Highly Soybean Meal Extract (SME) Effects on Erectile Function: Alterations in Corporal Smooth Muscle and Neuronal Nitric Oxide Synthase Expression

Abstract

The effects of soybean meal extract (SME) on erectile function (EF) in rats were analyzed in this study by specifically exploring changes in corpus cavernosum (CC) structure, neurophysiological biomarker levels, and hormonal dynamics. After a 14-day feeding period of 24 male juvenile rats, SME substantially decreased intracavernosal pressure (ICP) (50–55 cmH₂O) and testosterone levels (SME 100 = 1.43 ng/mL; SME 50 = 0.44 ng/mL). Histological and immunofluorescent analyses revealed a marked reduction in α-smooth muscle actin (α-SMA) and the expression of neural markers including neurofilament-1 (NF-1), neuronal nuclear (NeuN) antigen, β-III-tubulin, S100 protein, and neuronal nitric oxide synthase (nNOS) in the cavernous and dorsal penile nerves (DPNs). Western blot analysis was performed on whole penile tissue to substantiate these findings and to assess global protein expression. The results showed a dose-dependent modulation of α-SMA and downward trends in endothelial nitric oxide synthase (eNOS) and nNOS protein levels following SME treatment, confirming SME’s effect of SME on the smooth muscle phenotype and nitric oxide signaling. These results suggest that phytoestrogens in SME may disrupt hormonal balance, neuronal integrity, and vascular signaling, collectively impairing EF. This study underscores the importance of evaluating dietary SME exposure, particularly in relation to the reproductive health of young adult males.