AN ATTEMPT TO REPRODUCE EXPERIbfENTALLY THE PLQTTERN OF SALT AND WATER DISTRIBUTION OF AGE IN THE YOUNG

NEUROMYPOPfIYSECTOhf IZED ,QDRENALECTOhfIZED RAT1

S\ DXEY AI. FKIEL)MAN, BKIG~L) CUST~ZFSOK, ~ ~ O R O T I I I ' IIAMII,~~QN, AND

CONS.~NC.H L. FRIEDMAN Deparfnzent if Awatonly, L-nizlersity uf British Colunzbict, Vancouver, British Culumetin

lieceivcd Ilecember 10, 1965

Abstract Previous studies of the illteractiori of aldosterone, vasopressin, and corticos-

terone in ths ncurohypophysectornized adrenalectomized rat suggested that the salt and water distribution patten1 in the muscles of the ageti rat and that observed in simple aldosterone domiriance were similar. 'I'his was tested by mainta.iiiing youug ~leurohypo~)hysectolllized adrenalectornixed rats with aldos- terone alone for 2 xnollths and cormparing the resulting pattern with that of old rats, 27 months of age. Changes identical with those which occur spontaneously in the aged muscle, although of lesser degree, were reproduced in the young aninlals. Thus, total muscle sodillin increased in association with a ~orresp~r ldi i lg loss of potassium and a shift of water from cells to environment. ,As in the old :r~iinlais, a n illcrease iii total muscle water Ivas observed.

Introduction Jt is a Bong-stancling beIief of many endocrinologists tha t in age there is 3

general reduction of pituitary activity perhaps reflecting general hypothalamic failure (1). In 1947 Findley reasoned both fro~am clinical evidence and from a suggestion of IIeinbeclier tha t neurohypophyseal failure might underlie some of the inore obvious changes associated with ageing in rraan ( 2 , 3 ) . Startirig froirn this position, in 1955 we explored salt and water ha i~dl i i~g ill the aged rat tend concluded tha t neuroh~rpophyseal failure might well t ~ e present (4). We the11 studied the response of the neurohypophysis to direct osi~iotic stinlulation ancl found the gland highly unresponsive i11 age (5). Dicker and Nuia~a questioned this conclusiun but, in their experiments, used mature, not truly old rats (ti). Kodeck et aI. (7) presented a photograph illustrating a lrnarked reduction of ~le~arosecretory rrlaterial i11 the posterior pituitary of senesceilt animals as a n incidentr~l observation, but also confined their quantitative studies to mature rats. 1Iore recently, Dunihue (8) has produced convirxcing histological evidence of dq>ressed mcurohypophyseal activity in the aged rat.

Jn its basic features the pattern of salt and water distribution in the aged anitrlal nxty 1)e described as one of extensive accumulation of sodium in the bulk tissues of the body (skeletal ~rauscle, vascular tissue) associated with a corre- spondirsg loss of potassiunl (9). As is usual with salt accumulation, there is a redistribution of water from cells to environnle~lt so tha t the extracellular fluid vululne is greatly expanded a t the expense of the cells. As a continuing process, the pattern is, a t least in part , reversible, and we have shown that neurohypo- physeal extracts arc capable of p roduc i~~g some restitution (18, 11).

I'his work was carried ont with ths aid of grants from the Muscular llystropky Assoc-iatioaa of Canada aaid the illedical Research Council.

Canadian Jourlial of Pt~ysiology and Pl~artnacolog~r. Volume 4-1 (1961;)

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430 <'.lNADT.%N JOI-KS.11, OF PHUSIOI,OGY -1n-I) PIIAKblA.('OLOGY. VOL. 41, 19(iA

In our view, the pattern of salt and water distribution 11.l-iich results fro111 i~eurolaypop1~yse;~l failure depends riot only negatively on the irlissiilg ele~nents hut positively oil the effects of the reinailling adreisal funct io~~s. The picture ira the aged araimal does not resen~ble that of siilaple diabetes insipidus but is blunted and inore like that ill tkac neurohypophysecto~~~i~ed aclrenalectol~~ized rat rnaintairacd on aldosterone alone (12). We recentlj~ testccl the effect of administering a supplcnnenlt of corticosterone or cortisol in addition to ; L H ~

extract of the \\.hole posterior pituitary to the aged rat arad found enlla~aced hc~lefit in terms of appearance and of life-span (13). Clla~nbers (14) h,as reportthtf that a simil;+r cornhination restores the EE(; pnttern of the aged rat to\^-ards that of the niature adult.

