Cs-137 Metab in Active and Hyber

7/29/2019 Cs-137 Metab in Active and Hyber

1/16

JnReprinted from Mammalian Hibernation III edited by Kenneth C. Fisher, AlbertR. Dawe, Charles P. Lyman, Eduard Schdnbaum, Frank E. South, Jr. Publishedby Oliver & Boyd Ltd W, and by American Elsevier, New York, in the U-S.A.pf Atq- 2zft;ufq,,it:& 6;btic:3 gpatt-909CESIUM.137 METABOLISM INACTIVE AI\D HIBERNATING

CITELLUS LATERALIS*MenvIN L. RrrpnsEr,, Yu-CHoNG LIN,

Jevrns J. YouNc AND GoRDoN H. Bnvext .iq67"D ep ar tment d u"If{,:r#;I:'fr':^t.' Iry:i# *ioy ., * rTUalura I A^rrrrrrrr(,' tt,, H ; b ev^ na-fi on @

sy n',poiu vn, L( t; u' fDronfrl Aaatacl


2/16

220 RIEDESEL ET AL.the effect of temperature may be observed on the processes which limitthe rate of exchange of cesium between intracellular and extracellularspaces, and also between an animal and its environment. Richmond el a/.$96z) have related turnover of cesium to metabolic rate whereas comarand wasserman (1956) emphasized the role of tissue and cellular com-partments which retain cesium. Although skeletal muscle is consideredthe critical organ following administration of cesium, all tissues metabolizecesium (Ballou and rhompson r95B). Emphasis in cesium research hasbeen on long-term studies; and as a result, little information is availableregarding rate and mechanism of uptake of cesium by tissr.res.

MATERIALS AND METEIODSThe experimental animals, citellus lateralis, were collected in northernNew Mexico and had been in the laboratory two days to six months priorto experimentation. All animals received a single iniraperitoneal injectionof o'48 microcuries of cesium- r 37 (in o.r ml of buffered Ringer's soiution)per roo g body weight. Immediately after injection the first whole-bodycount was taken. urine and feces were separated in metabolism cages.our studies confirm earlier reports (Ballou and rhompson r95g, coirarand wasserman 1956, Richmond 1958) which establisl the uiine as theprincipal route of excretion of cesium-r37; therefore, urine and fecesactivities are not included in this report. Measurement of skin temperatureby placing a thermocouple at the base of the fur near the shouldeis of theanimals provided an indication of whether the animal was active or hiber-nating- skin temperature readings were taken without disturbing theanimals and averaged z'C lower than rectal temperatures.All measurements of radioactivity were made with the packard Instru-ment co. Model 4roA_auto-gamma spectrometer and a Model 44o, small-animal whole-body scintillation detector. The animals and tissues werecentred in the counting chamber, r r cm in diameter, 20 cm in iength. Thewhole-body counter permits frequent counting of intact animals andprovides a good_ comparison of tissue activity to whole-body activity asthe whole animal and tissues are counted undir identical conditions. Thestandard _source (o'r58 microcuries, cesium-r37) and background countsw-ere made daily. The mean and standard error'of 4o "rr"-tinrrte countsof the standard cesium-r37 source and the background were rrz 136c.p.g. 176 (s.e.) and r36r + 8 (s.e.), respectively.The term, hypothermia, refers to the condition of animals which havehad their body temperatures lowered as a result of cornbined cord exposureand carbon dioxide anaesthesia (Andjus et ar. ry56b). Animals were placedin jars (9oo rttl capacity) which were closed. *it-h ."."* caps and exposedto - rooc. opening the jar at 15- to zo-minute intervals ensured adequateoxygen supply. within 45 to 60 minutes the above procedure resulted inlowering of body temperature to rB" to zooc. subsequent immersion inice water and exposure to air at 8"c kept rectal temperature at Bo to rooc.Animals injected with cesium-r37 during hypothermia had rectal tem-peratures of 8" to rooC 3o minutes prior to injiction.


