Solute Excretion in Man during Changing Urine Flow Occurring Spontaneously and Induced by

Transcription

1 Downloaded from on Deember 6, Journal of Clinial Investigation Vol. 43, No. 1, 1964 Solute Exretion in Man during Changing Urine Flow Ourring Spontaneously and Indued by Vasopressin Injetion * (From the Department of Physiology, University of Manhester, Manhester, England) Studies of the effet of vasopressin on urinary exretion of eletrolytes have usually ompared urinary outputs or learanes before hormone injetion, in periods of stable urine flows, to learanes after injetion (1; see 2-4 for reviews of the extensive literature). There are few data onerning solute exretion during the transition from diuresis to antidiuresis; in this phase, aumulation of progressively more onentrated fluid in the dead spae of the renal trat invalidates onventional alulations of solute exretory rates and learanes, whih require steady-state onditions (5, 6). Study of the transition from diuresis to antidiuresis is, however, potentially useful in determining whether differenes between medullary solute onentrations in diuresis and antidiuresis (7-1) and the operation of ounterurrent mehanisms (11, 12) involve hanges in tubular solute transport. Furthermore, nonsteady-state onditions an provide information about renal solute transport mehanisms, as in Chinard's tehnique of omparing urinary onentrations before and after injetion of solutes into the renal artery (13). Aordingly, I have determined hanges in solute onentrations in samples obtained as frequently as possible during the rapid deline in flow after iv injetion of vasopressin. A similar tehnique was reently used in the dog (14). The rationale of the present experimental design is that if the only event involved in urinary onentration is the abstration of water from the nephron, then hanges in the onentrations of the various urinary solutes, relative to those in * Submitted for publiation Deember 17, 1962; aepted September 11, Reported in part at a Colloquium on Hormones and the Kidney, organized by the Soiety for Endorinology, at Cambridge, England, September 19-21, diureti periods, should be equal for all solutes. If a hange also ours in tubular reabsorption of some solute, its inrease in urinary onentration, relative to a preeding diureti steady state, would be different from that of another solute. In partiular, a hange in the onentration of solute ompared with that of a "glomerular substane" (13) suh as inulin would provide an index of the diretion and magnitude of any hange in tubular solute transport. Methods Group I experiments, performed on five healthy male subjets, ages 23 to 42 years, provide data on the relationship between endogenous reatinine and inulin exretion in a wide variety of irumstanes, inluding hanges in urine flow. The experiments were originally designed as investigations on phosphate Tm (15) and on the aute renal effets of ortisone and hydroortisone in man (16). Full tehnial details of experimental proedures were given in previous publiations (15, 16) other details are presented in the Results. Groups II experiments were performed on three healthy males, ages 28, 36, and 46 years, who had previously been on normal diets. After a morning of performing routine laboratory duties, subjets emptied their bladders between 1 p.m. and 2 p.m., sat down, and drank a large dose of water (2 ml per kg body wt) within 5 to 15 minutes. The water load was subsequently maintained onstant by drinking a volume equal to the volume of urine voided; no orretion was made for insensible loss of water. Subjet M drank beer (Na ontent, 7.5 meq per L; K ontent, 12 meq per L) in plae of water, the alohol ontent serving as an additional assurane of suppression of endogenous vasopressin prodution. Beause of this differene in proedure and beause plasma urea onentration delined during vasopressin experiments in this subj et, a ontrol experiment was performed with no vasopressin injeted and a onstant fluid load maintained by drinking beer. One maximal flows were attained, urine olletions were made by voluntary voiding at 5- to 1-minute intervals for several suessive periods to ensure that a stable diuresis was sustained. Vasopressin 1 (.5 mu 1 Pitressin, Parke, Davis, Detroit, Mih.

