Fast feedback regulation of acth by cortisol

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1991. Vol. 15. pp. 523-529

FAST FEEDBACK REGUUTION

OF ACTH BY COKTISOL

K. RANGA RAMA KRISHNAN, JAHES C. RITCHIS,ANANTHN. NANEPALLI. WILLIAM SAUNDERS,SHtJNWRILI, SANJSR'JVENKAT~. CHARLES 8. NRMKROFF, AND BiiRNARDJ. CARROLL Department of Psychiatry Duke Wniversity Kedical Center, Durham, NC, USA. (Final form, November f99D)

Krishnan, K. Ranga Rama, James C. Ritchis, A. N. Nanepalli, Willi%m S%undars. Shun Wei Li, Sanjeev Venkatayaman, Charles B. Nemeroff and Bernard J. Carroll: Fast feedback regulation of ACTH by cortisol. Prog. Nauro-Paychopharmacol.& Biol Pschiat. 1991, 15('0:523-529. 1.

2. 3.

Fast feedback regulation of ACTH by cortisol has not been well studied in humans. The authors studied the existence and characteristicsof fast feedback regulation in normal humans. Hydrocortisone hemisuccinate was infused at two different rates: 6 s&/hour and 12 m&/hour for two hours. The studi8s did not demonstrate the existence of fast feedback regulstion of basal ACTH concentration by cortisol in man. Further, the response was variable and the rate sensitive character was difficult to demonstrate.

Kevwords: adrenocorticotropin,cortisol, fast feedback, humans. m: adrenocortiaotropin (ACTR), area under the curve (AUC), Hypothalamo-pituitary adrenal (HPA).

Several abnormalities of the hypothalamo pituitary adrenal system have been found in depression:

these include hyparsecretion of cortisol, loss of normal circcldianrhythm and

abnormal cortisol response to daxaaathaoone et al. 1978). Syndrome

(Carroll et al. 1976, S%ch%r et al. 1973, Sachar

These findings are in many ways rkin to the abnonuliti8s seen in Gushing's

(Voight et

al.

1985).

Recently three

types

of

feedback raguI%tion of

adrenocorticotrophfchormone (ACTH) by cortisol have been idsntified on the basis of animal andinfeedback.

studies (Keller-Woodand Dallmann, 1984). They are frst, intarm8diate and delayed Fast

feedback is rate sensitive, saturable and is seen within a few minutes of the

application of a rising glucocorticoid signal (Keller-Wood and Dallmann, 1984; Dallmann and Yates 1969; Jones et al. 1972). The concept of fast feedback arose mostly from experiments on the inhibition of stress-induced ACTH secretion (Jones st al. 1972, K%neko and Hiroshige, 1978). The concept was extended on the basis of h

w

studies which provided evidence for

fast feedbeck inhibition of stimulated ACTH secretion (Kan8ko and Riroshige, 1978; and Jones et al. 1974). However, as suggested by Zimsermann et al. (1972), stress and non stress induced ACTR secretion may be dissociated on the basis of sensitivity to n8gatiV8 steroid feedback, so conclusions from Stress experiments may not apply to th8 regulation of basal secretion of ACTR (Zimmerman and Critchow, 1972). Data from normal human subjects on the existence of a rate sensitive f%st feedback are scarce and controversial (Reader et al. 1982, Carr et al. 1984, Reus and Dallmann. 1938). Reader et 529

524

K. R. R. Krishnanetal

al. (1982) in a study of two normal volunteers, using a bioassay for ACTH and a fluorimetric method for measuring cortisol, showed the existence of fast feedback with 2 rag,3 mg, 6 mg and 12 mg/hour rates of cortisol infusions. They noted a rapid decline in ACTH concentration 45 to 60 minutes after the onset of infusion at the 3 mg/bour rate and after 15 to 30 minutes at the 6 mg/hour rate.

However, the assay methods and the fact that just two subjects were

studied limit the generalizability of this study.