3/16

CESIUM-I37 iN CITELLUS LATERALIS 1t TData on cesium distribution at varying times after injection (up to z4hours) were obtained on hibernating ground squirrels; these animals werealways injected 6 to rz hours after they had entered hibernation. Data onhibernating animals at the first, second and third biological half timesinvolved (a) injection of active animals; (D) sacrificing animals at rhe first,second or third biological half time only if they had been hibernating twodays prior to the half time indicated.A standard procedure was followed just prior to and after sacrificingthe animals. The body weight was first measured. Background, standardsource, and whole body counts were measured for one minute. Then, theanimal was sacrificed by decapitation. organs and tissues were removed andweighed to the nearest o'or g. The whole liver (without gall bladder),heart, lung, spleen and stomach were counted; both kidneys were countedtogether whereas the right and left whole gastrocnernii were weighed andthe c.p.m. measured separately; the whole right femur was used, theupper 3 to 5 cm of the small intestine, r to r.5 g of abdominal skin ando.5 to r.5 g of blood. Tissues in paper tares were placed in the countingchamber, and the radioactivity of each tissue was determined by either asingle ten-minute count or the mean of three one-minute counts. countsper minute per gramme wet tissue were calculated.In order to assess the effect of temperature as well as time (see Linr964) on the cesium-r37 uptake, distribution and retention by tissues, itseemed most convenient to express the data in the form of the ratio:c.p.m./g wet tissueG/gEAy ilFt. Thus, since cesium is continuously being excretedso that the total amount in the whole body is always decreasing, the con-centration of the isotope in any tissue is always expressed in terms of theconcentration in the whole body at that moment. Hence a value forcesium-r37 of more than r'oo for this ratio would indicate an affinity of aparticular tissue, which is greater than the average aflfrnity of all of thetissues in the body. In retrospect it would have been more informative toexpress these activities as c.p.m. per g of water. unfortunately waterconcentrations were not determined.The following terms were used: Tissue Index and rissue RetentionIndex. Tissue Index (TI) indicates the relative tissue concentrations ofcesium-r37 (i.e. the above ratio) within z4 hours after injection, when theuptake process predominates. The same ratio will be called the TissueRetention Index (TRI) when it refers to the relative tissue concentrations(i.e. the above ratio) at the first, second, third and fourth biological halftimes; at these times retention rather than uptake is the major factorcontributing to the cesium-r37 concentration of the tissues. Lowering ofTRI of a specific tissue between the first and second half times representsa situation in which the rate of loss of the radio-isotope from the tissue isin excess of the rate of loss from the animal as a whole.

RESULTSExperiments conducted include: (a) measurement of tissue ind.ices on


4/16

aoa RIEDESEL ET AL.active, hypothermic and hibernating C. lateralis sacrificed within z4 hoursafter a single intraperitoneal injection of cesium-r37; (b) determination ofcesium-r37 retention curves on rats, active ground squirrels and hiber-nating ground squirrels exposed to temperatures of 2o" and ro'C; and (c)measurement of cesium-r37 tissue retention indices on C. lateralis activeand hibernating at various biological half times.

Cesium-r37 Uptake Following Intraperitoneal InjectionThe tissue index data collected on animals sacrificed within z4 hours afterinjection of the radio-isotope are presented in Tables I and II and Figs. rand z. The right and left skeletal muscle data were collected to show thereproducibility of the mean and s.d. values. Tissues of particular interestare blood, kidney, heart, skeletal muscle, liver and lung. Observationswhich are pertinent to this report include: (a) Kidney was the first tissueto concentrate the cesium and was the tissue with the highest TI in active,hypothermic and hibernating animals. Apparently an active transportsystem was concentrating the cesium in the kidney; and although thesystem was slowed down during hibernation and hypothermia, the kidneystill had the fastest uptake of cesium-r37. (D) The cesium content of bloodand plasma was always very low and 15 minutes post-injection of activeanirnals the cesium content of blood was lower than in any tissue (Table I).Tissue systems concentrating cesium were efiective at body temperaturesof roo and 27" C. (r) The TI of heart tissue six hours after injection of hypo-thermic and hibernating animals was higher than the heart index of activeanimals sacrificed six hours after injection, p values being o.or or less. Theblood flow to the heart and the cesium concentrating mechanism in hearttissue were temperature independent relative to blood flow and concen-trating mechanisms in other tissues. (d) Heart tissue of animals active atthe time of injection took up cesium-r37 faster than skeletal muscle. Thisdifference may be due to the greater blood flow per gramme of heart tissue;however, cardiac muscle appeared to have a cesium concentrating systemwhich was not present in skeletal muscle, or at least was not as rapid inskeletal muscle. (e) Tissues in the order of decreasing affinity for cesiumwere kidney, heart and liver (Table III). This order was not changed bylowering the body temperature prior to injecting cesium-r37.

