BIOLOGY

OF

44, 292-298

REPRODUCTION

Effect

of Aspiration

Function,

(1991)

of the

and Peripheral l(

Section

on Luteinization,

Gonadotropin

Concentrations

W. M.

RAND,2

Health,2

Tufts

de Recherche Centre

School

Agronomique,3 Tours,

Luteum

in the Mare

of Veterinwy 19348

of Medicine,

Station

de

Corpus

E. PALMER3

School Pennsylvania

Square,

University

de Recherches

and

of Pennsylvania

Studies,’ University Center, Kennett

of Community National

Follicle

Bolton

New Institut

Plasma

HINRICHS,’

of Reproductive

Department

Preovulatory

Boston,

de Physiologie

Nouzilly

Medicine

02111

Massachusetts

de Ia Reproduction

37380,

France

an inhibiting

effect

ABSTRACT Follicular cells

fluid

from

small-

This

study

was

in vitro.

gonadotropin follicles C).

to medium.sized conducted

and

concentrations, of mares

Mares

when

in Group

the

ovulation of the

fofficle

and

the

for

B than

other

groups.

control These

luteinization

mares. data

inhibitor,

support

and

in Group

the

indicate

of a normal

for development

Mares

in vitro

that

follicles

mm

findings

Follicular

fluid

induction,

may

be

controls. LH and FSH

to have fluid

and

during follicular maturation. smalland medium-sized teinization, progesterone ceptors

by FSH

follicular hances receptor horse,

fluid from progesterone induction granulosa

regulator

progesterone

cells

in vitro

large follicles (6-12 secretion, estrogen

[3,4]. In cells removed

of recep-

ulosa

cells ovulation,

[71; this may occur or when

follicular fluid. Little work has follicular fluid ers [8) reported

from that

follicles did not the oocyte and

Accepted

September

Received

June

fluid from inhibits luof LH re-

University

done

follicles drainage

mm diameter) ensecretion, and LH

B),

peripheral

the

preovulatory

or 40-44

mm

A had

(Group

a significantly

in duration of progesterone higher for mares in Groups

A

of secondary

ovulations

mares

in

contain

a

to medium-sized

days

did

than

follicles

of fofficular

on

the

effect

of aspiration

Since in the

maturation

may is not

essential

in premature inhibitors due

Road,

[11].

of

during Such

this ocThe ef-

proestrus aspiration

in may

due to removal of luteinfluid or in impaired CL

of follicular

induction have occurred.

fluid

before

optimum

and stimulation of progesterone Aspiration of follicular fluid from may also affect growth of secinhibin and other inhibitors

[9, 10].

an

it

one

or

interesting occasionally

LH concentrations

licular discrete

rise

to evaluate the effect preovulatory follicles ovarian characteristics model two

gradually

phase and peak after ovulation preovulatory LH surge seen

for this follicles

of of of

study. The per cycle

throughout

the

fol-

[12, 13], without the in most other species.

The exact stimulus for ovulation and luteinization in the mare is not known; however ovulation does occur at a precise interval following exogenous W administration [14]. Follicular and luteal characteristics in the mare are easily monitored by ultrasonography per rectum [15]. The pre-

of Medicine, North

fluid known.

luteinization in the follicular

to removal

the mare make mare ovulates

ovulatory Department

200 Westboro

follicular is not

This experiment was conducted aspiration of follicular fluid from varying maturity in the mare. The

whereas removal of result in partial lutein-

Dr. K. Hinrichs.

the rabbit is an induced ovulator, absence of ovulatory LH stimulation.

of folliculogenesis

during follicular maturation are cultured in vitro without

Medicine,

from

in Group

the putative ovulatory follicle ondary follicles by removing

in vivo. El-Fouly and coworkof follicular fluid from rabbit

address:

(Group

of granulosa

luteinization,

no difference significantly

smallfinal

LH receptor production

17, 1990.

of Veterinary

from the

function

[1, 2]. In contrast,

many species, including the from preovulatory follicles

result in luteinization, follicular fluid did

and current School

fluid during

result ization

8, 1990.

‘Correspondence Tufts

been

cells

incidence

on

aspirated

Mares

fect of removal of spontaneous ovulators

luteinize in vitro without gonadotropin stimulation [5,6]. It has been hypothesized that luteinization cannot occur unless a luteinization inhibitor (LI) is removed from the granand

was

were

was

mm

aspirated.

