The Regulation of Antidiuretic

Hormone Release in Man

I. EFFECTS OF CHANGEIN POSITION ANDAMBIENTTEMPERATUREON BLOODADH LEVELS

WILLAm E. SEGARand WARDW. MooRE

From the Departments of Pediatrics and Physiology, Indiana UniversitySchool of Medicine, Indianapolis, Indiana 46202

AB S T RA C T It has been postulated that altera-tions in the intravascular distribution of bloodaffect antidiuretic hormone (ADH) secretion inman. The studies reported here were designed toalter blood distribution by thermal and by posi-tional change to test this thesis.

Human blood ADHlevels have been shown tovary -with position: a mean value of 0.4 ±0.6(SD) uU/ml was obtained while the subject wassupine, a value of 1.4 + 0.7 buU/ml while sitting,and 3.1 ± 1.5 uU/ml while standing. In 79 controlsubjects, sitting comfortably for 30 min in a nor-mal environment, a blood ADH level of 1.65 ±0.63 pU/ml was found. It is suggested that sub-jects assume this position during experiments inwhich blood is drawn for measurement of ADHlevels.

In eight seated subjects the ADH level rosefrom 1.6 ± 0.4 to 5.2 ± 0.8 AU/ml after a 2 hrexposure at 50'C and fell to 1.0 ± 0.26 uU/mlwithin 15 min at 260C.

Six subjects with a mean ADHlevel of 2.2 ±0.58 MAU/ml sat quietly in the cold (13'C) for1 hr, and the ADHlevel fell to 1.2 + 0.36 MU/ml.After 15 min at 260C, the level rose to 3.1 + 0.78

Dr. Segar's present address is Section of Pediatrics,Mayo Clinic and Mayo Graduate School of Medicine,Rochester, Minn. 55901. Dr. Moore's present address isc/o The Rockefeller Foundation, G.P.O. Box 2453,Bangkok, Thailand.

Received for publication 5 February 1968 and in re-vised form 4 April 1968.

,uU/ml. The serum sodium and osmolal concentra-tions remained constant during all studies.

Water, sodium, and total solute excretion de-creased during exposure to the heat, whereas theurine to plasma (U/P) osmolal ratio increased.During cold exposure, water, sodium, and totalsolute excretion increased, and there was a de-crease in the U/P osmolal ratio.

These data are interpreted as indicating thatchanges in activity of intrathoracic stretch recep-tors, in response to redistribution of blood, alterADHsecretion independently of changes in serumosmolality. The rapidity of change of blood ADHconcentration indicates a great sensitivity and aprime functional role for the "volume receptors" inthe regulation of ADH secretion.

INTRODUCTION

There is evidence that at least two mechanismsregulate the release of antidiuretic hormone(ADH) and thereby control the tonicity andvolume of the body fluids. The first of these hasbeen elucidated by the investigations of Verney(1) and many subsequent workers (2-4) whohave demonstrated the existence of receptors,probably located in the hypothalamus (5), whichare sensitive to changes in the effective solute con-centration of the extracellular fluid. These recep-tors stimulate the release of ADHin response toincreased extracellular solute concentration and

The Journal of Clinical Investigation Volume 47 1968 2143

inhibit ADHsecretion when the extracellular fluidbecomes dilute.

The second mechanism was originally predictedby Peters (6). His suggestion that the fullness ofthe intravascular compartment could be "sensed"by the organism directed attention toward a searchfor receptors sensitive to changes in intravascularvolume which, in turn, might influence the releaseof ADH. Henry, Gauer, and Reeves (7, 8) havedemonstrated the presence of such receptors in thethoracic vessels of dogs. They observed that disten-tion of the left atrium was associated with an in-crease in urine flow, whereas diuresis was not ob-served during distention of other segments of theintrathoracic vascular system. Subsequent studieshave demonstrated that this response can beblocked by vagotomy (9). Thus, although thismechanism is well established in the experimentalanimal, its presence has not been demonstratedconvincingly in man.