Cesium-r37 ExcretionMetabolic rate and water turnover are key factors determining renalactivity; if they increase in rate so does renal excretion. Both of thesefactors are changed during hibernation. Therefore, the effects of coldexposure and limited water intake were examined.The rates of excretion of cesium-r37 by eight rats exposed to tem-peratures of roo and zooC are presented in Fig. 3. The slope at zooC(m : o.o3o9) compares favourably with the slope (zz : o.ozg7) reportedby Richmond (1958). At ro"C the rate of excretion is considerably fasterthan at zooC. Retention curves obtained from eight ground squirrels ex-posed to temperatures of rooC, however, were similar to those at zooC


5/16

CESIUM-r37 IN }TTELLUS LATERALIS 223TeeI,n I

Mean tissue indices of cesium-r37 in active ground squirrels(n : 6 at each time designated)

Time After fnjectionI mxn 3 mln 15 mtn rhr Jhr 6hr rz hr z4 hr

Bloods.d.Plasmas.d.Kidneys.d.Hearts.d.RightGastrocnemiuss.d.LeftGastrocnemiuss.d.Livers.d.Lungs.d.Spleens.d.Stomachs.d.Intestines.d.Skins.d.Femurs.d.

ro8o'30r'64o'963'99I.IOr'53o'43o'27o'r9o'32o'r+r'92o'3 rr'49o'422'4rr'72z'63r'545'592'36r'65r'24o'28o'12

r't6o'36r'72o'63s'675 Jlr'9+o'65o'4ro'o8o'38o't2r'87o'54r'30o'33r'56lo9r'54o'675'443'48o'50o'o8o'37o'25

o'27o'09o'53o'25r6'263'o8z'69o'50o'46o'r 5o'48o'r4z'88o'56r'ooo'34o'99o'5 rr'73o'975'7rr'85o'42o'r oo'48o'22

O'I Io'o5o'20o'r58'42z'843'$r05o'62o'30o'65o'353'3rr'o5r'43o'64r'65r'23r'74o'767'263'83o'3 ro'17o'48o'r9

o'17o'05O.I Io'r25'83r'703'80o'50r'ooo'17I.IIo'283'42o'32r'54o'23r'76o'45o'465'3 rr'53o'43o'r 6o'69o'30

o'I2o'o6o'07o'o44'r8r'362'55I'IOo'98o'69o'77o'53z'26I'02t'20o'57t'20o'83r'55a'673'09r'37o'4ro'25o'68o'39

o'r 8o'roo'30o'243'r8o'572'58o'26

o'20o'roO'I Io'r oz'89o'33I.76o'17

r'29o'23r'30o'r 82'39o'36t'28o'r72'09o'502'25o'84o'67o'6 ro'25y07o'24

r'93o'73o'65r'79o'34I 'I3o'2\.r8zo'982'13o'r 62'65o'2+o'56o'r8o'69o'38

(Fig. +). Apparently rats in air temperature of rooC have an increasedmetabolic rate, whereas rooc did not represent sufficient thermal stressfor ground squirrels to effect an increase in metabolic rate; so no changein the percentage retained at rooC could be observed over that at zo"C.The rate of cesium-r37 excretion by four ground squirrels deprived ofdrinking water, and four animals with water intake limited to five milli-litres per z4 hours, was slower than the excretion rate by control animalswith water ad lib. (Fig. S). Obviously limited water intake greatly delaysexcretion and so can be an important factor determining the characteristicsof cesium-r37 metabolism during hibernation.At this writing, we do not have sufficient data to describe the overallefiect of hibernation on cesium-r37 excretion. However, the slope ofretention curves (log per cent retention against time in days) for fouranimals in hibernation from four to 14 days ranged from o'oo7 to o'o5r,