There

ization. curred

secretion

In the pig, follicular (1-5 mm) follicles secretion, and induction

in granulosa

35-39

not

values

a higher

follicular

that

of follicular

A),

fluid

on luteinization

fluid

CL

an important

luteinization,

was

of follicular

Fotlicular

(Group

did

INTRODUCTION

tor

removal

mare.

follicle

than groups.

A tended

presence

in the

30-34

was

to have

of in vivo

preovulatory

earlier rise in peripheral progesterone concentrations secretion or peak progesterone production between and

shown

effect

the

of secondary

as controls

been

has

to investigate

diameter

D served

follicles

before

Grafton,

the

MA 01536.

292

follicle ovulation

preovulatory

reaches [16], follicle

and

an due may

average to the be

of 45 long

identified

mm

follicular as the

diameter phase, largest

ASPIRATION

PREOVtJIATORY

OF

293

FOLLICLES

follicle on the ovary as early as 6 or 7 days before ovulation, at about 30 mm diameter [15, 16]. Aspiration of the follic-

and with the other hand placed against the wall

ular

contents

the

ovary

folliclewas punctured. The follicular fluid was ing gentle suction applied with a 50-cc syringe

needle

can per

placed

be done

without

surgery,

by manipulating follicle

with

a

gust, vania.

through

the

flank

[17, 18].

pump set at -100 mm Hg until the follicle was empty and a small amount of blood was obtained. There were no dif-

AND

METHODS

ferences

in follicular

the two

methods

was

the natural Fourteen

conducted

during

breeding light horse

season mares,

15 yr, were used as subjects. in pasture with supplemental

The hay

daily

with

a stallion

to detect

of the 400-500

pation

and

ultrasound

examination

Au-

mares were kept outdoors and grain, and were teased evaluated

tracts

through

horse in Pennsylkg and aged 6-

were

reproductive

tween height and averaged to obtain

April

When

the

of all follicles over 20 mm, amination, were recorded.

late

estrus.

estrus,

per

mares daily

rectum.

as measured If there was

were

by pal-

Diameters

by ultrasound a discrepancy

width of a follicle, the the recorded diameter

in

exbe-

two values were for the follicle.

44 mm

and

Group

in diameter.

C, the Group

performed.

aspiration was largest follicle

was

first

D served If on than

greater

day

the 34

the

follicle

was

as a control first mm

cycle was not assigned to a group and was not the study. If, after assigning the mare to a group,

40-

and

day of estrus in diameter,

no the that

included in the largest

follicle ovulated before reaching the designated size for aspiration, that cycle also was not included in the study. If the follicle evidenced

was not by presence

completely of 5 mm

emptied

on aspiration,

or greater

diameter

in the follicle on ultrasound the cycle was not included

examination in the study.

After

ovulation,

to be teased

daily

mares

continued

trus. On they

the first day mares were were again randomly assigned

Each

mare

was

used

only

once

after

through

found to be to aspiration

in each

as

of fluid aspiration,

aspiration

volume

or dies-

in estrus, groups.

dissection

microscope.

pation

and

days were

the

scrubbed,

preovulatory

follicle

was

with The located

the mare ovary that with

one

on the flank ipsilateral follicle was shaved

and a small area was locally anesthetized

us-

ing 2% lidocaine. An equine trochar was introduced through the flank and an 8-inch (20.3 cm), 14-gauge needle was passed

retrieval

between

[19]. fluid

recorded,

and

ultrasound

examination

ter aspiration. Changes follicle and development cles were recorded. licles aspirated, were third

day

follicles

per

rectum

over 20 monitored

the

with

monitored

in the appearance and ovulation

a

by pal-

daily

for

7

mm in diameter until 10 days afof the

aspirated

of secondary

folli-

Control mares, which did not have folmonitored daily through ovulation until

of diestrus,

over

of an oocyte

The ovaries were

after aspiration; if follicles present, the ovaries were

the

was

for the presence

20 mm

Hormone

or

for

10 days

in diameter

were

after

ovulation

present

if

on the

ova-

Assays

Heparinized assays were of

was

taken

jugular blood daily from

estrus, continuing monitored, and

sequent estrus. was removed

sampling

changes

the time ovarian times weekly until

activity the sub-

centrifuged for 10 mm and at -20#{176}Cuntil analyzed.

