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Poult Sci 2006. 85:1885-1889
© 2006 Poultry Science Association
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ENVIRONMENT, WELL-BEING, AND BEHAVIOR: Research Note

Lack of Estrogenic or Antiestrogenic Actions of Soy Isoflavones in an Avian Model: The Japanese Quail

K. W. Wilhelms*,{dagger}, C. G. Scanes{dagger},{ddagger},§ and L. L. Anderson{dagger},{ddagger},1

* Interdepartmental Toxicology Program, {dagger} Department of Animal Science, and {ddagger} Department of Biomedical Sciences, Iowa State University, Ames 50011; and § Department of Poultry Science, Mississippi State University, Mississippi State 39762

1 Corresponding author: llanders{at}iastate.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Isoflavones are soy compounds that possess weak estrogenic and antiestrogenic activities. In addition, phytochemicals, including isoflavones, may play a role in regulating seasonal reproductive cycles. As soy is a common constituent in poultry diets, the effect of these compounds on the reproductive system of production birds may be of concern. The present study examined the putative effects of soy isoflavones supplemented into the diet at 1 and 5% using endpoints of growth and reproduction in the Japanese quail. Isoflavones did not exert an effect on growth, feed intake, growth:feed, or the weight of the estrogen-sensitive immature oviduct in female quail. Furthermore, isoflavones did not influence the growth of the oviduct stimulated by exogenous estradiol. Similarly, isoflavones did not influence growth, feed intake, or growth:feed in male quail. However, isoflavones at 1%, but not 5%, in the diet reduced photoperiod-induced testis development 40% vs. control. In contrast, isoflavones did not influence testis regression stimulated by exogenous estradiol in sexually maturing male quail. The present results suggest that isoflavones may exert modest endocrine disruptor-like effects on reproduction in male, but not female, quail.

Key Words: quail • isoflavone • reproduction • testis • oviduct


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Human health benefits have been reported for soy isoflavones, and these are thought to be due, at least in part, to the estrogenic activity of soy isoflavones (Kurzer, 2003; Dixon, 2004; McCue and Shetty, 2004). Two of the principle isoflavones in soybeans are genistein and daidzein, and these bind to estrogen receptors. For instance, genistein binds to both mammalian {alpha}- and ß-estrogen receptors, having a higher affinity for the ß- than {alpha}-estrogen receptors (Kuiper et al., 1997, 1998). Daidzein is considerably less potent than genistein for binding to either {alpha}- or ß-estrogen receptors (Kuiper et al., 1998).

There is evidence that soy isoflavones exert negative effects in rodent models. For instance, genistein fed to pregnant rats results in offspring with reduced BW and reduced feed consumption of the dams and pups (Delclos et al., 2001). Moreover, there are effects on reproductive development of male pups with decreased ventral prostate weights and aberrant or delayed spermatogenesis (Delclos et al., 2001). In contrast, no effects of genistein were observed in a multigeneration study (Flynn et al., 2000). Adult male rats fed a mixture of soy isoflavones exhibited no changes in reproductive indices, including testes and epididymis weight, testicular histology, spermatozoa morphology, spermatozoa production, and spermatid count (Faqi et al., 2004.)

Some phytoestrogens have clear estrogenic agonist effects. For instance, coumestrol fed to pregnant rats and their resulting offspring induces a persistent estrus state in dams and deficits of male behavior and in their male offspring (Whitten et al., 1995). It is possible that soy isoflavones exert estrogenic (agonist) or antiestrogenic (antagonist) effects. Evidence from rodent models strongly supports soy isoflavones as having antiestrogenic activity. Soy isoflavones antagonize estrogen-induced behaviors and estrogen receptor {alpha}- and ß-dependent gene expression in the brain (Foidart et al., 1999; Patisaul et al., 2001) and inhibit the effects of endogenous estradiol on uterus weight and the percentage of B lymphopoietic cells in bone marrow (Erlandsson et al., 2005). There also is evidence that genistein has antiestrogenic effects on gene expression in the chicken liver (Ratna, 2002). In addition, genistein decreases weight and affects estrogen-dependent gene expression within the rodent thymus (Cooke et al., 2006). However, genistein does not affect bone mineral density of the femur in rodent models (Erlandsson et al., 2005) or estradiol-induced endometrial hyperplasia in postmenopausal women (Murray et al., 2003). Moreover, incorporation of soy isoflavones into the diet of premenopausal women does not affect the length of the menstrual cycle or circulating concentrations of reproductive hormones, namely estrone, estradiol, sex hormone-binding globulin, androstenedione, and progesterone (Duncan et al., 1999; Maskarinec et al., 2004). Similarly, soy isoflavones have no effect on the luteinizing hormone response to a gonadotropin-releasing hormone provocation test in either pre- or postmenopausal women (Nicholls et al., 2002). Moreover, soy meal in formula does not exert hormonal effects in infants (Giampietro et al., 2004).

