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The effects of vagotomy on compensatory ovarian hypertrophy and follicular activation after unilateral ovariectomy.

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THE ANATOMICAL RECORD 214%-66 (1986)
The Effects of Vagotomy on Compensatory Ovarian
Hypertrophy and Follicular Activation After
Unilateral Ovariectomy
HUBERT W. BURDEN, IRVIN E. LAWRENCE, JR.,CARLTON P. SMITH, JR.,
JEANNE HOFFMAN, MARILYN LEONARD, DONALD J. FLETCHER,
AND CHARLES A. HODSON
Departments of Anatomv IH. W B.. I. E. L.C.PS.. J. H.. M. L.D.J . E ) and Obstetrics a n t i
Gvneco1og.v fC.A.H.). School o f Metircrnc~.Enst Corolinn Uniuersit.v. Grc.c,rrr-rlle,
NC27834
ABSTRACT
Following unilateral ovariectomy in the rat, the remaining ovary
undergoes rapid compensatory changes including a n increase in the number of
antral follicles (follicular activation) and a n increase in ovarian weight (compensatory ovarian hypertrophy). The ovary is innervated by the vagus nerve (Burden et
al., 1983). In the present study, the effects of right and left cervical vagotomy and
abdominal vagotomy on follicular activation and compensatory ovarian hypertrophy
in the remaining right or left ovary were compared 15 days after unilateral ovariectomy. Neither right nor left cervical vagotomy affected compensatory ovarian hypertrophy of the right or left ovaries but abdominal vagotomy depressed compensatory
ovarian hypertrophy in both the right and left ovaries. Left cervical vagotomy did
not inhibit follicular activation, but right cervical vagotomy prevented follicular
activation in the right but not left ovary. Also, abdominal vagotomy inhibited
follicular activation in the right but not the left ovary. In animals with both ovaries
which were subjected to the left or right cervical vagotomy or abdominal vagotomy
follicular counts in both right and left ovaries were similar. Collectively, these data
indicate that the vagus nerve participates in follicular activation after unilateral
ovariectomy. The data also indicate that the right ovary is more dependent on vagal
influences for follicular activation than the left ovary.
Removal of one ovary from a cycling rat results in a n
increase in the number of antral follicles [follicular activation (FA)] and a n increase in ovarian weight [compensatory ovarian hypertrophy (COH)] (Hatai, 1913;
Arai, 1920). Twice the normal number of ova are produced by the remaining ovary in the next cycle (Peppler
and Greenwald, 1970). This follicular compensation is
attributable to a n increased proliferation of smaller follicles rather than decreased follicular atresia and results in a doubling of the number of large follicles which
ultimately mature (Peppler and Greenwald, 1970).
The proliferation of small antral follicles and increased ovarian weight subsequent to unilateral ovariectomy (ULO) are believed to result from increased pituitary gonadotropin secretion brought about by decreased serum concentrations of ovarian steroids, i.e.,
reduced negative feedback (Ramirez and Sawyer, 1974;
DeGreef et al., 1975). However, Aron et al. (1948) noted
the rapidity of compensatory ovarian responses subsequent to ULO and suggested that nerves were also involved in this phenomenon. Recently, our laboratory
(Burden and Lawrence, 1977; Curry et al., 1984) and
others (Gerendai and HaIasz, 1976; Gerendai et al., 1978;
Gerendai, 1979; 1980; Nance et al., 1983) have reported
results which corroborate the suggestion that nerves are
involved in compensatory ovarian responses.
0 1986 ALAN R. LISS. INC.
The existence of direct neural connections between the
hypothalamus and ovaries has been postulated (Gerendai, 1979; Gerendai, 1980; 1984; Gerendai and Halasz,
1981; Kawakami et al., 1981; Nance et al., 1984) and
recently the existence of a functional difference in the
two halves of the hypothalamus in neuroendocrine regulation has been proposed (Nance et al., 1980; 1983;
1984; Mizunuma et al., 1983; Gerendai, 1984).
