Changes in Adrenocortical Function Precede the Onset of ... - CiteSeerX

BIOLOGY

OF

REPRODUCTION

Changes

17, 733-737

(1977)

in Adrenocortical

Estrus

in Rats

Function

Exposed JUDITH

Department

Precede

to Constant

of Persistent

Before

Puberty

A. RAMALEY

of Physiology

University

the Onset

Light

and

of Nebraska Omaha,

Biophysics,

Medical

Nebraska

Center,

68105

ABSTRACT The onset after

purpose

of

this

study

was

of persistent estrus in rats weaning age (S-LL-shift

to determine

whether

undergoing exposure to LL from a 14

changes

in adrenal

function

precede

to constant light either from birth h light, 10 h dark photoperiod).

the

(LL) or Serum

corticosterone shifts in response to a two minute ether stress administered at 0800 h at 25, 50 or 100 days of age were compared in LL, S-LL and LD (reared from birth in 14:10) rats. The patterns of serum corticosterone were comparable in all three groups at 25 days of age. At 50 days of age, the S-LL rats had higher basal corticosterone and showed an earlier stress response which persisted for 2 h while the other two groups showed a slower response that peaked at the 30 mm sample period and then fell to baseline by 60 mm. At 100 days of age, the LD rats continued to show a slower rise and more rapid fall while both LL exposed groups had higher basal levels, a more rapid response and persistent elevation past 60 mm. This difference in the appearance of a deviant stress pattern was associated with the onset of persistent estrus which began at 100 days of age in the S-LL rats and at 150 days in the LL rats. It therefore appears that changes in adrenocortical function precede the loss of ovulatory cycles in both LL-reared groups and that these changes (elevated basal corticosterone and a prolonged stress response) emerge earlier in the S-LL groups which developed persistent estrus earlier.

of

INTRODUCTION

Changes in adrenal cortical function have been shown to influence the onset of puberty and the maintenance of adult ovulatory cycles (reviewed in Ramaley, 1974; Rogers et al., 1974). Recently I reported that basal levels of serum corticosterone onset of persistent estrus in anovulatory low dose (Ramaley, was to function cycles

estrus

of

in by

to

a two

different

constant

to the

ether

that

will

rates. of

The

persistent (1973a)

light

responses after birth

of a (lOpg)

model

from

birth

more slowly than rats at 60 days of age. When

light

as young

adults,

estrus

within

4 weeks

rats while

enter placed placed

developed a high

birth

in for

compared

onset

MATERIALS

still

not

later.

in

In

a

that animals placed in LL anovulatory later than rats days of age, but earlier than

birth required

opening weaning

were

7 months

to stress

prepubertally

in age, of

LL. Therefore, the study,

rats and

placed in the results

persistent

AND

estrus

and LL at comin

the

METHODS

Adult rats were obtained from Sasco Laboratories, Omaha, Nebraska and were bred in our animal colony in a 14 h light, 10 h dark photoperiod (light on 0500 h). The females were allowed to deliver either in 14:10 (LD) or were placed in constant light (LL) at two weeks gestation. The litters were culled one day after birth to 8 females. Where necessary, females were shifted between litters to make up this number. At weaning (21 days of age) the animals were housed two per cage in hanging stainless steel cages. One group remained in LL throughout the experiment, one group was placed in LL at weaning and one group was placed in LL at 60 days of age. All animals were inspected daily for vaginal opening and daily smears by lavage were begun on that day and continued throughout the study. Persistent estrus was defined as 5 consecutive days of a fully cornified vaginal smear. Corticosterone

in rats

to persistent chosen

were vaginal or at

pared to the two groups.

this study of adrenal

stress

lead

from time

from

estrus

I found became at 60

LL

rats reared reduce the

was

estrus by constant found that rats reared

estrus light

Accepted Received

of

in LL

vaginal

study, at weaning placed in

the loss of ovulatory serum corticosterone

minute

in conditions at

administration proprionate

reared

pilot

changes in the precede the rats rendered

The purpose an examination

rats prior examining

the initiation light. Hoffmann in

the neonatal testosterone

1976). continue

response placed

by

rats

persistent

persistent in constant in constant persistent percentage

July 7, 1977. January 31, 1977.

733

RAMALEY

734 regimen

1. Effect of light

TABLE

on time of vaginal

opening. Time

May

In LL from birth in LL at weaning Reared in LD

Data

are expressed

‘Values

as mean

are significantly

Litter

1

34.3 34.1 37.6

±

2

± 1.2

33.0

± 1.6

± 0.4

33.9

t

39.2

±

1.0

±

error

from

for

summer

each groups

procedure (Ramaley, and interassay variability based on several determinations of a serum pool have been 5 percent and 8 percent respectively. Means for vaginal opening were compared by a two way ANOVA. Corticosterone values after stress were compared by Duncan’s multiple range test. In each series some animals were followed through to 200 days of age to determine the onset of persistent estrus while others were killed by decapitation at 25, 50 or 100 days of age at various times after a two minute ether stress administered at 0800 h. was

measured

Recently

1972).

by a fluorometric the intraassay

of Vaginal

Constant Photoperiod

LL

Light

Opening

(LL) or an Alternating (LD, 14 h Light, lob

Vaginal opening than in animals

2). alter

Exposure the onset

result been were

in Rats

was earlier housed in

in

Dark)

in rats reared 14:10 (Tables

to LL before weaning of puberty beyond that

did seen

of LL exposure after weaning, noted before (Fiske, 1941). Two studied in the summer (May-June)

two in the winter (November-December) in each case, vaginal opening was summer

(P