6/16

RIEDESEL ET AL.2+

zozE.U OItJ6E9zddoCP.; Om.q= ;'-ttcd'- d6lEo.p oIEE

alYEaP< x e

; i.i d\oi Fgrrr-I-6F^T 9;H'='oo CHo6.o .:i =o ts';o u,'-o otr{o XG@ h0o!=

ud,>o'dI'-I E-o I;or.odH(tr trH@O

;)-lsl

IslNI,l'l:l=ll+)al'lPI.I-l

Iu;lqllIq:l'l

:lol-,/a\alrlNl."1rl-l6l-t

I";lrl-l"t-l-l

I4l!l,ll:t=t5l-)

t:t:i:l:t:t:l=t-t-Lt,l=t,L

;

;=

;::

S'\l Bsl Frl 2$l *si{ Ti.Trrl r r >stsltt

F

;l;FIO>l\al>'13

o=-F


7/16

225ESIUM-I37 IN CITELLUS LATERALIS

zoFz:EUo o c!_i= 9.edC.53V i'^s_o

6 A\ i"E.g Nt'aaQ3EeHP!-.^ U'd F

tsHmo 2'O H


8/16

226 RIEDESEL ET AL.TesI,n II

Mean tissue indices of cesium-t37 in ground squirrels sacrificedduring hypother mia and hib ernation(n : 6 at each time designated)

Teslr IIIValues and timing of highest tissue indices

(Taken from Tables I and II)Highest Tissue Index

Hvbo. Active Hypo. Hiber.BloodKidneyFIeartLiverLung

r'r6t6'263'r63+-r'54

o'295'545'802'48r'46

o'656'ss4'36a tJI.5I

3 min15 minrhr3hr3hr

IO mln6hr6hr6hr6hr

ro min6hrrz hrrz hr6hr

Time After InjectionAnimals in Hypothermia Animals in Ilibernationro min I s n I o hr Itzhrlz+hr IO MLN 3hr 6hr tzhr e4 hr

Bloods.d.Kidneys.d.Hearts.d.RightGastrocnemiuss.d.LeftGastrocnemiuss.d.Livers.d.Lungs.d.Spleens.d.Stomachs.d.Intestines.d.Skins.d.Femurs.d.

o'29 lo'2r1o.25o'ro lo'16 lo.z:o'8o lo'sols's+o'43 lo'4ol3.tto'4o lo.zal.5.8oo'3+ lo.o9 jz.tott'o4 lo.rrlo.23o'o3 lo'o7io.r9tt'rr lo'rr o.z6o'o6 lo'o3 jo.r,ro3 lo.5olz.a8o'52 lo'3zlt.5to'48 lo.zZlr.+6o'r3 lo'r+lo.+qo'4r lo.sslo.sso.3o lo.ztlo.roo'3r lo.z4 | r.r5o'2o lo.tglo.Tz6'o+ l+'s6)s'+,v76 lt.solz.t+o'r8 I o'zol o.z6o'ro lo.r3 lo.r,o'o9 lo.z8]o.r7o'r7 lo.oalo.ra

o'ro I o'roo'o+ | o'o8z'o6 I z.sz,'27 | ,'r33'14 I 3's+lr8 | r'53Io.3r I o-42o'r -5 I o'r 3Io'38 | o.4ro'r -5 | o'r -5z'ry | 167o'88 | o'38ror I r.r4o'23 o.3-5o'62 | o'69o'3o I o.z7r'o7 ) r.o2o'4o I o'6rz'35 | r'8orr5 l o'7oo'25 ) o.32o'o8 | o.o5o'15 | o.z8o'o4 | o.17

o'65o'453'44z'16r'r7o'47o'25o'r9o'r6o'r 6o'89o'66O.I Ir'20o'55o'8 ro'374'38o'95o'52o'44o'25o'24

o'38o'43r'972'54o'85o'93o'roo'roo'07O'I II. I+r'33o'53o'46o'26o'3 ro'39o'3 rr'452'45o'07o'o6o'r 3o'28

o'2to'r 96'ss\'674'ooo'99o'39o'23o'32o'r83'r7I.4II.5Io'42o'90o'3 rr'44o'543'65r'2+o'35o'r 8o'3 3o'3 5

o'r4o'o95'4rr'574'36r'84o'45o'17o'36o'r44'73r'40r'37o'40I05o'49I .IOo'355'grr'99o'4ro'r 5o'r9o'r3

o'23o'r84'45o'35o'62o'5 ro.roo'43o't24'02r'55r'21o'20r'30o'+7r'36o'493'20o'95o'33o'09o'29o'r 5

Time of Highest Tissue fndex


9/16

co=c)6)E.cq)oq)o-ci)oJ

CESIUM-I37 IN CITELLUS LATERALIS

Doys After lnjectionFig. 3. Cesium-r37 retention by rats at roo and zooC following a single intra-peritoneal injection (n : 8 at each air temperature).whereas the slope of retention curves for ten active animals during thesame time period ranged from o'o87 to o'14 which replesents a twenty-folddecrease in excretion rate during hibernation.