There is evidence that sensory components from the
vagus nerve terminate in the ovary (Burden et al., 1983);
however, the precise intraovarian site of these terminals
has not been determined. We have previously shown
that abdominal vagotomy decreased COH after ULO
(Burden and Lawrence, 1977). In the present study, we
analyzed the effects of right vs. left cervical vagotomy
and abdominal vagotomy on compensatory weight gain
of the ipsilateral and contralateral ovary. We also morphometrically analyzed the effects of these neural lesions on the proliferation of follicles in the ovary
remaining after unilateral ovariectomy. Because of the
possible nonspecific debilitating effects of abdominal vagotomy, we also determined the effects of this surgery
on selected functional aspects of an additional endocrine
Received May 24,1985; accepted August 25,1985.
H.W. BURDEN ET AL.
62
TABLE 1. Effect of right (R) or left (L) cervical vagotomy (CV) or abdominal
vagotomy (AV) on body weight (mean f SEM) and ovarian weight (mean f. SEMI on day
15 after surgery
Body weight (g)
Group
day 1
Body weight (g)
day 15
Left ovary
weight (mg)
Right ovary
weight (mg)
Sham (ovaries and
vagi exposed) (6)'
191.0 f 2.7
219.6 f 4.2
30.5 f 1.9
30.9 k 3.0
LCV (10)
RCV (9)
AV (6)
189.2 f 1.9
189.4 2.9
196.0 k 4.9
220.3 f 4.3
213.6 f 4.8
188.5 f 14.2*
34.1 f 1.8
31.4 +_ 2.6
20.7 f 2.2**
36.5 f 2.0
28.6 k 2.0
23.6 k 2.2***
+
'Number of rats in parentheses.
*Significantly different from Sham and LCV (P < ,051.
**Significantly different from other groups (P < .05).
***Significantly different from LCV (P < .05).
gland, viz., the endocrine pancreas. This organ is in- glucagon, and somatostatin were assayed. Serum from
volved in numerous metabolic processes and is known trunk blood collected at the time of death was also frozen
to be innervated by the vagus (see review by Miller, and later assayed for glucose and insulin concentration.
1981) and we felt it might be a site where generalized
Glucose and Hormone Determinations
debilitating effects would be manifested.
Serum glucose was measured by the micromethod of
MATERIALS AND METHODS
Hoffman (1937) using a Technicon autoanalyzer (TechAnimals
nicon Instruments, San Francisco, CAI. Insulin was deNulliparous Sprague-Dawley rats obtained from the termined by radioimmunoassay (Morgan and Lazarow,
Animal Resources Center, East Carolina University, 1963) with crystalline rat insulin (Novo Research Instiwere used in the study. All animals were 8-9 weeks old tute, Copenhagen, Denmark) for the standard. Guinea
and weighed between 180 and 200 g at the initiation of pig anti-insulin serum and rabbit anti-guinea pig serum
the study. The rats were housed in a room with con- were raised and characterized in our laboratory. Gluca
trolled lighting (lights on 0500-1900 hours) and pro- gon was measured by radioimmunoassay (McEvoy et al.,
vided food and water ad libitum. The estrous cycle was 1977)with antiserum 2OC (provided by Dr. R.C. McEvoy,
monitored daily by vaginal lavages and only those rats Mount Sinai School of Medicine) and porcine pancreatic
showing two consecutive 4-5-day cycles were used in glucagon (Novo Research Institute) for standard. Somatostatin was determined by radioimmunoassay
experiments.
