Labora-tory, Boston City Hospital, Boston, Mass. All had normalphysical examinations and routine laboratory tests. No medi-cation including sedatives, diuretics, or any antihypertensiveagents had been taken by the patients. Informed writtenconsent was obtained in each case.

All subj ects were maintained on a constant activity pat-tern simulating their daily activity outside the hospital untilthe day of study. The diet for seven of the subj ects con-sisted of a constant 10 meq sodium/100 meq potassium iso-caloric diet (13-16). Another four subjects were given aconstant 200 meq sodium/100 meq potassium isocaloric diet.Studies were performed after the subjects achieved sodiumbalance, usually on the 5th or 6th day of dietary sodiumrestriction. 24-h urines were collected daily and analyzedfor sodium, potassium, and creatinine. All studies were be-

'Abbreviations used in this paper: A II, angiotensin II;PRA, plasma renin activity; TAMe, tosyl arginine methylester.

gun at 8 a.m. after an overnight fast, and the subjectswere supine for at least 12 h.

Intravenous saline infusion. Four sodium-restricted sub-jects (two men and two women) were given normal salineintravenously. 2 liters of normal saline (0.9%) were infusedat a constant rate of 500 ml/h for 4 h. Blood samples wereobtained for renin activity (PRA), A II, aldosterone, pre-kallikrein, kallikrein inhibitor, and bradykinin. After twobase-line samples, blood was drawn at 10, 20, and 30 min,and at 1, 2, and 4 h after the start of the infusion.

Intravenous glucose infusion. Three sodium-restrictedsubjects (two women and one man) received intravenousglucose as a sham or control procedure. 1 liter of 5%dextrose in water was infused at a constant rate of 500ml/h for 2 h as in the intravenous saline study. After twobase-line plasma determinations were obtained, all of theabove parameters (except aldosterone) were measured at30 min and at 2 h.

Upright posture study. Four subj ects in balance on a200 meq sodium/100 meq potassium diet were kept supineand fasting overnight. At 9 a.m. they assumed an uprightposition and began a constant activity program, walkinga fixed distance (200 ft) at a normal rate (3-4 ft/s). Bloodsamples were taken before 20, 60, and 120 min after as-sumption of the upright position.

Laboratory proceduresPlasma kallikrein and kinin measurements. Serial blood

samples were collected and processed separately for pre-kallikrein and bradykinin measurement. Determinations ofplasma prekallikrein were made by arginine esterase assay(17), and bradykinin was measured by radioimmunoassay,as previously described (18). Excellent correlation betweenthe esterase assay of kallikrein and assay by bradykinin hasbeen demonstrated (19). Kallikrein inhibitors were mea-sured by two different methods. The first utilizes the TAMe(tosyl arginine methyl ester) esterase method as described(17). In the second method, the kallikrein inhibitors wereassayed by incubating the subjects' plasma with purifiedkallikrein by a modification of a procedure previously re-ported (20). Plasma (75 Al) was incubated at 250C for 5min with 25 ,ul of purified human kallikrein at an initialconcentration sufficient to hydrolyze 80 ,umol of TAMe/h.Under these conditions, the percent inhibition = [E - (El-C) ]/E X 100%, where E = initial enzyme activity (purifiedkallikrein activity), El =residual enzyme activity after in-cubation with subjects' plasma, and C = control subjectplasma alone. The enzyme incubated with buffer for 5 minshowed no decrease of activity and no correction was neces-sary. The normal for plasma prekallikrein (mean±+SEM)is 97+4 umol/ml/h, normal plasma kallikrein inhibitor ac-tivity by the TAMe esterase method was 0.99+0.03 U(measured on 36 patients), and by the enzyme incubationmethod was 55±4.2% (8 patients). The normal plasmabradykinin level with ad libitum sodium intake was 1.38+0.45 ng/ml (14 patients). Plasma kininase activity wasmeasured by quantitating the destruction of ['H, 8phe]-bradykinin as previously reported (21).

Renin, angiotensin, and aldosterone measurements. Theserial blood samples were processed for PRA, A II, andaldosterone. PRA and A II were measured by a double-antibody radioimmunoassay (22), plasma aldosterone wasmeasured by a displacement analysis technique as previouslydescribed (23). In salt-depleted man, the normal fastingsupine value for PRA was 5.28±1 (SEM) ng/100 ml/3 h,for angiotensin II, 57+7 ng/ml, and aldosterone, 33±3 ng/

692 P. Y. Wong, R. C. Talamo, G. H. Williams, and R. W. Colman

100 ml. In sodium-loaded man, the normal fasting supinevalue for PRA was 1.5+0.5 ng/ml/h, and for angiotensin IIwas 15±2 pg/ml.