The studies to be reported support the conceptthat intravascular stretch receptors, presumablyintrathoracic, in response to alteration in leftatrial filling, alter ADHrelease independently ofchanges in serum osmolality in man. Furthermore,the rapidity of change of blood ADHconcentrationindicates a great sensitivity and a prime functionalrole for the "volume receptors" in the regulationof ADHsecretion.

METHODSVasopressin assay. The procedure of extraction, ab-

sorption, concentration, and bioassay of ADHwere modi-fied from methods described by Weinstein, Berne, andSachs (10), Share (11), Yoshida, Motohashi, and Oki-naka (12), and Moran, Miltenberger, Shu'Ayb, andZimmerman (13). These modifications and the dose-response relationship are described by Rogge, Moore,Segar, and Fasola (14). The method involves extractionof ADH from blood with trichloroacetic acid (TCA),removal of the TCA with ether, absorption on a columnof resin, Amberlite CG-50 (Rohm & Haas, Philadelphia,Pa.), and elution with 50% acetic acid. The eluent islyophilized and taken up in 1.0 ml of a solution contain-ing 0.85% NaCl and 0.03% acetic acid. Weinstein et al.(10) have demonstrated, and we have confirmed in iso-lated experiments, that the material contained in theeluent has the biological and chemical properties of vaso-pressin. It is soluble in 10% TCA, insoluble in ether,stable to the action of pepsin, and rapidly inactivated bytrypsin and by 0.01 M thioglycollic acid. It is present inthe blood of hydropenic subjects and disappears withhydration (15). Share (16) has performed studies on the

gradient elution of the eluate from carboxymethyl cellu-lose and demonstrated that the antidiuretic activityemerged as a single peak in a position similar to thatfound with highly purified arginine vasopressin.

The material is assayed by injection of 0.14.5 ml ofthe acidified saline solution containing the vasopressinoriginally present in 1.0-5.0 ml of blood into water-loaded(5 ml/100 g) ethanol-anesthetized Holtzman rats weigh-ing 150-200 g. During the assay the rats are maintainedat a constant ambient temperature (350C) in an Arm-strong incubator. The high ambient temperature is usedto prevent a fall in the rectal temperature of the ethanol-anesthetized bioassay animal, to maintain a constant cen-tral blood volume and constant renal hemodynamics, toinsure that all solutions are administered at a temperatureof 350C, and to maintain a constant temperature on theconductivity cell. The assay animals are maintained on aconstant fluid load by the continuous intravenous replace-ment of urine losses with an equal volume of a solutioncontaining 0.3% NaCl, 1.6% glucose, and 2% ethanol.All samples and solutions are administered intravenously.Urine conductivity is recorded continuously via a con-ductivity cell and recording device described by Rothe,Johnson, and Moore (17). The area under the conduc-tivity curve is taken as an index of response and is mea-sured by planimetry beginning with the initial upwarddeflection of the recording pen above a stable base lineand continuing for 10 min. A 2 X 2 factorial design isused to estimate the potency of the unknown solutions,and a complete assay consists of at least two injectionsof standard synthetic arginine vasopressin (Sandoz, Inc.,Hanover, N. J.) and at least two injections of unknown,each at two dose levels. The procedure detects 1 AU/ml(95% confidence limits) of arginine vasopressin (14).When kept in a frozen state until use, the synthetic argi-nine vasopressin has seemed to be a reliable referencestandard as indicated by the linearity and reproducibilityof the dose response curve (14). Since this standard wasnot checked against USP Reference Standard a signifi-cant error in absolute values may have been introduced.Since the aliquot of the acidified saline solution injectedinto the assay animal may contain the amount of vaso-pressin present in as much as 5 ml of blood, the assay willdetect concentrations of blood ADH as low as 0.20AU/ml. Recovery of arginine vasopressin (2.5-5.0 AU/ml) added to whole blood in 18 trials is 92 ± 5% (SEM).The specificity and limitations of such bioassay proce-dures for ADH have been reviewed recently by Share(18).

