Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5alpha-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague-Dawley rats

Abstract

Nutritional factors, especially phytoestrogens, have been extensively studied for their potential beneficial effects against hormone-dependent and age-related diseases. The present study describes the short-term effects of dietary phytoestrogens on regulatory behaviors (food/water intake, locomotor activity and body weight), prostate weight, prostate 5 -reductase enzyme activity, reproductive hormone levels, and testicular steroidogenic acute regulatory peptide (StAR) levels in adult Sprague-Dawley rats.Animals were fed either a phytoestrogen-rich diet containing ]600 µg/g isoflavones (as determined by HPLC) or a phytoestrogen-free diet. After 5 weeks of consuming these diets, plasma phytoestrogen levels were 35 times higher in animals fed the phytoestrogen-rich vs phytoestrogen-free diets. Body and prostate weights were significantly decreased in animals fed the phytoestrogenrich diet vs the phytoestrogen-free fed animals; however, no significant change in prostate 5 -reductase enzyme activity was observed between the treatment groups. Locomotor activity levels were higher in the phytoestrogen-rich vs the phytoestrogen-free animals during the course of the treatment interval. Plasma testosterone and androstenedione levels were significantly lower in the animals fed the phytoestrogen-rich diet compared with animals fed the phytoestrogen-free diet. However, there were no significant differences in plasma LH or estradiol levels between the diet groups. Testicular StAR levels were not significantly different between the phytoestrogen-rich vs the phytoestrogen-free fed animals.These results indicated that consumption of dietary phytoestrogens resulting in very high plasma isoflavone levels over a relatively short period can significantly alter body and prostate weight and plasma androgen hormone levels without affecting gonadotropin or testicular StAR levels.The findings of this study identify the biological actions of phytoestrogens on male reproductive endocrinology and provide insights into the protective effects these estrogen mimics exert in male reproductive disorders such as benign prostatic hyperplasia and prostate cancer.

Neurobehavioral effects of dietary soy phytoestrogens

“…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].…”

“…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.…”

“…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].…”

“…Dietary soy phytoestrogen treatment design. Animals were obtained at 50 days of age and placed on the Phyto-rich diet (containing 600 mg/g diet) [71,78,122]. At 80 -85 days of age, female rats were mated with breeder males on the Phyto-rich diet so that the offspring of these pairings would be exposed solely to this diet.…”