AB278. SPR-05 Purinergic regulation of nitric oxide mediated vasodilation in rat internal pudendal arteries

Objective: Internal pudendal arteries (IPA) provide 70% of total blood blow resistance to penile arteries and have been shown to undergo significant vascular remodeling due to aging, diabetes, chronic kidney disease, and cardiovascular disease. Balloon angioplasty and stent placement is a common treatment option to restore blood flow within IPAs; however, stent failure is disproportionately higher than coronary artery stents despite similar stents and placement techniques suggesting a unique IPA physiology. Non-adrenergic non-cholinergic (NANC) mediated vasodilation is well characterized in the penis, but IPA neurotransmitter release has yet to be characterized. The objective of this study is to characterize electric field stimulated (EFS) mediated neurotransmitter release in rat IPA and address the novel role of ATP as a neurotransmitter.

Methods: Proximal (internal iliac to gluteal artery) and distal (gluteal artery to penis) IPA segments excised from male Sprague-Dawley rats (350–475 g) were mounted into myographs. NANC vasodilation was assessed in precontracted IPAs following incubation with inhibitors of norepinephrine release (guanethidine; 10^-6 M) and cholinergic receptors (atropine, 10^-5 M) to assess neuronal nitric oxide (NO) release. This procedure was repeated with additional incubation of a NO synthase (NOS) inhibitor (L-NAME; 10^-6 M), selective P2X1 inhibitor (NF-449; 10^-5 M), or selective P2Y1 inhibitor (MRS 2500; 10^-6 M). EFS relaxation parameters used were 5 ms delay, 0.3 ms duration at 20V and 0.5–32 Hz. Concentration response curves to assess ADP, a P2Y1 receptor agonist, relaxation and α,β-MetATP, a stable P2X1 receptor agonist, contraction were also performed.

Results: NANC stimulation lead to greater relaxation in distal IPA (30% vs. 15%, P<0.05). Additional inhibition of NOS completely eliminated NANC relaxation in distal IPA; however, did not reduce proximal IPA relaxation. P2X1 or P2Y1 inhibition caused further distal IPA relaxation, but combined P2X1 and P2Y1 inhibition increased distal IPA relaxation from 30% to 53% without affecting proximal IPA relaxation. No significant differences were noted to α,β-MetATP mediated contractions via the P2X1 receptor. ADP mediated relaxation was markedly increased in proximal IPA (16%) compared to distal IPA (6%).

Conclusions: Functional physiological differences exist within the proximal and distal segments of the IPA. NANC-mediated relaxation in the distal IPA is greater than the proximal IPA and is mediated by NO-dependent mechanisms. Furthermore, the distal IPA undergoes additional purinergic regulation which is NO-independent. Understanding the physiology of this critical feeder blood vessel to the penis is crucial when developing novel treatments that target the vasculature to recover erectile function.

Funding Source(s): None

Keywords: Purinergic; nitric oxide (NO); internal pudendal arteries (IPA); in vitro contractility