Cesium Distribution after rst, 2nd, 3rd, and 4th BiologicalHalf TimesThe tissue retention indices (TRI) of skeletal muscle and skin increasedwith time, rst, znd, 3rd, and 4th biological half times, whereas the indicesof other tissues were unchanged or decreased with time (Fig. 6). The longternr retention of cesium-47 by skeletal muscle confirms reports on otheranimals (Richmond et al. 1962, Comar and Wasserman 1956). Theincreased activity of skin may be due to contamination from excreta oncages.

With the exception of heart tissue, the TRI values of active and hiber-nating animals were similar (Fig. 6). The TRI of heart tissue from hiber-nating animals was higher than the TRI of active animals at all threebiological half times, p values being o'o5 or less. The increase in TRI ofheart tissue may result from this tissue picking up cesium-r37 which hasbeen released into the blood by other tissues because, as noted above, hearttissue was very effective in concentrating cesium-r37 when body tem-perature was ro"C at the time of injection. It is important to recall thatthese animals were active at the time of injection of the cesium-r37 andfor part of the time interval between injection and sacrifice. They had beenin continuous hibernation a minimum of two days prior to sacrificing.A gross examination of the data presented here and in the literaturesuggests that the sequence of events following a single intraperitoneal in-jection of cesium-r37 in active animals was as follows:MHQ

/- m:-o.o3o91 (zo"c)


10/16

c.9o)a)E.C@,(J(lJo-oro

--.,

228 RIEDESEL ET AL,

2 S.D.

8rot2Doys After lnjectionFig. 4. cesium-r37 retentionby citelrus rateraris at roo and zooc following a singleintraperitoneal injection (n : 8 at each air temperature).

c.9c(l'll'E.c(Doq,o-cl,o-J

Fig. 5. Cesium-r37each group).Doys After lnjection

retention by Citellus lateralis varied by water intake (n : 4 in

No Woter; m'-0.o!Bg

5 ml Woler/24hrs; rn=-o.o6re

Wsler od libl 6=-9.9926


11/16

CESIUM-I37 IN CITELLUS LATERALISr. diffusion from the site of injection into capillaries andcirculation;z. rapid uptake of cesium by kidney tissue, highest TI 15after injection;

229general

minutes3. high rate of excretion of cesium by kidney, particularly during thefirst z4 hours after injection (Fig. 3, 4 and 5) (Richmond et al. ry62);4. concentration of cesium by other body tissues with highest TIoccurring at different times (heart, one hour; intestine, one hour;liver, three hours; stomach, three hours; etc.) (Tables I, II and III);5. the affinity of cells for cesium keeps the concentration in the bloodvery low with the highest TI for blood occurring within threeminutes after injection ;6. loss of cesium from tissues via blood and urine is very slow, and therate of loss by muscle tissue and bone is slowest as the TRI valueskeep increasing past the rst, znd, and 3rd biological half times.

These observations suggest that uptake and retention of cesium-r37 aredependent upon effective circulation as well as cellular processes con-cerned with active transport and binding of cesium. The maintenance ofhomeostasis during hibernation can be expected to be dependent upon thesame systems.DISCUSSION

