Involvement
of Beta-adrenoceptors in a Central Regulation of the Ovarian
Progesterone Release in Rats
Miguel Angel De Bortoli 1,
Marisa Hilda Garraza 1
Luis Inocencio Aguado 1,2
1. Laboratorio de Biología de la Reproducción
(LABIR), Universidad Nacional de San Luis, San Luis, Argentina.
2. CONICET career scientist.
Submitted:
November 12, 2001
Accepted: December 7, 2001
Key
words:
beta-adrenoceptors, intracerebroventricular, progesterone,
ovary, superior ovarian nerve
Abstract
The intracerebroventricular (i.c.v.) injection of epinephrine
modifies ovarian progesterone (P) release in rats on diestrus
day 2 (D2).
OBJECTIVES:
To investigate the characteristic of a central adrenergic
effect on the ovarian P release on D2. Also, the function
of the superior ovarian nerve (SON) is re-examined.
METHODS
AND RESULTS:P concentrations were measured using radioimmunoassay
techniques. The i.c.v. injection of 5 mg isoproterenol (beta-adrenergic
agonist) in SON-intact rats on D2, decreased the P levels
in ovarian vein blood from 1 to 25 min after injection (p<0.05).
Similar treatment in SON-transected rats did not modify the
P concentrations in ovarian vein blood between 1 and 25 min
after injection. After 5 µg propranolol (beta-adrenergic
antagonist) i.c.v. injection in SON-intact rats, the P levels
in ovarian vein blood increased from 2 to 4 min (p<0.05).
Similar treatment in SON-transected rats did not change the
P concentrations in ovarian vein blood during 25 min after
injection. The i.c.v. injection of 5 µg phenylephrine
(alpha-adrenergic agonist) in SON-intact or SON-transected
rats, did not modify the P levels in ovarian vein blood between
1 and 25 min after injection. After 5 µg phentolamine
(alpha-adrenergic antagonist) i.c.v. injection in SON-intact
or SON-transected rats, the P concentrations in ovarian vein
blood did not change during 25 min.
CONCLUSIONS:
These results suggest the participation of central beta-adrenergic
receptors in the neural regulation of the ovarian P release
in rats on D2, and, furthermore, that the central beta-adrenergic
input is conduced almost entirely through the superior ovarian
nerve.
Introduction
The
rat ovary has been described as receiving innervation from
two main sources: the ovarian plexus nerve that travels along
the ovarian artery, and the SON which is associated with the
suspensory ligament [1, 2]. Also, the neurons from which the
SON originates are located in para- and prevertebral ganglia
[3]. Microscopic studies show that the SON fibers end directly
on the secondary interstitial cells and near the theca interstitial
cells, while the fibers coming from the ovarian plexus nerve
are associated with the ovarian vascular system [2, 4]. Beta-adrenergic
receptors have been characterized in different populations
of ovarian cells [5]. The occupation of such receptors with
adrenergic agonists induces ovarian P and androgens release
in vitro [4, 5, 6].
Transection of the SON causes a drop in the number of the
ovarian beta-adrenergic receptors 48 hs later [7], while transection
leads to an increase of these receptors after 7 days [8].
Additionally, the electrical stimulation or the acute transection
of the SON performed in live anaesthetized animals enhances
or inhibits the P release from the ovary, respectively [9].
Furthermore, evidence of communication between brain neurons
and the ovary has been provided by electrical stimulation
of the central nuclei of rats [10, 11], producing changes
in both the release and synthesis of estrogen and progesterone
by the ovary.
The i.c.v. injection of epinephrine increases the P concentration
in ovarian vein blood of rat - in short times - on diestrus
day 1, and decreases it on D2 [12]. The epinephrine effect
is not mediated by LH and is driven almost entirely through
the SON. Also, this central adrenergic stimulus competes with
LH in ovarian P and androstenedione response on D2 [13].
Although important advances have been made in this field,
the physiological role of the ovarian innervation in modulating
steroids release remains incomplete. The objective of this
work was to investigate the characteristic of the central
adrenergic effect on the ovarian progesterone release in rats
on D2. Also, the participation of the SON was re-examined.
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