Dose-dependent effects of the antiprogestin, RU486, on sexual behavior of naturally cycling Fischer rats

Huperzine-A administration recovers rat ovary function after sympathetic stress

Chronic cold stress affects ovarian morphology and impairs fertility in rats. It causes an ovarian polycystic ovary (PCOS)-like phenotype, which resembles PCOS in women. The mechanism of cold stress action involves increased ovarian noradrenaline (NA) levels, which remain elevated after cessation of cold stress. By contrast, ovarian acetylcholine (ACh) levels are only transiently elevated and returned to control levels after a 28-day post stress period. Because ACh can exert trophic actions in the ovary, we hypothesised that a sustained elevation of ovarian ACh levels by intraovarian exposure to the ACh-esterase blocker huperzine-A (Hup-A) may interfere with cold stress-induced ovarian changes. This possibility was examined in female Sprague-Dawley rats exposed to cold stress (4°C for 3 h day^-1 for 28 days), followed by a 28-day period without stress. To elevate ACh, in a second group Hup-A was delivered into the ovary of cold stress-exposed rats. A third group was not exposed to cold stress. As expected, cold stress elevated ovarian NA, reduced the number of corpora lutea and increased the number of follicular cysts. It increased plasma testosterone and oestradiol but decreased plasma levels of progesterone. In the Hup-A group, ovarian levels of both, NA and ACh, were elevated, there were fewer cysts and normal testosterone and oestradiol plasma levels were found. However, progesterone levels remained low. Most likely, low progesterone was associated with impaired mating behaviour and low pregnancy rate. We propose that elevated intraovarian levels of ACh are involved in the rescue of ovarian function, opening a target to control ovarian diseases affecting follicular development.

Consequences of steroid-5α-reductase deficiency and inhibition in vertebrates

In 1974, a lack of 5α-dihydrotestosterone (5α-DHT), the most potent androgen across species except for fish, was shown to be the origin of a type of pseudohermaphrodism in which boys have female-like external genitalia. This human intersex condition is linked to a mutation in the steroid-5α-reductase type 2 (SRD5α2) gene, which usually produces an important enzyme capable of reducing the Δ⁴-ene of steroid C-19 and C-21 into a 5α-stereoisomer. Seeing the potential of SRD5α2 as a target for androgen synthesis, pharmaceutical companies developed 5α-reductase inhibitors (5ARIs), such as finasteride (FIN) and dutasteride (DUT) to target SRD5α2 in benign prostatic hyperplasia and androgenic alopecia. In addition to human treatment, the development of 5ARIs also enabled further research of SRD5α functions. Therefore, this review details the morphological, physiological, and molecular effects of the lack of SRD5α activity induced by both SRD5α mutations and inhibitor exposures across species. More specifically, data highlights 1) the role of 5α-DHT in the development of male secondary sexual organs in vertebrates and sex determination in non-mammalian vertebrates, 2) the role of SRD5α1 in the synthesis of the neurosteroid allopregnanolone (ALLO) and 5α-androstane-3α,17β-diol (3α-diol), which are involved in anxiety and sexual behavior, respectively, and 3) the role of SRD5α3 in N-glycosylation. This review also features the lesser known functions of SRD5αs in steroid degradation in the uterus during pregnancy and glucocorticoid clearance in the liver. Additionally, the review describes the regulation of SRD5αs by the receptors of androgens, progesterone, estrogen, and thyroid hormones, as well as their differential DNA methylation. Factors known to be involved in their differential methylation are age, inflammation, and mental stimulation. Overall, this review helps shed light on the various essential functions of SRD5αs across species.

[A role of progesterone and its metabolites in regulation functions of the brain]

The review presents literature data reflecting the nature and mechanism of the effect of progesterone and its metabolites on human and animal brain structures. Particular attention is paid to neuroprotective, anticonvulsant, anti-anxiety and sedative properties of this hormone, which determines the prospect of its use for the prevention and treatment of human neurodegenerative diseases, epilepsy, sleep disorders, and anxiety-depressive spectrum disorders, including premenstrual and climacteric syndromes.

