**9.2 The effects of bilateral ovariectomy or adrenalectomy performed using a dorsal or ventral approach**

Compared to animals with a ventral abdominal wall surgery, the effects of ventral bilateral ovariectomy one hour after surgery include lower testosterone and estradiol levels; while ventral bilateral adrenalectomy resulted in lower the progesterone levels (Figure 3). Similar effects were observed when surgeries were performed using the dorsal approach.

The effects of bilateral ovariectomy depend on the day of the cycle when surgery is performed (Flores et al., 2008). For instance, ventral bilateral ovariectomy on diestrus 1 resulted in lower progesterone levels than in animals with ventral wall surgery. These effects were not observed when the treatment was performed on diestrus 2, proestrus or estrus. In turn, dorsal bilateral ovariectomy on proestrus or estrus resulted in higher progesterone levels in serum than in rats with ventral abdominal wall surgery. The effects of bilateral adrenalectomy on progesterone were not impacted by the day of the cycle when surgery was performed or by the surgical approach (Flores et al., 2008). These results suggest that the neural information arriving to the adrenals and ovaries play different roles in regulating progesterone secretion by both organs.

Compared to ventral approach wall surgery treatment, animals with ventral bilateral ovariectomy had lower testosterone serum levels on each day of the estrous cycle. Similarly, ventral bilateral adrenalectomy performed on estrus resulted in lower hormone levels. Testosterone levels were not modified when the adrenals were removed on diestrus 1, diestrus 2 or proestrus. Compared to animals with dorsal wall surgery treatment, testosterone serum levels were lower in rats with dorsal bilateral ovariectomy performed on diestrus 2 or proestrus and higher when treatment was performed on estrus (Flores et al., 2008).

Compared to ventral or dorsal abdominal wall surgery treatment, ventral or dorsal bilateral ovariectomy performed on proestrus resulted in lower estradiol serum levels. Ventral bilateral adrenalectomy performed on diestrus 1 or 2 resulted in higher hormone levels, and

Fig. 2. Comparative effects of ventral or dorsal sectioning the abdominal wall on

effects were observed when surgeries were performed using the dorsal approach.

al., (2008) \* p<0.05 vs. control (MANOVA followed by Tukey's test)

in regulating progesterone secretion by both organs.

**ventral approach**

2008).

progesterone, testosterone, and estradiol serum levels. Based in data published by Flores et

**9.2 The effects of bilateral ovariectomy or adrenalectomy performed using a dorsal or**

Compared to animals with a ventral abdominal wall surgery, the effects of ventral bilateral ovariectomy one hour after surgery include lower testosterone and estradiol levels; while ventral bilateral adrenalectomy resulted in lower the progesterone levels (Figure 3). Similar

The effects of bilateral ovariectomy depend on the day of the cycle when surgery is performed (Flores et al., 2008). For instance, ventral bilateral ovariectomy on diestrus 1 resulted in lower progesterone levels than in animals with ventral wall surgery. These effects were not observed when the treatment was performed on diestrus 2, proestrus or estrus. In turn, dorsal bilateral ovariectomy on proestrus or estrus resulted in higher progesterone levels in serum than in rats with ventral abdominal wall surgery. The effects of bilateral adrenalectomy on progesterone were not impacted by the day of the cycle when surgery was performed or by the surgical approach (Flores et al., 2008). These results suggest that the neural information arriving to the adrenals and ovaries play different roles

Compared to ventral approach wall surgery treatment, animals with ventral bilateral ovariectomy had lower testosterone serum levels on each day of the estrous cycle. Similarly, ventral bilateral adrenalectomy performed on estrus resulted in lower hormone levels. Testosterone levels were not modified when the adrenals were removed on diestrus 1, diestrus 2 or proestrus. Compared to animals with dorsal wall surgery treatment, testosterone serum levels were lower in rats with dorsal bilateral ovariectomy performed on diestrus 2 or proestrus and higher when treatment was performed on estrus (Flores et al.,

Compared to ventral or dorsal abdominal wall surgery treatment, ventral or dorsal bilateral ovariectomy performed on proestrus resulted in lower estradiol serum levels. Ventral bilateral adrenalectomy performed on diestrus 1 or 2 resulted in higher hormone levels, and lower when surgery was performed using a dorsal approach; and an inverse result occurred when the animals were treated on estrus (Flores et al., 2008).

Bilateral ovariectomy and adrenalectomy modify progesterone, testosterone and estradiol serum levels depending on the day of the cycle and the surgical approach. Analyzing the effects of dorsal or ventral bilateral ovariectomy or adrenalectomy on progesterone, testosterone and estradiol levels, suggest that the stimulatory/inhibitory signals arising from the dorsal or ventral abdominal wall modifies the sensitivity of the theca interna and granulosa cells to the hormonal signals regulating their functions.

The results obtained from rats with bilateral ovariectomy or adrenalectomy suggests that the ovaries mainly produce testosterone and estradiol, while the adrenals are the main producer of progesterone. The effects of bilateral adrenalectomy performed on different days of the estrous cycle on testosterone and estradiol serum levels (Flores et al., 2008) suggest that endocrine signals arising from the adrenals (corticosterone and progesterone) play a role regulating ovarian steroids release. It is possible that at the CSMG level, bilateral adrenalectomy modified the functions of the neurons originating in the SON and the nerve of the ovarian plexus that innervate the ovaries.