of gonadotropins

for studying

samples (10 ml) for hormone mares starting on the first day

throughout then three

Blood was and stored

has been

in hormone

shown

plasma Daily

to be adequate

concentration

in the

horse

[201. Plasma LH concentrations viously described [21]. The ml;

and

the

intra-

and

were measured sensitivity of the

interassay

were 13% and 33%. Plasma FSH concentrations previously described [211.

by RIA as preassay was 1 ng/

coefficients

of variation

(CVs)

6 ng/ml,

and

23%. Plasma

the

intra-

progesterone

RIA as previously

group.

was performed tranquilization.

hand per rectum. A 10 X 10-cm area to the ovary bearing the preovulatory and

aspirated

examined

or oocyte

and

the

and

interassay

CVs were

concentrations

described intra-

were measured by RIA as sensitivity of the assay was

The

and

[22].

The

were

measured

sensitivity

interassay CVs were

13%

11%

and by

was

0.25

and

5%.

Aspiration

Aspiration of follicles standing in stocks, without contained

of the

fluid was

ng/ml

Follicle

emptying

of aspiration

ries.

On the first day of estrus, mares were randomly assigned to one of four groups. Mares in Group A had the preovulatory follicle (the largest follicle present on the ovary) aspirated on the first day the follicle was 30-34 mm in diameter; Group B, the first day the follicle was 35-39 mm in diameter;

aspirated usor a vacuum

puncturing

The study

the needle was follicle and the

and

Mares The

the needle, designated

rectum

MATERIALS

the

guiding of the

through

ity. By manipulating

the trochar cannula the

ovary

with

into the peritoneal cavthe

hand

in the

rectum

Analysis The

of Data Fisher

exact test was used to compare the numbers ovulations. The Mann-Whitney two-sample test used to compare groups to controls for days from the

of secondary was

time a 30-34-mm follicle progesterone concentrations ple

t-tests

with

significance were gesterone gesterone

the

was found to the first day that were over 1 ng/ml. Two sam-

Bonferroni used

adjustment

to compare

values remained concentrations.

above Repeated

the

of the

level

length of time

of pro-

1 ng/ml and peak promeasures analysis of

294

HINRICHS

variance

was

centrations used

used

to compare

over time,

to identify

icance

level

gesterone quired

using Cruncher

Hintze

The

were analysis

used of

statistical System,

test

with

logarithms

to achieve variance.

con-

range

differences,

natural

the NCSS Statistical

JL, Kaysville,

in hormone

Newman-Keuls

group

0.05.


1 fol-

mm in diameter to the onset of progesterwas 4.6 ± 0.5 days for Group A; 5.5 ± 0.6 B; 5.8 ± 0.8 days for Group C; and 6,25 ±

1.2 for controls. Time to onset of progesterone production was significantly shorter in Group A than in controls. The life span time progesterone

of the CL was concentrations

assessed

remained

by the over

length of I ng/ml.

The average

the effect

of hormone

was

centrations

lengths of CL life span (days) for the four groups Group A, 12.5 ± 3.7; Group B, 12.9 ± 2.7; Group C, ± 1.0; and control, 13.4 ± 1.24. These differences were

were 12.8

Concentrations

ovulation on peripheral cycles in which there

There

concentrations no significant

In Group

higher than for control showed a significant

of ovu-

2/8. There ovulation

individually

trols.

ferent FSH,

giving the appearance of a corpus hem[23]. Follicles that were seen to be collapsed examination did not refill with fluid over the 7 days,

echogenic

with

both

idly in Group A mares than in control LH and FSH values were significantly

The number of cycles A, 11; Group B, 6; Group

1/7.

for

group-by-day

Follicles

cytes

in each group thus used for comparison was as follows: Group A, 5; Group B, 4; Group C, 6; and control, 6. LII, FSH and progesterone concentrations for Groups A, B, and C from the day of aspiration to 6 days afterward are presented in Figure 1. In each case, the hormone concentrations were compared to those for control mares with cycles standardized so that Day 0 = the day that the preovulatory follicle was the designated size (i.e. Group A, 30A, LH and FSH were mares. Progesterone

RESULTS

tion

ET AL.

of secondary

follicle

hormone concentrations, was no secondary ovulation concentrations.

