Effect of Late Androgen Replacement Therapy on Erectile Function Through Structural Changes in Castrated Rats

Androgens and erectile dysfunction: from androgen deficiency to treatment

INTRODUCTION

Androgens play important roles in regulating the growth and development of the male reproductive system and maintaining libido and erectile function. The specific mechanisms by which androgen deficiency leads to erectile dysfunction (ED) are not yet fully understood.

OBJECTIVES

To understand the mechanisms and treatment of androgen deficiency-related ED.

METHODS

A literature search in the past 10 years was conducted in PubMed and Google Scholar to determine the effects of androgen deficiency on erectile function and the treatment of androgen deficiency.

RESULTS

Androgen deficiency can be caused by hypothalamic-pituitary lesions and injuries, testicular-related diseases and injuries, endocrine and metabolic disorders, the side effects of medication, and age. Androgen deficiency can lead to ED by inhibiting the NOS/NO/cGMP pathway (nitric oxide synthase/nitric oxide/cyclic guanosine monophosphate) and altering the expression of ion channel proteins, as well as by inducing oxidative stress, death, and fibrosis in penile corpus cavernosum cells. Testosterone replacement therapy is effective at improving the serum testosterone levels and erectile function in patients with androgen deficiency. For patients who need to maintain a low androgenic state, erectile function can be improved by lifestyle changes, treatment with phosphodiesterase type 5 inhibitors, low-intensity extracorporeal shock wave therapy, and stem cell therapy.

CONCLUSIONS

Androgen deficiency can affect the structure and function of the penile corpus cavernosum, leading to ED. Areas of further study include how androgen replacement therapy can improve erectile function and how to improve the maintenance of erectile function in patients with hypoandrogenic status.

Testosterone improved erectile function by upregulating transcriptional expression of growth factors in late androgen replacement therapy model rats

We previously showed that castration of rats reduced erectile function over time; when testosterone replacement therapy was started 4 weeks after castration, erectile function improved. In this study, we examined the mechanism of improvement in erectile function following testosterone replacement therapy in rats. Thirty 12-week-old rats were divided into castrated (Cast), castrated with subcutaneous administration of testosterone (Cast + T), and sham (Sham) groups. Erectile function and mRNA and protein expression were evaluated in the rats by using standard methods. To assess erectile function, we measured the intracavernosal pressure, mean arterial pressure, mRNA expression of endothelial growth factors, and protein expression of endothelial nitric oxide synthase (eNOS). The intracavernosal pressure/mean arterial pressure ratio was significantly lower in the Cast group, and testosterone administration significantly improved (P = 0.017). Compared to the Cast group, the Cast+T group exhibited significantly increased mRNA expressions of vascular endothelial growth factor A (VEGF-A), intercellular adhesion molecule 1 (ICAM-1), transforming growth factor-β (TGF-β), nerve growth factor (NGF), α-smooth muscle actin (α-SMA), caveolae associated protein 1 (Cavin-1), Cavin-2, Cavin-3, sirtuin 1 (Sirt-1), sphingosine-1-phosphate 1 (S1P1), S1P2, and S1P3 and eNOS protein expression. Testosterone replacement therapy improved erectile function in castrated rats by increasing growth factors and eNOS protein.

A review of experimental techniques for erectile function researches and development of medical technology using animal erectile dysfunction models in sexual and reproductive medicine

Background

Erectile dysfunction (ED) is one of the causes of male infertility and is a disease that requires treatment. The first‐line drugs for ED are phosphodiesterase 5 (PDE‐5) inhibitors, and further treatment options are currently limited. Medical technologies, such as genetic control and regenerative medicine, are developing rapidly. Research on erectile function is progressing rapidly, coupled with technological innovations in other areas.

Methods

A PubMed search using the keywords “animal (rat, mouse, rabbit, dog, and monkey)” and “erectile” was conducted, and all relevant peer‐reviewed English results were evaluated.

Main findings

The methods for evaluating erectile function include intracavernous pressure (ICP) measurements, isometric tension studies, and dynamic infusion cavernosometry. Papers also reported various disease model animals for the study of diabetes mellitus, cavernous nerve injury, and drug‐induced ED.

Conclusion

Basic research on ED treatment has progressed rapidly over the past 20 years. In particular, research on the mechanism of ED has been accelerated by the publication of a study on the evaluation of erectile function using ICP measurements in rats. In addition, molecular biological experimental methods such as polymerase chain reaction (PCR) and western blotting have become relatively easy to perform due to technological progress, thus advancing research development.