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Effects
of Leptin and Neuropeptide Y (NPY) on Hormones Release in Female
Rats
Monika
Borowiec,
Elzbieta Wasilewska-Dziubiñska,
Magdalena Chmielowska,
Ewa Woliñska-Witort
Boguslawa Baranowska
Department
of Clinical Neuroendocrinology, Medical Centre of Postgraduate
Education, Fieldorfa 40, 04-158 Warsaw, POLAND.
Submitted:
November 4, 2001
Accepted: November 26, 2001
Key words:
VIP, PACAP, progesterone, phenylonephrine, fenoterol,
25-hyroxycholesterol, culture of rat granulosa cells
Abstract
OBJECTIVES:
The aim of this study was to investigate the influence of
NMMA on the mechanism of leptin and NPY action in in vivo
and in vitro on pituitary hormone release by female rats in
diestrus.
METHODS:
In vivo experiments based on four-day ip injections of: 1)
murine recombinant leptin (mrLep); 2) human NPY; 3) saline;
4) NMMA (50 mg) was applied prior
to administration of mrLep; 5) NMMA (50 mg)
was applied prior to administration of NPY; 6) NMMA (50 mg);
7) NMMA (350 mg) was applied prior
to administration of mrLep; 8) NMMA (350 mg).
The blood samples for LH and FSH were collected after decapitation
of animals on the fifth day of study. In vitro experiments
studied the effects of these peptides on LH release from pituitary
cell culture.
RESULTS:
In vivo: Leptin+ NMMA (50 mg) stimulated
LH. NPY+ NMMA (50mg) increased
LH. NMMA (350 mg) stimulated FSH
release. In vitro: The stimulatory effect of leptin on LH
release in vitro was observed after 120 min of incubation,
but after 60 mins of incubation the inhibitory effect of leptin
on LH release was increased by NMMA. Leptin +NMMA (vs NMMA)
decreased LH release with highest statistical significance.
NPY 10 nM 60 min after incubation decreased LH release. There
was no effect of NMMA on LH release.
CONCLUSION:
In vivo results show, that NO probably mediates in leptin
action on LH release. Moreover, effects of leptin on LH release
from cultured pituitary cells are dependent on time of incubation.
NPY decreased LH release in vitro.
Introduction
There
is no doubt that leptin plays an important role in neuroendocrine
function of the organism. The 16-kilodalton protein, leptin
is widely distributed in many tissues e.g.: stomach [1], brain
[2] but the main source of leptin is white adipose tissue [3].
Observations and localization of leptin receptor in many brain
regions led to conclusion that the main site of leptin action
is hypothalamus, especially arcuate nucleus (ARC) [4, 5]. However,
the leptin receptor has been also identified in the pituitary
gland [6, 7]. In genetically obese ob/ob mice with lack of circulating
OB protein - leptin, the overexpression of neuropeptide Y gene,
an orexigenic factor was observed [8]. In these animals with
biochemical disturbances coexists the delay in puberty, for
immature mice, or infertility, in case of mature ones [9]. The
defect is probably due to hypothalamic deficiency of GnRH secretion,
as shown by reversing this inhibition of secretion of LH by
exogenous GnRH administration to the pituitary [10].
There
is a controversy regarding the influence of neuropeptide Y and
leptin on luteinizing hormone secretion. The first hormone probably
stimulates the LH secretion in the mechanism of facilitating
LH-RH (Gn-RH) action [11, 12]. However, evidences of central
administration NPY inhibiting effects on LH secretion via NPY-Y5
receptor subtype were also demonstrated [13]. The leptin effects
on LH release are unclear yet and still need to be evaluated.
In this paper we tried to thoroughly evaluate the mechanism
of leptin and NPY action on LH release in vitro and in vivo.
We used NMMA as the inhibitor of nitric oxide synthase. This
enzyme is important in the biochemical pathway of nitric oxide
(NO).
Materials
and Methods:
Animals; Materials; 1. Studies In Vivo; 2. Studies in Vitro;
Statistical Evaluation
Results:
Effects of Leptin, NPY and NMA on pituitay hormone release in
vivo;
Effects of Leptin, NPY and NMA on pituitay hormone release from
cultured pituitary cells
Discussion
The
aim of our study was to thoroughly investigate the effects of
leptin and neuropeptide Y (NPY) in the in vivo and in vitro
experiments in order to asses the secretion of luteinizing hormone
(LH) and follicle-stimulating hormone (FSH). We proposed to
investigate these effects in the intact cycling female rats,
choosing the peripheral form of leptin and NPY injections -
intraperitoneal (ip) and using NG -monomethyl-L-arginine (NMMA)
to asses the possibly role of nitric oxide (NO) in the mechanism
of leptin and NPY actions.
It was clearly demonstrated that ... ...
...
...
Conclusions
-
Leptin action on LH release in vivo in intact cycling female
rats in diestrus is ... ...
-
Effects of leptin on LH release from cultured pituitary cells
depend on ... ...
-
NPY reduced ... ...
- NMMA
had ... ...
Acknowledgments
The authors would like to thank NDDK’s National Hormone
and Pituitary Programm and Dr A.F.Parlow for providing rat LH
and FSH RIA reagents and standard preparations and murine leptin.
The work was supported in part by scientific programm No 501-2-2-25-40/99
and a grant No 4P05A 135 18 from The State Committee for Scientific
Research.
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