The

number

growth and only those were used of cycles

not

significant.

for

each

B, 6.9 These

group

The

average

(ng/ml)

peak was

2.1; Group C, 8.2 differences were also ±

Group ±

progesterone A, 9.06

4.2; and control, not significant.

production ±

3.3; 8.2

Group ±

2.7.

ASPIRATION

o-o

Group

A

PREOVULATORY

OF

295

FOLLICLES

(n

#{149} 5)

:::

10

(1

0

1

2

I

I

I

I

3

4

5

6

10 0-0

Group

A(n5)

#{149}-.

GroupD(n6)

#{163}.-.i

OroupA2(n6)

00

Group

.-.

GroupD(n.6)

B(n4)

5

I 0

Ii

012

0

1

2

4

3

5

6 0-0 6

0roupC(i6)

#{149}-#{149} Group

0 (n

#{149} 2)

5

4

I

3 2

e 0

1

from

Days

FIG. 1. (Group

mm

30-34mm

Mean (±SEM) A), 35-39 mm

follicle

LH, FSH, and progesterone (Group B), or 40-44 mm

1

2

Days

from

of follicular

DISCUSSION fluid from

follicles (Group A) was luteinization, as determined progesterone

values.

progesterone

production

The

immature

associated by the time

with time

from

in Group

aspiration

sistent (4 or 5 days in all 11 mares versus the time of a 30-34-mm follicle to onset production removal

in control mares). of the follicular fluid

cells able serum. horse

clear. horse

Channing follicles

in vitro, follicles However, granulosa

whereas 2-6 cm the cells

early rise in

to onset

remarkably

of con-

5-8 days from of progesterone

This early luteinization after suggests that LI may be pres-

ent in the follicular fluid at this stage of follicular In vitro evidence on the distribution of LI in horse is not atretic

et al. [24] reported inhibits luteinization

growth. follicles

that fluid from of pig granulosa

the effect of follicular fluid from vidiameter is not different from mare use of pig granulosa cells rather in the culture system may have

founded

the

results.

In

peared

to be

better

than

another plasma

study,

35-39mm

5

6

0

follicle

follicular

in stimulation

fluid

at 30-34 so that

1

2

than conap-

of proges-

I

3

Days from

40-44mm

mm diameter and that had a second Day 0 = the day that the preovulatory

follicle follicle

a

follIcle

was aspirated at a diameter was not aspirated in Group

terone and estrogen production by in vitro, but the assay was performed

preovulatory

significantly to the first

A was

4

concentrations for mares in which the preovulatory follicle (Group C), and that had no secondary ovulations. The follicle

Group A2 represents mares in which the preovulatory follicle was aspirated of aspiration. For each comparison, data for controls have been standardized size for aspiration (e.g. 30-34 mm for comparison to Group A).

Aspiration

3

of 30-34 D mares.

ovulate within 10 days was of the designated

horse granulosa by incubating

cells gran-

cells with fluid from the same follicle [25]. In the pig, to demonstrate the LI activity of follicular fluid, cells from large follicles are incubated with fluid from small follicles; ulosa

to demonstrate LS activity (stimulation of progesterone secretion), cells from small and medium follicles are incubated with fluid from large follicles [26]. In the pig, LI may be found in follicular fluid in small

or mid-size in follicles

follicles (up to 5 mm in size), while LS is found 6-12 mm in size. The difference in luteinizing

activity of follicular to the preponderance categories licles that estrogen at in 12 in

[27]. have production

fluid has been hypothesized of atretic follicles in the However, received

large follicles preovulatory

by preovulatory

to be smaller

due size

may represent folstimulation. In pigs, follicles

rises

sharply

Day 16-17, when follicles are growing from 5 to 10 mm diameter, and the LH peak occurs when follicles are 10mm diameter [28]. Although no discrete LH peak occurs the horse, if we assume that the signal for ovulation is

296

HINRICHS

ET AL.

