8
EFFECTS OF EXOGENOUS ADRENOCORTICOTROPIC HORMONE (ACTH) UPON PITUITARY ACTH CONCENTRATION AFTER PROLONGED CORTISONE TREATMENT AND STRESS * By DONALD A. HOLUB,t JULIAN I. KITAY t AND JOSEPH W. JAILER (Prom the Departments of Medicine, Obstetrics and Gynecology, Columbia University College of Physicians and Surgeons, and Presbyterian Hospital, New York, N. Y.) (Submitted for publication June 10, 1958; accepted October 9, 1958) Symptoms and metabolic abnormalities closely resembling those of hypoadrenalism have been reported following cessation of prolonged treat- ment with adrenal steroids (1-5). Sudden death following surgery has been reported in association with this syndrome and has been ascribed to fail- ure of the hypothalamic-pituitary-adrenal system to respond to stress (6-9). Since prolonged ad- ministration of corticosteroids produces adrenal atrophy in both man and laboratory animals (7, 10, 11), this failure has been attributed to adrenal insufficiency. Exogenous corticotropin (ACTH) will repair or maintain normal adrenal weight in the cortisone-treated animal (12). Consequently the addition of ACTH in various dosage sched- ules has been advocated for the purpose of main- taining or restoring normal adrenal responsive- ness to stress (5, 13-16). The efficacy of such combined therapy is not firmly established. In addition to producing adrenal atrophy, chronic treatment with steroids results in decreased pituitary ACTH content (17, 18). The failure of steroid-treated subjects to respond to stress may therefore reflect pituitary ACTH insufficiency rather than, or in addition to, adrenal insufficiency. ACTH administration, on the other hand, has been shown to increase pituitary ACTH content in the intact rat, despite stimulation of secretion of endogenous steroids (18). For this reason ACTH therapy has been studied in the cortisone- treated animal to determine whether such adjunc- tive therapy is capable of modifying the pituitary ACTH depletion which follows steroid adminis- tration, and whether it can enhance the pituitary response to stress. * Supported by a grant from the National Institutes of H4ealth (A-195). t Fellow of The National Foundation. t Commonwealth Fund Fellow in Medicine. METHODS All experiments were performed in male rats of the Sherman strain (100 to 140 Gm.), kept in a constant temperature room for at least one week prior to use. The diet consisted of Purina Laboratory Chow and water ad libitum. Three treatments were employed as follows: Physiological saline (0.1 ml.) was injected subcutane- ously once daily; 4 U.S.P. units of ACTH gel (0.1 ml.) was injected subcutaneously once daily; 2.5 or 5 mg. of cortisone acetate (either 0.1 or 0.2 ml.) was injected subcutaneously once daily. When adrenalectomized rats were used they were injected immediately after opera- tion and were given 1 per cent saline in the drinking water. Four experiments were performed as follows: Experiment 1. Intact rats were injected with 5 mg. of cortisone for 7 days. Groups of four animals each were sacrificed at 1, 2, 4, 7 and 10 days after the last injection. The pituitary glands of each group were pooled and extracted for ACTH. Intact rats injected with saline for 7 days and sacrificed 24 hours after the last injection served as a control group. -Experiment 2. Adrenalectomized rats were injected with either 5 mg. of cortisone or 4 U.S.P. units of ACTH plus 5 mg. of cortisone for 7 days. A control group received saline. The pituitary glands were extracted in- dividually for ACTH 24 hours after the last injection. Experiment 3. Intact rats were divided into five groups and treated according to the following 10 day schedule: Treatment 1 Treatment 2 Group (seven days) (three days) 1 (control) Uninjected Uninjected 2 Cortisone, 2.5 mg. Saline 3 Cortisone, 2.5 mg. plus Saline ACTH, 4 U 4 Cortisone, 2.5 mg. ACTH, 4 U 5 Cortisone, 2.5 mg. plus ACTH, 4 U ACTH, 4 U Twenty-four hours after completion of the inj ection schedule the animals in each group were subdivided into unstressed and stressed subgroups. Four hours after a scalding stress (19), both the unstressed and stressed subgroups were sacrificed simultaneously. This interval was chosen on the basis of previous experiments in which normal rats were scalded and sacrificed 1, 2, 4, 8 and 291

