Vol.
No. 1, 1977
75,
STIMULATION
OF PROLACTIN
INJECTION Andre
BIOCHEMICAL
DuPont*,
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
RELEASE
OF p-ENDORPHIN Lionel
Cusan*,
IN THE
AND
Fernand
RAT
BY 1NTRAVE:NTRICULAR
METHIONINE-ENKEPHALIN David
Labrie*,
H.
Coy**
and Choh
Hao Li***
*Laboratory of Molecular Endocrinology, Le Centre Hospitalier de l’universite Laval, Quebec, GlV 4G2, Canada; **V.A. Hospital and Tulane University La. 70146; and ***Hormone Research School of Medicine, New Orleans, Laboratory, University of California, San Francisco, California 94143 Received
January
7,1977
SUMMARY: A single dose of 0. 5 pg P-endorphin injected intraventricularly in unanesthetized male rats bearing chronic intraventricular and intrajugular cannulae led to a 7-fold stimulation of plasma prolactin (PRL) levels 10 to 20 min after injection of the peptide, whereas a dose of 500 ug methionineenkephalin (met-enkephalin) led to only a 4-fold stimulation of plasma PRL findings show that levels. Combined with our previous data, the present P-endorphin and met-enkephalin have a more potent and more rapid stimulatory effect on PRL than GH release after intracerebral injection. These data suggest a possible role of endogenous opiate-like peptides in the control of both PRL and GH secretion. Following brain been
reports
(l- 3), the pentapeptide isolated
from
is the same called
porcine
P-endorphin) met-enkephalin
7,8)
and bind
lateral
rat
(12).
recently
cerebral Since
morphine
(15, 16; Cusan
the effect
of P-endorphin PRL,
found
isolated have
that
potent
p-endorphin
stimulate
and Labrie,
sequence
of this
(P-LPH61e91, from
sheep
in has peptide
also
pituitaries
morphine-like
(6).
effects
hormone
the release unpublished
GH,
and met-enkephalin
growth
and met-enkephalin
0 1977 by Academic Press, Inc. of reproduction in any form reserved.
activity
(4,
(9-11).
can stimulate
prolactin;
The
COOH-fragment
first
receptor
ventricles
prolactin
Abbreviations: methionine-enkephalin.
of the
opiate
(met-enkephalin)
(5) brain.
and P-endorphin
We have into
(4) and calf
of f3-lipotropin
to the opiate
of endogenous
Tyr-Gly-Gly-Phe-Met
as the N-terminal
Both
Copyright All righfs
of the presence
growth
secretion
of both observations),
on PRL hormone;
injected
release.
in the
GH (13,14)
and
we studied
The met-enkephalin,
present
76 ZSSN 0006-291X
Vol. 75, No. 1, 1977
data potent
show
for the first
stimuli
of PRL
BIOCHEMICAL
time than
that
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
the two endogenous
opioid
peptides
are
more
GH release.
