A Comparison Between the Effects of Estrogen and Soy Extract on Chronic Pain in Male Rats

In addition to its effect on reproductive organs, estrogen exhibits complex effects on brainstructure, function and behavior. in this regard, the influence of gonadal hormones especiallyestrogens on nociception has recently been accepted. soybean is known as an importantphytoestrogen containing plant that is used as an alternative for estrogen replacement therapy.in this study, the influences of soy extract and estrogen on formalin-induced nociception inmale rats were examined. in the first experiment, the effect of soy extract added to drinkingwater (60 mglkg per day) on the nociception was assessed and compared with a control group(with soy-free drinking water). there was a significant decrease in nociception in rats thatreceived soy extract for two weeks. furthermore, different doses of soy extract (50, 150 and200 mglkg) were injected subcutaneously 30 min before formalin test to assess its effect onacute and chronic pain perception. it was observed that different doses of soy extract hadsimilar antinociceptive effects that were significantly different from saline injected controlgroup. in other experiment, rats treated with a single dose of 150 ug of 17-~ estradiol (s.c.)48 h prior to the formalin test, to be compared with a control group just received estrogenvehicle (dmso). acconding to our results estradiol did not show any significant effecton pain suppression. these results suggest that the antinociceptive effect of soy extract onchronic pain is not aresult of its phytoestrogenic activitiy, it might atherefore be related toother substances within soy extract.