Estrogen-dependent estrous behavior in rabbits is antagonized by the antiprogestin RU486

Estrogen receptor-alpha (ERα) dimerizes with unliganded progesterone receptor (PR) in target tissues to trigger genomic and non-genomic effects. In ovariectomized rats the antiprogestin RU486 or antisense nucleotides against PR antagonize estradiol-induced sexual receptivity. We determined the relevance of unliganded PR for the expression of estrogen-dependent scent-marking (chinning) and sexual receptivity by injecting RU486 to: a) ovariectomized (ovx) rabbits given estradiol benzoate (EB; 5μg/day); b) intact rabbits. Chinning and lordosis were quantified in ovx animals before (5days; baseline) and during hormonal treatments: EB+RU486 (20mg/day; n=18) or EB+vehicle (n=18). On treatment day 4 LQ (lordosis quotient) increased in both groups, relative to baseline (mean±se): LQ=1±5 (baseline) vs 25±21 (EB+RU486) and 2±6 (baseline) vs 37±29 (EB+vehicle). On day 9 LQ values were: 22±23 (EB+RU486) and 54±39 (EB+vehicle). Chinning increased only in the EB+vehicle group (day 9=55±46 vs baseline=17±20 marks/10min). In intact rabbits one RU486 injection: reduced the LQ from 72±7to 36±8 five hrs later, increased the latency to receive first ejaculation from 45 to 98s, and decreased the number of ejaculations received in the test from 3 to 2 but did not modify mounting latency or chinning. Results support a participation of unliganded PR for the induction (ovx) and maintenance (intact) of rabbit estrous behavior by estrogens.

The ventromedial hypothalamus oxytocin induces locomotor behavior regulated by estrogen

Our previous studies demonstrated that excitation of neurons in the rat ventromedial hypothalamus (VMH) induced locomotor activity. An oxytocin receptor (Oxtr) exists in the VMH and plays a role in regulating sexual behavior. However, the role of Oxtr in the VMH in locomotor activity is not clear. In this study we examined the roles of oxytocin in the VMH in running behavior, and also investigated the involvement of estrogen in this behavioral change. Microinjection of oxytocin into the VMH induced a dose-dependent increase in the running behavior in male rats. The oxytocin-induced running activity was inhibited by simultaneous injection of Oxtr-antagonist, (d(CH2)5(1), Try(Me)(2), Orn(8))-oxytocin. Oxytocin injection also induced running behavior in ovariectomized (OVX) female rats. Pretreatment of the OVX rats with estrogen augmented the oxytocin-induced running activity twofold, and increased the Oxtr mRNA in the VMH threefold. During the estrus cycle locomotor activity spontaneously increased in the dark period of proestrus. The Oxtr mRNA was up-regulated in the proestrus afternoon. Blockade of oxytocin neurotransmission by its antagonist before the onset of the dark period of proestrus decreased the following nocturnal locomotor activity. These findings demonstrate that Oxtr in the VMH is involved in the induction of running behavior and that estrogen facilitates this effect by means of Oxtr up-regulation, suggesting the involvement of oxytocin in the locomotor activity of proestrus female rats.

Repeated estradiol benzoate treatment protects against the lordosis-inhibitory effects of restraint and prevents effects of the antiprogestin, RU486

The following experiment was designed to test two specific questions: (1) Does the antiprogestin, RU486, reduce emergence of lordosis behavior and/or proceptivity in rats given repeated treatment with 10μg estradiol benzoate (EB) and/or a single high dose (40μg) of EB? (2) Does RU486 accentuate the effects of a 5min restraint experience on sexual behaviors in rats given repeated treatment with estradiol benzoate (EB) and/or a high dose of EB? RU486 was used to determine if a high dose and/or repeated treatment with EB enhanced proceptivity and reduced the response to mild stress through an intracellular progesterone receptor-mediated process. Ovariectomized Fischer rats were injected with a single dose of 10 or 40μg estradiol benzoate (EB) or received 4consecutiveweeks of treatment with 10μg EB. Forty-eight hours after the last treatment with EB, rats were injected with 5mg/kg of the antiprogestin, RU486, or the RU486 vehicle. That afternoon, rats were monitored for sexual behaviors. Sexually-receptive rats were then restrained for 5min and again tested for sexual behaviors. A separate set of rats received 4consecutiveweeks of 10μg EB treatment before treatment with a higher (5mg/rat) dose of RU486. Lordosis to mount ratios, lordosis quality, proceptivity, and resistance were monitored. RU486 had no effect on the emergence of sexual behaviors but did accentuate the lordosis-inhibitory effect of restraint in rats given a single treatment with EB. Rats treated for 4consecutiveweeks with EB showed no effect of restraint and were unaffected by RU486. These findings lead to the suggestion that repeated EB initiates select behavioral effects that are not mimicked by acute EB treatment and that the intracellular progesterone receptor may not be involved.