Materials
and Methods
Adult male Sprague-Dawley rats (obtained from Canadian Breeding St. Constant, Quebec) weighing 225-275 g upon arrival were kept Farms, in a sound-attenuated and temperature-controlled room (24 f Z°C ) and exposed to 14 hr light/l0 hr dark cycles (lights on at 5:00 and off at 19:OO hr). Purina rat chow and water were available ad libitum. In order to minimize stress-induced inhibition of GH release, animals were handled twice a day for 7 to 10 days before insertion of a catheter (Venocath No. 18 Abbott) into the right superior vena cava under Surital (50 mg/kg, ip) anesthesia. The animals were then implanted stereotaxically with a metallic cannula (guage 25) in the left lateral ventricle according to the coordinates (A=5.4, D=2, D=3) described by De Groot (17). The cannula was fixed to the skull with a polymerizing acrylate (Yates Flash Acrylic). This chronic technique permits a minimum of manipulations of the animal at the time of the experiment performed 2 days after implantation of the cannulae. Animals were then injected intravenously through the intrajugular catheter with 0. 2 ml of sheep somatostatin antiserum,kindly supplied by Dr. A. Arimura, 5 min before injection of the indicated doses of (3-endorphin or met-enkephalin or the vehicle alone (40 ~1 of 0.9% NaCl) over a 3-min period (18). p-Endorphin and met-enkephalin were synthesized by the solidphase method as described (10, 19). Samples of 0.7 ml blood were then withdrawn into heparinized syringes at the indicated time intervals. A volume of 0, 7 ml of saline containing heparin was injected after each blood sampling Plasma was separated by centrito minimize extracellular volume changes. fugation at 1200 x g for 40 min at 2-4OC and kept at 20°C until assayed. Plasma GH and PRL were measured in duplicate by double-antibody radioimmunoassay (20,21) using rat hormones (GH-1-2, PRL-I-1, GH-RP-1 and PRL-RP1) and rabbit antisera (anti-GH-S-2 and anti-PRL-S-2) kindly provided by Dr. A. F. Parlow for the National Institute of Arthritis and Metabolic Diseases, Rat Pituitary Hormone Program. Purified goat antirabbit y-globulins were a product of Endocrinolab Ltd., Quebec. Radioimmunoassay data were analysed with a Hewlett-Packard desktop calculator using a program written in this laboratory and based on model II of Rodbard and Lewald (22). Data are expressed as mean f S. E. M. Statistical significance was evaluated according to the multiple -range test of Duncan-Kramer (23). Results As illustrated of P-endorphin
in Fig.
(P-LPH61-91
1, the intraventricular ) led to a rapid
77
injection
and significant
of 0.5 to 25 ng stimulation
of PRL
Vol.
75,
No. 1, 1977
BIOCHEMICAL
BIOPHYSICA!
AMD
/
1
t”
RESEARCH COMMUNICATIONS
CONTROL /3-ENUOAPHIN (0.5yg) 08 ID (2v9) b, PI (5v9)
o...o
H D-4 H
.... ._..._. ...... .. ............ ._... -5
0
5
10
20
30
45
60
MINUTES AFTER INJECTION
Fig.
I
release rise
was
Effect of increasing doses of P-endorphin on plasma prolactin (PRL) levels in the rat. Adult male rats bearing intraventricular and intrajugular cannulae were injected intravenously with 0. 2 ml of sheep somatostatin antiserum 5 min before the intraventricular injection of the indicated amounts of synthetic /3-endorphin. PRL measurements were performed at the indicated times intervals after administration of P-endorphin. Data are presented as mean f S. E. M. of triplicate measurements of pooled plasma samples from 8 to 9 animals per group.
in
unanesthetized already
stimulation decrease
freely-moving
evident
5 min
(approximately of plasma
of P-endorphin
(2.5
a 30- to 60-fold
and
after
7-fold)
hormone
rats.
levels
injection
With of the
was measured at later
time
being
measured
between
0.5
peptide
after
25 pg) led to a progressive
increase
the
10 min
intervals. increase
pg dose,
a marked
and a maximal with The
a slow higher
of PRL
20 and 60 min
after
doses
release, injection
of 25 pg of the peptide. Fig. peptide
2A shows
of P-endorphin,
that
methionine-enkephalin,
was much
less
potent
78
the NH2-terminal than
P-endorphin
penta-
to stimulate
Vol. 75, No. 1, 1977
BIOCHEMICAL
A
o--o o--o o--o
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
CONTROL ENKEPHALIN (500 lg) ENKEPHALIN (1000 rg)
,\\ \\\ \‘1 \‘\\ I \\\ \ MINUTES AFTER INJECTION
Fig.
PRL
2
Effect of 0. 5 or 1. 0 mg of methionine-enkephalin on plasma PRL (A) and GH (B) levels in the rat. The experiment was performed described in Fig. 1. Data are expressed as mean f S. E. M. of triplicate measurements of individual plasma samples obtained.
release
D In fact,
at the 500 to 1000
led to approximately
4- to 6-fold
Maximal
was
peptide
stimulation with
a rapid
seen
in Fig.