Statistical method. The statistical analyses were per-formed as described by Snedecor and Cochran (24) witha Mathatron 4280 computer (Mathatronics Div., BarryWright Corp., Waltham, Mass.). The zero time values forall hormone determinations were arbitrarily set at 100%.This value was then calculated. The means of the percentagechange at the different time intervals were compared to thebase line (100%) by Student's t test with Bessel's correc-tion for small sample size. The null hypothesis that thecurves describing the changes in hormonal levels after salineinfusion were similar was tested by the paired Student's ttest.

For this study, the level of significance is taken as P<0.05 and value reported as mean+SEM unless otherwisestated.

RESULTSSodium restriction values. The mean, fasting, su-

pine, 8 a.m. levels of A II, renin activity, and aldos-terone were not significantly different from those ofthe group of normal sodium-depleted subjects previ-ously reported from our laboratory (13-16). The mean±-standard error of the hormones was as follows: PRA= 5.61±0.82 ng/ml/h; A II = 64±+12 pg/ml; aldos-terone (four subjects only) = 42+5 ng/100 ml. Themean prekallikrein = 99±4.5 iLmol/ml/h, and percentkallikrein inhibition = 56+4.2 are not significantly dif-ferent from normal, nonsalt-depleted subjects. The bra-dvkinin level of 3.56±1.0 ng/ml is higher than thatof 1.38±0.45 ng/ml in normal, nonsodium-depletedsubj ects.

Sodium loading valutes. The mean, fasting, supine8 a.m. levels of A II and renin activity were not sig-nificantly different from those of the group of normalsodium-loaded subjects previously reported from ourlaboratory (15). The mean-i±standard error of the hor-mones, was as follows: PRA= 1.7+0.33 ng/ml/h; A II= 32.5±+1.8 pg/ml. The mean prekallikrein = 86.4±6.3unLol/ml/h was not significantly different from that ofnormal, nonsalt-depleted subjects. The bradykinin levelof 0.54±0.01 ng/ml was significantly lower than 3.56+1.0 ng/ml in the normal, sodium-depleted subjects.

Intravenous saline infusion. The results of the sa-line infusion study are summarized in Table I andFig. 1. The base-line levels of prekallikrein in thesefour subjects were normal. Serial blood samples showedno significant change in prekallikrein or kallikrein in-hibitor values in any of these subjects. On the otherhand, there was a rapid decline of bradykinin levelsduring the first 30 min of the saline infusion. Brady-kinin levels fell significantly by 10 min after the startof saline infusion and reached a stable plateau value ofabout 40% of the base-line concentration (p < 0.001).The fall in bradykinin paralleled the fall in PRA, A II,

and aldosterone (Fig. 1 and Table I). The rate ofchange in the latter three parameters is similar to thosepreviously described (16). Furthermore, the rate ofchange of the four parameters is significantly correlated(p < 0.01). The kininase values were determined inthree of the four subjects studied. There was no detect-able change during the study.

Intravenous glucose infusion. The base-line prekal-likrein levels of subjects in this group were normal.After glucose infusion, there was no significant changeof prekallikrein or kallikrein inhibitor. Furthermore,there was no alteration in bradykinin, PRA, or A IIlevels (Fig. 2). This was in distinct contrast to thegroup of subjects with saline infusion who exhibited arapid decline in bradykinin, PRA, and A II.

Upright posture study. After assumption of the up-right posture in the subjects on a 200 meq sodium/100 meq potassium diet, plasma prekallikrein and kalli-krein inhibitor did not change (Table II). In contrast,plasma bradykinin rose significantly from 0.54±0.01(SETM) ng/ml to 0.96+0.13 at 20 min and remainedin this range to 120 min. The PRA rose from 1.65±0.33ng/mIl/h to 3.6±0.85 at 20 min, and 5.3±0.9 at 60 min,and remained in this range to 120 min. Similarly,A II rose from 32.5±1.82 pg/ml to 50.8±3.6 at 20 min,and gradually rose to 61.3+5.9 at 120 min.