2 Downloaded from on Deember 6, per kg body wt) was then injeted within 1 to 2 minutes via an indwelling polyethylene annula inserted into a forearm vein at the beginning of the experiment. The times of injetion in the two experiments on eah subjet differed; therefore possible diurnal rhythmi hanges in solute exretion ourring during the developing antidiuresis in one experiment ould be assessed against equivalent ontrol diureti periods in the other. During the derease in urine flow, olletions were made as often as was onsidered likely to give omplete bladder emptying, or at least 1 ml of urine, and was aordingly adjusted with the time after vasopressin injetion. Colletions were then ontinued at less frequent intervals until flows had returned towards or to the preinjetion diureti values. Blood samples were olleted at intervals via the polyethylene annula, reeived into heparinized tubes, entrifuged immediately, and the plasma pipetted off. Analytial methods. Creatinine determinations on urine were made by the method of Bonsnes and Taussky (17) and on plasma by that of Brod and Sirota (18); inulin by the method of Dik and Davies (19); urea by the miroliffusion method of Conway (2), subtrating an ammodia blank or, oasionally, the ammonia onentration as determined by aeration and titration (21); osmolality by a modifiation of the freezing-point depression method of Johlin (22); sodium and potassium by flame photometry; and hloride by eletrometri titration (23). Results Group I experiments: omparison of reatinine and inulin exretion. Unpublished data obtained in previous experiments (15, 16) have been ex- TABLE I Comparisons of inulin and endogenous reatinine exretion* No. of No. Range of Creatinine/inulin ratio sub- of initial urine jets periods flows Mean SE Range ml/min A. Stable flows, phosphate infusions.t R1 = CCr/CIn B. Flows dereased at least 25 %.t R2 = Ur/Usn, period 2: UCr/Uin, period C. Flows inreased at least 25 %. Rs = UCr/UIn, period 2: Ur/Usn, period p, that: RI = 1..1 > p >.5 R2 = 1..4 > p >.3 Rs = > p >.9 R2 = Rs p =.6 * R = reatinine to inulin ratio, C = learane, In = inulin, Cr = reatinine, and U = urine. t Data derived from published experiments (15). * Data derived from published experiments (15, 16). amined with referene to a) omparison of endogenous reatinine and inulin learanes during periods with stable urine flows and plasma onentrations and b) omparison of hanges in urinary onentrations of reatinine and inulin in periods when abrupt hanges in flow ourred. The results, together with a statistial analysis, are presented in Table I. Under steady-state onditions during phosphate infusions for determinations of phosphate Tm, the mean reatinine to inulin learane ratio (R1, Table IA) was 1.3 in 23 omparisons on 4 subjets (D, Y, M, and T) (15). The small differene from a value 1. did not quite reah onventional levels of statistial signifiane (.1 > p >.5). In a wide range of experimental proedureswith and without phosphate infusion, with and without ortisone or hydroortisone injetion, in the morning and afternoon-abrupt hanges in urine flow sometimes ourred with onsequent hanges in urinary reatinine and inulin onentrations. In some periods a hange in hydration or the previous performane of a painful or nauseous proedure may have aused a hange in the endogenous prodution of vasopressin; in others the auses of suh hanges in flow were unertain. Tables IB and IC present the relative hanges in urinary reatinine and inulin onentrations on 3 suh oasions during 19 experiments on 5 subjets (D, L, M, T, and Y) (15, 16) in whom the flow inreased or dereased abruptly by at least 25%. There was no signifiant hange in reatinine to inulin urinary onentration ratio from one period to the next, either when the flow dereased (R2, Table IB) or inreased (R3, Table IC) from a wide range of initial values; there was also no signifiant differene between the ratio observed during dereasing flows, R2, and that found during inreasing flows, R3 (p =.6). These results point to the onlusions that during alterations in urine flow the relative hanges in urinary reatinine and inulin onentrations are similar and that reatinine may be used as an in- (lex of hanges in tubular water ontent. Group II experiments: onstant water load. Detailed data from the ontrol experiment M, in whih vasopressin was not administered, are given