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Page 1: ADRENOCORTICOTROPIC (ACTH)dm5migu4zj3pb.cloudfront.net/manuscripts/103000/103801/... · 2014. 1. 29. · EFFECTS OF EXOGENOUS ADRENOCORTICOTROPIC HORMONE (ACTH) UPON PITUITARY ACTH

EFFECTS OF EXOGENOUSADRENOCORTICOTROPICHORMONE(ACTH) UPONPITUITARY ACTH CONCENTRATIONAFTER

PROLONGEDCORTISONETREATMENTAND STRESS*

By DONALDA. HOLUB,t JULIAN I. KITAY t AND JOSEPHW. JAILER

(Prom the Departments of Medicine, Obstetrics and Gynecology, Columbia University Collegeof Physicians and Surgeons, and Presbyterian Hospital, New York, N. Y.)

(Submitted for publication June 10, 1958; accepted October 9, 1958)

Symptoms and metabolic abnormalities closelyresembling those of hypoadrenalism have beenreported following cessation of prolonged treat-ment with adrenal steroids (1-5). Sudden deathfollowing surgery has been reported in associationwith this syndrome and has been ascribed to fail-ure of the hypothalamic-pituitary-adrenal systemto respond to stress (6-9). Since prolonged ad-ministration of corticosteroids produces adrenalatrophy in both man and laboratory animals (7,10, 11), this failure has been attributed to adrenalinsufficiency. Exogenous corticotropin (ACTH)will repair or maintain normal adrenal weight inthe cortisone-treated animal (12). Consequentlythe addition of ACTH in various dosage sched-ules has been advocated for the purpose of main-taining or restoring normal adrenal responsive-ness to stress (5, 13-16). The efficacy of suchcombined therapy is not firmly established.

In addition to producing adrenal atrophy,chronic treatment with steroids results in decreasedpituitary ACTHcontent (17, 18). The failure ofsteroid-treated subjects to respond to stress maytherefore reflect pituitary ACTH insufficiencyrather than, or in addition to, adrenal insufficiency.ACTH administration, on the other hand, hasbeen shown to increase pituitary ACTH contentin the intact rat, despite stimulation of secretionof endogenous steroids (18). For this reasonACTHtherapy has been studied in the cortisone-treated animal to determine whether such adjunc-tive therapy is capable of modifying the pituitaryACTH depletion which follows steroid adminis-tration, and whether it can enhance the pituitaryresponse to stress.

* Supported by a grant from the National Institutes ofH4ealth (A-195).

t Fellow of The National Foundation.t Commonwealth Fund Fellow in Medicine.

METHODS

All experiments were performed in male rats of theSherman strain (100 to 140 Gm.), kept in a constanttemperature room for at least one week prior to use.The diet consisted of Purina Laboratory Chow and waterad libitum. Three treatments were employed as follows:Physiological saline (0.1 ml.) was injected subcutane-ously once daily; 4 U.S.P. units of ACTHgel (0.1 ml.)was injected subcutaneously once daily; 2.5 or 5 mg. ofcortisone acetate (either 0.1 or 0.2 ml.) was injectedsubcutaneously once daily. When adrenalectomized ratswere used they were injected immediately after opera-tion and were given 1 per cent saline in the drinkingwater.

Four experiments were performed as follows:Experiment 1. Intact rats were injected with 5 mg.

of cortisone for 7 days. Groups of four animals eachwere sacrificed at 1, 2, 4, 7 and 10 days after the lastinjection. The pituitary glands of each group werepooled and extracted for ACTH. Intact rats injectedwith saline for 7 days and sacrificed 24 hours after thelast injection served as a control group.

-Experiment 2. Adrenalectomized rats were injectedwith either 5 mg. of cortisone or 4 U.S.P. units of ACTHplus 5 mg. of cortisone for 7 days. A control groupreceived saline. The pituitary glands were extracted in-dividually for ACTH24 hours after the last injection.

