Altered sexually dimorphic nucleus of the preoptic area (SDN-POA) volume in adult Long–Evans rats by dietary soy phytoestrogens

Neurobehavioral effects of dietary soy phytoestrogens

“…In studies with SpragueDawley rats fed the Phyto rich diet, the plasma isoflavone concentrations were expectedly 35-to 76-fold higher than values found in animals fed the Phyto-free diet [69,121,122]. With Long-Evans rats, plasma isoflavone concentrations were also higher but the magnitude of the difference between the diet treatments was less [78], suggesting a possible strain difference in the absorption, metabolism or bioavailability. In general, females tended to have slightly higher total plasma isoflavone concentrations than males, although the difference was not statistically significant.…”

“…Overall, a 20-fold higher circulating isoflavone concentration was observed between animals fed the phyto-rich and phyto-free diets. The major plasma phytoestrogen in the Phyto-rich diet fed animals was equol (a specific metabolite of the soy isoflavone aglycones, daidzein, and presumably genistein) [69,78,121,122]. The plasma phytoestrogen concentrations are similar to that of adults living in Asia (1 -2 mM) where the average intake of soy protein is 4-8 g/day or 20 -50 g of soy food products [1,2,4,5].…”

“…This custom diet is referred to, hereafter, as the Phyto-free diet. The exact composition of the two diets: percentage protein, fat, carbohydrate levels, amino acid, vitamin and mineral levels have been published elsewhere [78,122]. For comparison, other commercially available diets, like the Purina no.…”

“…Using these diets, more than five studies have been conducted by our laboratories examining two different strains of rats (i.e., Sprague -Dawley and Long -Evans animals) [69,78,113,[120][121][122]. In studies with SpragueDawley rats fed the Phyto rich diet, the plasma isoflavone concentrations were expectedly 35-to 76-fold higher than values found in animals fed the Phyto-free diet [69,121,122].…”

“…considered to be reflective of the typical intakes of people in Western populations where soy foods are rarely consumed [1,2,4,5,69,78]. Therefore, we have designed our animal model to mimic the typical exposure levels of phytoestrogens to these two contrasting populations.…”