2B that
dose,
thus
opioid
peptide.
indicating
return
increases
measured
stimulation
levels
PRL
after
between
of GH release sensitivity
methionine-enkephalin
of plasma
10 to 20 min
to basal
a greater
pg doses,
was
levels,
injection
respectively. of the
30 and 45 min. observed
of the PRL
than
only
effect
the
of endogenous
sensitive
--in vivo
somatostatin
model
which
on GH secretion
79
minimizes (18),
at the
GH responses
the inhibitory we have
penta-
It can be
Discussion Using
as
recently
1000 to the
ug
Vol. 75, No. 1, 1977
found
that
potent
P-endorphin
stimuli
for
The
stimulatory
5 min
after
at 10 min.
long-lasting about
80% between
(Fig+
decrease
demonstrate
that
can be more
P-endorphin
and met-enkephalin’was
of time
of both
after
peptides
on plasma
the effect
on PRL
GH levels
of P-endorphin
GH release:
while
injection
PRL
levels
with
various
release
could
appeared
plasma
after
injections
first
was
be measured somewhat
GH levels
more
decreased
by
of 25 pg of P-endorphin was
measured
do however
display
(12),
up to 60 min
1). and met-enkephalin
in the various
endorphin
has been
28).
P-endorphin
met-enkephalin statin
should
likely
that
Our
duration
previous
the
Fig.
effect
activity (8,
more
assay,
more
that
than
(25)
injected
of P-endorphin
(12) and the present potent
p-
potent
of met-enkephalin
26) while
findings
of morphine
2) is observed
be neutralized observed
pig ileum
different
data
met-enkephalin
is indicate to
release.
stimulatory (12,
markedly
(24) or 4 to 5 times
analgesic
is 500 to 2000 times
GH and PRL
In the guinea
to be equipotent
to be of short
(27,
Since
used.
The --in vivo
appears
long-lasting
bioassays
found
met-enkephalin.
centrally
induce
can be
GH release.
effect
of plasma
data
intraventricularly
the effect the
intraventricularly
The present
as a function
30 and 60 min
activities
that
both
than
P-Endorphin
than
of both
Moreover,
on PRL
no significant
effect
injection,
(12).
injected than
While
injected
rat
release
release
of the peptides.
found only
PRL
on PRL
doses
in the
and met-enkephalin
stimuli
detected
AND EIOPHYSICAI. RESEARCH COMMUNICATKINS
and met-enkephalin
of GH release
P-endorphin potent
BIOCHEMICAL
increased
by excess
(13,
in animals somatostatin
GH release
P-endorphin
where
circulating
somato-
(18,
ZS), it is
antiserum
is due to stimulated
G_H- releasing activity (GH- RH) from the hypothalamus 1 After completion of the manuscript, two reports the effect of met-enkephalin on prolactin release attention. 80
14),
(12). (34,35) in rats,
(12) and
release
of
which described came to our
BIOCHEMICAL
Vol. 75, No. 1, 1977
Increasing inhibitor
of PRL
peptides
exert
through
inhibition
layer
striatal
further
supported
at least
by apomorphine
effect
suggests
secretion
the dopamine
(30,31).
part
by the
observation
antagonists
possible
nerve
it was
--in vitro that
led to inhibition haloperidol
role
(32)
opiates
effect
endings
found .
of dopamine
that
stimulatory
from
Indeed,
release
or L-Dopa
marked
release
eminence.
dopamine
a physiological It is thus
of their
of dopamine
of the median
inhibits
while
evidence
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
stimulation of morphine and pimozide
and
on PRL
opioid release
in the external
recently
Such
as
that
a mechanism
/3-endorphin is
of dopamine
receptors
analgesia
in mice
had the opposite
(33). References
1. 2. 3. 4. 5. 6.
7. 8. 9. 10. 11. 12. 13. 14. 15.