Experiment 3. Intact rats were divided into five groupsand treated according to the following 10 day schedule:

Treatment 1 Treatment 2Group (seven days) (three days)

1 (control) Uninjected Uninjected2 Cortisone, 2.5 mg. Saline3 Cortisone, 2.5 mg. plus Saline

ACTH, 4 U4 Cortisone, 2.5 mg. ACTH, 4 U5 Cortisone, 2.5 mg. plus ACTH, 4 U

ACTH, 4 U

Twenty-four hours after completion of the inj ectionschedule the animals in each group were subdivided intounstressed and stressed subgroups. Four hours after ascalding stress (19), both the unstressed and stressedsubgroups were sacrificed simultaneously. This intervalwas chosen on the basis of previous experiments in whichnormal rats were scalded and sacrificed 1, 2, 4, 8 and

291

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DONALDA. HOLUB, JULIAN I. KITAY AND JOSEPH W. JAILER

24 hours after stress; the maximal depletion of pituitaryACTHwas observed to occur at 4 hours. The pituitaryglands of each subgroup were pooled and extracted forACTH.

Experiment 4. Intact rats were divided into two groups

and treated according to the following 10 day schedule:

Treatment 1 Treatment 2Group (seven days) (three days)

1 (control) Cortisone, 2.5 mg. Saline2 Cortisone, 2.5 mg. plus Saline

ACTH, 4 U

Twenty-four hours after the last injection the animalsin each group were subdivided into unstressed andstressed subgroups. Four hours after the scalding stress,both the unstressed and stressed subgroups were sacri-ficed simultaneously. The pituitary glands of each sub-group were pooled and extracted for ACTH.

The pituitary glands of the experimental animals were

extracted for ACTHaccording to the method of Birming-ham and co-workers (20). These extracts were sub-sequently assayed for ACTH by incubation with ratadrenal slices in vitro by a modification of the method ofSaffran and Schally (21) previously described (18).The pituitary extracts of the appropriate control animalswere each assayed against a standard ACTH prepara-

tion. The absolute potencies of these control extracts are

expressed as concentration of ACTH per mg. anteriorpituitary tissue, and are included in Tables I, II and III.The pituitary extracts of the appropriate control animalsthen were employed as "house" standards in each experi-ment and assigned arbitrary potencies of 100 per cent.The pituitary ACTH concentrations in the various ex-

perimental groups are expressed as per cents of theirrespective controls. These percentages represent an arith-metic conversion of the mean log potency ratios obtainedand are presented in this form solely for purposes ofclarity. The absolute potencies of the various experi-

TABLE I

Changes in pituitary adrenocorticotropic hormone (A CTH)concentration in intact rats following termination

of chronic cortisone administration

Days Pituitaryafter last ACTHas % Combinedcortisone Number control adrenalinjection of rats level* weightt

mg.

Control 9 100t1 4 41 4 9§ 16 32 4 32 4 6§ 164 14 4 284 5§ 16417 4 47 4 8§ 16 4

10 4 58411§ 16 3

* Antilog M 1 2.303 Si (antilog M).t Mean standard error of the mean.t Absolute potency, 41 mUACTHper mg.

p S 0.01.

TABLE {I

Effects of concurrent ACTHadministration upon pituitaryACTHdepletion caused by cortisone in

adrenalectomized rats

PituitaryACTHas %

Number controlGroup of rats level*

Saline (control) 10 lootCortisone 7 62 ± 7tCortisone plus ACTH 8 74 :1 5t

* Antilog M+ 2.303 SI; (antilog M).t Absolute potency, 50 mUACTHper mg.t p . 0.01.

mental groups can be derived by simple multiplication ofthese per cents by the absolute potencies of the ap-propriate control extracts. Comparisons of differencesin ACTH potency were determined from the mean logpotency ratios and their respective log standard errors(M + si) and not upon the arithmetic percentages (anti-log M+ 2.303 sM antilog M) presented in the tables. Thedata are calculated in the form of concentration of ACTHper mg. anterior pituitary tissue. Total ACTH con-tent of the individual pituitary glands or pools was alsocalculated; however, in no instance do the values forACTHcontent deviate significantly from those presentedfor concentration. Individual pituitary glands in Ex-periment 2 were assayed once each and the pituitary poolsin Experiments 1, 3 and 4 were assayed two to fourtimes each. Statistical evaluations were calculated ac-cording to the methods of Bliss (22) and Snedecor (23).

