Modulation of Luteinizing Hormone Pulse Amplitude by the Frequency ...

BIOLOGY

OF

REPRODUCTION

38,

Modulation Luteinizing

ERIC

143-149

(1988)

of Luteinizing Hormone Pulse Amplitude by the Frequency of Hormone-Releasing Hormone Stimulation and by Testosterone in Castrated, Hypothalamic-Lesioned Male Rats’

C. PETRIE3’5

Endocrinology

ALVIN

M. MATSUMOTO,4’6

Section3

and

Seattle

Geriatric

Veterans

Population and University

of

and

and

Center4

Metabolism5

Geriatric Medicine6 of Medicine

Washington

Seattle,

Clinical

Center

in Reproduction

of Endocrinology Gerontology Department

and

Medical

and Research

for

J. BREMNER2’3’5

WILLIAM

Education

Research,

Administration

Center

Divisions

and

School

Washington

of Medicine

98108

ABSTRACT The quency

frequency of of luteinizing

spontaneous luteinizing hormone (LH) hormone-releasing hormone (LHRH)

pulses pulses

is thought from the

to be a direct hypothalamus.

result of the By contrast,

frethe

amplitude of spontaneous LH pulses may be controlled by several factors other than the amplitude of LHRH pulses. We tested two hypotheses: 1) that LHpulse amplitude is determined in part by the frequency of LHRH pulses of constant magnitude, and 2) that testosterone (T) exerts a direct feedback effect on the pituitary

gland

to regulate

Gonadal

LHpulse

feedback

eliminated

by

amplitude. was

lesioning

the

and T levels (0.15 ± 0.02 gonado tropic hypogonadal During an 8-h period, catheters

the

into

LHRH

pulse

in half

of

constant

at

infused

with

received

medial

basal

vein,

was

animals

castrating

by

adult

hypothalamus.

mm

20

(n10)

blood

and during

during

the

male Serum

ng/ml), measured several state of the animals. unanesthetized, unrestrained

jugular

interval

the

-

eliminated

weeks

rats LH

(n2O).

levels

after

(0.19

animals

were

4 hours;

in the

other

20 mm throughout the study. Within both of T to achieve a physiological level of T in serum

LHRH

± 0.04

hypothalamic

ng/ml

with

were pulse

10 animals,

these groups, (2.46 ± 0.36

40ng

was ± SEM)

the

pulses

of

hypo-

LHRH

via

at 10-mm intervals. was doubled to 40

interval pulse

one-half ng/ml

mean

confirmed

drawn the

secretion

RP-2,

lesioning,

injected

samples for LH measurement the first 4 h in all animals. The

next

Endogenous

interval

of

the

at 4 h),

was

maintained

animals

while

The mm

(n=5)

the

were

other

half

vehicle.

Doubling increase in

the mean

than

vehicle-infused

infused

animals

interval

between

LH

pulse

LHRH

amplitude

animals

(p