which

might

have

the follicle, 10

I

‘ A

I

I

I

I

I

0

1

2

3

4

inhibit

that

bined induce

with increased LH stimulation, early luteinization. rise

such

in FSH

receptor

after

5

follicular suppression

fluid has been shown of FSH and follicular

The

in FSH

rise

either

6

tact. after

10

suggests

prevents

the

It is notable aspiration,

could

E C

I

be

rectly

n, -1

#{149}

that

release

to

pre-ovulatory

aspiration of

fol-

a sufficient when the

to produce

[24] and by mare [31,32].

of follicular

these

hormones amount follicular

that the follicles even though those

expected

i

23456

7

Group

A (n

5)

Group

B (n

4)

Group

C (n =6)

A-

A

ml

the

to reduce wall is left

did not aspirated

7-15

fluid into

refill with at 30-34

more

piin-

fluid mm

fluid

before

ovulated, as determined from follicles in Group

A

S

centrations,

I

days

/

from

3

aspiration

4

5

or ovulation

presence in the

received ovulatory gous to mid-size possible include

stimulation and thus follicles in the pig. stimuli for the increased

2 days before would not yet may

early luteinization FSH seen after

that

[9] or depress

directly

followed

suppress

be

aspiration.

are

the

size

mares by hemiovariin plasma FSH con-

of a second

differences follicle

ovuhave

homoloin Group aspiration,

of the follicular wall present study. However,

seen in horse mares control of secondary

ovuand follicle

follicle

about

study, the ovulations following 30-34-mm group occurred 3-8

Major of the

in

[10]. Removal of these compomay have been associated with

by ovulation present in the

of fol-

folliculogenesis

at the

between

these

time

of aspiration

total and

[11, 33], follicular

suggesting growth

two

population the continued

and, subsequently, another important

ence may be that pony mares rarely ovulate [11] and do not show the mid-cycle follicular

of

of the CL differ-

two follicles development

differences in the between horses and

ponies. The

approximately at 30-34 mm

factors

of a pool

or removal, the removal of half of the follicles in the case of hemiovariectomy,

6

FIG. 2. Mean LH, FSH, and progesterone concentrations for mares in which the preovulatory follicle was aspirated at a diameter of 30-34 mm (Group A), 35-39 mm (Group B), or 40-44 mm (Group C), and that had no secondary ovulations. The follicle was not aspirated in Group D mares. The data are standardized so that Day 0 = the day the preovulatory follicle was aspirated (Groups A, B, and C) or the day ovulation was detected (Group D).

by the follicle then the follicles

absence

36.7 mm) in pony in a prolonged rise

later. In the aspiration

after

studies

Days

contain

growth

diameter resulted

15 days follicular

2

may

follicle

(average ectomy

/

I

fluid

in the

the tendency for an increased incidence of secondary lations in Group A mares. In a study by Driancourt Palmer [33], complete removal of the preovulatory

/

GroupD(nz6)

-A

secondary

bloodstream

response to gonadotropins nents, and the rise in FSH,

/

4-

to the

licular fluid. Follicular

.

a 0-0

Other mares

com-

helped

B and Group C. The rise in FSH levels would seem to indicate either that the granulosa cells stopped producing these hormones after aspiration or that they are not released di-

5,

received lation,

compo-

This,

have

by rat bioassay activity in the

the time they would normally have from the amount of fluid recovered

I

[29].

could of the

within

fluid

formation

aspiration

bloodstream, or removes tuitary suppression, even

A

of LH receptors

of the follicular

licle may be due to removal of inhibin or estrogen. Estrogen supresses FSH secretion in the mare [30]. Inhibin has not been isolated in the horse, but its presence in mare

5

-1

formation

nents

The

0#{149}

enhanced

in the absence

B is not removal

cause

of the

immediately of factors

increase

in LH seen

in Groups

A and

apparent, but may be associated with present in the follicular fluid. Estrogen

has been shown to be a stimulator of LH release in the mare [20, 30], so estrogen withdrawal is probably not the cause of the LH rise. Removal of testosterone, another component

of horse

follicular

fluid

[34],

could

be

related

to the

ASPIRATION

increase

in

LH.

