NEUROENDOCRINOLOGY
LETTERS
including
Psychoneuroimmunology, Neuropsychopharmacology,
Reproductive Medicine, Chronobiology
and Human Ethology, ISSN 0172–780X
Effects of estradiol benzoate on the ultrastructure of the
pinealocyte in the ovariectomized rat
by Ilter Kus, Hakan Oner, Candan Ozogul,
Ahmet Ayar, Oguz Aslan Ozen, Mustafa Sarsilmaz
& Haluk Kelestimur
Submitted:
April 25, 2002 Accepted: June 13, 2002
Key
words: pinealocyte, ultrastructure, ovariectomy, estradiol, rat
Abstract
OBJECTIVE:
The aim of this study was to examine the effects of ovariectomy
and ovariectomy followed by estradiol benzoate administration
on the ultrastructure of pinealocytes in female rat.
DESIGN:
For this purpose 15 female Wistar rats were used. Animals
were divided into three groups. Group I and II were designated
as sham-ovariectomized (control) and ovariectomized, respectively.
Group III was ovariectomized and daily injected with estradiol
benzoate for one month. At the end of the experiment, all
animals were anesthetized with ketamine for fixation by vascular
perfusion. Pineal glands of groups I, II and III were removed.
All specimens were examined by electron microscopy.
RESULTS:
Ovariectomy caused an increase of lipid droplets, mitochondria
and ribosomes. Rough endoplasmic reticulum was extensive in
the cytoplasm. Estradiol administration to ovariectomized
rats resulted in formation of less extensive lipid droplets,
mitochondria and ribosomes compared to pinealocyte ultrastructure
of both control and ovariectomized rats. Extensiveness of
rough endoplasmic reticulum in the pinealocytes of estradiol-administrated
rats was similar to that in controls.
CONCLUSIONS:
The results confirm relationship between the pineal gland
and gonads in the rat and it has been suggested that estradiol
benzoate reverses the ultrastructural changes, which indicate
increased cell activation, occurring in the pinealocytes after
ovariectomy.
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Introduction
Introduction
The mammalian pineal gland contains two types of parenchymal
cells. The pinealocytes which form the majority of parenchymal
cells and responsible for melatonin secretion in the pineal
gland. Glial cells serve as supporting cells and they are fewer
in number than pinealocytes [3, 5, 6, 12, 34].
Melatonin is released by the pineal gland during the dark phase
of the day. In many mammals, the pineal gland is involved in
the hypothalmo-hypophysial-gonadal-axis by circadian pattern
of melatonin secretion [1, 42]. It is generally accepted that
melatonin has inhibitory effects on both male and female gonads
by direct (via the melatonin receptors in the reproductive organs)
and indirect (via inhibition of LH release) mechanisms [39].
However, gonadal steroid hormones change both the function and
ultrastructure of the pineal gland in various species [7]. It
has been reported that both gonadal steroid hormones and gonadotropins
modulate melatonin secretion via specific pineal receptors [22].
Animal studies have demonstrated androgen and estrogen receptors
in rat pinealocytes [13]. Additionally presence of androgen
and estrogen receptors in the human pinealocytes has also been
shown [22].
The results of the investigations concerning the effect of gonadal
steroid hormones on the pineal gland are controversial. Several
morphological and biochemical studies indicate an increased
activity of pinealocytes following gonadectomy and this increase
was inhibited by administration of gonadal steroid hormones
[11, 14, 16–18, 20, 29, 32, 33, 36, 41]. Furthermore, It
has been reported that, high levels of melatonin have been found
in women with stress-induced [2] and exercise induced hypothalamic
amenorrhea [21]. Luboshitzky et al, [23] have shown that melatonin
secretion increases in men with a deficiency of gonadotropin-releasing
hormone (GnRH) and decreases to normal levels during testosterone
treatment. However, Satodate et al, [37, 38] reported that depression
in pineal functions after ovariectomy in the rat. Furthermore,
biochemical findings demonstrate that the decrease in melatonin
and protein synthesis in the pineal gland following gonadectomy
in female and male rats is restored to the normal level following
estradiol or testosterone treatment [7, 9, 10, 15, 26, 27, 35,
40].
In the present study, we have examined the effects of ovariectomy
and ovariectomy followed by estradiol benzoate administration
on the ultrastructure of the rat pinealocytes.