3 Downloaded from on Deember 6, SOLUTE EXCRETION DURING CHANGING URINE FLOW 3 TABLE II Data during maintenane of onstant water load, experiment Mf* Urinary onentration U/P ratio Urine Time flow UOMS UCr Uure UN& UK UCi UNH4 Osm Cr Urea min m1/min Osm/kg mg/l mmoles/l meq/l meq/l meqil megil Subjet M (46 years, 1.83 m2) i i * Osm = osmolality, U/P ratio = urine to plasma onentration ratio. TABLE III Data from diureti periods immediately preeding, and periods of maximal onentrations subsequent to, vasopressin injetion Urinary onentration U/P ratio Time from Urine injetion flow UOSIII UCr UUrea UN& UKC UCi UNH4 Osm Cr Urea min ml/min mosm! mg/l mmoles/l meqil meqil meq/l meq/l kg H2 Experiment MI (46 yrs, 1.83 M2) vasopressin,.5 mu/kg body wt, iv , , Experiment M vasopressin,.5 mu/kg body wt, iv , , Experiment Ti (36 yrs, 1.63 M2) vasopressin,.5 mu/kg body wt, iv , , , Experiment T vasopressin,.5 mu/body wt, iv , , Experiment Wi (28 yrs, 1.76 M2) vasopressin,.5 mu/kg body wt, iv Experiment W vasopressin,.5 mu/kg body wt, iv , ,

4 Downloaded from on Deember 6, in Table II. Urine flow remained fairly onstant, with only small hanges in the urinary onentration and learane of reatinine. The progressive falls in urinary osmolality, sodium, and potassium onentrations are onsidered to be manifestations of diurnal eletrolyte exretory rhythms. A similar deline in urine urea onentration was aompanied by a fall in plasma urea onentration from 5.53 mmoles per L at minutes to 4.78 mmoles per L at minutes; onsequently urea urine to plasma (U/P) onentration ratio and urea learane remained more onstant. Similar data for the diureti periods immediately preeding vasopressin injetion in all experiments are presented in Table III. In Figures 1 and 3, urinary onentrations in preeding and sueeding samples are given as ratios relative to onentrations in the ontrol diureti periods, sine, in the present ontext, differenes in the relative hanges in onentration are onsidered to be signifiant. The onentrations of some solutes remained stable in the preliminary periods, but there was a progressive hange in onentration and output of other solutes. In ex- 2 O C b- u WI Time after vasopressin i njetion (mi ns) FIG. 1. URINARY OSMOLALITY, UREA, NONUREA SOLUTE, AND CREATININE CONCENTRATIONS. These are ratios relative to ontrol diureti values given in Table III; vasopressin injetion at zero time.

5 Downloaded from on Deember 6, SOLUTE EXCRETION DURING CHANGING URINE FLOW periment M2 a spontaneous fall in urea onentration ourred; in some experiments urinary osmolality tended to fall, partiularly when sodium onentration also delined. These hanges, like those noted in experiment M, are onsidered to be effets of diurnal exretory rhythms. Vasopressin injetion. The latent period between vasopressin injetion and the earliest detetable hange in water exretion, a rise in reatinine U/P ratio or urinary onentration, was 3 to 5A minutes. The magnitude and duration of the antidiuresis differed between subjets (Figures 1 and 3); individual data are therefore presented. Maximal urinary onentrations are inluded in Table III; note that the times at whih these were attained were not simultaneous for all solutes (see Figures 1 and 3). If hanges in urinary onentration were due entirely to altered water reabsorption, then the inreases in onentrations relative to the preeding diureti state would be similar for all urinary solutes. The relative hanges in reatinine, urea, osmolality, and nonurea solute (osmolalurea) onentrations are given in Figure 1 and sodium, potassium, ammonium, and reatinine onentrations in Figure 3. Comparison of the relative hanges shows that during the developing antidiuresis there were marked and onsistent differenes