RESULTSANDDISCUSSION

Although pituitary ACTHdepletion is known tooccur after prolonged steroid administration (17,18), no data are available concerning the durationof this depletion following cessation of the steroidtherapy. A significant fall in pituitary ACTHconcentration to 41 per cent of control occurs incortisone-treated rats 24 hours after the last in-jection when compared to saline-injected controls(Table I). However, the maximal depletion to28 per cent of control is not observed until 4 daysfollowing treatment. This possibly reflects a con-tinuing effect of cortisone due to delayed releaseof the steroid from the sites of injection. There-after, pituitary ACTH concentration increasesgradually with a significant increment above the4 day value noted 10 days after treatment. How-ever, the latter level is still significantly lower thanthe control value. Despite this repletion of pitui-tary ACTH, repair of adrenal atrophy has not

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EFFECT OF ACTH ON PITUITARY ACTH DEPLETION

TABLE III

Effects of exogenous ACTHupon pituitary ACTHconcentration after steroid withdrawal and stress in intact rats

Group Before stress After stress

Pituitary Pituitary CombinedTreatment Treatment No. of ACTHas % No. of ACTHas % adrenal

No. 1 2 rats control level*.t rats control level*4T weighti. 11

Experiment 3 mg.1 Uninjected Uninjected 8 100 (control)¶ 3 34 ± 10** 25 ± 1 (14)2 Cortisone Saline 3 39 ± 8** 3 20 ± 8** 14 ± 1 (9)3 Cortisone Saline 3 53 7** 3 18 ± 3** 17 ± 1 (9)

plus ACTH4 Cortisone ACTH 3 33 4 8** 4 22 ± 3 18 ± 1 (10)5 Cortisone ACTH 3 29 ± 4** 4 26 ± 4 21 4 1 (10)

plus ACTH

Experiment 4Cortisone Saline 4 100 (control) 5 40 ± 6**Cortisone Saline 4 81 4 12 6 43 4 7**

plus ACTH

* Antilog M± 2.303 Su (antilog M).t Calculation of significance of effects of treatment on pituitary ACTHbefore stress based on comparison with

unstressed, uninjected control group.t Calculation of significance of pituitary ACTHdepletion after stress based on comparisons with respective pre-

stress groups.§ Mean ± standard error.

Number of animals studied indicated in parentheses.Absolute potency, 63 mUACTHper mg.

** p . 0.01.

begun by the tenth day (Figure 1 ). These dataare compatible with the hypothesis that ACTHrelease is negligible after cessation of cortisonetreatment in the unstressed rat and that the ACTHsynthesized during this period is stored ratherthan secreted. Prolonged adrenal atrophy after

100

4

I-

50E000

IL-

0U.,0o Adrenol weight

- -0-. -----------

1 2 4 7 10DAYS AFTER LAST CORTISONE INJECTION

FIG. 1. CHANGESIN PITUITARY ACTH CONCENTRA-TION AND ADRENALWEIGHT FOLLOWINGCORTISONEAD-MINISTRATION FOR SEVEN DAYS

Graphic representation of data presented in Table I.

Note persistent adrenal atrophy despite evidence of ris-ing pituitary ACTHconcentration 10 days following lastcortisone injection.

cortisone therapy has been observed previously inthe rat (11) and also in man (7) ; in the latter re-port, adrenal atrophy (associated with- suddendeath following stress) was seen four and one-halfmonths after completion of steroid treatment.

Since prolonged cortisone administration re-sults in marked pituitary ACTH depletion, Ex-periments 2, 3 and 4 were designed to determinewhether ACTH treatment can alter the pituitaryACTHcontent of cortisone-treated rats. A sig-nificant fall to 62 per cent of control occurs inadrenalectomized rats treated daily with 5 mg.cortisone alone compared to saline-injected con-trols (Table II). Concurrent administration ofACTH results in a significant fall to 74 per centof the control level. The apparent difference of 12per cent, although not significant, suggests thatcombined therapy may partially overcome the de-pletion of pituitary ACTHconcentration inducedby very large doses of cortisone.

Various schedules of combined ACTH andsteroid therapy have been advocated for clinicaluse, e.g., administration of ACTH concurrentlywith steroids, ACTH following cessation of ster-oid treatment or ACTH both during and aftersteroid therapy. Consequently, these injection

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DONALDA. HOLUB, JULIAN I. KITAY AND JOSEPH W. JAILER

* UVSTRESSED* STRESSED

Trecfment I CONTROLCORTISONECORT.+ACTH CORTISONE CORT. +AC.THTreotmen/ 2 SALINE SALINE A CTH ACTH

FIG. 2. EFFECTS OF ACTH ADMINISTRATION UPON PITUITARY ACTHCONCENTRATIONIN CORTISONE-TREATEDRATS BEFOREAND AFTER STRESS

Graphic representation of data presented in Table III. Pituitary ACTHconcentrations are expressed as percentages of the control (uninj ected)unstressed subgroup.

schedules were followed in Experiment 3 in ad-dition to a group receiving cortisone withoutACTH and an uninjected control group (TableIII).