10 ml of whole blood was withdrawn from the ante-cubital vein and transferred directly to 4 volumes of cold12.5% TCA and carried through the extraction andpurification procedure. No precautions against pain weretaken; the blood was drawn rapidly to minimize stasis,and glass syringes were used. The extracts were frozenimmediately and stored in the frozen state until the timeof assay.

Sodium, potassium, chloride, creatinine, and osmolalityanalyses of blood and urine were conducted by conven-tional methods.

2144 W. E. Segar and W. W. Moore

TABLE IEffect of Body Position on Blood ADH

Concentration in Man

Blood ADH

Reclining; Sitting; Upright;Subject 60 min 60 min 20 min

pU/ml1* 0.0t 1.5 3.12* 1.2 1.7 1.93 0.0t 1.9 4.04 0.0t 1.0 1.65 0.0t 1.5 3.26 1.3 2.3 5.97 0.0t 1.0 1.98 0.4 1.5 3.1

Mean 0.4 1.4 3.1SD 0.6 0.7 1.5

ADH, antidiuretic hormone.* Samples taken during upright, then sitting and recliningposition. All others taken in reversed order.t NoADHdetected. Maximal concentration of blood ADHis therefore less than 0.20 gU/ml.

RESULTS

Volunteer male human subjects were usedthroughout. In the first experiment the effect ofalteration of position on blood ADH level wasdetermined in eight subjects. In six instances theinitial sample was obtained after the subject hadbeen lying supine for 60 min, a second specimenwas drawn after sitting quietly for 60 min, anda final sample was obtained after 20 min of quietstanding. In the latter position the subject wasresting against a high stool. The subjects' legswere held motionless in a dependent position and

bore little weight. In two subjects the sequence ofpositions was reversed with no difference in re-sults. Each blood sample was analyzed for sodium,chloride, and solute concentration, as well as forADH. The results are summarized in Table I.The mean ADHlevel in the recumbent positionwas 0.4 + 0.6 ,U/ml. The mean value in the sittingposition was 1.4 + 0.7 j/U/ml, and this value in-creased to 3.1 ± 1.5 ,uU/ml after 20 min of quietstanding. The serum Na, C1, and solute concentra-tions remained unchanged during these studies.The lowest ADHlevel was obtained in each sub-ject after reclining, the highest after standing 20min.

In the course of these and subsequent experi-ments, blood ADHdeterminations have been con-ducted on samples taken at the end of controlperiods from subjects on 79 separate occasions. Ineach instance the subject was an adult male whoemptied his bladder and sat quietly for at least 30min before the blood and urine samples were ob-tained. Each sample for ADHassay was drawnduring the midmorning, and each subject hadeaten his usual breakfast but had consumed nofluid since that time. In each the urine to plasmaosmolal ratio (Uosmoi/Pomo1) was between 1.95and 3.75. The mean blood ADHconcentration forthis group was 1.65 ,uU/ml with a standard devia-tion of 0.63 uU/ml. The distribution of thesevalues is illustrated in Fig. 1.

The blood ADH level was measured before,during, and after an abrupt increase in environ-mental temperature in a second study. Eightcomfortably seated subjects had a blood sample

Uosmol-osmol VALUESFROM1.95 to 3.75sosmol

N = 79XR 1.65SD= 0.63

0 0 00 000000000000

0

00

00

@000000

0000 0 0 0@00 00000*000. *0000

0000*0000000000000

FIGURE 1 Distribution of blood antidiu-retic hormone (ADH) concentration (X)in adult male subjects (clothed, seated,room temperature 260C) studied on 79separate occasions (N).

