In vitro effect of relaxin in the rat corpus cavernosum under hyperglycemic and normoglycemic conditions

Relaxin, an endogenous peptide hormone, elicits vascular relaxation by its direct effect or by modulating the endothelium-dependent relaxation response and is clinically evaluated for the treatment of coronary artery disease. However, its effect on penile tissue has not been explored yet. This study aimed to investigate the effect of serelaxin, recombinant human relaxin-2, on rat corpus cavernosum (CC) under healthy and hyperglycemic conditions. Strips of CC obtained from thirty-nine male Wistar rats weighing 300-350 g were used in organ baths for isometric tension studies to investigate the serelaxin-mediated relaxation (10-12-10-7 M) under normoglycemic conditions and the effect of serelaxin on endothelium-dependent [nitric oxide (NO)- and prostacyclin-mediated] relaxation responses under hyperglycemic conditions. The in vitro hyperglycemia model was created by 3 h of incubation with 44 mM glucose monohydrate +120 μM methylglyoxal. NO-dependent relaxation responses were evaluated by cumulative acetylcholine (10-9-10-4 M) administration in the presence of indomethacin (10-6 M). Prostacyclin-mediated relaxation was evaluated by cumulative administration of iloprost (10-9-10-6 M), a prostacyclin analog. Maximum relaxation responses to serelaxin were not significantly different compared to the time-control (p = 0.480). Three hours of incubation of rat CC in hyperglycemic conditions impaired NO- and prostacyclin-mediated relaxation responses (p = 0.032 and p = 0.047, respectively). Serelaxin coincubation worsened NO-mediated relaxation responses (p = 0.016) but did not affect prostacyclin-mediated responses (p = 0.425). Together, our results demonstrate that in vitro administration of serelaxin does not cause relaxation in penile tissue and short-term in vitro serelaxin treatment in hyperglycemic conditions mimicked diabetes modulates endothelium-dependent responses by worsening NO-mediated responses. Serelaxin exerts different effects via different mechanism on endothelium-dependent responses depending on the dose and duration of exposure. Therefore, proper timing and dosing of serelaxin administration in the penile tissue need to be investigated in further studies in diabetic animal models.

Bilateral orchiectomy deteriorates the structure and function of seminal vesicles in a rat model

The effects of hormone levels on ejaculation are known. In addition to thyroid hormone levels, testosterone levels are also associated with ejaculation, but no consensus has been reached on this issue. Thus, we investigated the effect of decreased testosterone levels due to bilateral orchiectomy on the chemical stimulation-induced ejaculation phases in rats. Twenty-one male Wistar rats were randomized into the orchiectomy, sham, and control groups, with seven rats in each group. Bilateral orchiectomy was performed. The ejaculation parameters were evaluated 5 days after the sham and bilateral orchiectomy operations and the waiting period in the control group. The seminal vesicle (SV) phasic contraction number and increase in basal pressure amplitude were significantly lower in the orchiectomy group (6.9 ± 3.3 and 0.6 ± 0.3 mmHg) than in the sham and control groups (11.2 ± 1.7 and 1.0 ± 0.4 mmHg, and 14.5 ± 6.6 and 1.1 ± 0.2 mmHg, respectively; p = 0.016 and p = 0.03, respectively). The interval between the SV contractions was significantly longer in the orchiectomy group (166.2 ± 104.3 s) than in the sham and control groups (76.0 ± 15.5 s and 63.1 ± 31.1 s, respectively; p = 0.014 (between groups), orchiectomy vs sham p = 0.040 and orchiectomy vs control p = 0.018). The SV weights of the rats were significantly lower in the orchiectomy group (0.14 ± 0.01 g) than in the sham and control groups (0.37 ± 0.05 g and 0.48 ± 0.03 g respectively; p < 0.0001 (between groups), orchiectomy vs sham p < 0.0001 and orchiectomy vs control p < 0.0001). The groups showed no significant differences in ejaculation time, SV basal pressure, SV maximum amplitude, and bulbospongiosus muscle contraction electromyographic activity. Our results partially clarified the relationship between decreased testosterone levels and ejaculation. Decreased testosterone levels caused statistically significant changes in SV functions and affected the ejaculation emission phase.

Vagus nerve bundle stimulation using 1505-nm laser irradiation in an in-vivo rat model

Laser nerve stimulation using near-infrared laser irradiation has recently been studied in the peripheral nervous system as an alternative method to conventional electrical nerve stimulation. Bringing this method to the vagus nerve model could leverage this emerging stimulation approach to be tested in broader preclinical applications. Here, we report the capability of the laser nerve stimulation method on the rat vagus nerve bundle with a 1505-nm diode laser operated in continuous-wave mode. Studies of the stimulation threshold and laser-induced acute thermal injury to the nerve bundle were also performed to determine a temperature window for safe, reliable and reproducible laser stimulation of the rat vagus nerve bundle. The results show that laser stimulation of the vagus nerve bundle provides reliable and reproducible nerve stimulation in a rat model. These results also confirm a threshold temperature of >42°C with acute nerve damage observed above 46°C. A strong correlation was obtained between the laser time required to raise the nerve temperature above the stimulation threshold and the mean arterial pressure response. Advantages of the method such as non-contact delivery of external stimulus signals at mm scaled distance in air, enhanced spatial selectivity and electrical artefact-free measurements may indicate its potential to counteract the side effects of conventional electrical vagus nerve stimulation.

Protective effects of wheat germ oil against erectile and endothelial dysfunction in streptozotocin-induced diabetic rats

Our aim was to investigate the protective effect of wheat germ oil (WGO) at different doses on diabetes mellitus (DM)-induced erectile and endothelial dysfunction. Twenty-four male Wistar rats weighing 250-300 g were divided into four groups as; control group treated with saline, DM group, DM group treated with 3 ml/kg WGO (DM + 3WGO group), DM group treated with 6 ml/kg WGO. Type 1 DM was induced by intraperitoneal injection of 60 mg/kg streptozotocin (STZ). STZ-induced diabetic rats received saline, 3 ml/kg WGO, and 6 ml/kg WGO via oral gavage daily for 5 weeks. The density of WGO used was 0.92 g/ml. The protective effect of WGO was evaluated by (i) in vitro vascular function, (ii) in vivo erectile function, and (iii) oxidative stress parameters in both aorta and penile tissue. Acetylcholine-mediated relaxation in the aorta and erectile functions decreased significantly in the DM group (p = 0.018 and p = 0.005). WGO (3 and 6 ml/kg) improved vascular functions in the DM groups (p = 0.001 and p = 0.014). The beneficial effect of WGO on erectile function appeared at higher doses of WGO. However, a higher dose of WGO substantially increased the oxidative stress parameters in both aorta and penile tissue. These findings suggest that the improvement in vascular or erectile function by WGO was not related to antioxidant effects, and new studies are needed to clarify the mechanism.