for some solutes and that the magnitude of suh differenes varied in time. Osmolality and urea onentrations. Within 3 to 1 minutes of vasopressin injetion, the inrement in urea onentration ratio was evidently less than that of any other urinary onstituent (Figure 1). The maximal deviation from osmolality and reatinine onentration ratios ourred during the developing antidiuresis before maximal urinary osmolality and reatinine onentrations were attained. Later, during periods of maximal antidiuresis and with the subsequent onset of diuresis in Subjets T and W, these differenes beame smaller or disappeared. Similar differenes between the relative hanges in osmolality and reatinine onentrations are primarily attributable to altered urea exretion, sine, exept in experiments with marked hanges in sodium onentration, reatinine and nonurea solute onentration ratios were similar (Figure 1). The magnitude of the effet of dereasing urine flow on urea exretion is most learly seen by plotting urea to reatinine learane ratio (i.e., urea U/P: reatinine U/P) against reatinine U/P (Figure 2). If the onlusions onerning Group I experiments an be extended to the irumstanes in vasopressin experiments, this shows the exreted proportion of filtered urea in eah sample. Several points are obvious. First, urea exretion was lower during antidiuresis than in diuresis. Seond, during the rapid fall in flow, urea exretion fell to values even lower than those 5 a a a# 6._ agd a- GD 9 oa OM I AM 2 I Il II lii II I I 1111 I I Cre a ti n ne U/ P ra tio FIG. 2. RELATION BETWEEN UREA TO CREATININE CLEARANCE RATIO AND CREATININE U/P RATIO IMMEDIATELY PRE- CEDING (, A) AND FOLLOWING ( *, A) VASOPRESSIN INJECTION. Minimal published values (O) at similar, stable urine flows are inluded for omparison (24, 25). ot I AT 2

6 Downloaded from on Deember 6, ml M2 to 1..6 IC U 3 1,CRE AT IN INIE ^ it ~~~V AMM ONIUM / e 2 XSODIUM I 1 x ~~~~~~~~~I OPOTASSIuUM. -2TI T2 -V- : a. 2 Lt X I x flo L ~~2 ~~~ I ~ ~ ~ ~ W WI I I I I 5 I Time after vasopressin ; njetion (mins) FIG. 3. URINARY SODIUM, POTASSIUM, AMMONIUM, AND CREATININE CONCENTRATIONS. These are ratios relative to ontrol diureti values given in Table III; vasopressin injetion at zero time. observed during maximal or sustained antidiuresis. Urea exretion in this phase was less than the minimal values at similar, but stable, urine flows (inulin U/P ratios) reported by other workers (24, 25); these values are inluded in Figure 2 for omparison. This large hange in tubular urea transport was a rapid effet, ourring within 15 minutes of vasopressin injetion in most experiments (Figure 1). Third, as low urine flows were sustained, a large inrease in the exreted proportion of filtered urea ourred with little hange in reatinine U/P (M1, M2, and W2). Finally, as urine flow subsequently inreased, urea exretion inreased towards the preinjetion ontrol values; only in T1 did the learane ratio exeed that found in the sample immediately prior to vasopressin injetion, and even here the ratio fell within the range of values found in earlier diureti ontrol samples. These effets on urea exretion are equally evident in similar plots of urea to nonurea solute learane ratios against nonurea solute U/P ratios. Eletrolyte onentrations. The inreases in ammonium onentration ratio during the transition from diuresis to antidiuresis were also on-

7 Downloaded from on Deember 6, SOLUTE EXCRETION DURING CHANGING URINE FLOW sistently smaller than those of reatinine (Figure 3), but were larger and evident earlier after vasopressin injetion than the inreases in urea ratio. Later, with the persistene of antidiuresis in M and the onset of diuresis in T and W, the hanges in ammonium onentration ratio showed no onsistent differenes from those of osmolality, urea, or reatinine. Assessment of any effet of vasopressin on sodium exretion is diffiult in view of the spontaneous fall in sodium onentration noted in some experiments. In experiments XV1 and \V2 the relative hanges in sodium onentration were losely similar to those in