The second study by Reus et al. (1938)

employed a similar cortisol infusion rate of 5 mc~Kg/minute and in a comparison of four depressed patients with four normal controls failed to demonstrate the predicted negative correlation coefficients between cortisol and ACTH concentrations. Further, their data suggested a high variability in both rate of cortisol rise and of ACTH decline. Carr et al. (1984) in a similar study stated that a decline in ACTH concentration but not beta endorphin concentration occurred 15 minutes after the onset of a cortisol infusion. They studied only three control subjects and ten depressed patients and suggested that some depressed patients may exhibit rises in plasma ACTH during cortisol infusion. However, the validity of their results is open to question in view of the small number of control subjects and the low sensitivity of the ACTH assay used. As a prelude to studying fast feedback in patients with depression, we decided first to establish whether fast feedback was a robust and reproducible phenomenon in normal humans (using a highly specific and sensitive assay for ACTH) and, if so, which rates of infusion would best allow us to study it. Methods Subiects Fourteen normal, healthy, male volunteers (14) who were free of after obtaining informed consent.

all

medications

were studied

The volunteers were carefully evaluated to rule out any

medical disorders, psychiatric disorders or substance abuse.

The study was done at the

Clinical pesearch Unit at Duke University Medical Center.

Hydrocortisone hemisuccinate (Solvcortef,Upjohn). Study Desien When subjects were studied more than once, the infusions were conducted a week apart. The study was done at the Clinical Research Unit at Duke University Medical Center. intravenous catheters were placed, one in each forearm, at 0800 h.

Two

Normal saline was infused

through one catheter for one hour followed by hydrocortisone hemisuccinate for 120 minutes (Solucortef Upjohn). The infusions were given using an infusion pump (IVAC Corporation, San Diego, CA). Blood was collected through the other catheter at -30, -15, 0, 5, 10, 15, 30, 45, 60, 75, 90, and 120 minutes after the start of Solucortef administration. The hydrocortisone infusion rates were 6 mg/hr (N-6). 12 mg/hr (N-6). A control group (N-6), from whom blood was collected at the same time points after infusion of saline was also studied.

Various doses

ofhydrocortisone hemisuccinate (Solucortef)were dissolved in the same volume of normal saline so that the volume administered per unit time was kept constant.

Fast feedba~kregula~on

ofACTH

525

by cortisol

Assessment Instruments: Laboratorv Instruments Cortisol was measured by a competitive protein binding method (Ritchie et al. 1985). The interassay coefficient of variation (C.V.) was 12.6% and intraassay coefficient of variation was 5.6%. ACTH was measured by radioimmunoassay(Krishnanet al. 1986). The primary antiserum for this assay was produced in our laboratory by immunizing rabbits with the thyroglobulin conjugate of ACTH 11 to 24. This fragment was

chosen

to maximize the epitope of the anti-serum

to bioactfvity (steroidogenicactivity) of ACTH 1-39 and to reduce cross reactivity with other pro-opfomelanocortin derived peptides. The epitope of the antiserum was in the 18-24 region of the ACTH molecule. The sensitivity of the assay (minimal detectable quantity) for 1 ml of plasma is 1 pg/ml (0.22 pmol/L). The interassay C.V. was 12% and the intra-assay C.V. was 7%. Mean basal plasma ACTH concentration at 8:00 a.m. with this assay was 4.41

pmol/L and mean

plasma ACTH concentration at 8:00 a.m. after the administration of 1 mg of dexamethasone at 1l:OO p.m. the night before was 0.22 pmolfl. Data Analvsis The two groups which received hydrocortisone hemisuccinate were independently compared to the control groups using 't' tests.

To,assess the possibility of fast feedback in ACTH due

to the cortisol response, the slope of the response for each hormone was calculated using five time intervals: O-120 minutes, O-60 minutes, O-45 mfnutes, O-30 minutes, and O-15 minutes. Spearman correlation coefficients were calculated between the slopes for cortisol and the slopes for ACTH. In addition, the correlationbetween peak levels, maximum change, area under the curve and these slopes were calculated. If fast feedback was present, one would expect a significant negative correlation, i.e., the rise in cortisol would parallel a decrease in ACTH. Results Fig la and lb, and Tables 1 and 2 show the results.

20

16

6

_

0

0

16

SO

60

46

76

90

TIME (minutes) -

Pm

...A..

6

MQ

- 4 .12 MG

Fig la. Mean plasma ACTH for the placebo (PBO) 6 mg and 12 mg groups.

806

120

K. R. R. Krlshnan et aL

526

O/11111111 0 l6

60

60

46

76

SO

lo6

lZ0

TIME (mhutes) Fig lb.