In birds, isoflavones and other phytochemicals may, in part, regulate seasonal reproductive cycles through inhibition of reproductive behavior (Leopold et al., 1976; de Man and Peeke, 1982; Panzica et al., 2005). It has been established that some isoflavones (e.g., genistein) can be deposited in the egg (Lin et al., 2004). This may suggest that reproduction in birds, whether exposed in ovo or ex ovo, can be influenced by isoflavones. The present studies examined whether soy isoflavones in the diet exert deleterious effects, including estrogenic or antiestrogenic activity, in Japanese quail using the following as endpoints: 1) growth and feed consumption, 2) the estrogen-sensitive oviduct in the female on a short daily photoperiod (to suppress reproductive development, allowing only extremely low endogenous estrogen concentrations to be present), and 3) male reproductive organs (testes) during sexual development. The Japanese quail has proven to be a very useful model for examining putative endocrine disruptors, such as the environmental contaminants bisphenol A, tetrabromobisphenol A, o,p'-DDT (Halldin et al., 2005) and atrazine (Wilhelms et al., 2005, 2006a, b), on wild birds and poultry Birds have both {alpha}- and ß-estrogen receptor genes, with at least 2 proteins translated from the {alpha}-estrogen receptor mRNA (Griffin et al., 1999).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Birds
All procedures were performed at the Iowa State University Poultry Science Research Center and were approved by the Iowa State University Committee on Animal Care (protocol 7-2-5195). Japanese quail (Coturnix coturnix japonica) eggs were purchased from Lake Cumberland Game Bird Farm and Hatchery (Monticello, KY). The quail were reared from hatch in battery cages under a short day length (8L:16D) with free access to feed and water for the control group given the basal quail diet (Table 1Go) and the treatment groups (Table 2Go). At 4 wk of age, the females were identified based on plumage, separated from the males, transferred to individual cages (23 x 15 x 18.5 cm), and treatments were initiated. A short photoperiod was maintained throughout the experimentation to prevent sexual maturation so that the reproductive hormone-responsive organs (oviduct) would be maximally responsive to any stimulus. At 6 wk of age, the males were placed into individual cages, dietary treatment was imposed, and the photoperiod increased to 16L:8D so that testicular growth and maturation would occur.


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  		Table 1. Basal quail diet composition on an as-fed basis
 

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  		Table 2. Quail diet components of soy isoflavones (ISF) in the presence or absence of estradiol
 
Experimental Design and Treatments
The effects of soy isoflavones (Novasoy 70% isoflavone extract, Archer Daniels Midland Co., Decatur, IL) on indices of growth and reproduction were examined, with isoflavones being administered via the diet added at either 1 or 5% (corrected for percentage of isoflavones; n = 8 birds per treatment). This extract, produced from ethanol extraction, possesses the common ratio of major isoflavones found in soy (5:4:1 of genistein, daidzein, and glycitein). Noncaloric filler of similar consistency (Solka-Floc, International Fiber Corp., North Tonawanda, NY) was used as a negative control and to correct for volume differences between isoflavone groups. Estradiol (E2, Sigma-Aldrich, St. Louis, MO) was administered at 100 ppm in the presence or absence of soy isoflavones, both as a positive control for estrogen-like activity and as a control for putative antiestrogenic effects of the soy isoflavones. We hypothesized that soy isoflavones would either exert an estrogenic effect in stimulating oviduct development and growth (females) and, via negative feedback, inhibiting testicular development following photostimulation (males) or antagonize the effects of estradiol. All treatments were administered for 14 d.

Quail were randomly assigned to treatment groups and then weighed. Feed intake was recorded, and data were corrected for spillage. On d 14, the quail were reweighed and euthanized by decapitation. The oviduct and testes were weighed.

Statistical Analysis
All statistics were performed using SAS Version 9.0 (SAS Institute Inc., Cary, NC). Values were analyzed by 1-way ANOVA. Where treatment effects were found (P ≤ 0.05), means were separated by Dunnett’s t-test. Results are presented as mean ± SEM.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Effects of Soy Isoflavones on Growth and Feed Consumption
The effect of soy isoflavones on average daily gain, feed consumption, and feed:gain in female Japanese quail on short daily photoperiods and on male quail transferred to long day lengths to induce gonadal development was examined. No effects were observed on any of these indices in all treatment groups (data not shown).

Effects of Soy Isoflavones on Oviductal Growth
Table 3Go shows the effect of soy isoflavones on oviductal weight or oviduct as a percentage of BW in female Japanese quail on short daily photoperiods. Soy isoflavones had no discernible effect on either oviductal weight or the oviduct as a percentage of BW. In contrast, estradiol induced a dramatic increase in oviduct weights. However, the soy isoflavones did not either augment or diminish the effect of estradiol.