Interpretation of TI DataThe TI data have been used to interpret circulatory changes which occurduring hypothermia and hibernation, particularly the TI values for blood,kidney, cardiac and skeletal muscles, liver, and lung.Cesium-r37 appears to be present in blood as a free (unbound) elec-trolyte. This is indicated by (a) the rapid uptake of cesium from blood bykidney and other tissues, and (D) the blood having consistently lower TIand TRI values than any other tissue except during the first few minutesafter injection.A comparison of the highest TI values in the blood of active animals(at three minutes) and in that of hypothermic and hibernating animals (atten minutes), indicates that the rate of blood flow to the site of injection ofcesium (i.e., peritoneal cavity) is decreased by a factor of at least threeduring hypothermia and hibernation. The circulatory adjustments duringhypothermia and hibernation appear to be similar judging from the blooddata and the time of appearance of the peak radioactivity in tissues.With the exception of the intestine, which is probably contaminated,the kidney appears to have the highest TI values of any tissue under nearlyall conditions, suggesting that the kidney is concentrating cesium by somemechanism, e.g., active transport. If the magnitude of the peak TI valuescan be used to indicate the rate of activity of this active transport system,then comparing the active to hypothermic and to hibernating animals the9ro of the process is r'5 and r'2, respectively. On the other hand, thesmall urine production characteristic of hibernation implies reduced blood


12/16

RIEDESEL ET AL.30

\otbii

F,Tul9ol]elR-lEal>

ozzotrzFElFFnI:-

IF8gE';-:! 9iFLF*a r5 .F o ' 'A9.2 6j '.8g U.; T E HI F 6 5'=.+e:!'( *"? :.':= @ o e.V :.8 +.1 o!E;'dEEd.; t g


13/16

231ESIUM-r37 IN CTTELLUS LATERALTS

-9r asa 'scrob0fr{

-leluol=;t6El3-lE=l:l>uozzoFzuFUEU)FFI

I

=U

zn;:_FNNx30Nt Nor-rNlllg :nsslL

6-oc!

sj


14/16

aaa RIEDESEL ET AL,flow to the kidney, and supports the hypothesis that the lower tissueindices of kidney tissues during hypothermia and hibernation are theresult of the effect of temperature on effective blood flow to the kidney.The time required to reach a peak rI in the kidney in the active animal(r5 min, Tib,l: I) indicates a twenty-fold increase over that in the hypo-thermic and hibernating animal (6 hr, Table II) in the time required tocirculate cesium from the peritoneal cavity to the kidney. The blood dataindicated a three-fold decrease in circulation to the peritoneal cavity;therefore, there was a six- to seven-fold decrease in thelcirculation to thekidney. The authors are of the opinion that both a cellular active transportsystem and circulation of blood are determinants in the cesium-r37 upiakeby kidney tissue.- There are two points regarding metabolism of cesium-r 37 by hearttissue: (a) the TI of the heart is always higher than the Ti of .k.l"tulTyt"l" during the fi.rst rz hours after injectiin (Tables I and II; Fig. r).(6) The TI of heart tissue reached a higher value when the cesium wasinjected into hypothermic and hibernating animals (Tables I and II;Fis. r) than when injected into active animals. The higher tissue indicesof heart tissue than of other tissues may simply be a result of greater bloodflow, and the higher values in hypothermia and. hibernation than in theactive animal may result from the fact that the decrease in blood flow tothe heart is less than the decrease in blood flow to other tissues duringhypothermia and hibernation. In other words, the blood flow to the heartis reduced in hypothermia and hibernation; but the decrease to hearttissue is less than the decrease to other tissues. It takes approximately sixhours for the heart TI to reach its peak in hypothermra u"d hibernation,whereas it takes three hours in active animals. These data indicate a two-fold decrease in circulation time from the peritoneal cavity to the heart.However, the blood rI data demonstrated a three-fold decrease in circu-lation to the peritoneal cavity. Therefore heart tissue must have a favour-able.electrochemical gradient for concentrating cesium-r37 which may befacilitated by cooling. At least the mechanism taking ,rp ce.inm-r3i inheart tissue is less sensitive to lowering temperature than the mechanism

operative in other tissues thereby accounting for higher TI of heart tissueduring hypothermia and hibernation. A favourable electrochemicalgradient in heart tissue as described by Ling (1962, 1965) would represenra_ temperature independent electrolyte concentrating mechanism. Anelectrochemical gradient which facilitates uptake of cesium and is tem-perature independent v'ould be consistent with both the TI and TRI data.Liver cells do not appear to have a particular affinity for cesium-r37.The difference in the time required to reach the highest fI in active (th;;ehours), hypothermic (six hours), and hibernating (six hours) indicates thatthe blood flow to the liver is reduced by a factor of two during hypo-thermia and hibernation.The TI values obtained on lung tissue suggest there is no particularcesium-concentrating or -retaining system operating within lung iells. Thetime required to reach the highest tissue indic"r indicut".l two-fold