reatinine and nonurea solute, whereas in experiments M1 and M2, the relative inreases in sodium onentration were smaller (Figures 1 and 3). Inreases in potassium onentration ratio tended to be greater than those of other urinary onstituents at some stages of the developing antidiuresis (Figure 3). In M, potassium ratio remained higher during the persistent antidiuresis; in the other subjets, this relative inrease was more transient. In every experiment, the sodium to potassium onentration ratio fell relative to that present in the diureti ontrol sample; again this fall was persistent in M but in T and W was only a transient event during the developing antidiuresis. Disussion The sequene of hanges in urine flow after vasopressin injetion and the rapidity of its effet on water reabsorption are well-known (26). The present Group II experiments show that the ation of vasopressin on water exretion is aompanied by onsistent effets on urea and ammonium exretion during the developing antidiuresis. Interpretation of quantitative and temporal differenes between hanges in solute onentrations after vasopressin injetion depends on the reognition and evaluation of other possible ontributory fators: 1) Changes in plasma solute onentrations and urinary solute outputs over prolonged periods, beause of variable hydration or diurnal exretory rhythms, were minimized by maintenane of a onstant water load, by performane of the experiments in the afternoon, and by the hoie of a single iv, rather than ontinuous, injetion of vasopressin. Thus, hanges in urine to plasma onentration ratios of osmolality, urea, nonurea solute, and reatinine were similar to those of urinary onentrations. Spontaneous variations in sodium exretion have, however, learly ontributed to the postvasopressin hanges observed in some experiments. 2) Changes in glomerular filtration rate (GFR) ause unequal hanges in the exretion of different urinary solutes (27, 28). Maintenane of a onstant water load obviates hanges in GFR that might follow variations in plasma volume and plasma protein onentration. The design of Group II experiments preluded valid alulations of GFR during the rapid hanges in urine flow, but urrent theory suggests little effet of vasopressin on GFR (29). Both 3) aumulation of solute in the dead spae of the renal trat beause of abstration of water and 4) bladder-emptying errors affet exretory rates, but sine all urinary solutes would be equally affeted, relative hanges in onentrations would remain equal. Bladder-emptying errors would obsure, rather than enhane, the magnitude of differenes in onentration ratios. 5) The use of endogenous reatinine as a "glomerular substane" might also ause differenes between hanges in solute onentrations. The extensive literature, with differing onlusions, on omparisons of reatinine and inulin learanes in man has been reviewed reently (3). The results of the present Group I experiments (Table I) are taken to validate the use of reatinine as an index of water reabsorption and of hanges in tubular solute transport. Furthermore, the hanges in urea and ammonium exretion are still evident when ompared with urinary solutes other than reatinine, suh as nonurea solute. Many previous investigations on the relation between solute (e.g., urea) exretion and urine flow have employed variations in water intake as the means of induing hanges in flow. Consequently, fators 1 and 2 disussed above may have ontributed to any observed hanges in solute exretion. In view of these onsiderations, differenes in the relative hanges in solute onentrations after vasopressin injetion in the present experiments are onsidered to be due to altered tubular transport. If hanges in solute exretion were due solely to altered intratubular onentrations, then the 7