The Regulation of Antidiuretic Hormone Release in Man

I I I I I I0.5 1 1.5 2 2.5 3

BLOODADH paU/ml

2145

drawn after a control period of 60 min at normalroom temperature (260C). They were then ex-posed to an environmental temperature of 500Cin a constant temperature room. After a 2 hrexposure to the hot environment a second bloodsample was obtained. The subjects were returnedto a comfortable environment (260C), and a thirdblood specimen was obtained 15 min later. Eachsubject voided before and at the termination of thecontrol period, the 2 hr period of exposure to heat,and the 15 min period after removal from the heat.

The blood specimens were analyzed for ADHconcentration, and the serum concentration oftotal solute, sodium, potassium, and chloride wereobtained. Urine was analyzed for sodium, potas-sium, chloride, creatinine, and total solute.

The mean blood ADHlevel during the controlperiod was 1.6 + 0.4 FtU/ml of blood. After ex-posure to heat the mean value rose to 5.2 ± 0.7,MU/ml and then fell 15 min later to 1.0 0.3,uU/ml. These results and other data are sum-marized in Table II. In each case the highest bloodADHconcentration occurred after 2 hr exposureto the heat, and in each case the ADHconcentra-tion fell below control values after the subject wasreturned to a normal environment. The subjectslost an average of 1.13 kg of weight during theexperiment, but changes in the serum concentra-tion of sodium and chloride and in serum osmo-lality were not detectable.

Changes in urine-to-serum (U/S) solute con-centration ratio and in urine flow are also sum-marized in Table II. Adequate urine collectionswere obtained from six of the eight subjects. Al-though each individual was moderately hydropenicinitially, the U/S osmolal ratio rose from 2.66 +

0.46 to 3.27 ± 0.51. This increase in U/S osmolalratio is significant (P < 0.001). During the finalperiod there was a further slight increase in U/Sosmolal ratio to 3.42 + 0.31, a value significantlyabove control, but not different from the valueobtained after heat exposure.

Urine flow decreased significantly in each sub-ject during exposure to the heat. Minute volumewas 1.1 + 0.3 ml/min during the control periodand fell to a mean value of 0.6 + 0.2 during heatexposure (P < 0.001). In each instance minutevolume increased during the period after heat ex-posure, although in only one subject did it re-turn to control values. During the 15 min recoveryperiod the mean minute volume was 0.8 ± 0.2 ml/min.

There was also a significant decrease in sodiumexcretion per minute during heat exposure (TableII). Initially the mean sodium excretion was 201+ 97 IzEq/min. During the experimental period

this value fell to 97 + 43 IzEq/min (P < 0.01)and then rose to 122 + 34 ptEq/min during re-covery. This latter value also differs significantlyfrom the initial control value (P < 0.05). A

TABLE I IEffect of Increase in Ambient Temperature on Blood ADHConcentration

and on Serum and Urine Composition in Man

Period 1 Period 2 Period 3 P*

Ambient temperature 260C 500C 260C 1-2 2-3 1-3Blood ADH(MU/ml) 1.6 d 0.4t 5.2 0.7 1.0 1: 0.3 <0.001 <0.001 <0.01SNa (mEqiliter) 142 ± 1 142 i 1 142 i 1 NS NS NSSosmol (mOsm/kg) 296 ± 3 296 ± 3 295 i 3 NS NS NSV (ml/min) 1.1 4 0.3 0.6 4 0.2 0.8 ± 0.2 <0.01 NS <0.05UOSmOi/SOSmOI 2.66 i 0.46 3.27 i 0.51 3.42 :4 0.31 <0.001 NS <0.001UNaV (IAEq/min) 201 d 97 97 ± 43 122 :1 34 <0.01 NS <0.05UKV (.uEq/min) 78 i 43 72 -4 31 102 41 34 NS <0.01 <0.05UoemoIV (M"Osm/min) 832 ± 304 546 ± 175 759 4 93 <0.01 <0.01 NSUCRV(mg/min) 1.43 ± 0.15 1.31 i 0.26 1.48 -t 0.22 <0.01 NS NS

ADH, antidiuretic hormone; SNa, serum sodium concentration; UOsmOi/Sosmoi, urine-to-serum solute concentration ratio;V, minute volume; UN.V, sodium excretion; UKV, potassium excretion; Uo.moiV, total solute excretion; UCRV, creati-nine excretion.* The probability of differences between experimental periods is tested by applying Student's t test on paired observa-tions for each subject.t Mean =1: standard deviation.

