Serum and Pituitary Luteinizing Hormone During Luteinizing Hormone

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male rats do not show this self-priming effect. To examine some of the ... in male rats using serum collected from decapitated animals for hormone ... Castration.
BIOLOGY

OF

REPRODUCTION

29,

912-918

(1983)

Serum and Pituitary Luteinizing Hormone and Serum Androgens During Luteinizing Hormone Releasing Hormone Self-Priming in Immature and Pubertal Male Rats J.

S.

NAZ1AN

Department

of

College

Physiology

of Medicine

University

of

Tampa,

South

Florida

Florida

33612

ABSTRACT Pubertal

and

young

adult

male

rats

release

more

luteinizing

hormone

(LH)

in

response

to

luteinizing hormone releasing hormone (LHRH) if they are pretreated with LHRI-I than if they are pretreated with saline. Immature male rats do not show this self-priming effect. To examine some of the possible causes of this difference, immature or pubertal male rats were anesthetized with ketamine HCI and received 3 i.v. injections of 10 ng/100 BW LHRJ-I or saline at 30-mm intervals (Times 0, 30 and 60 mm) and they were decapitated at Times 0, 15, 30, 45, 60, 75 and 90mm. Serum and pituitary LH and serum testosterone and androstenedione were determined by radioimmunoassay. A self-priming effect was apparent in pubertal rats. LH levels in response to the third LHRH injection were significantly higher compared to the response to the first injection. No self-priming effect was evident in immature rats. No changes in pituitary LH that could account for this difference were apparent. Serum testosterone levels in response to the LHRH priming were relatively higher in immature rats than in pubertal animals at 30, 45 and 60 mm. Serum androstenedione levels were relatively higher in pubertal rats at 45 mm. These data indicate that LHRH self-priming effect can be demonstrated in male rats using serum collected from decapitated animals for hormone analysis. They also suggest that a different relative response of serum androgens may be one cause of the appearance of LHRH self-priming during the sexual maturation of the male rat. INTRODUCTION One

the

of

course

the changes that of sexual maturation

is the development luteinizing hormone

takes

of a self-priming releasing hormone

(Nazian and Mahesh, adult male rats release

1980b). more

development of this effect known. Castration eliminates effect (Nazian and Mahesh,

is not currently the self-priming 1979b). Pretreat-

effect of (LHRH)

ment

can

or young hormone

and

place during in the male rat

Pubertal luteinizing

LHRH

(Nazian develops show and

challenge

regardless

and Mahesh, between 34 no

46

statistically The

evidence days of factor

of any age, when

significant (Nazian, 1981). or factors responsible

testicular effect

1980a).

These

June 20, 1983. March 21, 1983. requests: Dr. Stanley

the

effect

(Nansel

Physiology, College of Medicine - Box South Florida, Tampa, FL 33612.

Nazian,

Dept.

8, University

to

suggests the steroid response

in

be

part,

immature

responsible rat

to

al.,

of

greater

of

than more

912

inhibition is that

effect

on

1979).

the

failure

a self-priming

latter

could result. An priming injections

LH

synthesis for

of

the

effect.

If

during the priming rats, then a greater

the

in immature males. LH being available

This

possibility that the during priming may, for

show

preeffect that

have a rapid direct to modify the self-

et

observation dynamic

degree of possibility

J.

suggest

steroids in the rise in serum appears

androgens can the pituitary

on

the (Nazian

observations

more testosterone is released process in immature male Accepted Received ‘Reprint

prevent effect

of testicular the pubertal concentrations

priming

effect, is first for

Mahesh,

self-priming

cede the expression of the self-priming (Nazian, 1981). It has also been suggested

This effect age, when rats

self-priming the effect

of the

testosterone

of pretreatment

1979b). days of

androstenedione

the involvement process. Indeed,

(LH) in response to a LHRH challenge if they are pretreated with LHRH than if they are pretreated with saline. Immature male rats release essentially that same amount of LH after

with

development

in older

alternate have

a

animals

This would result in release. The experi-

HORMONE

ments these

reported

here

were

questions.

pubertal stages

rats were priming.

single

large

weaning from were maintained

group

the

of

of

immature

and

at

rats

was

WI).

at

They of tem-

(14L:1OD) with food and They were housed 4-6 per cages. Developmental stages

were as defined previously (Nazism and Mahesh, 1979a,b). Immature rats were used at 29, 30 or 31 days of age; pubertal rats were used at 49, 50 or 51 days of age. In this colony, based on such criteria as secondary sexual organ growth, negative feedback sensitivity and serum testosterone concentrations, puberty begins about Day 40 and is essentially complete by Days 65-70. All animals were anesthetized with ketamine HCI (10-20 mgJlOO g BW) i.p. supplemented with additional i.m. injections as needed (Nazism, 1981). Beginning at 0800-0900 h rats received 3 i.v. (jugular) injections of 10 ng/100 g BW LHRH or saline at 30-min intervals. Synthetic LHRH (lot No. 21-103-DH) was obtained from the National Pituitary Agency and the NIAMDDK. Groups of 6 rats were decapitated at Time 0 (prior to any injection) 15, 30, 45, 60, 75 and 90 min. LHRH or saline injections were given at Time 0, 30 and 60 min. Serum was frozen until subsequent determination of LH, testosterone and androstenedione by radioirnmunoassay. Pituitaries were carefully dissected, the posterior lobes removed and the anterior lobes weighed and individually stored frozen in 1 ml of 0.9% saline. Subsequently they were thawed and homogenized in 2 ml of phosphate-buffered saline (pH=7.5) (PBS) with a Teflon glass homogenizer. Glassware and the Teflon pestle were washed with the storage saline and an additional 1 ml of PBS. All washings and the homogenate were combined and centrifuged at 3000 rpm for 15 min. All procedures were carried out at 0-4#{176}C. The supernatant was refrozen until assayed for LH by radioimmunoassay.

TABLE

1. Hormone

levels

at Time

0 (Mean

±

LH

10.9 LH

content

LH

concentration

913 and

Statistical

Analyses

pituitary LH were determined by using an antibody (#15) obtained Niswender (Niswender et al., 1968) rat LH (Nazian, 1981). LH values by and are expressed in terms of the RP-1. Serum concentrations of androstenedione were also determined by radioimmunoassay using previously published techniques (Nazian, 1981) Data were analyzed and significance determined using Student’s t test for comparisons between two groups and Duncan’s new multiple range test for multigroup comparisons.

RESULTS

Serum prior

and

to the

age

pituitary

start

groups

are

LH

were compared

rats

testosterone higher in

tive

Time

Serum

Table

1.

levels

just

in the

two

Serum

significantly and pituitary

levels pubertal

were rats.

LH

different. concen-

significantly to immature

significant difference dione concentrations Due to these differing analyses pituitary first calculated

priming

in

were not content

of

Serum 10-fold

hormone

LHRH

given

concentrations Both pituitary tration pubertal

of

higher

in males.

approximately There was

no

in the serum androstenebetween the two ages. baselines, in subsequent

LH and serum as the percentage

steroids of the

were respec-

0 value.

LH

(Fig.

1)

Treatment ng/100 g

BW

(P0.05

49.9

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