Growth hormone enhances regeneration of nitric oxide synthase-containing penile nerves after cavernous nerve neurotomy in rats

Purpose: As growth hormone has been reported to improve nerve regeneration, we studied the effect of rat growth hormone (GH) on the regeneration of nitric oxide synthase (NOS)-containing penile nerves and the neurons in the pelvic ganglia after unilateral cavernous nerve neurotomy in rats. Materials and Methods: Male rats were divided into three groups: sham operation (n = 14); unilateral neurotomy of a 5 mm. segment of the cavernous nerve (n = 14) with subsequent injection of buffer solution only; and unilateral neurotomy with GH injection (n = 14). Electrostimulation of the intact cavernous nerve was performed at 1 and 3 months. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was used to identify NOS in penile nerve fibers of the mid-shaft segment and in neurons of the pelvic ganglia. Results: One month after unilateral neurotomy, both the buffer alone and GH-treated groups showed a significant decrease in NOS-containing nerve fibers in the dorsal and intracavernosal nerves on the side of neurotomy. At 3 months, the number of NOS-containing nerve fibers in the buffer alone group did not increase, while the OH-treated group showed a significant increase. In the OH-treated group at 3 months, more NOS-positive neurons in the pelvic ganglia were found on the intact side than on the side of neurotomy (p <0.034), indicating that the regeneration derives from pelvic ganglion neurons on the intact side. Furthermore, electrostimulation in the OH-treated group revealed a greater maximal intracavernosal pressure and a shorter latency period at 3 months than in those given buffer alone. Conclusions: Our results show that GH injection significantly enhances the regeneration of NOS-containing fibers in the dorsal and intracavernosal nerves after unilateral cavernous nerve injury. We believe that GH administration may present a new and more physiologic approach to the treatment of erectile dysfunction after radical pelvic surgery.