Abstract
The superior ovarian nerve (SON) provides neuropeptide-Y, norepinephrine and vasoactive intestinal peptide (VIP) to the ovaries. Ovarian steroidogenesis is modulated by the SON. In the cyclic rat, the acute steroidogenic response to ovarian microinjection of VIP is asymmetric and varies during the estrous cycle. In the present study, we analyze whether the differential effects of VIP in each ovary are modulated by the neural signals arriving through the SON. Cyclic female rats were submitted on diestrus-1, diestrus-2, proestrus, or estrus to a unilateral section of the SON, and immediately afterward, the denervated ovary was either microinjected or not with VIP. Animals were sacrificed 1 h after treatment. The injection of VIP into the left denervated ovary performed on diestrus-1 decreased progesterone levels in comparison with the left SON sectioning group; similar effects were observed on proestrus when VIP was injected into either of the denervated ovaries. Compared to the left SON sectioning group, VIP treatment into the left denervated ovary on diestrus-2 or proestrus decreased testosterone levels, whereas on diestrus-1, proestrus or estrus, the same treatment resulted in higher estradiol levels. Compared to the right SON sectioning group, VIP injected into the right denervated ovary yielded higher testosterone levels on diestrus-1 and estrus and lower testosterone levels on proestrus. VIP injection into the right denervated ovary increased estradiol levels on diestrus-2 or estrus while decreasing them on proestrus. Our results indicate that in the adult cyclic rat, the set neural signals arriving to the ovaries through the SON asymmetrically modulate the role of VIP on steroid hormone secretion, depending on the endocrine status of the animal. The results also support the hypothesis that the left and right ovary respond differently to the VIPergic stimulus.
Highlights
The function and control of endocrine-paired organs are not identical (Klein and Burden, 1988; Frankel et al, 1989; Morán et al, 2005; Tóth et al, 2007; Gerendai et al, 2009; Domínguez and Cruz-Morales, 2011)
We showed that one or 24 h after microinjecting Vasoactive Intestinal Peptide (VIP) into the left or right ovary, steroid hormone levels were different depending on the treated ovary, the day of the estrous cycle and the time elapsed between treatment and autopsy
Given that during the rat’s estrous cycle, the adrenal glands are the main source of progesterone (Flores et al, 2008), and under stress conditions is the only source of progesterone (Budec et al, 2002; Romeo et al, 2004; Kalil et al, 2013; Kalász et al, 2014), we suggest that the higher progesterone levels found in sham surgery treated animals are due to the stress caused by the perforation of the peritoneum
Summary
The function and control of endocrine-paired organs are not identical (Klein and Burden, 1988; Frankel et al, 1989; Morán et al, 2005; Tóth et al, 2007; Gerendai et al, 2009; Domínguez and Cruz-Morales, 2011). Regarding the spontaneous release of oocytes, the left ovary appears to be more competent than the right (Domínguez et al, 1989). Such asymmetries are related to the innervation received by the ovaries (Domínguez et al, 2011); this innervation is different for the left and right ovary (Klein and Burden, 1988; Tóth et al, 2007; Gerendai et al, 2009). The rat ovary is innervated by two sympathetic sources, the ovarian plexus nerve and the SON (Lawrence and Burden, 1980). The SON is the main source of NE (Aguado and Ojeda, 1984b) and VIP to the ovary (Dees et al, 1986; Advis et al, 1989)
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