Effects of Simulated Long Duration Spaceflight on Erectile Function

The goal of NASA along with other space agencies in the world is to send manned missions to the moon in the coming years, and eventually to Mars. The long-term health risks of spaceflight have been attributed primarily to cosmic radiation and microgravity and the adverse effects as seen in the astronauts and model animals include DNA damage, mitochondrial dysregulation, oxidative damage, epigenetic changes, telomere length changes and microbiome shifts all of which affect the cardiovascular system. However, little is known about the effect of spaceflight on erectile function which is an important quality of life aspect for men. The aim of our study was to investigate the effect of simulated long duration space flight on erectile function. We hypothesized that both hindlimb unloading (HLU) and radiation will adversely affect erectile function. 86 adult male Sprague-Dawley rats were used for these studies. Half the animals underwent 4 weeks of HLU, and all animals were divided into 3 groups: those that received sham radiation, 0.75 Gy, and 1.5 Gy galactic cosmic radiation, respectively at the Ground-based GCR simulator at the NASA Space Radiation laboratory. The animals were then monitored for 6-9 months before they were sacrificed, following which Corpus cavernosum (CC) and the distal internal pudendal arteries (dIPA) were harvested and used for ex vivo functional assessment. Tissue and wire myography studies were performed to assess adrenergic and endothelium-dependent vasoconstrictions using phenylephrine (PE), norepinephrine, and endothelin. This was done by measuring the cumulative dose-responses to the agonists in both the CC and dIPA. Endothelium-dependent and -independent relaxations were also assessed using acetylcholine and diethylamine nononate. Non-adrenergic non-cholinergic (NANC) transmission was assessed using electrical stimulation (Estim); 30V electric pulses were delivered to the tissues with frequency ranging from 1-32Hz following the administration of atropine and guanethidine and pre-constriction with PE. Finally, Estim was done without atropine and guanethidine to assess the parasympathetic mediated relaxation in the tissues. The effects of HLU and radiation on the contractile and relaxation responses were assessed by two-way repeated measures ANOVA. HLU and radiation significantly reduced both endothelium-dependent and -independent vasodilatation in the dIPA and CC. Also, HLU and radiation significantly reduced the adrenergic constriction of CC in response to PE and norepinephrine. However, neither HLU nor radiation influenced the endothelium-dependent vasoconstriction in the dIPA. Finally, radiation reduced the relaxation in both CC and dIPA while HLU increased the dIPA relaxation following Estim for both the parasympathetic mediated and NANC mediated responses. These results therefore showed the effects of HLU and radiation on erectile function, with exposure to cosmic radiation being primarily responsible for the detrimental effects. Further research needs to be done on this subject to show more mechanistically how spaceflight can affect erectile function and ways to combat the problem to ensure that astronauts can return to their normal sexual lives after long trips to space. © FASEB.