Cortisol

PBO

concentrations

,,,“... 6 MQ

for

the placebo

Table

-*-Pm (PBO) 6 mg and 12 mg groups.

1

Mean + S.D. of Plasma Cortisol and ACTK Concentrations At Each Time Point in the Placebo Group, 6 MG and 12 MG Groups Placebo

Time (Minutes) CORTISOL

ACTH

* (p)

0 5 10 15 30 45 60 90 120

11.7 10.3 11.3 10.8 10.5 9.8 9.8 9’.2 10.0

0 5 10 15 30 45 60 90 120

9.91 14.7 13.4 10.5 12.5 10.7 10.5 6.6 7.8

The ssme subjects Represents

(N=6)

+ f + + f + + + +

3.9 3.5 4.2 4.3 3.4 2.8 2.7 2.0 2.1

t + f ? + + f f +

4.0 19.5 18.9 11.6 14.4 11.7 5.0 3.1 4.1

6 mg*(N=6) 17.9 17.4 16.1 19.0 21.4 25.2 25.4 25.9 25.3

+ + f + f f f f f

9.2 6.8 3.1 5.1 5.0 6.8 7.3 8.8 7.7

1.5.6 13.2 18.0 19.1 15.1 14.9 11.5 7.6 10.5

f + t t f f f + f

9.8 13.6 20.1 24.3 15.4 18.5 14.1 8.6 12.6

(P)

(.047) (.05) (.013) (.0012) (.0017) (.0024) (.0067) (.0039)

12 mg(N=6) 15.6 22.4 23.9 26.4 30.2 34.3 37.4 35.6 36.9

f + + + + + + + +

3.2 7.3 3.6 4.3 2.1 8.9 7.0 4.4 7.0

13.5 0.6 13.1 12.4 11.6 17.0 15.5 15.2 14.0

+ + -+ +t ? t f +

10.6 0.4 15.3 15.1 8.8 20.2 27.3 26.7 23.0

had 6 mg and 12 mg doses.

the p-values

for

t-tests

comparing each active

dose to placebo.

(P)

(.0045) (.0002) (.OOOl) (.OOOl) (.0007) (.OOOl) (.OOOl) (.OOOl)

Fast feedback regulationofACTH

527

by cortisol

Table 2 Mean + S.D. of Peak, Max, and Area Under the Curve for Plasma Cortisol and ACTH Concentrations in Three Groups: Placebo, 6 MG Dose, and 12 MG Dose

Variable

Placebo

Peak Cortisol

Level

27.1 f

7.6

(.005)

40.6 i

7.3

(.0001)

1.7 f

3.2

9.2 f

4.7

(.oO88)

25.0 -c

7.4

(.0002)

f

511.4

(.OOOt)

22.0 t

25.6

**

2800.1

f

805.0

(.0035)3964.4

18.8 f

17.4

24.3 f

22.4

8.8 f

16.8

8.7 f

14.1

Maximum Change From Baseline (ACTH) Area Under the Curve (ACTH)

1170.6 f 669.6

1479.1

8.6 ?.

f 1664.4

la. and lb. show the mean plasma

6 mg and 12 mg groups. point

are significantly

greater

There was no difference under

the

curve

(AUC)

groups.

Both

cortisol

concentrations

concentration

the

p-O.012

The plasma

cortisol

in plasma

ACTH concentrations.

for plasma

cortisol

12 mg

and ACTH

group have

than the placebo

cortisol

were

also higher

However,

plasma ACTH concentrations. for plasma ACTH and plasma

peak,

Using

higher

AUC

the time period

for each and Max

studied.

Max and area

of these

change

between

negative

three

in plasma

the peak cortisol

than for 6 mg (p-0.005).

The Max

to the 6 mg (p-O.015 groups

correlation

at any of the five intervals,

and O-15 minutes.

and ACTH at each time

't' test,

for the 12 mg group compared

There was no significant

for the placebo,

2 shows the peak

a paired

there was no difference

cortisol

O-30 minutes,

Table

significantly

for the 6 mg and 12 mg groups

concentration

a higher

group.

all

concentrations

concentrations

for the 12 mg dose was significantly

respectively).