Hughes, J. (1975) Brain Res. 88, 295-308. Pasternak, G. W., Goodman, R. and Snyder, S. H. (1975) Life Sci. 16, 1765-1769. Terenius ,- L. and Wahlstrom, A. (1975) Acta Physiol. Stand. 94, 74-81. ?%ghes, J. , Smith, T. W., Kosterlitz, H. W., Fothergill, L. A., Morgan, B. A. and Morris, H. R. (1975) Nature 258, 577-579. Simantov, R. and Snyder, S. H. (1976) Life Sci. 18, 781-788. Li, C. H. , Barnafi, L. , Chretien, M. and ChungTD. (1965) Nature 208, 1093-1094; Li, C. H. and Chung, D. (1976) Nature 260, 622-624,‘ Li, C. H. and Chung, D. (1976) Proc. Natl. Acad. Sci. USA -73, 1145- 1148. Chang, J. K. , Fong, B.T. W. , Pert, A. and Pert, C. B. (1976) Life Sci. 18, 1473 Bradbury, A. F., Smyth, D. G. and Snell, C. R. (1976) Nature 260, 793-795. Li, C. H. Lemaire, S. , Yamashiro, D. and Doneen, B. A. (1976) Biochem. Biophys. Res. Commun. 71, 19-25. Morin, O., Caron, M. G., De Lean, A. aa Labrie, F. (1976) Biochem. Biophys. Res. Commun., in press. DuPont, A., Cusan, L., Garon, M., Labrie, F. and Li, C. H. Proc. Natl. Acad. Sci. USA, in press. Kokka, N., Garcia, J. F., George, R. and Elliott, H. W. (1972) Endocrinology 90, 735-743. Ferland, L., Labrie,?‘. , Coy, D. H., Arimura, A. and Schally, A. V. (1976) J. Mol. Cell. Endocrinol. 4, 79-88. Meites, J. , In Neuroendocrinology, Voly 1 (L. Martini and W. F. New York, 1966, pp. 669-707. Ganong, eds. ), Academic Press,
81
Vol. 75, No. 1, 1977
16. 17. 18. 19.
20. 21. 22.
23. 24. 25. 26. 27. 28. 29. 30. 31.
32. 33. 34. 35.
BIOCHEMICAL
AND BIOPHYSICAL
RESEARCH COMMUNICATKX~S
Tilis, G., Hickey, J. and Guyda, H. (1975) J. Clin. Endocrinol. Metab. 41, 797-800. De Grooz J. (1959) Trans. R. Neth. Acad. Sci. 52, l-40. Ferland, L. , Labriek F. , Jobin, M., Arimura ,A. and S&ally, A. V. (1976) Biochem. Biophys. Res. Commun. 68, 149-156. Coy, D. H., Kastin, A. J., Schally, A. V., Morin, O., &ron, M. ,S., J. M., Fertel, R., Bernston, G. G. and Labrie, F. , Walker, Sandman, C. A. (1976) Biochem. Biophys. Res. Commun., in press. Birge, C. A., Peake, G. T. , Mariz, I. K. , and Daughaday, W. H. (1967) Endocrinology 81, 195-200. Gdell, W. D. , Rayford P. L. and Ross, G. T. (1967) J. Lab. Clin. Med. 70, 973-980. Rodbard, Dznd Lewald, J. E. (1970) I n: 2nd Karolinska Symposium on Research Methods in Reproductive Endocrinology (Diczfalusy, E. , ed. ), Geneva, pp. 79- 103. Kramer, C. Y. (1956) Biometrics 12, 307-310. A. and Liz. H. (1976) Proc. Natl. Cox, B. M., Goldstein, Acad. Sci. USA 73, 1821-1823. N. and Guillemin, R. (1976) Bloom, F., SegaT D., Ling, Science 194, 630-632. Belluzi, J. D. , Grant, N., Garsky, V., Sarantakis, D., Wise, C. D. and Stein, L. (1976) Nature 260, 625-626. L. F., Wei, Eynd Li, C. H. (1976) Proc. Loh, H. H., Tseng, Natl. Acad. Sci. USA 73, 2895-2898. Bradley, A. F., SmythT D. G., Snell, C. R., Birdsall, N. J. M. and Hulme, E. C. (1976) Nature 260, 793-795. Ferland, L., Labrie, F. , Arimura, A. and Schally, A. V. (1976) J. Mol. Cell. Endocrinol., in press. MacLeod, R. M. and Lehme yer, J. E. (1974) Endocrinology -94, 1077- 1085. Schally, A. V. , DuPont, A., Arimura, A., Takahara, J., Redding, T. W. , Clemens, J. and Shaar, C. (1976) Acta Endocrinol. 82, 1-14. D. A. , Sampath-Kharma, S., Mar, J. B., Loh, H. H., Brase, Way, E. L. and Li, C. H. (1976) Nature 264 , 567-568. TuIunay, F. C. , Yano, I. and Takemori, KE. (1976) Eur. J. Pharmacol. 35, 285-292. Lien, E. L.,enichel, R. L., Garsky, V., Sarantakis, D. and Grant, N. H. (1976) Life Sci. 19, 837-840 (1976). Hall, T. R., Advis, J. P., Smith, A. F. and Meites, J. (1976) IRCS Medical Sci. - 4, 559.