Animals treated with 2.5 mg. of cortisone with-out suplementary ACTH showed a depletion inpituitary ACTHconcentration to 39 per cent ofthe control level four days after steroid with-drawal. This decrease is consistent with that seenin Experiment 1, in which twice the dose of cor-tisone caused a fall in pituitary ACTH to 28 percent of the control level at a comparable intervalfollowing cessation of steroid administration.

No significant modification of this pituitaryACTHdepletion is observed in any of the groupsreceiving exogenous ACTHin addition to steroids.As in Experiment 2, however, the animals in-jected with ACTH and cortisone concurrently(Group 3) demonstrate a pituitary ACTH con-centration suggestively, but not significantly,greater than that obtained in animals given corti-sone alone.

The hypothesis that exogenous ACTH is capa-ble of improving the pituitary response of ratsstressed after withdrawal of cortisone was testedby determining the effects of a scalding stress onpituitary ACTH concentration (Table III, Fig-ure 2). Pituitary ACTHin uninjected rats afterscalding is 34 per cent of the control level, repre-

senting a fall of 66 per cent. On the other hand,the rats pretreated with cortisone (Group 2)show a poststress pituitary ACTHlevel of 20 percent, in contrast to the pre-stress level of 39 percent. This difference of 19 per cent, althoughstatistically significant, is less than one-third thatobtained in control animals. These findings sug-gest that ACTH release in response to stress ismarkedly reduced in rats during the period ofsteroid withdrawal.

It is assumed, in the above interpretation of thedata, that the markedly smaller difference betweenpre- and poststress pituitary ACTH concentra-tion in cortisone-treated rats primarily reflectsdiminished ACTH release. It is recognized thatpituitary ACTH levels at any moment representthe algebraic sum of the synthesis and the releaseof ACTH. Negative ACTH balance, i.e., a de-crease in pituitary ACTH level, may reflect re-

duced synthesis, accelerated release, or both con-

ditions occurring concurrently. Positive ACTHbalance, i.e., an increase in pituitary ACTH level,may represent accelerated synthesis, reduced orblocked release, or a combination of the two.When no change in ACTH balance is observedafter an experimental procedure, no conclusioncan be drawn as to the rates of synthesis and re-lease, other than that the two processes are inequilibrium. In Experiment 3 (Table III, Fig-

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EFFECT OF ACTH ON PITUITARY ACTH DEPLETION

ure 2), the fall in pituitary ACTHfollowing stressis over three times as great in the control animals(Group 1) as in the cortisone-treated rats (Group2). If one proposes that equal quantities ofACTHwere released by the two groups, then arate of synthesis three times normal must be as-sumed for the group pretreated with cortisone.This last assumption appears untenable, in viewof the data presented in Experiment 1 in whichtreatment with cortisone resulted in a severe de-pression of pituitary ACTH synthesis, as mani-fested by a striking and persistent decrease inpituitary ACTH content and adrenal weight.Therefore, a more appropriate explanation ap-pears to be that the threefold difference in nega-tive ACTHbalance between Groups 1 and 2 afterstress represents primarily a difference in theamounts of ACTH released by the two groups.The only assumption underlying this interpretationis that ACTH synthesis in the two groups isequivalent; the data of Experiment 1 indicate thatthis assumption is quite conservative. These con-siderations also apply to the discussion of the datawhich follow.

The rats pretreated with ACTH concurrentlywith cortisone (Group 3) also demonstrate a sig-nificant further reduction in pituitary ACTH asa result of stress. However, the change observeddoes not differ significantly from that obtainedin rats given cortisone alone (Group 2), and issimilarly much reduced in comparison to that ob-served in control animals. In contrast to the fore-going groups, rats injected with ACTHconsecu-tively (Group 4) or concurrently plus consecu-tively (Group 5) do not exhibit significant falls

in pituitary ACTH after the scalding stress.These data would suggest that ACTH therapy,when continued to the time of stress as in theselast two groups, actually inhibits the release ofACTHfrom the pituitary gland. The findings areconsistent with previous experiments (19) whichdemonstrated that administration of exogenousACTHprevented release of endogenous ACTHinresponse to stress, via an extra-adrenal mechanism.