O-45 minutes,

ACTH and cortisol

were

than those for the placebo group throughout

6 mg and

and AUC for cortisol

parameters

Table 1 shows the mean f S.D. of plasma

in the three groups.

15.8

1710.3 f 2586.4

Using paired t-tests, the levels for the cortisol greater for 12 mg when compared to 6 mg.

Figures

(P)

3.1

1196.7 f 263.8

Peak ACTH Level

12 mg"*

(P)

13.4 +

Maximum Change From Baseline (Cortisol) Area Under the Curve (Cortisol)

(N=6)

between

O-120 minutes,

There was also no negative

peak, Max change and area under the curve for plasma cortisol concentration

and

in peak Max or AUC the slopes

O-60 minutes,

correlation

between

for any of the ACTH

slopes. Discussion Our

studies

concentrations character

do

not

suggest

by cortisol

has been

difficult

in man.

existence Further,

of

fast

the response

feedback

regulation

is variable

of

basal

ACTH

and the rate sensitive

to demonstrate.

Fehm et al. (1979) demonstrated using supramaximal

the

fast, rate sensitive

doses of cortisol.

feedback

In these subjects,

in hypoadrenal

resting ACTH secretion

human

subjects

is very high

K. R. R. Krishnan et al

528

and the demonstration feedback 1978).

primarily

The only studies

out in dogs. cortisol

Both

in dogs

Our study,

using

regulation

of basal

or stress

earlier

ACTH

(Krishnan

plasma

secretion

such that plasma

corticotrophin

and maximal

lack change

Whether

of basal

a

concentrations significance

It is possible

between

the role of non-ACTH between

in ACTH concentrations

of ACTH by

were kept in

of fast feedback

that fast feedback

regulation

is of significance

relationship

relationship

ACTH were carried

1982).

at the 12 mg/hr dose is similar

of

fast

and Hiroshige,

regulation

fast feedback

secretion

demonstrated

(Kaneko

feedback

cortisol

in humans.

positive

et al. 1988) and may reflect The

fast

about the physiological

by cortisol

which

release

regulation

to demonstrate

rates of infusion.

induced

studies

ACTH

1978; Cowan and Layberry,

concentrations

cortisol.

concentrations

unable

The lack of a significant

and basal plasma

of

ACTH

Animal

induced)

looked at fast feedback

were

of cortisol

at higher

study.

(stress

range, raises questions

may be observed of stimulated

which

studies

doses

much easier.

stimulated

(Cowan and Windle,

the physiological

further

of fast feedback

examined

by cortisol

in humans

basal plasma

merits

cortisol

to what we had reported

mechanisms

maximal

may also reflect

in the control

change

in

cortisol

such mechanisms.

Conclusions Our

study

phenomenon

of

fast

feedback

is too inconsistent

HPA dysregulation

in normal

subjects

to use as a dependent

among depressed

under

basal

variable

conditions

suggests

in the investigation

that

the

of possible

patients. Acknowledsement

This study was supported RR0030

General

Clinical

in part by Clinical Associate

Research

Center

Program

Physician

Award Supplement

to NIHMHN-

and by MN-39593.

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J. (1976) Neuroendocrine regulation CARROLL, B. J. CURTIS, G. C. andMENDELS, Limbic system-adrenocortical dysfunction. Arch Gen Psychiat =:1039.

Rate

in depression:

COWAN, T. S. and LAYBERRY, R. A. (1982) Feedback suppression of ACTH secretion by cortisol in dogs: lags after large signals equal those following very small signals. Canad J of Physiol and Pharmacol fi:1281. COWAN, T. S. andWINDLE, W. T. (1978) Progressive suppression of adrenocorticotropin secretion in resting adrenalectomized dogs by low stepwise infusions of cortisol. Endocrin 103:117. DALLMAN, M. and YATES, F. E. (1969) Dynamic asymmetries in the corticosteroid feedback pathway and distribution metabolism binding elements of the adrenocortical system. Ann N Y Acad Sci =:696. FEHM, H. L. VOIGHT, K. H. KUMHER, integral corticosteroid feedback Invest 63~247.

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529

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Inquiries and reprint requests should be addressed to:

Dr. K. Ranga Rama Krishnan Department of Psychiatry Duke University Medical Center Box 3215 Durham, NC 27710