I t seenled to us that our interpretation would be stre~agtheried if the 1,asic features of the pattern of salt and ater distribution in age could t )e rcprc)tlnced experimentally in young arsi11l:~ls. The required state of relative 1ninera1oc.o~- ticoid doininance could presunlably be re~~roduced by adnlinistering relativcl~ high anlounts of altlosteroile with little or 110 corticosterone, in the a1)scnc.c of ne~arohypophyseal function. This combination mas tested in the present experilncn t . I t slioultl be eari~>hasizecI that this s t u d j ~ n as iiot concerned 1i.i t h the n hole cora~plex of ageing but only ~vith one of the processes basic to it.

Methods The preparation of aniinals with diabetes i~isipidus kcis bteri dcscri1)etl in the

previous papers of this series. );rot11 the pool of animals so prcparetl a group with a high rate of water turnover \\.as selected :end adrenal<~ctornizecl on the first d a y of the experi~nent. 'They were given d-aIdosterone in o i l subcutaneousIy a t :a dosage of 2.5 pg/rat (clpprosimately I 0 pg,/lQO g) 6 d a j ~ s each week throughout the experiment. This was give11 together wit11 10 pg of a saline suspcnsiora of corticosteronc: per 100 g in the first half of the experi~nent, but cortic-osteroalc 14 :is disco~itirlucd for the last half, when it was felt that its presence naerely iri a trace clc~sage might blur tBle issues. After 3 ~nonths the expcriine~it was teraninatcd m-ith tlitb usual partiti011 analyses for salt and water distribution.

Old rats of our SJ'F-derived colony were 2 years of age a t t h t~ start of the experiirlerlt and coiisecluentlqr 27 rnonths old at its c*onclusion. The J-oung intact c-ontrol rats 311~1 the ricurohj-~)oplzysectoia~ized adrc~l<llec:to~ilize(l rats were ;~pproxiniatel!- 4 months old at the ~t i lht and 7 ~nonths old a t the end.

Results The experilllent consisted of three groups of rats. (;roup I coiasisted of intact

controls, group 2 of untrcrtted old rats, i~11d group 3 of r~curol~ypophj~sectoilized radrenalectomized rats ~naintained on I he relatively high aldosterone dosage. The pattern of salt and water distribution is presented in Table I.

'l'he usual changes of the pattern iri age were ol~scrved in group 2. 'l'hus, in the muscle, total Na content was i11cre:lsec-l as was extra-ellular ;tnd, to sonze

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Salt aud \v,~ter distribiltioil pattern in the aged rat coinpared to t h , ~ t i11duct.d iu the 11c-urohypoph~sccto1~1i~ed adreilalec.toini~ed rat maill taincd in relative miiieralocort icoid

do~nirl:*tace. Experiment 1 RB/2 - - -- - - - - -- - - - -- -- - .- - -- - -- - - -- - - -- - -

Group ::, ~ O L I I ~ ~

Group 1, (;roi~p 2, I>. I . rldrenex 4- yo1111g C O I I ~ rol old coiltrol aldostero~~e (25 ,ug/rat)

Plasma [Sa], ~neq/liter [I<], mec~/liter e.c.f., ~nl/l(K) g

Muscle (gastrocilemiu>), i<~t-frct: wet e.c..f., rnl/kg 76 4 3 3 . 7 124.2f10 I* 93 R f :3 O* Cell water, ml/kg 674.7% 2 $1 63'7.7f $1 7* fiCi7 1 f :$ 0 'Total water, ml/kg '751 l f 1 . 4 762 O3I1.6" 760 Xf 0 ti* Na,, nlec~/k:: 1 0 B6f 0 34 17 48f I .&* 13 O&O 43* Na,, meq/kg 6 . 7 2 f 0.59 7.6r(&O !I5 7 44fO 55 Total Na , meq/kg 17.39f 0 34 25 1 7 f l . X 6 * 20 44%0 44" Total K, ~ncq/kg 1 1 5 . 4 3 ~ 0 8 I04 7f 2 (i* I10 Bf 0.3*

A4vernge weight, g 404% 7 5.55%2!4 3 2 9 f 21

* p < 0.02 (groups 2, 3 vs. group 1). NOTE: D.I. = diabetes insiridus ; Adrenex = atlrenalectomizeil; e.c.f. = extrac.ellular flrlitl volnnir : Na, - c'xtl-a-

cellular Na; N a i = intracrllml~tr Ns; f indicates standard error.

extent, in tracellular Na 21s well. 'Z'his was associated with a corresporidiiig loss of total ~snuscle K which, of course, reflects a loss all~iost entirely frcsn~ cells. Water was shifted fro111 cells to environment, and a small increase in total water content was observed. In plresrna, the only notable change was an increasc 111 the extracclIular fluid volumlc.