Definite adrenal atrophy persists following with-drawal of cortisone (Table III, Figure 3). All ofthe groups receiving ACTHin addition to the cor--tisone show significant increments in adrenalweights, as would be expected. The most effectivemaintenance of adrenal weight is seen in thoseanimals receiving ACTHboth during and follow-ing cortisone treatment (Group 5). When themean adrenal weights are adjusted for variationsin body weight by analysis of covariance, thisgroup actually shows hypertrophy of the adrenalswhen compared to controls.' However, this groupmanifested the most significant inhibition of pitui-tary ACTH release in response to stress (videsupra).

Since the data suggest that concurrent adminis-tration of ACTH to the cortisone-treated animalincreases pituitary ACTH concentration follow-ing steroid withdrawal, a more precise experi-mental design was employed (Experiment 4),which involved a direct comparison of pituitaryACTH in the group receiving combined therapyto the group receiving cortisone alone, the latter

1 Adjustment of mean adrenal weights for variationsin body weight does not otherwise alter the significantdifferences depicted in Figure 3.

I-- -- -- - ---P

Treotmenl 1 CONTROL- CORTISONE CORT.+ACTHCORTISONE CORT+ACTHTreatment2 SALINE SALINE ACTH ACTH

'(.05< .05

<.05

FIG. 3. EFFECTS OF ACTHADMINISTRATION UPONADRENALWEIGHT INCORTISONE-TREATEDRATS

Means of the combined adrenal weights in the control and treatmentgroups of Experiment 3. Standard errors of these means are presented inTable III. Dotted lines indicate significant differences (at the 5 per centlevel of confidence) among the various mean adrenal weights.

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DONALDA. HOLUB, JULIAN I. KITAY AND JOSEPH W. JAILER

serving as control (Table III). No significantdifference between the pituitary ACTH concen-trations of the two groups is seen, however, andthe depletions in pituitary ACTHfollowing stressare significant and similar in both groups wheneach is compared to its unstressed control.

It would appear then that in the rat receivingprolonged steroid therapy the administration ofACTHdoes not prevent or ameliorate the deple-tion of pituitary ACTHwhich results after corti-sone. Nor is the diminished amount of ACTHreleased in response to severe stress increased bysuch therapy. The rat receiving ACTHup to 24hours before stress shows the blockading effect ofexogenous ACTHupon pituitary ACTH releasein response to stress (19). However, adminis-tration of ACTHdoes prevent or repair adrenalatrophy in steroid-treated animals. In view of theinhibition of ACTH synthesis and release whichhas been demonstrated in animals receiving eithercortisone alone, or combined treatment, the sig-nificance of this effect of ACTH is uncertain. Itis possible that, with the ACTH-induced preserva-tion of adrenal mass, the adrenal response to stressmay be normal during the period of steroid with-drawal, despite the severe reduction in ACTHre-lease. In the absence of data concerning adrenalsteroid production under these conditions, no con-clusions may be drawn concerning the adrenal re-sponse to stress. It should be emphasized thatmeasurement of pituitary, and not adrenal, re-sponsiveness to stress is the object of the presentexperiments.

The failure of exogenous ACTHto raise pitui-tary ACTH concentration in the steroid-treatedrat in the above experiments is in striking con-trast to the rise in pituitary ACTHseen followingACTH treatment in the normal or adrenalecto-mized rat (18, 19). The fall in pituitary ACTHafter cortisone treatment is thought to representinhibition of ACTH synthesis, and perhaps alsoinactivation of stored pituitary ACTH. Exogen-ous ACTH apparently is unable to reverse thesteroid-induced inhibition of ACTHsynthesis anddepletion of ACTHstores.

Uncautious extrapolations from these studiesto the clinical problems associated with steroidadministration and withdrawal are not warranted.It is important to note that the dosages of hor-mones used in these experiments, calculated on the

basis of body weight, represent amounts far in ex-cess of those usually employed in the treatment ofhuman disease. Moreover, important species dif-ferences may well exist between man and the ratinsofar as pituitary-adrenal physiology is con-cerned.