Administration

press LH secretion increase in mares

of

OF

testosterone

in mares [35], and passively immunized

may

luteum

gesterone tions, was development.

production and peak progesterone concentranot affected by aspiration at any stage of follicular Ultrasound examination also indicated that

morphologically normal mal luteal function has ture

follicles during

and

mares

[37-39]

granulosa tissue study, aspiration aspiration tubing, piration, resulting

the follicle.

The

as determined

CL formed been found

oocyte and

after after

recovery

has

been

by length

a

Abnorof ma-

in humans,

on FSH values

of pituitary

were

similar,

suppression

probably

by inhibin

amount

reflect-

or estrogen

been

demonstrated

high

in the

aspiration

group;

this

probably

terone

production

from

the

histologically groups

but

is a result with

[42]. LH values

remained ovulation

of the

resulting

of

removed from the follicle. In the present was stopped when blood was seen in the and the follicle was not flushed after asin minimal loss of granulosa tissue from normal CL function in Group A mares sug-

in rapdue has

declined

in the more

rapid

suppression

proges-

of LH release

pituitary. It must be noted that at a definite point (between

while 0800

was performed

monkeys,

to the

loss

both cases. Progesterone values, however, rose more idly after ovulation than after aspiration. This may be to preovulatory luteinization of the follicle wall, which

of pro-

aspiration. aspiration

related

ing

297

FOLLICLES

and ovulation

sup-

LH concentrations against androgens

[36]. Corpus

function,

PREOVULATORY

aspiration h and 1100

h on the morning of the day of aspiration), ovulation may have occurred at any time in the 24 h previous to the day of detection of ovulation. Duplicate analyses were performed Day

assuming

ovulation

had

0, with no significant This study raises many

occurred

change questions

24 h previous

in results. about the

incidence

to and

gests that the follicular fluid was not needed past 30-34 mm diameter to modulate LH receptor formation or stimulation of granulosa cells for proper luteinization.

function of follicular fluid investigation is warranted

Evidence hibition of

on granulosa cell function in vitro. The results of this study also emphasize the need for further work on the origin of LI and its prevalence in atretic versus growing follicles.

gested

has been luteinization the oocyte

that

presented that links [8,40,41], and may be the source

the oocyte to init has been sugof the luteiniza-

from

the

tion inhibitor found in follicular study, few oocytes were recovered ular fluid; this low recovery rate

fluid [41]. In the present in the aspirated follicis expected when aspir-

Because

ating

follicles

granulosa

immature

(nonstimulated)

[17-19].

No

00-

cytes were recovered in the Group A cycles, had significantly earlier onset of progesterone

yet this group production

than

the

did

controls.

It is possible,

however,

procedure disrupted communication and adjacent granulosa cells and thus

that between lowered

aspiration

the oocyte the effective

amount of LI present. In Groups B and C, there were no apparent differences in time from aspiration to onset of progesterone production between the mares from which oocytes were bers are too

and small

were not recovered, although the numto make any meaningful comparisons.

The aspiration size work done by Pierson

groups were and Ginther

chosen on the basis of [16], who reported that

the average diameter of the follicle the day tion was 45 mm. However, the average size

before of the

ovulafollicle

before ovulation in control mares in this study was 39 mm, and 5 of 8 control mares ovulated before the follicle reached 40 mm. For this reason, mares in Group C, with the follicle aspirated in that reaching

at 40-44 mm, constitute an atypical group of mares they were selected for the preovulatory follicle at least 40 mm. This, and the fact that only 2 con-

trol

mares

and pare

had no hormone

make

any

ficult. When

(the

2 control

mares

that

secondary ovulations) concentrations with interpretation

of the

ovulated were those

results

after

available of Group from

40 mm to comC mares

Group

C dif-

various

of

pared (Fig. 2), did not entirely

effects

of aspiration

it is evident that mimic ovulation.

and

ovulation

are

com-

removal of follicular fluid The effects of aspiration

categories

the

ease

be studied and serve as a useful cell

LS in the mare. Further effects of follicular fluid

of preovulatory

with

which

manipulated model for

mare

individual

in the mare, in vivo study

follicles

follicles

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Effect of aspiration of the preovulatory follicle on luteinization, corpus luteum function, and peripheral plasma gonadotropin concentrations in the mare.

Follicular fluid from small- to medium-sized follicles has been shown to have an inhibiting effect on luteinization of granulosa cells in vitro. This ...
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