(Fletcher et al., 1980)with synthetic cyclic somatostatin
General Surgical Technique
(Calbiochem Biochemicals, San Diego, CA) and antiAnimals were anesthetized at estrus (day 1) with serum R10 (provided by Dr. J.K. Stewart, Virginia Comchloral hydrate (350 mgikg intraperitoneally) and either monwealth University). The intra- and interassay
left or right cervical vagotomy or abdominal vagotomy coefficients of variation for the insulin assay were 2.8%
was performed. For cervical vagotomy, the vagus nerve and 11.1%, respectively; for glucagon, 2.8% and 9.3%;
was isolated from the carotid sheath and a 5-mm portion for somatostatin, 2.5% and 6.9%.
of the nerve was resected. For abdominal vagotomy, the
Morphometric Analysis
liver was reflected, the esophagus was exposed, and the
anterior and posterior vagal trunks were separated from
Ovaries were embedded in paraffin, serially sectioned
the esophagus and carefully avulsed with fine forceps. a t 7 pm, and stained with hematoxylin and eosin. The
The presence of a n enlarged distended stomach was tissue was viewed with a Zeiss Photomicroscope I1 interinterpreted as positive evidence for a complete abdomi- faced with a n Apple ne Microcomputer and a Bioquant
nal vagotomy. In sham-operated animals, the cervical II (R&M Biometrics, Nashville, TN) image analysis sysvagus was exposed bilaterally, but not cut. In the unilat- tem. The procedure for counting follicles was modified
eral ovariectomy studies, either the left or right ovary from Peppler (1971). Briefly, each section was examined
was exposed through a dorsolateral incision, ligated at and antral follicles containing a n oocyte with a nucleothe hilar area, removed, weighed, and fixed in Bouin's lus were measured. Follicles containing a n oocyte with
solution. At day 15, all animals were decapitated, and a pyknotic nucleus or ten or more granulosa cells with
the remaining ovary was weighed and fixed in Bouin's pyknotic nuclei were designated atretic. All antral follisolution for morphometric analysis.
cles, both healthy and atretic, were assigned to one of
The pancreas was dissected, trimmed of gut and major three size classifications: 150-415 pm, 416-570 pm, and
lymph nodes, weighed, and kept a t 0°C until homogeni- over 570 pm diameter. These diameters were calculated
zation. Cold acid-ethanol was added and the pancreas from area measurements based on the assumption that
was homogenized using a Polytron homogenizer (Brink- the follicles were spheres. To obtain follicular area (pm'),
mann Instruments, Westbury, NY). Homogenates were the microscope image was projected on a television monheated for 5 minutes in a 70°C water bath, adjusted to itor interfaced with a digitizer pad. The projected follicle
a volume a t 5 ml, and stored at -20°C until insulin, was measured utilizing the digitizer pad and cursor of
63
VAGOTOMY AND OVARIAN HYPERTROPHY
TABLE 2. Effect of right (R)or left (L) cervical vagotomy (CV) or abdominal vagotomy (AV) on body weight (mean
SEMI and weight of the remaining ovary (mean f SEMI on day 15 after unilateral ovariectomy (ULO) in rats
Group 1
RULO (913
LULO (7)
LCV-RULO (14)
LCV-LULO (21)
RCV-RULO(14)
RCV-LULO (18)
AV-RULO (16)
AV-LULO (15)
Body weight (g)
day 1
Body weight (g)
day 15
Weight (mg) of
initial ovary
Weight (mg) of
remaining ovary
187.8 f 2.8
188.1 f 1.9
190.2 k 2.0
187.5 f 1.3
189.1 & 2.0
191.2 + 2.0
192.8 f 1.8
189.0 f 1.7
220.4 f 3.7
214.0 f 3.0
215.4 f 2.7
215.3 f 2.1
213.5 f 2.5
219.1 k 2.9
190.4 f 9.7
166.2 f 8.7*
36.2 -)r 1.0
38.0 f 2.0
31.7 f 2.0
29.5 1.3
29.5 f 1.4
31.0 f 0.7
35.3 f 1.2
33.0 1.3
55.4 f 2.2
56.0 + 3.0
51.3 k 1.7
48.8 f 1.7
49.5 f 1.1
48.8 + 1.4
34.6 f 2.6
31.1 +_ 3.1
Percent gain in
ovarian weight','
*
53.4 5.3
48.2 f 6.1
67.2 f 8.0
69.5 k 7.4
72.2 k 8.1
58.1 f 4.3
-2.4 f 6.6*
-2.2 + 9.5"
'Calculated in relation to initial ovary weight.