DISCUSSION

This study demonstrates that in sodium-depleted in-dividuals, saline infusion produces a rapid fall ofplasma bradykinin at a rate similar to that observedfor A II and PRA. In the control subjects infused withglucose and water, no significant changes occur. Con-versely, after dietary sodium loading, upright postureleads to a parallel rise in PRA, A II, and bradykinin.These studies thus indicate a close correlation ofbradykinin levels with renin activity and A II, instudies which acutely suppress or activate the renin-angiotensin system. The results of the present study arein agreement with those of Streeten, Keer, Keer, Prior,and Dalakos (25) where plasma bradykinin concen-tration was found to be significantly higher after 2 hof upright posture when compared to the correspondingsupine fasting value. Presumably, plasma renin activityand A II levels of these patients were also higher inthe upright posture.

The mechanism responsible for the changes in brady-kinin levels in these studies is not known. To explainthis phenomenon, it is first necessary to examinewhether the changes in bradykinin levels are due toaltered production, a different rate of destruction, orboth. As the formation of angiotensin is accompaniedby a rise in the releasing enzyme, renin, one might ex-pect that a rise in bradykinin levels would be accom-

Kinin and Renin-Angiotensin Interrclations (693

TABLE IResponse of the Kallikrein-Bradykinin and Renin-Angiotensin Systems to Saline Infusion in Normal Subjects

on a 10 meq/100 meq K Diet; Normal Saline Infused at 500 ml/h for 4 h

0 Time 10 min 20 min 30 min 60 min 120 min 240 min

pre KKn, lumol/ml/hG. M.R. E.M. E.P. E.

MeanSE

KKn Inhibit, %G. M.R. E.M. E.P. E.

MeanSE

BK, ng/mlG. M.R. E.M. E.P. E.

MeanSE

KAG. M.R. E.M. E.

MeanSE

PRA, ng/ml/hG. M.R. E.M. E.P. E.

MeanSE

A II, pg/mlG. M.R. E.M. E.P. E.

MeanSE

Aldo, ng/100 mlG. M.R. E.M. E.P. E.

MeanSE

117 104 98110 96 9989 79 95

108 105 111106 96 101

5 5 3

73 74 6452 51 5453 48 4960 62 6359 59 574 5 3

7.805.561.280.913.891.46

27.732.833.531.3

1.5

4.67.27.7

12.07.91.3

11288

100154113

12

4328375842

5

4.123.120.600.912.190.74

2.141.620.500.501.190.36

98 92 78 117108 97 114 10287 93 96 7391 113 86 8796 99 94 95

4 4 7 8

61 63 7145 34 4151 57 4461 52 6254 52 55

3 5 6

1.311.280.500.620.930.19

1.122.020.400.400.980.34

30.630.425.629

1.3

6450605758

3

0.941.780.400.690.950.26

1.450.940.500.750.910.18

26.131.828.929

1.1

3.4 2.4 3.3 2.5 2.2 2.84.3 3.8 4.9 4.0 2.7 2.67.0 - 6.0 3.1 3.0 2.2- 9.5 8.0 7.5 6.0 4.04.9 5.2 5.6 4.3 3.5 2.90.9 1.8 0.8 1.0 0.7 0.3

58 54 4778 65 6062 57 45

149 104 9487 70 6218 10 10

45 38 2545 49 4044 42 3475 65 6952 48 42

7 5 8

46 36 34 19 1724 24 23 14 1537 31 23 23 2251 64 51 34 5240 39 33 22 26

5 8 6 4 7

1915112317

2

694 P. Y. Wong, R. C. Talamo, G. H. Williams, and R. W. Colman

pre KKn, prekallikrein; KKn Inhibitor, kallikrein inhibitor activity by enzyme incubation expressed in percentinhibition; BK, bradykinin; Aldo, plasma aldosterone in ng/100 ml; KA, kininase activity expressed as percentagedestroyed.

same as that of our published normal value of 97±4SE ,nmol/nml/h in normal subjects with normal saltintakes (17). This would suggest that plasma l)rekal-likrein levels do not change with salt intake or changesin posture. This is confirmed both by the base-line so-dium-restricted and sodium-loaded levels and by theconstant prekallikrein levels during saline infusion whilebradykinin was falling, and during upright posturewhen bradykinin was rising. Once activated, kallikreincombines stoichiometricallv with C1 esterase inactivator,resulting in depletion of both enzyme and inhibitor.However, the mean kallikrein inhibitor during thesaline and glucose infusion and upright posture is notsignificantly different from that of the mean base-linevalue, suggesting there has been no change in activationof prekallikrein during these acute studies. Thus, noapparent change in plasma kallikrein accounts for thechange of bradykinin after sodium infusion and up-right posture.