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  		Table 3. Effects of 3 wk of soy isoflavones (ISF) treatment in the diet (in the presence or absence of estradiol) on the oviduct weight of female Japanese quail on a short daily photoperiod (8L:16D)
 
Effects of Soy Isoflavones on Male Reproductive Development
Table 4Go shows the effect of soy isoflavones on testicular weight or testes as a percentage of BW in male Japanese quail transferred from a short daily photoperiod to a stimulatory long day length. Soy isoflavones at 1% of the diet modestly depressed testicular development; testes weight and testes somatic index were reduced (P < 0.05) by 54 and 40%, respectively. Testes weights in quail receiving estradiol were markedly smaller, being reduced (P < 0.001) by 98% for both absolute and relative testes weights. There was neither augmentation nor reduction of the estradiol effect in the presence of concomitant treatment with soy isoflavones.


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  		Table 4. Effects of 3 wk of soy isoflavones (ISF) treatment in the diet (in the presence or absence of estradiol) on the absolute and relative testes weights of male Japanese quail transferred to a long daily photoperiod (16L:8D) from a short daily photoperiod (8L:16D)
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
In contrast to the effects of soy isoflavones in some other studies in both mammals and birds, there was no effect of soy isoflavones on average daily gain, feed consumption, or feed:gain in either male or female Japanese quail close to mature BW (data not shown). This is in contrast to the effects of soy isoflavones reported for some other species. For instance, genistein fed to pregnant rats and their resulting offspring decreases BW and feed consumption of both the dams and pups (birth weight and at 50 d; Delclos et al., 2001). At very high concentrations, soy isoflavones depress the growth rate and gain:feed in commercial broiler-type chickens (Payne et al., 2001). Although the Japanese quail is a useful model for poultry species, it would appear that young rapidly growing broiler chickens are more sensitive to adverse effects of soy isoflavones. Chickens are reported to be more sensitive than other avian species to multiple toxicants (Scanes and McNabb, 2003).

There are reports of avian models in which phytoestrogens have been demonstrated to exert estrogen-like activity or antagonize estrogen activity. For instance, both estradiol and the grape phytoestrogen, resveratrol, stimulate expression of estrogen-regulated mRNA stabilizing factor in the chicken liver (Ratna and Simonelli, 2002). However, the soy isoflavone genestein stimulates at high concentrations (agonist activity) but at lower concentrations depresses estradiol-induced expression of estrogen-regulated mRNA stabilizing factor in the same system (antagonist activity; Ratna, 2002). Another soy isoflavone, daidzein, neither stimulates expression of estrogen-regulated mRNA stabilizing factor nor antagonizes estrogen-stimulated expression of estrogen-regulated mRNA stabilizing factor (Ratna, 2002). In the present study, there was no evidence that soy isoflavones had either estrogen agonist or antagonist activity in female quail. As would be expected, estradiol induced massive growth of the quail oviduct. Soy isoflavones failed to influence oviductal growth per se or in the presence of concomitant estradiol administration (Table 3Go).

There was, however, a modest effect of soy isoflavones at 1% in the diet on male reproductive development. In male Japanese quail transferred from a short daily photoperiod to a stimulatory long day length, there is rapid growth of the testes, increasing in weight from <10 mg to ~2 g in 3 wk (Follett et al., 1985). Soy isoflavones at 1% of the diet modestly depressed testicular development, as indicated by reduced testes weights and testicular BW ratio (testes somatic index; Table 4Go). No such effect of soy isoflavones on male reproductive development was observed with the higher dose of the soy isoflavones (Table 4Go). The depression in testicular weights in the quail receiving estradiol treatment greatly suppressed testicular growth, presumably due to the negative feedback effect on gonadotropin secretion (Davies et al., 1976; Wilson et al., 1983). As with female quail, there was no evidence that soy isoflavones antagonized the effect of estradiol.

Delclos et al. (2001) found that there were effects on the reproductive development of male pups with decreased ventral prostate weights and aberrant or delayed spermatogenesis. In contrast, no effects of genistein were observed in a multigeneration study (Flynn et al., 2000). Adult male rats fed a mixture of soy isoflavones exhibit no changes in reproductive indices, including testes and epididymis weight, testicular histology, spermatozoa morphology, spermatozoa production, and spermatid count (Faqi et al., 2004.). The present results suggest that high concentrations of isoflavones in the diet may exert modest endocrine disruptor-like effects on the reproductive system of the male, but not the female, quail.


   ACKNOWLEDGMENTS
 
We thank David F. Cox, Department of Statistics, Iowa State University, for the invaluable statistical advice. We thank George Brant, Department of Animal Science, Iowa State University, for advice on poultry diets. This work was supported by the Center for Designing Foods to Improve Human Nutrition (USDA Special Grant no. 20043411514842), the Iowa Agriculture and Home Economics Experiment Station, Ames, IA, and by Hatch Act and State of Iowa funds.

Received for publication March 2, 2006. Accepted for publication July 4, 2006.


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