15/16

CESIUM-i37 IN CITELLUS LATERALIS a;\ -)decrease in effective blood flow to lung tissue during hypothermia andhibernation.The data presented on stomach, intestine, spleen, bone and skin aredifficult to interpret for several reasons. Residual food material within thedigestive tract would have a marked effect on the TI and TRI values. Noattempt was made to remove contents of stomach or intestine as such aprocedure may wash out cesium-r37. The size of the spleen, o.r to o.3 g,was near the limit of the weighing procedure. Changes in cesium-r37content of bone are not apparent except on a long-term basis because ofthe low metabolic rate of bone. Contamination of cages, fur, and skin byexcreta complicates the skin data. Future studies should clarify cesium-r37metabolism in these tissues and in nerve tissue.

Interpretation of TRI DataInitial uptake of cesir.rm is determined by circulation, diffusion and cellmembrane characteristics whereas long term retention (at rst, znd and 3rdbiological half times) involves these and possibly other mechanisms whichretain cesium within subcellular compartments. Typical subcellular com-ponents which may be involved in retaining cesium include: cell organelles,cell proteins or some cell metabolites such as amino acids which have anaflftnity for electrolytes (cesium). The concentration of potassium inmitochondria is higher than in other celL parts (Price et al. ry56), but thereis no evidence that mitochondria or other cell organelles concentratecesium.The TRI of heart tissue was the only TRI value changed (p value ofo'o5 or less) by 48 hours of hibernation at the various biological half times(Fig. 6). Earlier reports on cesium metabolism (Ballou and Thompson1958, Richmond 1958) have explained skeletal muscle retention of cesiumby protein binding. Frotein binding may very well account for the longturnover time of cesium in skeletal muscle, but the differences betweenthe cardiac and skeletal muscle TRI data are most likely related todifferences in the characteristics of the cell membranes and of blood flowto these tissues. With the exception of respiratory pigments and enzymeconcentrations the proteins within these tissues are similar, therefore theintraceliular protein binding of cesium-r37 in cardiac and skeletal muscleshould be similar. The increased cesium-r37 in the hibernating heart maybe explained as foltrows: (a) the heart cell systerr for concentrating cesium-r37 is temperature independent relative to the system operating in othertissues, (6) a high blood flow to the heart ensures that heart cells couldpick up cesium-r37 released from any tissue.With the exception of heart tissue, hypothermia and hibernation didnot change the TRI of the tissues examined at the rst, znd, and 3rd bio-logical half times. These findings support the hypothesis that a tempera-ture independent process, such as protein binding is the primary factordetermining retention of cesium-r37 by body tissues.The similarities between the chemical characteristics of potassium andcesium are readily recognized (Finstone and Kinsley 196r); however,


16/16

23+ RIEDESEL ET AL.Comar and Wasserman (1956) have pointed out numerous examples ofdifferences in the biological metabolism of potassium and cesium. Appli-cation of findings and hypotheses set forth in this report to potassiummetabolism during hypothermia and hibernation may be helpful in thedesign of experiments regarding potassium, but additional applicationwould be tenuous.

SUMMARYWater intake and environrriental as well as body temperatures can effectmarked changes in cesium-r37 metabolism. The distribution of cesium-q7among body tissues following a single intraperitoneal injection demon-strates the following: (a) animals made hypothermic by artificial methodshad a cesium-r37 metabolism similar to that in animals hibernating during,and immediately following, the time of injection; (6) lowering of bodytemperature slows down the rate at which cesium-r37 is distributedamong body tissues; (c) heart tissue uptake of cesium-r37 is less tempera-ture dependent than uptake by other tissues; (d) the kidney uptake ofcesium apparently involves a concentrating system as well as changes inblood flow; and (e) hibernation at the rst, 2nd, and 3rd biological halftimes did not effect a major change in the distribution of cesium-r37among body tissues with the exception of an increase in the amount ofradio-isotope in cardiac muscle.

Pl;nted ;n G/eat Br;ta;n

Documents

Cs-137 Metab in Active and Hyber