These findings do not rule out the release of a tissuekallikrein. Nearly 40 yr ago (26) it was first reportedthat urinary kallikrein was reduced in patients withhypertension. These early findings were recently con-firmed by Margolius, Geller, Pisano, and Sjoerdsmla(27), who also reported that patients with essential hy-pertension have decreased urinary kallikrein excretion.

60K

III 130 60 90 120 150 180 210 240

TIME (MIN)

FIGURE 1 Response of the kallikrein-bradykinin and renin-angiotensin systems to saline infusion, expressed as percentof base-line value in normal subjects on a 10 meq Na/100meq K diet; normal saline infused at 500 ml/h for 4 h.

panied by an increase in one of the major enzymes re-

sponsible for its production, plasma kallikrein. Kallikreinis a proteolytic enzyme that releases bradykinin froma plasma a2 globulin, termed kininogen. Free kallikrein(determined by spontaneous esterase activity) was notdecreased in the plasma with saline infusion or in-creased with upright posture. Since in the plasma, kalli-krein arises from the action of activated Hagemanfactor or its fragments on the precursor prekallikrein,one might expect to find a decrease in prekallikrein ifthe enzyme were converted to the active form, i.e. withsodium restriction or upright posture. Although thereare no published reports of plasma prekallikrein innormal sodium-depleted subjects, the mean plasma pre-

kallikrein of 98±11.6 SE umol/ml/h is essentially the

6_

PRA 2-(nglmllh)

50 -

ANG/OIT(pg/lmn/ t__

30 -

6-BRADYK/NIN L

(ng/m/i)

Pre KALL//KRE/NGomo//m//h)

110-

90-

70L 1 _ _ ;_

0 30 60 120

TIME (Ml'n1

FIGURE 2 Response of the kallikrein-bradykinin and renin-angiotensin systems to 5%c glucose infusion, expressed as

percent of base-line value in normal subjects on a 10 meq

Na/100 meq K diet; 5% glucose solution infused at 500ml/h for 2 h.

Kinin and Renin-Angiotensin Interrelations 695

100

PRA 80

60

40

100

80LAJJ

K~

LQ*

40

ANGlOTENS/INHT

8R/?tYK/N//NN60

40

100

PreKLZ//KREIN 80

II

TABLE IIResponse of Kat'likrein-Bradykinin and Renin-A ngio'ensin

Systems to Upright Posture in Normal Subjectson a 200 meq Na/100 meq K Diet

0 Time 20 min 60 min 120 min

Prekallikrein, ,.mol/ml/hA. B. 99 87.3 104 92.3Y. L. 84.4 87.0 88.8 108.1K. H. 67 75.1 61.2 64.5K. S. 95.5 79.4 108.4 87.0

Mean 86.4 82.2 90.6 87.98SE 6.3 2.5 9.25 7.8

Bradykinin, ng/mlA. B. 0.54 1.0 0.91 1.0Y. L. 0.58 0.62 0.49 1.0K. H. 0.51 0.88 1.28 0.72K. S. 0.51 1.34 0.39 1.12

Mean 0.54 0.96 0.77 0.96SE 0.01 0.13 0.18 0.07

PRA, ng/ml/hA. B. 2.4 2.5 3.4 4.0Y. L. 1.6 4.5 6.9 6.0K. H. 0.6 1.4 3.6 4.6K. S. 2.0 5.8 7.2 6.8

Mean 1.65 3.6 5.3 5.35SE 0.33 0.85 0.9 0.55

A II, pg/mlA. B. 38 48 50 50Y. L. 31 48 60 81K. H. 28 44 46 56K. S. 33 63 61 58

Mean 32.5 50.8 54 61.3SE 1.82 3.6 3.2 5.9

These same authors have recently reported that sodium-restricted normal subjects excrete more urinary kalli-krein than sodium-loaded patients (28). These studiesare in contrast to those of Adetuyibi and Mills (29)and Marin-Grez, Cottone, and Carretero (30), whohad previously shown that urinary kallikrein excretionis positively correlated with sodium excretion, i.e., thegreater the sodium excretion, the higher the kallikreinlevel. While the relationship of urinary kallikrein to

plasma bradykinin is unclear, these reports suggest a

possible role for renal kallikrein and kinins in bloodpressure regulation and sodium excretion.