2146 W. E. Segar and W. W. Moore

TABLE IIIEffect of Decrease in Ambient Temperature on Blood ADHConcentration and on Serum

and Urine Composition in Man

Period 1 Period 2 Period 3 P*

Ambient temperature 260C 130C 260C 1-2 2-3 1-3Blood ADH(puU/ml) 2.2 i 0.61 1.3 4± 0.4 3.1 4- 0.8 <0.005 <0.001 <0.02SN, (mEqiliter) 142 i 1 143 4± 1 142 A1 NS NS NSSOMOI (mOsm/kg) 293 i 3 293 i 3 293 ± 3 NS NS NSV (mi/min) 0.8 ± 0.2 1.1 0.2 1.0 ± 0.2 <0.01 NS <0.01UOsmOI/Sosmoi 3.37 ± 0.25 3.08 i 0.26 3.03 i 0.38 <0.05 NS <0.05UNaV (AEqiml) 166 i 41 243 ± 36 222 4 41 <0.005 <0.05 <0.05UiKV (uEq/min) 68 ±t 27 84 i 28 77 i 25 <0.05 NS NSUoGmOiV(pOsm/min) 756 ± 162 964 i 137 842 i 23 <0.01 <0.05 <0.05UcRV(mg/min) 1.18 ± 0.29 1.21 ± 0.22 1.09 ± 0.19 NS <0.05 NS

See Table II for explanation of abbreviations.* The probability of difference between experimental periods is tested by applying Student's t test on paired observationsfor each subject.I Mean ± standard deviation.

significant increase in potassium excretion occurredduring the final 15 min period, but potassiumexcretion did not change during the period of heatexposure. Alterations in total solute excretion re-flected changes in the excretion of sodium. Totalsolute excretion fell from 832 + 304 to 546 + 175,uOsm/min during heat exposure (P < 0.01)and rose to the control value during recovery. Cre-atinine excretion decreased by a small (8.5%o) butstatistically significant amount during heat ex-posure.

In the last of this series of experiments sixslightly hydropenic volunteers clothed only inshorts and undershirts were exposed to a coldenvironment. Again the subjects were seatedduring a 60 min control period at 260C, a 60 minperiod of exposure in a constant temperature roomto an ambient temperature of 130C, and a 15 minrecovery period at room temperature (260C).Blood for ADH determinations and serum forsodium, potassium, chloride, and osmolal deter-minations were obtained at the end of each period.Urine was collected at the conclusion of eachperiod and was analyzed for sodium, potassium,chloride, total solute, and creatinine. Gross shiver-ing did not occur during the period of coldexposure.

Changes in blood ADHconcentration are illus-trated in Table III. The initial ADH level was2.2 + 0.6 ,uU/ml. This value fell to 1.3 ± 0.4 dur-ing the period in the cold and then rose to 3.1 +

0.8 uU/ml after 15 min in comfortable environ-ment. These changes were consistent; in each sub-ject the lowest ADH was obtained after coldexposure, and in each the highest value was foundafter recovery. Changes in the serum concentra-tions of sodium, potassium, chloride, and solutecould not be detected.

A mild diuresis occurred in each subject duringthe experimental period. Mean minute volumeincreased significantly (P < 0.01) from 0.8 +

0.2 ml/min to 1.1 ± 0.2 ml/min, and remainedelevated during the recovery period (1.0 + 0.2ml/min, P < 0.01). The U/S osmolal ratiofell significantly (P < 0.05) from 3.37 + 0.25to 3.08 + 0.26 and 3.03 ± 0.38 during the periodsof cold exposure and during recovery, respectively.