'ARCSIN conversion was used for calculation of significance of percent gain in body weight.
3Number of rats in parentheses.
*Significantly different from other groups (P < ,0001).
TABLE 3. Effect of abdominal vagotomy at estrus (day I) in unilaterally ovariectomized rats on serum and pancreas
parameters (mean f SEM) 15 days later
Group
Sham
Abdominal
(g)
Insulin
concentration
(ng/mgwet
weight)
Glucagon
concentration
(ng/mg wet
weight)
concentration
(ngimg wet
weight)
0.70 k 0.04 (12)
0.75 k 0.04 (13)
50.6 f 5.3 (12)
44.3 f 3.0 (13)
2.11 f 0.17 (12)
2.46 f 0.16 (13)
0.19 k 0.03 (12)
0.21 k 0.02 (13)
Serum
glucose
(mg/dl)
Serum
insulin
(ng/ml)
Wet weight
pancreas
129 f 3 (19)l
126 f 5 (13)
1.5 f 0.1 (19)
1.4 k 0.2 (13)
Somatostatin
vapotomv
'Number in parentheses is number of animals.
the image analysis system. The basement membrane of ble 2). Also, abdominal vagotomy combined with either
the follicle image was circumscribed and the measure- left or right unilateral ovariectomy reduced ovarian
weight at day 15 (Table 2).
ment so obtained was stored for subsequent analysis.
Statistics
Pancreatic Weight and Islet Hormone Values
Multisample numerical data were analyzed by analysis of variance (ANOVA). If significance was obtained
with ANOVA, the Scheffe's test was used for group comparisons. Differences between right and left ovarian
weights and right and left ovarian follicle populations
in animals with both ovaries were assessed with the
paired t test. Also in the ULO study, the number of
follicles in the remaining ovary a t day 15 was compared
to the number at day 1using the paired t test. Glucose,
insulin, glucagon, somatostatin, and pancreatic weight
values in sham-operated and vagotomized rats were
compared with the Student's t test.
Abdominal vagotomy did not alter serum levels of
insulin or glucose, pancreatic wet weight, or the concentration of insulin, glucagon, or somatostatin in the pancreas (Table 3).
RESULTS
Body and Ovary Weights
Ovarian Follicles
In rats bearing both ovaries, neither right nor left
cervical vagotomy nor abdominal vagotomy at day 1
altered the number of follicles in the right or left ovary
at day 15 (Table 4). In the sham-operated rats, there
were more healthy large antral follicles in the right
ovary (Table 4).
After left or right unilateral ovariectomy at day 1,
there was a n increase in the number of healthy antral
follicles in a t least one size category in the remaining
ovary at day 15 (Table 5). This ovarian response is referred to as follicular activation (FA). Left cervical vagotomy did not alter FA in the left or right ovary, but
right cervical vagotomy inhibited FA in the right, but
not left ovary. Likewise, abdominal vagotomy also inhibited FA in the right, but not the left ovary (Table 5).
'
In animals bearing both ovaries, neither sham surgery
nor left or right cervical vagotorny altered body weight
nor left or right ovarian weight on day 15 after surgery.
In contrast, abdominal vagotomy depressed body weight
and both left and right ovarian weight at this time
(Table 1).
