Differential effects of soy-containing diets on the reproductive tissues growth and reproductive hormone secretion in male rats.

The effects of feeding a breeding diet containing soy products to pregnant and lactating females on reproductive tissues and secretion of the reproductive hormones in their male progeny, immediately after weaning (postnatal day - PND 22) and after reaching puberty (PND 60) were studied. Similarly, the response of adult males to a soy maintenance diet over shorter (PND 160) and longer (PND 280) periods of time was examined. The relative weights (standardized by body weight) of the testes, epididymis and prostate, and the concentrations of luteinizing hormone (LH), testosterone and prolactin (PRL) were used as the examined endpoints. In rats on PND 22, no significant differences in the relative organs weights and the plasma hormones concentrations were found between the experimental and control groups. In rats on PND 60 which continued consuming a soy breeding diet, the relative tissue weights did not differ significantly, while the mean plasma LH and PRL concentrations were higher (p<0.01-0.001) compared to the controls. In rats on PND 160 fed soy maintenance diet, the higher relative testes (p<0.01) and epididymis (p<0.05) weights as well as plasma testosterone (p<0.001) concentration were recorded compared to the controls. In rats on PND 280 fed a soy maintenance diet, the relative weights of all reproductive tissues were similar to those of controls, however, the weight of the body and the real weights of the reproductive tissues were lower (p<0.05) than in controls. The mean plasma concentrations of the reproductive hormones did not differ significantly between the two groups. In conclusion, a supplement of soy in the rat diet may affect growth and/or development of the reproductive tissues in male rats and also affect concentrations of reproductive hormones. The effects depend on the period of life when the soy diet is applied.