Sodium excretion increased from a mean of 166+ 41 pEq/min during control to 243 + 36 ,uEq/min (P < 0.005) during the experimental pe-riod and to 222 + 41 uEq/min (P < 0.05) dur-ing the recovery period. The decrease in sodiumexcretion during recovery differs (P < 0.05)from that observed during exposure to cold.Total solute excretion paralleled sodium excre-tion. During the period of cold exposure soluteexcretion rose from 756 + 162 ,uOsm/min to 964+ 137 ,&Osm/min (P < 0.01) and then fell to842 + 23 ,uOsm/min during recovery, a value stillsignificantly above control (P < 0.05), and sig-nificantly less than the value for mean solute ex-

The Regulation of Antidiuretic Hormone Release in Man 2147

cretion during cold exposure (P < 0.05). Thesedata are summarized in Table III.

DISCUSSION

Each of the experiments described above was de-signed to alter the intravascular distribution ofblood by thermal and positional change withoutconcurrent changes in plasma osmolality. As such,they test the thesis that, in man, alterations infilling of certain portions of the intravascular com-partment influence the release of ADH.

Hemorrhage is known to cause an increase inblood ADHlevels in the rat and dog. Share (11),in a series of experiments designed to producesmall gradual changes in blood volume, demon-strated that progressive reduction in extracellularfluid volume led to a progressive rise in bloodvasopressin titer. Reexpansion of blood volume toa level slightly greater than control restored bloodADH concentration to approximately controlvalues.

Although the evidence that relatively smallchanges in blood volume alter blood ADHconcen-trations is impressive, the location of the "volume"or "stretch" receptors which initiate this responseis uncertain. Henry, Gauer, and their associates(7, 8) have amassed a large body of data whichsuggests that a volume receptor concerned withADH release has an intrathoracic site. Positivepressure breathing, which would decrease filling ofthe intrathoracic vessels, has been shown in dogsto induce antidiuresis (19), whereas negativepressure breathing, which would facilitate fillingof intrathoracic vessels, results in diuresis (20).These same investigators have subsequently shownthat when a balloon is inflated in the left atrialappendage of an anesthetized dog, urine volume isincreased (8). More direct evidence that a leftatrial stretch receptor is involved in the regulationof ADHrelease has been provided by Baisset andMontastruc (21), Share (22), and Shu'ayb,Moran, and Zimmerman (23), and Johnson,Moore, and Segar (24) have shown that when aballoon in the left atrial appendage is inflated pro-gressively so that small increments in transmuralpressure are produced, blood ADHconcentrationfalls progressively and proportionately as thetransmural pressure is increased. The variations intransmural pressure produced in the experiments

of Johnson et al. are within a physiologic range asopposed to the far greater pressure changes pro-duced in similar experiments of other investigatorswho obtained comparable results (21-23).

There is also evidence that receptors elsewherein the cardiovascular system may play a role in thecontrol of vasopressin release. Carotid occlusionhas been shown to increase ADH release, andShare and Levy (25) have demonstrated that thedecreased activity of the carotid sinus barorecep-tors after carotid artery occlusion induces an in-crease in ADHrelease. These receptors would beof functional significance, however, only whenmarked changes in mean arterial blood pressureoccur. The activity of a left atrial volume recep-tor would not be altered by change in mean arte-rial pressure, but it would be altered by any cir-cumstance, physiological or pathological, thatmight alter the filling of that chamber.

Each of the procedures described in this studywould be expected to alter filling of the left atriumas well as the filling of other intrathoracic capaci-tance vessels. The effect of alterations in positionon filling of the low pressure intrathoracic vesselsseems apparent. It has been estimated that 80%of the blood pooled in the extremities duringorthostasis comes from the thoracic vascular bed(26). Presumably left atrial filling would be leastduring standing and greatest when the subject issupine. As a result of the stretch induced by leftatrial filling in the supine position afferent im-pulses arising in the wall of the left atrium aretransmitted by vagal fibers to centers in the centralnervous system which, in turn, inhibit ADH re-lease. With standing, and the resultant decreasein stretch, the stretch or baroreceptor becomesinactive, and the absence of inhibitory stimuliallows ADHrelease. The well known antidiuresisof quiet standing results (27).

