Brain neuronal activation induced by flibanserin treatment in female rats

Effects of cabergoline and dimethylcabergoline on the sexual behavior of male rats

RATIONALE

Cabergoline (CAB) is an ergot derivative typically prescribed for the treatment of hyperprolactinemia. It suppresses the release of prolactin through agonist actions on dopamine (DA) D2 receptors; however, it possesses binding affinity for other DA and 5-HT receptors. Side effects that exacerbate valvular heart disease can occur with high doses.

OBJECTIVE

The present study examined the acute, subchronic, and chronic dose-response effects of CAB and a derivative dimethylcabergoline (DMC) which acts as an antagonist instead of agonist at 5-HT 2B receptors, on appetitive and consummatory sexual behaviors of male rats.

METHODS

CAB (0, 0.03, 0.15, or 0.3 mg/kg/ml) was administered daily to sexually experienced male rats (N = 10/dose) by oral gavage for a total of 68 days. Sexual behavior was tested every 4 days during this period for a total of 16 trials. On the 17th trial, rats were administered their dose of CAB, and 4 h after were overdosed with sodium pentobarbital, perfused intracardially, and their brains processed for Fos immunohistochemistry. DMC (0, 0.03, 0.15, 0.3 mg/kg/ml) was administered daily to sexually experienced male rats (N = 10/dose) by oral gavage for a total of 36 days. Sexual behavior was tested every 4 days for a total of 9 trials.

RESULTS

CAB increased anticipatory level changes, intromissions, and ejaculations significantly across all timepoints, with the medium and high doses being most potent. The medium and high doses also increased Fos protein significantly within the medial preoptic area, whereas in the nucleus accumbens shell, the low and medium doses decreased Fos protein but the high dose increased it significantly from control. Similar to CAB, the medium and high doses of DMC increased the number of ejaculations significantly. Rats in all drug dose groups appeared healthy for the duration of the experiments.

CONCLUSIONS

Both CAB and DMC facilitate ejaculations, and CAB further facilitates measures of anticipatory sexual motivation and intromissions. These data suggest that both could be used as treatments for sexual arousal disorders and ejaculation/orgasm disorders with little or no untoward side effects at low doses.

Cardioprotective Effect of Flibanserin against Isoproterenol-Induced Myocardial Infarction in Female Rats: Role of Cardiac 5-HT2A Receptor Gene/5-HT/Ca2+ Pathway

Myocardial infarction (MI) is a life-threatening ischemic disease and is one of the leading causes of morbidity and mortality worldwide. Serotonin (5-HT) release during myocardial ischemia plays an important role in the progression of myocardial cellular injury. This study was conducted to investigate the possible cardioprotective effect of flibanserin (FLP) against isoproterenol (ISO)-induced MI in rats. Rats were randomly divided into five groups and were treated orally (p.o.) with FLP (15, 30, and 45 mg/kg) for 28 days. ISO was administered subcutaneously (S.C.) (85 mg/kg) on the 27th and 28th days to induce MI. ISO-induced myocardial infarcted rats exhibited a significant increase in cardiac markers, oxidative stress markers, cardiac and serum 5-HT levels, and total cardiac calcium (Ca2+) concentration. ISO-induced myocardial infarcted rats also revealed a remarkable alteration of electrocardiogram (ECG) pattern and significantly upregulated expression of the 5-Hydroxytryptamine 2A (5-HT2A) receptors gene. Moreover, ISO-induced myocardial infarcted rats showed significant histopathological findings of MI and hypertrophic signs. However, pretreatment with FLP significantly attenuated the ISO-induced MI in a dose-dependent manner, as the effect of FLP (45 mg/kg) was more pronounced than that of the other two doses, FLP (15 and 30 mg/kg). The present study provides evidence for the cardioprotective efficacy of FLP against ISO-induced MI in rats.

BP101 Peptide Promotes Female Sexual Receptivity in the Rat

INTRODUCTION

Low sexual desire is a frequent sexual problem in women, with only one drug for the condition approved by the Food and Drug Administration.

AIM

To evaluate the ability of a novel synthetic peptide, BP101, to facilitate sexual behavior after intranasal administration or infusion into certain brain areas in female rats.

METHODS

Bilaterally ovariectomized female rats, primed with a suboptimal combination of estradiol benzoate (EB) and progesterone, were used as a model of low sexual motivation. Sexual behavior was tested with stud male rats after acute (experiment 1) or long-term (experiment 2) intranasal administration of BP101 or peptide infusion into the olfactory bulb, medial preoptic area, ventromedial hypothalamic nucleus, or ventral tegmental area (experiment 3).

MAIN OUTCOME MEASURES

Frequency of solicitations (SF), as an indicator of sexual motivation in female rats, and lordosis frequency and ratio, as measurements of female consummatory sexual behavior.

RESULTS

Acute intranasal BP101 administration moderately increased SF, with the highest tested dose of 300 μg/kg causing an 80% increase. Female rats receiving BP101 75 or 300 μg/kg daily on days 6 to 16 of the peptide administration displayed twofold higher SF compared with the placebo-treated animals, an increase comparable to optimally hormone-primed female rats. Infusion of BP101 1 and 5 μg per rat into the medial preoptic area, but not into the olfactory bulb, ventromedial hypothalamic nucleus, or ventral tegmental area, increased SF in female rats supplemented with EB 10 or 20 μg. The effect was relatively more pronounced in female rats receiving EB 10 μg (≈300%) compared with EB 20 μg (≈50%) with direct brain infusions.

CONCLUSION

BP101 displays a potent stimulatory effect on sexual motivation in the female rat, and the medial preoptic area seems to be the site of its action. BP101 is effective in female rats receiving different hormone supplementations, making the present data generalizable to pre- and postmenopausal women with hypoactive sexual desire. Andreev-Andrievskiy A, Lomonosov M, Popova A, et al. BP101 Peptide Promotes Female Sexual Receptivity in the Rat. J Sex Med 2017;14:336-346.

Flibanserin: First Global Approval

Flibanserin (Addyi™) is chemically described as a benzimidazole and is being developed by Sprout Pharmaceuticals for the treatment of hypoactive sexual desire disorder (HSDD). The drug has a high affinity for serotonin 5-HT1A and 5-HT2A receptors (5-HT1A agonist/5-HT2A antagonist) and is believed to treat HSDD by increasing levels of dopamine and noradrenaline and lowering levels of serotonin in the brain. Flibanserin has been approved in the USA for the treatment of premenopausal women with acquired, generalized HSDD. Earlier phase III development of the agent for HSDD in the EU and Canada had been discontinued by Boehringer Ingelheim, following regulatory feedback. Boehringer Ingelheim had also evaluated flibanserin for the treatment of depression but, due to displaying very mild antidepressant activity, its development in this indication was discontinued. This article summarizes the milestones in the development of flibanserin leading to its first approval for HSDD.

Treatment for hypoactive sexual desire

Flibanserin acts at cortical, limbic, hypothalamic, and brainstem nuclei to inhibit serotonin release by binding to 5-HT1A autoreceptors and block postsynaptic action of serotonin at 5-HT2A receptors. This gradually disinhibits the turnover of other monoamines like dopamine and noradrenaline that are critical for sexual desire.

Mechanism of action of flibanserin, a multifunctional serotonin agonist and antagonist (MSAA), in hypoactive sexual desire disorder

Flibanserin is a novel multifunctional serotonin agonist and antagonist (MSAA) that improves sexual functioning in premenopausal women who suffer from reduced sexual interest and desire.