However, clinical observations by Kyle, Meyerand Canary (24) in patients with Cushing's syn-drome due to adrenal tumors correlate quite closelywith the present animal studies. Adrenal insuffi-ciency is frequently encountered following re-section of such neoplasms. This has been attrib-uted to the associated atrophy of the contralateraladrenal gland (25). Kyle's two patients, how-ever, manifested persistent adrenal hypofunctionfor one to two years postoperatively after cessa-tion of repeated courses of ACTH. AlthoughACTHwas capable of stimulating the adrenals toproduce normal levels of steroids, discontinuationof ACTH therapy was quickly followed by re-lapse into the hypoadrenal state. It was con-cluded, therefore, that the basic lesion in thesepatients was located in the pituitary gland ratherthan in the adrenals, since therapy directed at re-storing adrenal weight was incapable in itself ofreturning adrenal function to normal.

On the other hand, Bondy and co-workers (26,27) considered hypothalamic-pituitary-adrenalfunction to be normal in patients who had receivedprolonged ACTHand steroid therapy, despite thepresence of "steroid withdrawal" symptoms. Aconclusion of normal pituitary responsiveness wasinferred from a rise in plasma corticoid level fol-lowing the stress of hypoglycemia. The discrep-ancy between this conclusion and that obtained bydirect measurements in rats in the present studyperhaps may be explained by differences in thespecies and treatments employed. Final conclu-sions must await the development of techniques forthe direct evaluation of pituitary ACTH reservein man.

SUMMARY

1. P i t u i t a r y adrenocorticotropic h o r mo n e(ACTH) concentration is significantly depletedfollowing chronic administration of cortisone in therat. Persistence of adrenal atrophy despite par-tial repletion of pituitary ACTH levels 10 daysafter cessation of treatment suggests that ACTHrelease during this period is negligible and that

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EFFECT OF ACTH ON PITUITARY ACTH DEPLETION

newly-synthesized ACTH is stored rather thansecreted.

2. The steroid-induced depletion of pituitaryACTH concentration is neither prevented norameliorated by the addition of ACTHin a varietyof dosage schedules. Adjunctive ACTHadminis-tration does not modify the striking reduction inACTH release after stress which occurs in thecortisone-treated animal.

3. Adrenal atrophy following steroid treatmentcan be prevented or repaired by the administrationof ACTH. The significance of this action ofACTH is uncertain, in view of the derangementsin pituitary ACTH synthesis and release whichare observed to exist in animals receiving eithercombined therapy or cortisone alone.

ACKNOWLEDGMENTS

Weare indebted to Dr. C. J. O'Donovan of the UpjohnCompany, Kalamazoo, Mich., for supplies of ACTHgeland cortisone acetate. Miss Myra Feder provided ex-pert technical assistance.

REFERENCES

1. Forsham, P. H., Thorn, G. W., Frawley, T. F., andWilson, L. W. Studies on the functional state ofthe adrenal cortex during and following ACTHand cortisone therapy (abstract). J. clin. Invest.1950, 29, 812.

2. Sprague, R. G., Mason, H. L., and Power, M. H.Physiologic effects of cortisone and ACTH 'inman in Recent Progress in Hormone Research,G. Pincus, Ed. New York, Academic Press Inc.,1951, vol. 6, p. 315.

3. McIntosh, H. W., and Holmes, C. B. Some evidencesuggesting the suppression of adrenocortical func-tion by cortisone. Lancet 1951, 2, 1061.

4. Calkins, E., Bauer, W., Engel, L. L., and Carter, P.Metabolic and endocrinologic consequences ofabrupt cessation of long-term cortisone therapy inrheumatoid arthritis (abstract). J. clin. Endocr.1955, 15, 856.

5. Arlotti, 0. Steroid withdrawal syndrome. Minervamed. (Torino) 1957, 48, 4143.

6. Fraser, C. G., Preuss, F. S., and Bigford, W. D.Adrenal atrophy and ireversible shock associatedwith cortisone therapy. J. Amer. med. Ass. 1952,149, 1542.

7. Salassa, R. M., Bennett, W. A., Keating, F. R., Jr.,and Sprague, R. G. Post-operative adrenal corti-cal insufficiency: Occurrence in patients previouslytreated with cortisone. J. Amer. med. Ass. 1953,152, 1509.

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