82
No. 1, 1977
75,
STIMULATION
OF PROLACTIN
INJECTION Andre
BIOCHEMICAL
DuPont*,
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
RELEASE
OF p-ENDORPHIN Lionel
Cusan*,
IN THE
AND
Fernand
RAT
BY 1NTRAVE:NTRICULAR
METHIONINE-ENKEPHALIN David
Labrie*,
H.
Coy**
and Choh
Hao Li***
*Laboratory of Molecular Endocrinology, Le Centre Hospitalier de l’universite Laval, Quebec, GlV 4G2, Canada; **V.A. Hospital and Tulane University La. 70146; and ***Hormone Research School of Medicine, New Orleans, Laboratory, University of California, San Francisco, California 94143 Received
January
7,1977
SUMMARY: A single dose of 0. 5 pg P-endorphin injected intraventricularly in unanesthetized male rats bearing chronic intraventricular and intrajugular cannulae led to a 7-fold stimulation of plasma prolactin (PRL) levels 10 to 20 min after injection of the peptide, whereas a dose of 500 ug methionineenkephalin (met-enkephalin) led to only a 4-fold stimulation of plasma PRL findings show that levels. Combined with our previous data, the present P-endorphin and met-enkephalin have a more potent and more rapid stimulatory effect on PRL than GH release after intracerebral injection. These data suggest a possible role of endogenous opiate-like peptides in the control of both PRL and GH secretion. Following brain been
reports
(l- 3), the pentapeptide isolated
from
is the same called
porcine
P-endorphin) met-enkephalin
7,8)
and bind
lateral
rat
(12).
recently
cerebral Since
morphine
(15, 16; Cusan
the effect
of P-endorphin PRL,
found
isolated have
that
potent
p-endorphin
stimulate
and Labrie,
sequence
of this
(P-LPH61e91, from
sheep
in has peptide
also
pituitaries
morphine-like
(6).
effects
hormone
the release unpublished
GH,
and met-enkephalin
growth
and met-enkephalin
0 1977 by Academic Press, Inc. of reproduction in any form reserved.
activity
(4,
(9-11).
can stimulate
prolactin;
The
COOH-fragment
first
receptor
ventricles
prolactin
Abbreviations: methionine-enkephalin.
of the
opiate
(met-enkephalin)
(5) brain.
and P-endorphin
We have into
(4) and calf
of f3-lipotropin
to the opiate
of endogenous
Tyr-Gly-Gly-Phe-Met
as the N-terminal
Both
Copyright All righfs
of the presence
growth
secretion
of both observations),
on PRL hormone;
injected
release.
in the
GH (13,14)
and
we studied
The met-enkephalin,
present
76 ZSSN 0006-291X
Vol. 75, No. 1, 1977
data potent
show
for the first
stimuli
of PRL
BIOCHEMICAL
time than
that
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
the two endogenous
opioid
peptides
are
more
GH release.