In rats subjected to unilateral ovariectomy, neither
DISCUSSION
sham surgery nor left or right cervical vagotomy altered
The
results
of
the
present
study indicate that compenbody weight or ovarian weight at day 15 (Table 2). In
contrast, abdominal vagotomy combined with left uni- satory weight gain of the remaining left or right ovary
lateral ovariectomy reduced body weight at day 15 (Ta- after ULO is not altered by ipsilateral or contralateral
64
H.W. BURDEN ET AL
TABLE 4. Effect of right (R) or left (L) cervical vagotomy (CV) or abdominal vagotomy (AV) at estrus on follicular
development (mean number of follicles f SEM) in the right and left ovary 15 days after surgery
Group
Sham (4)'
Right ovary
Left ovary
RCV (4)
Right ovary
Left ovary
LCV (4)
Right ovary
Left ovary
AV (4)
Right ovary
Left ovary
150-415 p m
416-570 p m
Over 570 pm
Healthy
Atretic
Total antral
follicles
Healthy
Atretic
Healthy
Atretic
55.5 f 2.4
52.5 f 12.0
27.0 f 3.5
23.0 f 5.9
16.5 f 1.6
17.3 t 5.7
7.5 f 0.6
10.3 rf- 1.1
2.5 f 0.6
1.5 0.6
1.3 f 0.5
O*
0.8 f 0.5
0.5 f 0.3
40.5 k 5.0
47.5 f 11.3
18.5 f 3.6
21.8 k 8.1
14.3 k 1.9
16.8 f 2.9
2.3 k 1.3
3.8 f 1.3
0.5 f 0.5
1.3 f 0.6
4.0 f 1.4
3.8 f 1.5
0.8 f 0.8
0.3 f 0.3
56.8 f 5.2
52.5 f 4.7
30.5 f 3.6
30.0 f 3.0
20.3 f 3.1
15.0 f 2.3
5.0 f 2.0
4.5 f 1.7
0.8 f 0.5
2.0 f 0.7
0.3 f 0.3
0.5 f 0.3
0
0.5 f 0.3
42.3 f 6.6
43.8 f 6.5
18.0 f 2.3
17.0 t 2.1
19.8 ir 3.3
21.0 f 5.1
4.0 ir 1.5
4.3 f 1.8
0.5 f 0.5
1.5 f 0.6
0
0
0
+
0
'Number in parentheses is number of animals.
*Significantly different from right ovary (P < .05).
TABLE 5. Effect of right (R) or left (L) cervical vagotomy (CV) or abdominal vagotomy (AV) and R or L unilateral
ovariectomy NJLO)at estrus (day 1) on follicular activation (mean number follicles f SEM) in the remaining
left or rkht ovary 15 days later
Group
Right ULO (4)'
Day 1R ovary
Day 15 L ovary
Left ULO (3)
Day 1L ovary
Day 15 R ovary
LCV-RULO (4)
Day 1R ovary
Day 15 L ovary
LCV-LULO (5)
Day 1L ovary
Day 15 R ovary
RCV-RULO (4)
Day 1R ovary
Day 15 L ovary
RCV-LULO (3)
Day 1L ovary
Day 15 R ovary
AV-RULO (3)
Day 1R ovary
Day 15 L ovary
AV-LULO (4)
Day 1L ovary
Day 15 R ovary
416-570 p m
150-415 pm
Total antral
follicles
Healthv
53.3 If- 9.6
78.8 f 7.2
Over 570 p m
Healthv
Atretic
Atretic
Healthv
Atretic
31.5 f 6.7
31.5 f 3.2
19.3 f 2.5
30.3 6.6
1.0 k 0.7
11.0 k 3.1*
1.3 f 0.8
1.3 f 0.5
0
4.5 f 4.2
0.3 f 0.3
0.3 f 0.3
42.3 f 8.5
56.0 f 4.6
22.3 f 3.8
27.7 f 2.7
19.0 f 5.0
13.0 f 4.0
0.3 t 0.3
13.3 f 2.4*
0.3 f 0.3
1.3 f 0.9
0
0.7 f 0.3
0.3 f 0.3
0
34.5 f 3.8
61.3 f 10.1*
20.5 f 4.1
33.0 f 8.8
10.0 f 0.6
17.3 f 2.1*
2.3 k 1.0
8.8 f 3.0
1.0 f 0.4
1.5 f 0.6
0
0.3 f 0.3
0.8 f 0.5
0.5 k 0.3
49.0 t 8.5
60.4 f 9.4
26.6 k 5.1
31.8 f 5.0
18.6 f 4.2
12.8 f 3.1
2.8 f 1.2
8.4 f 1.7*
0.8 f 0.4
4.0 f 1.0*
0
1.0 k 0.8
0.2 f 0.2
1.8 f 0.8
48.3 f 6.8
50.5 f 6.8
28.0 f 4.9
21.5 3.2
18.8 f 2.8
12.8 f 2.9
0.5 t 0.5
11.3 f 0.9*
0.5 k 0.3
2.3 f 0.5*
0
2.5 f 2.5
0.5 f 0.5
0.3 t 0.3
50.0 f 2.5
57.7 f 4.1
28.0 f 4.2
29.0 f 1.7
20.7 f 2.0
22.7 f 4.6
0
4.3 f 2.2
1.0 f 0.0
1.3 f 0.7
0.3 f 0.3
0.3 f 0.3
0
0
50.7 f 14.7
59.3 f 15.0
30.0 f 7.6
25.3 k 6.6
16.3 t 7.7
17.0 f 5.3
0.3 f 0.3
6.7 k 1.9*
0.7 f 0.7