8 Downloaded from on Deember 6, expeted relation between solute output (or learane) and urine flow might be similar to that lassially desribed for urea during steady or slowly delining urine flow (29, p. 63). In the present experiments, however, urea exretion fell to values lower than those previously observed at simliar but stable urine flows (24, 25) and even lower than those found in more onentrated urine samples (Figure 2). These observations are similar to those reported in the dog after vasopressin injetion (14) and to a transient fall in urea learane-"abatement"-in sheep (31). The phenomenon appears to be the onverse of "exaltation"-a transient rise in urea learane after water administration to values higher than those found at similar but steady flows, originally desribed by Shannon in the dog (32) and sine observed in other speies (33) inluding man (24). These differenes between urea exretion during steady and nonsteady urine flows suggest the operation of fators additional to hanges in intratubular urea onentration. In terms of suggested ations of vasopressin (34), suh fators might inlude a diret effet on tubular permeability to urea (35) or on an ative transport mehanism (36). Alternatively, peritubular urea onentration may rise beause of loal aumulation in a sink or pool. Thus, if the olleting duts are permeable to urea during antidiuresis (12, 33, 35), delivery of more onentrated fluid from the distal tubule would lead to diffusion of urea into the medulla and a derease in urea exretion. Operation of the medullary vasa reta as a ounterurrent exhange system (12) would ause the sequestration of a pool of urea, progressively limiting further urea diffusion until a new steady state was attained; urea learane would be lower than at similar but steady flows (Figure 2), and the hanges in urine urea onentration, reatinine, and nonurea solute would differ in time and magnitude (Figure 1). With the establishment of a steady state of antidiuresis and of a medullary urea onentration gradient, net bak diffusion of urea would be limited to that lost into the irulation; the inrease in urea to reatinine learane ratio at almost onstant reatinine urine to plasma onentration ratio in the present experiments (Figure 2) is onsistent with the attainment of suh a steady state. Similar onsiderations apply to the hanges in ammonium onentration after vasopressin injetion. Under steady-state onditions, the rate of exretion of ammonium is usually onsidered independent of urine flow (and so of intratubular ammonium onentration), exept when the urine is alkaline (37, 38). The hanges in ammonium onentration observed here therefore suggest the involvement of fators alternative or additional to inreases in intratubular onentration. The pattern of hange is again ompatible with aumulation in a tubular sink or peritubular pool in the nonsteady state, although hanges in intratubular ph annot be exluded as a fator. Differenes between ammonium and reatinine exretion indued by rapid injetion into the dog's renal artery have similarly been explained by transitory diffusion of free ammonia into and out of a tubular sink (39). The existene of a medullary onentration gradient of ammonium during antidiuresis has not been speifially investigated but is evident in published data onerning the dog kidney (Table I) (9). Bak diffusion of free ammonia from, or dereased diffusion into, the olleting dut might ontribute to the generation of suh a gradient. The only onsistent feature of hanges in sodium and potassium exretion was a derease in sodium to potassium onentration ratio, transient in 2 subjets; a similar hange in the first 2 minutes after vasopressin injetion in the dog was believed related to the large dose used, rather than a physiologial aompanient of endogenous vasopressin seretion (14). In those experiments where spontaneous hanges in sodium exretion were least evident, the similarity between hanges in reatinine and nonurea solute onentrations (Figure 1) also argues against a marked over-all effet on eletrolyte exretion during the developing antidiuresis. The absene of any onsistent differene between the relative hanges in solute onentration ratios during the subsequent diuresis in T and W (Figures 1, 3) means that these hanges were primarily determined by diminished water reabsorption. During this phase, urea to reatinine learane ratios did not learly exeed the values of the preliminary diureti periods (Figure 2), although the ratios were higher than most of the values at omparable, but stable, urine