Materials
and Methods
Adult male Sprague-Dawley rats (obtained from Canadian Breeding St. Constant, Quebec) weighing 225-275 g upon arrival were kept Farms, in a sound-attenuated and temperature-controlled room (24 f Z°C ) and exposed to 14 hr light/l0 hr dark cycles (lights on at 5:00 and off at 19:OO hr). Purina rat chow and water were available ad libitum. In order to minimize stress-induced inhibition of GH release, animals were handled twice a day for 7 to 10 days before insertion of a catheter (Venocath No. 18 Abbott) into the right superior vena cava under Surital (50 mg/kg, ip) anesthesia. The animals were then implanted stereotaxically with a metallic cannula (guage 25) in the left lateral ventricle according to the coordinates (A=5.4, D=2, D=3) described by De Groot (17). The cannula was fixed to the skull with a polymerizing acrylate (Yates Flash Acrylic). This chronic technique permits a minimum of manipulations of the animal at the time of the experiment performed 2 days after implantation of the cannulae. Animals were then injected intravenously through the intrajugular catheter with 0. 2 ml of sheep somatostatin antiserum,kindly supplied by Dr. A. Arimura, 5 min before injection of the indicated doses of (3-endorphin or met-enkephalin or the vehicle alone (40 ~1 of 0.9% NaCl) over a 3-min period (18). p-Endorphin and met-enkephalin were synthesized by the solidphase method as described (10, 19). Samples of 0.7 ml blood were then withdrawn into heparinized syringes at the indicated time intervals. A volume of 0, 7 ml of saline containing heparin was injected after each blood sampling Plasma was separated by centrito minimize extracellular volume changes. fugation at 1200 x g for 40 min at 2-4OC and kept at 20°C until assayed. Plasma GH and PRL were measured in duplicate by double-antibody radioimmunoassay (20,21) using rat hormones (GH-1-2, PRL-I-1, GH-RP-1 and PRL-RP1) and rabbit antisera (anti-GH-S-2 and anti-PRL-S-2) kindly provided by Dr. A. F. Parlow for the National Institute of Arthritis and Metabolic Diseases, Rat Pituitary Hormone Program. Purified goat antirabbit y-globulins were a product of Endocrinolab Ltd., Quebec. Radioimmunoassay data were analysed with a Hewlett-Packard desktop calculator using a program written in this laboratory and based on model II of Rodbard and Lewald (22). Data are expressed as mean f S. E. M. Statistical significance was evaluated according to the multiple -range test of Duncan-Kramer (23). Results As illustrated of P-endorphin
in Fig.
(P-LPH61-91
1, the intraventricular ) led to a rapid
77
injection
and significant
of 0.5 to 25 ng stimulation
of PRL
Vol.
75,
No. 1, 1977
BIOCHEMICAL
BIOPHYSICA!
AMD
/
1
t”
RESEARCH COMMUNICATIONS
CONTROL /3-ENUOAPHIN (0.5yg) 08 ID (2v9) b, PI (5v9)
o...o
H D-4 H
.... ._..._. ...... .. ............ ._... -5
0
5
10
20
30
45
60
MINUTES AFTER INJECTION
Fig.
I
release rise
was
Effect of increasing doses of P-endorphin on plasma prolactin (PRL) levels in the rat. Adult male rats bearing intraventricular and intrajugular cannulae were injected intravenously with 0. 2 ml of sheep somatostatin antiserum 5 min before the intraventricular injection of the indicated amounts of synthetic /3-endorphin. PRL measurements were performed at the indicated times intervals after administration of P-endorphin. Data are presented as mean f S. E. M. of triplicate measurements of pooled plasma samples from 8 to 9 animals per group.
in
unanesthetized already
stimulation decrease
freely-moving
evident
5 min
(approximately of plasma
of P-endorphin
(2.5
a 30- to 60-fold
and
after
7-fold)
hormone
rats.
levels
injection
With of the
was measured at later
time
being
measured
between
0.5
peptide
after
25 pg) led to a progressive
increase
the
10 min
intervals. increase
pg dose,
a marked
and a maximal with The
a slow higher
of PRL
20 and 60 min
after
doses
release, injection
of 25 pg of the peptide. Fig. peptide
2A shows
of P-endorphin,
that
methionine-enkephalin,
was much
less
potent
78
the NH2-terminal than
P-endorphin
penta-
to stimulate
Vol. 75, No. 1, 1977
BIOCHEMICAL
A
o--o o--o o--o
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
CONTROL ENKEPHALIN (500 lg) ENKEPHALIN (1000 rg)
,\\ \\\ \‘1 \‘\\ I \\\ \ MINUTES AFTER INJECTION
Fig.