If changes in production of kinin are not the majorcause of the decrease of kinin with saline infusion or

its increase with upright posture, it is necessary to

consider the pathways of bradykinin inactivation. There

is a striking parallel between bradykinin removal andthe conversion of A I to A II in the circulating blood,as well as in the pulmonary capillary bed.

Recently, the plasma angiotensin-converting enzymeand kininase II (a dipeptidyl-peptidase) have beenshown to be identical (31). This enzyme converts A Ito A II by removing the COOH-terminal His-Leu anddestroys bradykinin by removing its COOH-terminalPhe-Arg. Along the pulmonary capillary endothelialsurface there seems to be a membrane-bound enzymesimilarly capable of these two actions (32). In addi-tion, bradykinin is destroyed at this site by at leastfour other peptide hydrolases (33, 34). Thus, a changein kininase activity might account for the acute changesin bradykinin. The absence of any change in kininaseactivity during the saline infusion would make this anunlikely possibility. However, one could postulate thatchanges in renin and the formation of A II are pri-mary. In this case an increasing level of renin, andthus of A I in salt depletion or upright posture mightlead to competitive inhibition of kininase II (convertingenzyme), i.e. a change in its function without a changein activity. Thus, if the affinity of A I for this enzymeis high, and the levels of the peptide are elevated, in-hibition of kinin destruction might occur. However,this is unlikely to provide a complete explanation, sinceunder normal circumstances kininase II accounts foronly about 10% of the total circulating kininase ac-tivity; the rest is due to kininase I.' In the pulmonaryvascular bed other potent kinin-destroying enzymes arealso readily available (33). Thus, whether the changesin bradykinin in these studies are secondary to the re-lease of a tissue kallikrein (as discussed) or to achange in the function of the kininases without a changein the measured activity remains to be clarified(Scheme).

Gcenzeration pathways DegradationPlasma kallikreiin Plasma kininases

Sy'Stemil

Bra-(lnkinl

? Tissue kallikreins Tissue kininase->(e.g. urinary (e.g. I)ulmonarykallikrein) circulation, ?

other endothelialhvdrolases)

The significant parallel changes in A II and brady-kinin levels in response to acute manipulation wouldsuggest that these hormones are physiologically inter-related. These substances have opposite effects on thevascular smooth muscle. Infusion of A II at doses in

2 R. C. Talamo. Unpublished observation.

696 P. Y. Wong, R. C. Talamo, G. H. Williams, and R. W. Colman

the range of 5 ng/kg/mm in normal subjects usuallyproduces vasoconstriction (35). On the other hand, in-fusion of bradvkinin at levels of 500-1,500 ng/kg/minproduces vasodilation (36, 37). This gives an effectivedose ratio of angiotensin to bradykinin of appoximately1: 100-1: 500, levels that are close to the ratios ofthese two hormones in the plasma of our normal sub-jects. The physiological significance of this relationshipis unclear. However, it is known that in sodium-de-pleted man the high plasma levels of A II are notassociated with a rise in blood pressure and further-more, with sodium restriction, the vascular responseto A II is blunted both in man and in the experimentalanimal (35-38). The mechanisms previously proposedfor this phenomenon include a change in total bloodvolume or a change in the affinity of angiotensin forits vascular receptor (2). An alternative proposal onthe basis of the present study would be a decreasedvascular sensitivity due to an increase in bradykininlevels.

Since in this study, the changes in bradykinin cor-related not only with changes in A II, but also withplasma aldosterone, it is possible that alterations inbradvkinin levels are related to changes in concentrationof aldosterone, as suggested by Margolius et al. (28),rather than of A II.

ACKNOWLEDGMENTSThe authors are indebted to Dr. C. S. Davidson, ThorndikeMemorial Laboratory, for his help, support and encourage-ment, and to Dr. M. L. Tuck for his help. The excellenttechnical assistance of Ms. R. L. Emanual, E. A. Greene,and N. Neyhard is gratefully acknowledged.

The clinical studies were carried out on the Clinical Re-search Centers of the Peter Bent Brigham Hospital (sup-ported by grant 8-M01-FR-31-06) and Thorndike MemorialLaboratory (grant RR-76, Division of Research Resources,National Institutes of Health).

This research was supported in part by 2 T01 AM 05413,United States Public Health Service research grant HE14479, and the John A. Hartford Foundation 9893, and bycareer development awards AM-31937 (to Dr. Talamo)and HE-48075 (to Dr. Colman).

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