It seems likely that alterations in blood ADHwhich result from changes in environmental tem-perature are also mediated by the intrathoracicstretch receptors. If this is the case, peripheralvascular beds open in a hot environment and fillwith blood whereas the central blood volume, in-

cluding the intrathoracic volume, decreases. In acold environment the converse occurs. Peripheralvascular resistance increases, peripheral blood vol-ume is diminished, and that volume of blood that

2148 W. E. Segar and W. W. Moore

has been in the peripheral beds increases filling ofthe capacitance vessels, including those in thethorax (28). The phenomenon of cold diuresisprovides suggestive evidence for relationship be-tween intrathoracic blood volume and alterationsin blood ADH. Gauer and Henry (8) report thatthey have observed an increase in central venouspressure upon taking a subject from a hot intoa cold environment, and they as well as Bader,Eliot, and Bass (29) have postulated that colddiuresis results from a decrease in ADHsecretion.

In hot room experiments reported here, themarked increase in blood ADH level could resultfrom either a redistribution of blood due to anincreased flow to peripheral beds or to the lossof extracellular fluid from sweating or both. Sinceno measurable changes in serum sodium or totalsolute concentrations occurred, it is not likely thatan "osmoreceptor" could have mediated the ADHrelease. The abrupt drop in blood vasopressinconcentration that occurred within 15 min afterreturn to a normal ambient temperature providesevidence that the changes in ADH concentrationwere the result of redistribution of blood. Hadeither the loss of extracellular fluid due to sweatingor an undetectable increase in body solute concen-tration been the prime stimulus for ADH release,the blood ADH concentration should have re-mained elevated during the recovery period. Lau-son (30) has reviewed available half-life data forblood ADHin man and has noted the variability ofpublished values (3.9-46 min). From our ownstudies in patients with untreated diabetes insipi-dus, we have estimated that ADH half-life isapproximately 7 min,' a finding which indicatesthat ADHrelease was markedly inhibited immedi-ately after removal of the subjects from the hotenvironment; otherwise the precipitous drop inADH concentration noted over a 15 min periodcould not have occurred.

During exposure to a cold environment the se-quence of events is presumably reversed. Withincreased resistance to flow in peripheral vascularbeds, central filling is increased, and ADHreleaseis inhibited. When the subject is returned to anormal environment flow to the peripheral beds isincreased, filling of intrathoracic capacitance ves-

1 Segar, W. E., and W. W. Moore. Unpublished ob-servation.

sels is decreased, inhibition of ADH release isdiminished, and blood ADH levels become ele-vated. In this situation there is no significantchange in weight, the total extracellular volumeremains constant, and total solute concentration isnot altered.

It is possible that heating and cooling the sub-ject influence ADH release directly via unknownpathways. The changes in cutaneous blood vesselscaused by the alterations in ambient temperatureare mediated by the autonomic nervous systemgoverned, presumably, by controls located in thehypothalamus. Afferent information from the skinthermal receptors reaching the hypothalamus may,conceivably, affect centers regulating ADH re-lease. It is true, also, that stress of any sort mayresult in ADHrelease (18). However, the fall inblood ADH during cooling, which was the lesscomfortable of the two procedures, and the obser-vation that the ADHlevel increases after recoveryfrom cooling, indicate that the results cannot beattributed to a nonspecific stress effect.