9 Downloaded from on Deember 6, SOLUTE EXCRETION DURING CHANGING URINE FLOW flows (24, 25); a fration of the derement in urea exretion during the developing antidiuresis was not exreted during the ensuing diuresis. These observations, together with the rapidity of the effet of vasopressin on urea exretion (Figure 1), are ompatible with a hange in tubular permeability to urea, as suggested by Jaenike (35) for the olleting dut of the dog. The relevant data, however, are too few to exlude other possibilities. If the present observations an be related to the generation of solute onentration gradients in the renal medulla during antidiuresis, the aumulation of a medullary pool of urea, and possibly of ammonium, involves inreased transport out of the tubule. The magnitude of the effet on urea exretion supports the suggestion (12) of a unique role of urea in the urinary onentrating proess. Summary 1. In 23 learane periods with urine flows stable during phosphate infusions in 4 subjets, the mean reatinine to inulin learane ratio was 1.3 (± SD,.8; probability that ratio is unity,.1 > p >.5). 2. During 3 instanes of spontaneous inreases or dereases in urine flow in a variety of experimental irumstanes-with and without phosphate infusion, with and without ortisone or hydroortisone injetion, in the morning and afternoon -there were no signifiant differenes between hanges in reatinine and inulin onentrations relative to those in the preeding urine samples. 3. In 2 experiments on eah of 3 subjets maintained on a onstant water load of 2 ml per kg body weight, hanges in osmolal, endogenous reatinine, urea, nonurea solute (osmolal-urea), sodium, potassium, and ammonium onentrations indued by vasopressin injetion were ompared in suessive frequent urine samples during the rapid fall in urine flow: a) During the deline in urine flow, the inrements in osmolality and urea onentrations (and U/P ratios) relative to those in the preeding diureti periods were smaller than those in reatinine and nonurea solute onentrations (and U/P ratios); urea to reatinine learane ratios fell transiently to values smaller than those previously reported at similar but steady urine flows, with minimal values attained before maximal reatinine and nonurea solute onentrations (or U/P ratios). b) Ammonium exretion relative to that of reatinine or nonurea solute also fell. ) There were no onsistent differenes between the hanges in nonurea solute and reatinine onentrations. 4. After maximal antidiuresis, the relative hanges in urinary onentrations were not onsistently different for any solute. 5. The quantitative and temporal pattern of the hanges in urea and ammonium onentrations during the developing antidiuresis is onsistent with aumulation in a tubular sink or peritubular pool, probably ontributing to the generation of medullary onentration gradients. Referenes 1. Thomson, W. B. The effet of oxytoin and vasopressin and of phenylalanyl3-oxytoin on the urinary exretion of water and eletrolytes in man. J. Physiol. (Lond.) 196, 15, Selkurt, E. E. Sodium exretion by the mammalian kidney. Physiol. Rev. 1954, 34, Thorn, N. A. Mammalian antidiureti hormone. Physiol. Rev. 1958, 38, Wesson, L. G., Jr. Hormonal influenes on renal funtion. Ann. Rev. Med. 1961, 12, Bojesen, E. The transport of urine in the upper urinary trat. Ata physiol. sand. 1954, 32, Wesson, L. G., Jr. Glomerular and tubular fators in the renal exretion of sodium hloride. Mediine (Baltimore) 1957, 36, Ullrih, K. J., and K. H. Jaraush. Untersuhungen zum Problem der Harnkonzentrierung und Harnverdunnung. tuber die Verteilung von Elektrolyten (Na, K, Ca, Mg, Cl, anorgenishem Phosphat), Harnstoff, Aminosiiuren und exogenen Kreatinin in Rinde und Mark der Hundeniere bei vershiedenen Diuresezustanden. Pflugers. Arh. ges. Physiol. 1956, 262, Bray, G. A. Freezing point depression of rat kidney slies during water diuresis and antidiuresis. Amer. J. Physiol. 196, 199, Levitin, H., A. Goodman, G. Pigeon, and F. H. Epstein. Composition of the renal medulla during water diuresis. J. lin. Invest. 1962, 41, Gottshalk, C. W. Miropunture studies of tubular funtion in the mammalian kidney. Physiologist 1961, 4, Wirz, H., B. Hargitay, and W. Kuhn. Lokalisation des Konzentrierungsprozesses in der Niere durh direkte Kryoskopie. Helv. physiol. pharmaol. Ata. 1951, 9, Berliner, R. W., N. G. Levinsky, D. G. Davidson, and M. Eden. Dilution and onentration of the 9

