Tamoxifen and raloxifene produce conditioned taste avoidance in female rats: A microstructural analysis of licking patterns

Effects of estrogen and estrus cycle on pharmacokinetics, absorption, and disposition of genistein in female Sprague-Dawley rats

Genistein is an active soy isoflavone with anticancer activities, but it is unknown why it has a higher oral bioavailability in female than in male rats. Our study determined the effects of estrus cycle on genistein's oral bioavailability. Female rats with various levels of estrogen were orally administered with genistein or used in a four-site rat intestinal perfusion experiment. Rats in "proestrus" group (with elevated estrogen) had significantly reduced (57% decrease, p < 0.05) oral bioavailability of total genistein (aglycone + conjugates) than those in "metoestrus" group (with basal level of estrogen). Female ovariectomized rats, due to lack of estrogen, showed oral bioavailability of total genistein similar to the "metoestrus" group but higher (155% increase, p < 0.05) than the "proestrus" group. On the basis of intestinal perfusion studies, the increased bioavailability was partially attributed to the higher (>100% increase, p < 0.05) hepatic disposition via glucuronidation and possibly more efficient enterohepatic recycling of genistein in the "metoestrus" group. Furthermore, chronic exogenous supplementation of estradiol in ovariectomized rats significantly reduced (77%, p < 0.05) the oral bioavailability of total genistein, mostly via increased sulfation (>10-fold) in liver, to a level comparable to those in the "proestrus" group. In conclusion, the oral bioavailability of total genistein was inversely proportional to elevated estrogen levels in female rats, which is partially mediated through the regulation of hepatic enzymes responsible disposition of genistein.

Estrogenic involvement in social learning, social recognition and pathogen avoidance

Sociality comes with specific cognitive skills that allow the proper processing of information about others (social recognition), as well as of information originating from others (social learning). Because sociality and social interactions can also facilitate the spread of infection among individuals the ability to recognize and avoid pathogen threat is also essential. We review here various studies primarily from the rodent literature supporting estrogenic involvement in the regulation of social recognition, social learning (socially acquired food preferences and mate choice copying) and the recognition and avoidance of infected and potentially infected individuals. We consider both genomic and rapid estrogenic effects involving estrogen receptors α and β, and G-protein coupled estrogen receptor 1, along with their interactions with neuropeptide systems in the processing of social stimuli and the regulation and expression of these various socially relevant behaviors.

Activation of central, but not peripheral, estrogen receptors is necessary for estradiol's anorexigenic effect in ovariectomized rats

Estradiol appears to exert its anorexigenic effect by activating nuclear estrogen receptors (ERs), which are expressed widely in peripheral tissues and in the brain. Here, we used ICI-182,780 (ICI), a pure antiestrogen with limited ability to cross the blood-brain barrier, to assess the relative involvement of peripheral vs. central ERs to estradiol's anorexigenic effect. Food intake was measured after peripheral (sc) administration of ICI or vehicle in ovariectomized rats treated with acute injections of estradiol benzoate and sesame oil over a 2-wk period. Uterine weight was assessed as a biological assay of peripheral ER activation. In a second experiment, food intake was measured after central (lateral ventricular) administration of ICI or vehicle in ovariectomized rats receiving acute injections of estradiol benzoate and oil over a period of 10 d. In order to assess the possible spread of ICI from the brain to the periphery, vaginal cytology samples were examined as a biological assay of peripheral ER activation. Peripherally administered ICI failed to attenuate estradiol's anorexigenic effect at a dose that was sufficient to block estradiol's uterotrophic effect. This suggests that peripheral activation of ERs is not necessary for estradiol's anorexigenic effect. Although central infusion of 4 nm ICI blocked estradiol's anorexigenic effect, it did not attenuate estradiol's ability to increase the presence of cornified cells in vaginal cytology samples, suggesting that ICI did not leak into the periphery. We conclude that activation of central, but not peripheral, ERs is necessary for estradiol's anorexigenic effect.

