Pubertal development of penile Nitric Oxide Synthase (NOS)-containing nerve fibers in the rat
Objectives: To evaluate the expression of nitric oxide synthase (NOS)-containing nerve fibers in penile tissue in different age groups in the rat and to measure serum testosterone levels during this developmental process. Material and Methods: Fifteen male Sprague-Dawley (SD) rats divided into 3 equally numbered groups of different age (40 days (d), 54d and 65d) were used in this study. Penile erection was evaluated using cavernous nerve electrostimulation. Before sacrificing the rats, a penile midshaft specimen was taken for nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining and blood samples were collected to evaluate the testosterone levels. Results: Electrostimulation of the cavernous nerve revealed no significant difference in the maximal intracavernous pressure in the different age groups (44.9 ± 6.4, 54.8 ± 24.8, 45.9 ± 16.8 cm H2O, respectively; p>0.05), but the latency of the response to electrostimulation was significantly shorter in 54d and 65d than in 40d-old rats (5.4 ± 0.8 and 5.0 ± 0.7 vs. 9.0 ± 5.4 sec., respectively; p<0.05). NADPH diaphorase staining revealed a significantly greater number of fibers in the corpus cavernosum (CC) and dorsal nerves (DN) of 54d and 65d-old rats compared to 40d-old rats (CC: 192.3 ± 34.5 and 238.8 ± 32.7, respectively, vs. 126.0 ± 11.3 p<0.0l, DN:
941.5 ± 77.8 and 848.4 ± 264.3, respectively, vs. 560.0 ± 114.2 p<0.05), but the differences between 54d and 65d-old rats were not statistically significant. Serum testosterone concentrations were significantly different between the 40d and the 54d-old rats (total: 6.5 ± 4.6 nmol/L vs. 16.8 ± 14.2 nmol/L vs. 22.8 ± 16.2; p<0.05, free: 16.8 ± 14.2 nmol/L vs. 73.5 ± 56.6; p<0.05), but the differences between the 54d and 65d-old rats (total: 22.8 ± 16.2 vs. 19.5 ± 8.9 nmol/L, free: 73.5 ± 56.6 vs. 58.7 ± 34.3 nmol/L) were not statistically significant. Conclusion: The number of NADPH-positive fibers increases with age; however similar tumescence was recorded following electrostimulation in all age groups. NOS-nerve growth correlates with serum testosterone level. The increase of NADPH-positive fibers was accompanied by a decrease in the delay of onset of penile erection following electrostimulation.
Key words: Growth process, nitric oxide nerve fibers, penis, erection, blood testosterone, rats