4.3 f 2.4
3.0 t 2.1
5.0 f 2.6
0.3 f 0.3
1.0 f 0.6
54.7 f 8.4
51.0 & 5.6
33.7 f 6.2
21.0 I 2 . 9
13.0 f 1.7
20.0 f 2.6
5.3 t 2.6
5.0 f 2.6
1.7 f 0.3
4.7 f 2.0
0.7 f 0.7
0.3 t 0.3
0.3 f 0.3
0
~
+
'Number in parentheses is number of animals.
*Significantly different from day 1 (P < .05).
cervical vagotomy at 15 days. Gerendai and Nemeskeri
(1983) reported that when right cervical vagotomy was
combined with left ovariectomy, the weight of the remaining right ovary 48 days later was significantly less
than that from animals with unilateral ovariectomy
alone. Since there was a trend toward this in our study,
perhaps a period longer than the 15 days after ULO is
required for this effect. In contrast to cervical vagotomy,
abdominal vagotomy a t the time of unilateral ovariectomy inhibited compensatory weight gain of both the
left or right ovary 15 days later. This corroborates our
previous studies (Burden and Lawrence, 1977) but is in
contrast to the results of Sanders and Peppler (1982).
These investigators maintained that abdominal vagotomy did not alter ovarian weight gain following ULO
but did alter ovarian function in rats with both ovaries
(Sanders and Peppler, 1982).
In an earlier study, it was reported that abdominal
vagotomy did not affect ovarian weight a t 15 days in
rats with both ovaries intact (Burden and Lawrence,
1977). In the present study we report that abdominal
vagotomy decreased ovarian weight a t 15 days in rats
VAGOTOMY AND OVARIAN HYPERTROPHY
with both ovaries intact. We offer the following explanation for these discrepant results: In the earlier study
ovarian weights (average of 2 ovaries) were reported as
mgI100 g body weight. In the present study, absolute
ovarian weights, both left and right, are reported and
the right ovary is heavier than the left in abdominally
vagotomized rats. Also right ovarian weight of abdominally vagotomized rats is not significantly different from
right ovarian weight of the sham group in the current
study. We believe that the combination of averaging the
weight of the right and left ovaries and expressing the
results as mg/100 g body weight masked differences in
ovarian weight attributable to vagotomy in the earlier
study.
In the current study, right cervical vagotomy and abdominal vagotomy produced seemingly disparate results
in the remaining right ovary after ULO: compensatory
ovarian hypertrophy was not significantly altered at 15
days, but follicular activation was reduced. It is generally believed that compensatory weight gain of the ovary
remaining after ULO is caused by a n increased number
of corpora lutea, resulting from a doubling of the number of follicles which ovulate (Peppler and Greenwald,
1970). Perhaps follicular activation did occur in the animals in the cycle immediately after ULO, but by 15
days, this response was attenuated, while ovarian weight
was still elevated, because of the presence of older corpora lutea. Alternatively, perhaps follicular activation
and compensatory ovarian hypertrophy may not be a
cause and effect phenomenon. Nerves might participate
in the process of follicular development without affecting the weight of the ovary.