Activation of ERα is necessary for estradiol's anorexigenic effect in female rats

While there is considerable evidence that the ovarian hormone estradiol reduces food intake in female rats, it is unclear which estrogen receptor (ER) subtype, ERα or ERβ, mediates this effect. While several studies have demonstrated that activation of ERα, but not ERβ, is sufficient to reduce food intake in ovariectomized (OVX) rats, there are limited data regarding which receptor subtype is necessary. Here we used the selective ERα and ERß antagonists, MPrP and PHTPP, respectively, to investigate this question. We found that antagonism of ERα, but not ERβ, prevented the decrease in food intake following acute administration of estradiol in OVX rats. In addition, antagonism of ERα prevented the estrous-related, phasic reduction in food intake that occurs in response to the rise in circulating levels of estradiol in cycling rats. We conclude that activation of ERα is necessary for the anorexigenic effects of exogenous and endogenous estradiol in female rats.

Raloxifene and/or estradiol decrease anxiety-like and depressive-like behavior, whereas only estradiol increases carcinogen-induced tumorigenesis and uterine proliferation among ovariectomized rats

Controversy surrounds the efficacy and safety of 17beta-estradiol (E2)-mimetic therapies to women for treatment of menopausal symptoms. An important question is the nature of the trophic actions of E2-mimetics in the brain for behavioral processes versus in the periphery for beneficial effects related to osteoporosis, or unwanted proliferative effects in the reproductive tissues, such as mammary glands and uterus. Of recent interest are the effects of selective estrogen receptor modulators, which can have tissue specific actions, for these processes. In the present study, the effects were determined of E2 alone, or co-administered with a selective estrogen receptor modulator, raloxifene, for anxiety-like, depression-like, and trophic peripheral effects in ovariectomized rats that were exposed to a chemical carcinogen (7,12-dimethylbenz(a)anthracene), or not. Once per week, rats were administered vehicle, E2 (0.09 mg/kg) and/or raloxifene (1 mg/kg) subcutaneously 44-48 h before testing in a positive control, E2-dependent behavior (lordosis), depression (forced swim test), and anxiety (elevated plus maze) behavioral assays. In addition to behavioral endpoints, incidence and number of tumors, and tumor, pituitary gland, and uterine weight 14 weeks after carcinogen-exposure, and weekly hormone treatments, were analyzed. Rats administered 7,12-dimethylbenz(a)anthracene had an increased number and size of tumors, compared with vehicle treatment. E2 + raloxifene increased the number of tumors. Administration of E2 or E2 +raloxifene, but not raloxifene alone, increased pituitary and uterine weight, compared with vehicle administration. E2 or E2 + raloxifene, but not raloxifene alone, also increased the incidence of lordosis and reduced the depression-like behavior in the forced swim test (i.e. decreased time spent immobile) compared with vehicle administration. However, administration of E2 or raloxifene reduced anxiety behavior in the elevated plus maze (i.e. increased time spent on the open arms of the maze), compared with vehicle treatment. Together these data show that E2 and/or raloxifene can have some effects to alter the behavior of ovariectomized rodents, depending upon the task. As well, E2, with or without raloxifene, can also have clear trophic actions in peripheral tissues, such as carcinogen-induced tumors, uterus, and pituitary glands.

Tamoxifen produces conditioned taste avoidance in male rats: an analysis of microstructural licking patterns and taste reactivity

Estrogen receptor activation has been shown to reduce body weight and produce a conditioned reduction in food intake in male rats that is putatively mediated by estradiol's suggested aversive effects. Evidence has shown that the selective estrogen receptor modulator tamoxifen used in the prevention and treatment of breast cancer may also produce changes in food intake and body weight, which are known to impact cancer development and survival. The purpose of the present study was to examine whether tamoxifen produces a conditioned reduction in intake similar to estradiol by producing a conditioned aversion. A one bottle lickometer test was used to examine conditioned changes in sucrose drinking, while the taste reactivity test was used to measure rejection reactions, which serve to index aversion in rats. A backward conditioning procedure that consisted of 3 conditioning days and one vehicle test day was used to examine conditioned changes in 0.3 M sucrose intake and taste reactivity. Our results show that tamoxifen produced a conditioned reduction in sucrose drinking in a one bottle fluid intake test that was similar to the effects produced by estradiol (positive control); however, no active rejection reactions were produced by either tamoxifen (1 and 10 mg/kg) or estradiol. The present results suggest that tamoxifen, at the doses used in the present study, acts as an estrogen receptor agonist to regulate food intake and that the conditioned reduction in intake produced by tamoxifen and estradiol reflects conditioned taste avoidance rather than conditioned taste aversion.