Cl~anges identical 1t.i th those lvhich occur spontaneously in the aged nluscle were here reproduced in the ~~eurohypoph~~sec ton~izec~ adrenalecton~ized rztt maintained with aldosterone, although to a lesser degree. 111 the ~l lair i ta i~~ed animals a sigiiificarit iricre;tse in total ~lluscle sodiulll was observed due i~iostly to an increase in the extracellular but nleasurable also in the intr;~cellular compartmlent. Again, there was ii corresponding loss of total muscle I< and a shift of water fro111 cells to environment. As in the old anilraals, total water of the muscle wilS increased. The ~naintaincd young a~iimals differed from the old in that there was a slriall rise in plasm;i K concentration ;LI~ (% no expansion of the extracellu1:er fluid volume.

Discussion I t has been appreciated for a long tinre that :L disturbance in salt r~nd \i ilter

balance is a prorrlinent featurc of the ageing proc-ess. 111 11lan i t has been described in terrns of both water turnover and the urinary osrnolarity (15). In the rat i t <:an be measured by any ~riethocl designed to estitnlate the degree of m-ater turnover (12). This rilay range fro111 the deinonstration of an enhanced excretion of a salt and water load to the derilonstratiorl of a t-liminishetl concen- tratirzn of urinary sodiuin arid potassium. \Ve have described the syndrotlle as a

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432 CANAr>IAN JOUKNAL OF PIIUSIOLOGU AND PIIARMACOLOGU. VOL. 41, 1966

blunted type of diabetes insipidus to indicate that although it shares liaaany features in conlrnonl with diabetes illsipidus the indices of an enhanced rate of uTtm ter turnover are more subtle.

Clur first studies of the aged rat were directed tocvards deterinini~ag whether or not ncurohypophyseal fennetlo11 was, in fact, diminished. We found that the iaeurohypophysis is relatively unresponsive to a direct intracarc~tid osiliotic stiimtalation ( 5 ) ; others have found Ilistological evidence of diminished activity (7, 3 ) .

Insofar as adrerial cortical activity is concerned there is no direct evidence collceriiing the relative levels of mineralocorticoid and gluco~ort i~oid activity in the aged adrenal. In terms of salt and water distribution, however, the pattern is corlsistent witla that of illinera~ocorticoid doniinance. In this state there is an accuruulatioia of sodiurn and a corresponding loss of potassiuin in the bulk tissues of the B~ody, associated with a shift of water froram cells to environment. In the present experiment we have slilo\\-ra tlaat the pz~ttern of age can to some extent be reproduc:ed in the young neurol~ypoplrysectotnized adrcnalectomized rat by nini~ltaining the animal in relative aldosterone dominance. 'The amount of aldosterone used was not excessive (10 pg/BOO g) in terms of present estimates of the rriaintenauce recluiremealt for the rat (16).

'The sitasation a\-e have created does not wholly reproduce the pattern of age, nor is it to be expected that i t would. First, no vasopressin was given, so that the ~vatcr turnovcr levels in the maintained animals were well above those in the old animals. Secontl, the pa-trtic~llar horrnonal trcatnieiat which ave used is not the only one which could have produced the syndrome. 411 that is necessary is tllat the sotlium-accumuli~ting effect of aldosterone predoi~iiilate over the desalting effect of corkicosterone or of vasopressin (17). Third, the young rat maintained by an>- corntjination of horrnoraes differs ira allnost all other respects l ro~n the ageti aniriaal for, of course, ageing does not consist of one single set of distort ions but of their naultiple combiiaations.

Considering these limitations, the experinlent reported here has reproduced thc salt and water clistrilsution pattern of age with reasonx8,le laithfulness and supports the interpretation that the pattern in age is one of relative rnineralo- corticoid do~ni~lance.

Acknowledgment 'The d-aldosterorie used in this work was supplied through the courtesy of

Dr. C. IYalter AIurph y, Ciba Conlpa~ly Limited, AIontreal.

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