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VOLUME 3, NUMBER 1
ABSTRACTS
The role of insulin-like growth factor-I in neuroendocrine function and
the consequent effects on sexual maturation: inferences from animal models
Varadaraj Chandrashekar1,2 and Andrzej Bartke2,3
2Department of Physiology, Southern Illinois University School of Medicine, Carbondale,
IL 62901, USA and
3Internal Medicine, Southern Illinois University School of Medicine,
Springfield, IL 62794, USA
Summary
It is known that growth hormone (GH) plays an important role in growth and
development.Additionally, emerging evidence suggest that it also influences
hypothalamic-pituitary-gonadal function. We have found that GH from different
species has different effects in mice. In rodents, human GH (hGH) binds to
both GH and prolactin (PRL) receptors; it has both somatotrophic and
lactotrophic effects. Since PRL has a profound effect on neuroendocrine
function, the results obtained from hGH treatment or from transgenic animals
expressing the hGH gene reflect PRL-like effects of this hormone. However,
bovine GH (bGH) is purely somatogenic and therefore the effects of bGH
represent the function of the natural GH produced in rodents. Furthermore,
our studies in mice and rats have shown that not all effects of GH are
stimulatory and the duration of exposure of the hypothalamo-hypophyseal-gonadal
system to GH might influence the secretions of gonadotropins and gonadal steroids.
In humans, excess productions of GH in acromegaly and GH resistance in Laron
syndrome adversely affect reproduction. Similarly, it has been demonstrated
that in transgenic mice expressing various GH genes, in insulin-like growth
factor-I (IGF-I) gene-knockout mice, in GH receptor gene-disrupted (GHR-KO)
mice, and in Ames dwarf mice the onset of puberty and/or fertility is altered.
Therefore, excess or subnormal secretion of GH can affect reproduction. We
have shown
that the hypothalamic-pituitary functions are affected in transgenic mice
expressing the GH genes, Ames dwarf mice and in GH receptor gene knockout
mice. The majority of the GH effects are mediated via IGF-I and the
aforementioned effects may be due to the GH-induced IGF-I secretion
or due to the absence of this peptide production. It is important to
realize that the syntheses and actions of IGF binding proteins are
controlled by IGF-I. Furthermore, some IGF binding proteins can inhibit
IGF-I action. Therefore, the concentrations of IGF binding proteins and
the ratio of these binding proteins and IGF-I within the body might play
a pivotal role in modulating IGF-I effects on the neuroendocrine-gonadal
system.
Reproductive Biology 2003 3 (1):
1Address for correspondance: Dr. V. Chandrashekar, Department of Physiology, Life
Science II Building, Southern Illinois University School of Medicine,
Carbondale, Illinois 62901-6512, USA e-mail: vchandrashekar@siumed.edu
Effect of central infusions of neuropeptide Y on GnRH/LH axis in ewes during the early anoestrous period
Anna Wojcik-Gladysz1Tomasz Misztal, Marta Wankowska, Katarzyna Romanowicz, Jolanta Polkowska.
The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Jabłonna, Poland
Summary
Neuropeptide Y (NPY) is a putative mediator of many physiological processes in
the central nervous system including reproductive functions. In this study we
examined the effect of NPY on the GnRH/LH secretory activity in early anoestrous
ewes. Crossbreed ewes one week (group 1w, n=7) and six weeks (group 6w, n=7)
after the last oestrous cycle were infused with Ringer solution (control) or
50 µg of NPY to the third ventricle for 5 minutes. Blood samples were collected
during the days of infusion over six hours at ten minute intervals and then
the ewes were slaughtered and their brains fixed in situ. Immunoreactive (ir)
GnRH in the median eminence and LH cells in the adenohypophysis were localised
by immunohistochemistry technique. Data were generated using computer analysis
to determine the optical density for immuno-staining and the proportion of ir
LH cells. Plasma LH was determined by radioimmunoassay. It was found that
investigated anoestral groups differed only in the optical densities of ir GnRH
and ir LH, which were lower in group 6w compared to group 1w (p<0.001).
LH concentrations and parameters of pulsatile LH secretion were similar in
both anoestral groups. Acute NPY infusions induced in group 1w decreased
both in ir GnRH and ir LH optical densities and in area fraction for ir
LH cells (p<0.001) whilst it increased in plasma LH concentration (p<0.05)
compared to vehicle infused animals. There was no changes in the secretory
activity of the GnRH/LH axis following NPY infusion in group 6w. In conclusion,
we suggest that NPY may be involved in the central regulation of reproductive
function in ewes, however, the sensitivity of the GnRH/LH axis to NPY
modulation declines throughout the early anoestrous period.
Reproductive Biology 2003 3 (1):
1Address for correspondance: The Kielanowski Institute of Animal Physiology
and Nutrition, Polish Academy of Sciences, 05-110 Jablonna, Poland.