Fig. 3. Comparative effects of ventral bilateral ovariectomy or ventral adrenalectomy on progesterone, testosterone and estradiol serum levels. Based on data published by Flores et al., (2008) \* p<0.05 vs. abdominal wall surgery (MANOVA followed by Tukey's test)

### **9.3 The effects of unilateral ovariectomy**

The acute effects of hemiovariectomy on progesterone, testosterone, estradiol, and LH concentrations in serum depends on the surgical approach and the day of the cycle when surgery is performed (Barco et al., 2003; Flores et al., 2005, 2006, 2011; Cruz et al., 2006). Figure 4 shows the comparative effects of ventral unilateral mechanical stimulation of the SON and unilateral ventral ovariectomy, performed on each day of the estrous cycle, on progesterone, testosterone and estradiol serum levels analyzed one hour after treatment. The ventral mechanical stimulation of the left or right SON of rats in estrus resulted in higher progesterone levels. While extirpating the left ovary eliminated the progesterone levels increase, extirpating the right ovary did not. Regardless of the day of the estrus cycle

Hormonal and Neural Mechanisms Regulating Hormone Steroids Secretion 21

The ovaries receive innervations arriving through the SON, the ovarian plexus nerve, and the vagus nerve. Since each nerve carries different neural information, we postulate that the unilateral or bilateral sectioning of each nerve will produce different effects on the secretion

The SON and the ovarian plexus nerve carry catecholaminergic fibers that innervate endocrine ovarian cells. These fibers are distributed in the peri-follicular theca layer and are closely related to the theca internal cells. According to Burden (1978) and Aguado (2002), most neurons originating in the SON fibers are located in the CSMG. Aside from the catecholaminergic innervation, the SON provides VIP (Garraza et al., 2004) and NO (Casais et al., 2007) innervations to the ovaries. 24 and 72 hrs after unilateral or bilateral sectioning of the SON of pre-pubertal rats, NA levels in the denervated ovary were lower than in

Aguado & Ojeda (1984) observed that after sectioning both SON on proestrus the secretion of progesterone and estradiol from both ovaries dropped immediately (four minutes). Progesterone secretion was recovered 15 minutes later, but estradiol levels kept low. Sectioning the SON on estrus did not modify hormone secretion. The effects of denervation depended on the hour of the day when surgery was performed. According to the authors, their results support the idea that the CNS controls directly the hormone release by the

In gilts, sectioning the plexus and the SON during the middle luteal phase of the estrous cycle lowered the number of dopamine-beta-hydroxylase- and/or neuropeptide tyrosineimmunereactive nerve terminals. The treatment also lowered the levels of progesterone, androstenedione, and testosterone in the fluid and the wall of follicles. Neurectomy increased the immune expression of cholesterol side-chain cleavage cytochrome P450, lowered the expression of 33-hydroxysteroid dehydrogenase, and lowered the plasma levels of LH, progesterone, androstenedione, testosterone, estrone and estradiol-17beta. The results suggest that ovarian innervations play a role regulating the steroidogenic activity of

Figure 5 shows the comparative effects of ventral unilateral mechanical stimulation of the SON on ovarian hormone secretion. From the graph, it is apparent that progesterone and testosterone levels in serum were modified by mechanically manipulating the SON, while

As with unilateral ovariectomy, the acute effects of ventral unilateral sectioning of the SON on progesterone, testosterone and estradiol serum levels presents asymmetry and vary

Ovarian denervation performed by unilaterally sectioning the vagus nerve, by a ventral approach, has different effects on normal cyclic rats and ULO rats. Sectioning the left vagus nerve resulted in lower ovulation rates than in sham operated animals; while sectioning the right vagus nerve did not modify ovulation rates. Sectioning the right or left vagus nerves to right-ULO rats (left ovary in-situ) reduced compensatory ovarian hypertrophy. Sectioning the left vagus nerve to ULO rats induced different effects depending on which ovary remained in-situ. Left-side vagotomy performed to right ULO rats (left ovary in-situ) resulted in higher ovulation rates, compensatory ovarian hypertrophy, and number of ova shed; while the same procedure to left ULO rats (right ovary in-situ) resulted in a decrease

according the day of the cycle when surgery was performed (Flores et al., 2011).

**9.4 The effects of unilateral or bilateral ovarian denervation**

untouched (control) or laparotomized animals (Chávez et al., 1994).

of steroid hormones by the ovaries.

ovaries.

the ovary (Jana et al., 2007).

of the same parameters.

changes in estradiol serum levels are not significant.

Testosterone

Fig. 4. Comparative effects of ventral unilateral mechanical stimulation of the SON and ventral unilateral ovariectomy performed each day of the estrous cycle on: progesterone (ng/mL), testosterone and estradiol (pg/mL) one hour after surgery. \* p<0.05 vs. surgery. Ventral surgery; mechanical stimulation of the SON; unilateral ovariectomy (ULO)

Sugery Stimulation ULO

Sugery Stimulation ULO

rats were treated on, stimulating the left SON resulted in higher testosterone levels, while stimulating the right SON did not have an apparent effect on testosterone. Higher testosterone levels in serum resulting from the stimulation of the left SON were eliminated when the right ovary was subsequently removed. In rats on estrus, stimulating the left or right SON increased estradiol levels, and ventral ovariectomy eliminated it.

These results suggest that mechanically stimulating the SON on estrus day stimulates the transport of cholesterol to the mitochondria, and the performance of the enzymes participating in the synthesis of progesterone and estradiol in both ovaries. Effects on testosterone levels were observed only when the left ovary was manipulated, suggesting an asymmetric participation of the ovarian innervation in regulating testosterone, and that such asymmetry depends on the day of the estrous cycle.

In other studies, the acute and non-acute effects of dorsal unilateral ovariectomy on progesterone, testosterone and estradiol serum levels vary according to the time elapsed between surgery and autopsy (Morales et al., 2011).