The alterations observed in urine volume and inurine solute concentration, as measured by theU/S osmolal ratio, in the course of these experi-ments are reasonably consistent with the changesin blood ADH concentration. A marked anti-diuresis occurred during warming and was asso-ciated with a significant increase in U/S osmolalratio. During the brief recovery period urine flowand U/S ratio did not change significantly. Simi-larly, a mild diuresis occurred with cooling, andthe urine became slightly more dilute. During re-covery neither urine flow nor urine solute concen-tration changed. Of interest, also, are the changesin sodium and total solute excretion that occurredin the course of these experiments. Both sodiumexcretion and total solute excretion decreased sig-nificantly while the subjects were in a hot envi-ronment, and the urine solute concentration rose tocontrol values, whereas urine sodium excretion in-creased but remained below control values duringrecovery. The converse occurred while the sub-jects were in a cold environment. Both urine so-dium and total urine solute excretion increasedsignificantly and remained elevated, although lessso, during recovery. The mechanisms responsiblefor these alterations in sodium and solute excretionare not clearly established. These changes could

The Regulation of Antidiuretic Hormone Release in Man 2149

TABLE IVEffect of Head-Down Tilting on Blood ADHLeveland Serum Na Concentration in Comatose Patients

Initial values After 48 hr tilt

Blood BloodDiagnosis ADH SNa ADH SN,

mEq/ mEq1#U/ml liter jsU/ml liter

Myxedema coma 3.4 128 1.2 142Posthypoxic coma 4.2 117 0.9 155Hemophilus influenzaeMeningitis with coma 11.7 114 1.7 138

See Table II for explanation of abbreviations.

be a direct result of alterations in blood ADHperse, although our own studies,2 as well as those ofothers (31), indicate that ADH has little effecton mineral excretion, of alterations in blood al-dosterone secretion, a thesis which cannot be sup-ported or disproven by these data, or a result ofchanges in the production of release of a "thirdfactor" (32-35). The release of such a "natriuretichormone" with increased filling of the capacitancevessels could account for the natriuresis notedduring cold exposure, and the inhibition of releaseresulting from decreased filling of the intrathoracicvessels could explain the antinatriuresis noted afterwarming. Finally, since precise clearance data arenot available, small changes in glomerular filtrationrate may be responsible for the observed altera-tions in sodium and solute excretion.

The work herein reported is, we believe, ofclinical significance. First, a "normal" blood ADHlevel in the slightly hydropenic, clothed subjectseated in a comfortable environment has beenestablished. Because of the wide variation in bloodADH concentration that results from alterationin position, it is necessary that control data becollected under prescribed conditions. A sittingposition seems most appropriate.

The supine position is less satisfactory. Al-though low levels of ADHare found in the con-scious volunteer who has been supine for 60 min,the levels will remain low only if blood return tothe thorax is optimal. During sleep and particu-larly during coma, blood may pool in the vesselsof the extremities or abdomen, and ADH levels

2 Balsley, J., P. Moseley, W. E. Segar, and W. W.Moore. Unpublished observation.

should then increase. The antidiuresis of sleepmay be on this basis, although we have not testedthis thesis. We have, however, some preliminarydata on ADH levels during coma (Table IV).Such individuals have high blood ADH levels.However, in each of the three cases studied afterslight head-down tilting (50), the blood ADHlevels returned in 48 hr to values within thenormal range. Each of these three subjects hadmarked hyponatremia initially, and in each theserum sodium concentration became normal, al-though each remained on a constant water andelectrolyte intake. Each had a brisk diuresis withtilting. These observations, although far from con-clusive, suggest that the hyponatremia observedin association with severe central nervous system(CNS) disease may be explained on the basis ofinadequate filling of thoracic capacitance vessels.The large amount of ADH produced probablyrepresents a physiological response to inadequateatrial filling and is not due to the release of"inappropriate" amounts of vasopressin as a re-sult of CNS disease per se (36).

ACKNOWLEDGMENTS

The authors wish to acknowledge their gratitude to MissShirley Lartius, Mrs. Arlene Lukenbill, Mrs. IrmaSmith, and Mrs. Catheron Williams for technicalassistance.

This work was supported by grants H-06308 and HE-10401, U. S. Public Health Service and The Riley Mem-orial Association.

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