email: a.wojcik@ifzz.pan.pl
Histology of salmonid testes during maturation
Dziewulska Katarzyna1, Domagala Jozef
Department of General Zoology, University of Szczecin, Poland
Summary
The commonly applied classification systems of fish gonad maturity divide the
maturation process into certain stages. However, the scales do not entirely
reflect the continuity of the maturation process. Based on light microscope
observations, the paper describes a comprehensive pattern of testicular
transformations during maturation. The study was carried out on precocious
underyearling and 1-year-old males of sea trout (Salmo trutta m. trutta L.),
1-year-old males of salmon (Salmo salar L.), and males of brown trout
(Salmo trutta m. fario L.) aged from 7 months to 4 years. A total of 821
gonads collected during all seasons of the year were examined. The fish
were fixed in Bouin's fluid. Histological slides of the mid-part of the
gonad were made using the standard paraffin technique. The 3-6 µgm sections
were stained with Heidenhain haematoxylin. Histological changes of testes
during maturation were similar in the three species studied. Immature and
resting gonads contained type A spermatogonia in lobules only. The appearance
of cystic structures containing type B spermatogonia in the lobules signalled
the beginning of the sexual cycle in male gonads. Type B spermatogonia
underwent synchronous mitotic divisions resulting in an increase in the total
number of spermatogonia. As the spermatogenesis continued, the gonads showed
a gradual increase in the number of cysts containing cells at all the
spermatogenetic stages: type B spermatogonia, primary and secondary
spermatocytes, spermatids, and spermatozoa. The well-formed spermatozoa
were released to the lobule lumen once the Sertoli cells and spermatozoa
connections broke up and the cyst disappeared. This was a continuous process
observed throughout the spawning season. The spermatozoa were moved to the
efferent duct. While some of the germ cells were completing spermatogenesis,
the lobules contained less and less cysts with type B spermatogonia, primary
and secondary spermatocytes, and spermatids; eventually all the cells completed
spermatogenesis. At the end of maturation, vacuoles, up to 18.9 µgm in final
diameter (brown trout), appeared in the Sertoli cells. The vacuoles were
visible in the lobule wall epithelium for a prolonged period of time. In most
salmonid individuals examined, the reproductive cycles were observed to
overlap. In some fish, the preparation for another cycle began very early,
i.e., at the and of preceding spermatogenesis, which had not been observed
before. Gonad maturation in some males was incomplete.
Reproductive Biology 2003 3(1):
1Address for correspondence: Department of General Zoology, University of Szczecin, ul. Felczaka 3a, 71-412 Szczecin, Poland;
e-mail: katarzyna.dziewulska@univ.szczecin.pl
The effects of estradiol on ß-endorphin, GnRH and galanin content in the oviduct and the uterus of ovariectomized gilts
Stanisław Okrasa1,2, Mariusz T. Skowronski2,
Jaroslaw Staszkiewicz2, Genowefa Kotwica2,
Mirosław Lakomy3 and Adam J. Ziecik4
2Department of Animal Physiology;
3Department of Animal Anatomy, University of Warmia and Mazury, Olsztyn;
4Institute of Animal Reproduction and Food Research of Polish
Academy of Sciences, Olsztyn; Poland
Summary
Steroid hormones are known to affect synthesis and/or release of some
peptides in the central nervous system and peripheral tissues.
In the present study we determined changes in ß-endorphin, GnRH and
galanin contents in uterine and oviductal tissues of ovariectomized
(OVX) gilts following treatment with estradiol benzoate (EB) at a
dose inducing a preovulatory-like LH surge. Seven month old gilts
(90-100 kg of body weight; BW) were used in the study. Four weeks
after ovariectomy, experimental animals were injected intramuscularly
with EB (15 µg/kg BW) at 24 h (n = 5), 48 h (n = 6) or 72 h (n = 5)
before slaughter. Three control gilts received corn oil vehicle.
Tissues were sampled from the ampulla and isthmus of the oviduct
and from the perioviductal, middle and paracervical regions of the
uterine horn for determination of ß-endorphin, GnRH and galanin content.
Significant increases of ß-endorphin content were found in all
regions of the uterus either 24 h or 48 h after priming with EB.
In oviductal tissue, ß-endorphin concentration only tended to
increase in response to EB. GnRH content in tissues originating
from gilts receiving EB fluctuated from a stimulation in the ampulla
of the oviduct and in the paracervical uterus to an inhibition in
the middle part of the uterus. A significantly increased concentration
of galanin in response to EB was observed exclusively in the
paracervical part of the OVX pig uterus. The results suggest
an involvement of ß-endorphin, GnRH and galanin in the regulation
of uterine function in pigs during the periovulatory period
Reproductive Biology 2003 3(1):
1 Address for correspondence: Department of Animal Physiology,
University of Warmia and Mazury, 10-718 Olsztyn, ul. Oczapowskiego
1A, Poland;
e-mail: okrasa@uwm.edu.pl
Effect of antioxidants added to boar semen extender on the semen survival time and sperm chromatin structure
Barbara Szczesniak-Fabianczyk1,2, Michal Bochenek2, Zdzislaw Smorag2, Florian Ryszka3
2Department of Animal Reproduction, National Research Institute of Animal Production, Balice/Krakow;
3Department of Applied Pharmacy and Drug Technology, Silesian Medical Academy, Sosnowiec, Poland
Summary
The aim of the experiment was to determine the effect of potential antioxidants
(adenosine, L cysteine hydrochloride, ascorbic acid, magnesium fumarate and
prolactin) supplementing the Biosolwens extender on semen survival time and
sperm chromatin structure. The semen motility was examined every day and the
susceptibility of sperm chromatin to denaturation was evaluated on collection
day and day 15 of storage. The addition of magnesium fumarate to Biosolwens
extender increased sperm survival but resulted in the highest increment in
the proportion of sperm with damaged chromatin. Biosolwens supplemented with
200 mg of L-cysteine hydrochloride brought the best results. It is possible
that lower concentrations of this component would act in a more protective
manner. The examination of the chromatin structure appears to be an useful
tool for investigation of semen preservation.
Reproductive Biology 2003 3 (1):
1 Address for correspondence: Department of Animal Reproduction, National Research Institute
of Animal Production, 32-083 Balice;
e-mail: bfabianc@izoo.krakow.pl