Excessive penile norepinephrine level underlies impaired erectile function in adenosine A1 receptor deficient mice.

Introduction: Penile erection is a complex neurovascular physiological event controlled by multiple factors and signaling pathways. A considerable amount of evidence indicates that adenosine plays a significant role in cavernosal smooth muscle relaxation. However, the specific role of adenosine and its receptors in erectile physiology and pathology is not fully understood.

Aim: To determine the role of the adenosine A1 receptor (ADORA1) in penile erection.

Method: Adenosine A1 receptor deficient (Adora1-/-) mice and aged-matched wild-type (WT) mice were utilized. We evaluated the in vivo erectile function by measuring the intracavernosal pressure (ICP) in response to cavernous nerve stimulation (CNS). Enzyme-linked immunosorbent assay was used to measure the norepinephrine (NE) plasma concentration in the corpus cavernosum and systemic circulation. We also evaluated the myosin light chain phosphorylation (p-MLC) in penile tissue pre- and post-CNS.

Main Outcome Measurement: The main outcome measurement of this research was the evaluation of in vivo erectile response to CNS by measuring the ICP in Adora1-/- mice and WT mice and to identify the localization and specific neuron types of ADORA1 expression by dual immunostaining and immunofluorescence co-localization.

Result: In vivo, both the ratio of CNS-induced Maximum ICP to mean arterial pressure and CNS-induced slope in Adora1-/- mice were significantly lower than WT mice. At the cellular level in penile tissue, we determined that ADORA1 was highly abundant in neuronal cells. During penile erection, Adora1-/- mice exhibited a higher level of NE plasma concentration in the penis than WT mice. And WT mice had a significantly greater reduction in p-MLC compared to Adora1-/- mice.

Conclusion: Our results show that ADORA1 is enriched on neuron cells where it functions to control NE release. Activation of this receptor during penile erection results in reduced NE release and reduced cavernosal smooth muscle contraction, therefore facilitating penile erection.