PRL
2
Effect of 0. 5 or 1. 0 mg of methionine-enkephalin on plasma PRL (A) and GH (B) levels in the rat. The experiment was performed described in Fig. 1. Data are expressed as mean f S. E. M. of triplicate measurements of individual plasma samples obtained.
release
D In fact,
at the 500 to 1000
led to approximately
4- to 6-fold
Maximal
was
peptide
stimulation with
a rapid
seen
in Fig.
2B that
dose,
thus
opioid
peptide.
indicating
return
increases
measured
stimulation
levels
PRL
after
between
of GH release sensitivity
methionine-enkephalin
of plasma
10 to 20 min
to basal
a greater
pg doses,
was
levels,
injection
respectively. of the
30 and 45 min. observed
of the PRL
than
only
effect
the
of endogenous
sensitive
--in vivo
somatostatin
model
which
on GH secretion
79
minimizes (18),
at the
GH responses
the inhibitory we have
penta-
It can be
Discussion Using
as
recently
1000 to the
ug
Vol. 75, No. 1, 1977
found
that
potent
P-endorphin
stimuli
for
The
stimulatory
5 min
after
at 10 min.
long-lasting about
80% between
(Fig+
decrease
demonstrate
that
can be more
P-endorphin
and met-enkephalin’was
of time
of both
after
peptides
on plasma
the effect
on PRL
GH levels
of P-endorphin
GH release:
while
injection
PRL
levels
with
various
release
could
appeared
plasma
after
injections
first
was
be measured somewhat
GH levels
more
decreased
by
of 25 pg of P-endorphin was
measured
do however
display
(12),
up to 60 min
1). and met-enkephalin
in the various
endorphin
has been
28).
P-endorphin
met-enkephalin statin
should
likely
that
Our
duration
previous
the
Fig.
effect
activity (8,
more
assay,
more
that
than
(25)
injected
of P-endorphin
(12) and the present potent
p-
potent
of met-enkephalin
26) while
findings
of morphine
2) is observed
be neutralized observed
pig ileum
different
data
met-enkephalin
is indicate to
release.
stimulatory (12,
markedly
(24) or 4 to 5 times
analgesic
is 500 to 2000 times
GH and PRL
In the guinea
to be equipotent
to be of short
(27,
Since
used.
The --in vivo
appears
long-lasting
bioassays
found
met-enkephalin.
centrally
induce
can be
GH release.
effect
of plasma
data
intraventricularly
the effect the
intraventricularly
The present
as a function
30 and 60 min
activities
that
both
than
P-Endorphin
than
of both
Moreover,
on PRL
no significant
effect
injection,
(12).
injected than
While
injected
rat
release
release
of the peptides.
found only
PRL
on PRL
doses
in the
and met-enkephalin
stimuli
detected
AND EIOPHYSICAI. RESEARCH COMMUNICATKINS
and met-enkephalin
of GH release
P-endorphin potent
BIOCHEMICAL
increased
by excess
(13,
in animals somatostatin
GH release
P-endorphin
where
circulating
somato-
(18,
ZS), it is
antiserum
is due to stimulated
G_H- releasing activity (GH- RH) from the hypothalamus 1 After completion of the manuscript, two reports the effect of met-enkephalin on prolactin release attention. 80
14),
(12). (34,35) in rats,
(12) and
release
of
which described came to our
BIOCHEMICAL
Vol. 75, No. 1, 1977
Increasing inhibitor
of PRL
peptides
exert
through
inhibition
layer
striatal
further
supported
at least
by apomorphine
effect
suggests
secretion
the dopamine
(30,31).
part
by the
observation
antagonists
possible
nerve
it was
--in vitro that
led to inhibition haloperidol
role
(32)
opiates
effect
endings
found .
of dopamine
that
stimulatory
from
Indeed,
release
or L-Dopa
marked
release
eminence.
dopamine
a physiological It is thus
of their
of dopamine
of the median
inhibits
while
evidence
AND BIOPHYSICAL RESEARCH COMMUNICATIONS
stimulation of morphine and pimozide
and
on PRL
opioid release
in the external
recently
Such
as
that
a mechanism
/3-endorphin is
of dopamine
receptors
analgesia
in mice
had the opposite
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