The loss of body weight following abdominal vagotomy
has been reported by numerous workers (see review by
Louis-Sylvester, 1983)and this effect has been employed
by some investigators as a criterion for completeness of
surgery (Clarkson et al., 1982). Because of this weight
loss, the possibility of nonspecific effects of this surgery
on ovarian function is always a question. In the present
study, we evaluated selected parameters of the endocrine pancreas as a control because this organ is also
innervated by the vagus nerve (Miller, 1981).Since the
pancreas is involved in numerous metabolic processes,
we felt the condition of this organ would reflect the
generalized metabolic state of the animal. We found no
differences in pancreatic weight, serum glucose, or insulin, nor in pancreatic hormone concentrations 15 days
after abdominal vagotomy. Although we cannot rule out
the possibility that abdominal vagotomy may affect pancreatic function over a longer time interval (e.g., 6-8
weeks), it would appear that the endocrine pancreas is
less sensitive to this procedure than is the ovary. It is
clear that the results obtained with the ovary are attributable to the vagotomy itself and not to the reduced
weight loss, i.e., reduced metabolism, of the animal.
Previous studies have also demonstrated that levels of
high- and low-density lipoproteins were normal in abdominally vagotomized rats (Ojeda et al., 1983).Ovarian
function is not altered in animals subjected to reduced
food intake to mimic the body weight loss induced by
vagotomy (Burden and Lawrence, 1977; Allen et al.,
1983). Collectively, these observations suggest that altered ovarian functions subsequent to vagotomy are not
nonspecific effects attributable to weight loss. Rather,
65
we believe the ovarian effects are caused, a t least in
part, by interruption of specific vagal-ovarian nerves
(Burden et al., 1983).
The results of the current study indicate that neither
left nor right cervical vagotomy nor abdominal vagotomy in rats bearing both ovaries preferentially alters
left or right ovarian weight on day 15. In contrast, following left ULO, the data indicate that the compensatory follicular responses of the right ovary are facilitated
by a n intact vagus nerve. Both right cervical vagotomy
and abdominal vagotomy inhibited follicular activation
in the right ovary after ULO. One might expect cutting
the left cervical vagus to have no effect on ovarian
function since this nerve contributes primarily to the
anterior vagal trunk which innervates the liver, stomach, and pancreas (Hebel and Stromberg, 1976). In contrast, the right cervical vagus contributes primarily to
the posterior vagal trunk, which goes into the celiac
ganglion and is subsequently distributed to more caudal
viscera (Niederhausern, 1953).Our data also show more
large, healthy follicles in the right ovary in intact rats
bearing both ovaries. This corroborates a n earlier observation of Buchanan (1974). Our data also suggests that
function of the right ovary is more dependent than the
left ovary on intact vagal connections. This difference is
more obvious after left unilateral ovariectomy.
We have demonstrated previously that nerves are involved in follicular development after ULO in guinea
pigs (Curry et al., 1984).The mechanism by which nerves
promote folliculogenesis after ULO is uncertain; however, the present study in rats indicates that follicular
development after ULO in the right ovary, but not the
left, is modulated by the vagus nerve. We hypothesize
that right ovarian function is relatively more dependent
on vagal innervation than left ovarian function. Experiments to test this hypothesis are currently in progress.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the secretarial
help of Sue Chapman. This work was supported by grant
HD 06899 from the National Institute of Child Health
and Human Development, United States Public Health
Service.
LITERATURE CITED
Arai, H. (1920) On the cause of the hypertrophy of the surviving ovary
after semi-spaying (albino rat) and on the number of ova in it. Am.
J. Anat., 28:59-79.
Aron, M., C. Aron, and J. Marescaux (1948)Les facteurs du fonctionnement ovarien. Recherches de morphologie experimentale sur certains facteurs intrinseques de ce fonctionuement. C. R. Assoc. Anat.,
3510-47.
Allen, L.G., C.A. Hodson, H.W. Burden, and I.E. Lawrence, Jr. (1983)
Effect of vagotomy on postcastration gonadotropin secretion in
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effect, ovarian, follicular, activation, compensatory, hypertrophic, ovariectomy, unilateral, vagotomy
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