10 Downloaded from on Deember 6, urine and the ation of antidiureti hormone. Amer. J. Med. 1958, 24, Chinard, F. P. Comparative renal exretions of glomerular substanes following 'instantaneous' injetion into a renal artey. Amer. J. Physiol. 1955, 18, Jaenike, J. R. Aute effets of the administration of vasopressin during water diuresis in the dog. J. lin. Invest. 1963, 47, Longson, D., J. N. Mills, S. Thomas, and P. A. Yates. Handling of phosphate by the human kidney at high plasma onentrations. J. Physiol. (Lond.) 1956, 131, Mills, J. N., and S. Thomas. The aute effets of ortisone and ortisol upon renal funtion in man. J. Endor. 1958, 17, Bonsnes, R. W., and H. H. Taussky. On the olorimetri determination of reatinine by the Jaffe reation. J. biol. Chem. 1945, 158, Brod, J., and J. H. Sirota. The renal learane of endogenous "reatinine" in man. J. dlin. Invest. 1948, 27, Dik, A., and C. E. Davies. Measurements of the glomerular filtration rate and the effetive renal plasma flow using sodium thiosulphate and p-amino-hippuri aid. J. dlin. Path. 1949, 2, Conway, E. J. Mirodiffusion Analysis and Volumetri Error. London, Crosby, Lokwood and Son, Hawk, P. B., B. L. Oser, and W. H. Summerson. Pratial Physiologial Chemistry, 12th ed. London, Churhill, 1947, p Johlin, J. M. The freezing point determination of physiologial solutions. The usual errors and their elimination. J. biol. Chem. 1931, 91, Sanderson, P. H. Potentiometri determination of hloride in biologial fluids. Biohem. J. 1952, 52, Chasis, H., and H. W. Smith. The exretion of urea in normal man and in subjets with glomerulonephritis. J. lin. Invest. 1938, 17, Murdaugh, H. V., Jr., B. Shmidt-Nielsen, E. M. Doyle, and R. O'Dell. Renal tubular regulation of urea exretion in man. J. appl. Physiol. 1956, 13, O'Connor, W. J. Renal Funtion. London, Arnold, 1962, p Lauson, H. D., and D. D. Thompson. Effets in dogs of derease in glomerular filtration rate on ation exretion during intravenous administration of unreabsorbable anions. Amer. J. Physiol. 1958, 192, Davidson, D. G., N. G. Levinsky, and R. W. Berliner. Maintenane of potassium exretion despite redution of glomerular filtration during sodium diuresis. J. dlin. Invest. 1958, 37, Smith, H. W. The Kidney. Struture and Funtion in Health and Disease. New York, Oxford University, 1951, pp. 63, Doolan, P. D., E. L. Alpen, and G. B. Theil. A linial appraisal of the plasma onentration and endogenous learane of reatinine. Amer. J. Med. 1962, 32, Shmidt-Nielsen, B., H. Osaki, H. V. Murdaugh, Jr., and R. O'Dell. Renal regulation of urea exretion in sheep. Amer. J. Physiol. 1958, 194, Shannon, J. A. Glomerular filtration and urea exretion in relation to urine flow in the dog. Amer. J. Physiol. 1936, 117, Shmidt-Nielsen, B. Urea exretion in mammals. Physiol. Rev. 1958, 38, Kleeman, C. R., and R. E. Cutler. The neurohypophysis. Ann. Rev. Physiol. 1963, 25, Jaenike, J. R. The influene of vasopressin on the permeability of the mammalian olleting dut to urea. J. dlin. Invest. 1961, 4, Bray, G. A., and A. S. Preston. Effet of urea on urine onentration in the rat. J. dlin. Invest. 1961, 4, Orloff, J., and R. W. Berliner. The mehanism of the exretion of ammonia in the dog. J. lin. Invest. 1956, 35, MaKnight, A. D. C., J. M. MaKnight, and J. R. Robinson. The effet of urinary output upon the exretion of 'ammonia' in man. J. Physiol. (Lond.) 1962, 163, Balagura, S., and R. F. Pitts. Exretion of ammonia injeted into renal artery. Amer. J. Physiol. 1962, 23, 11.