Experimental Study of Growth Factors on Regeneration of Cavernosal Nerves in the Rats

Jung, Gyung Woo; Kim, Dae Hwan; Kim, Doo Hong; Kim, Dong Woo; Yoon, Jin Han

Abstract

PURPOSE
Nitric oxide (NO) has recently been identified as the main neurotransmitter involved in the nonadrenergic-noncholinergic (NANC) pathway and is responsible for penile erection. Nitric oxide synthase (NOS)-containing nerve regeneration can be seen 6 months after unilateral cavernosal nerve neurotomy in rats. However its molecular mechanism is still unknown. It is believe that growth factors are involved in this phenomenon. In this study I investigated the change of NOS containing nerve fibers and the RNA expression of insulin like growth factor (IGF)-I, nerve growth factor (NGF), transforming growth factor (TGF)-alpha, TGF-beta 1, TGF-beta 2, TGF-beta 3, vascular endothelial growth factor(VEGF), nNOS and eNOS on the penis after cavernosal neurotomy in rats.
MATERIALS AND METHODS
Male rats were divided into three groups: sham operation (n=12); unilateral neurotomy of a 5-mm segment of the cavernosal nerve (n=18); and bilateral neurotomy (n=18). Electrostimulation of the cavernosal nerve of pelvic ganglion was performed at 1,3 and 6 months. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was used to identify NOS in the penile nerve fibers. The gene expressions for growth factors, nNOS and eNOS were investigated in corporal tissue by reverse transcriptase-polymerase chain reaction (RT-PCR) using specific oligonucleotide primers.
RESULTS
One month after neurotomy, both unilateral and bilateral neurotomy groups showed significant decreases in NOS-containing nerve fibers on the dorsal and intracavernosal nerves on the side of neurotomy and significantly lower mRNA expressions of nNOs, IGF-I and TGF-beta 2, and the unilateral neurotomy group showed higher mRNA expression of eNOS and VEGF189. At 3 months, the number of NOS-containing nerve fibers in the unilateral neurotomy group increased only slightly but at 6 months, those in the intracavernosal nerve increased in a significant amount (p<0.0001),however mRNA expressions of nNOs, IGF-I and TGF-beta . , showed significant increases as early as at 3 months, After bilateral neurotomy, the NOS-positive nerve fibers in the dorsal and intracavernosal nerve were significantly decreased at 1 month and remained so at 6 months; no erectile response could be elicited by pelvic ganglion stimulation. In the unilateral neurotomy group at 6 months, more NOS-positive neurons in the pelvic ganglia were found on the intact side than on the side of the neurotomy (p<0.005), indicating that the regeneration derived from pelvic ganglion neurons on the intact side. Furthermore, electrostimulation in the unilateral neurotomy group revealed a greater maximal intracavernosal pressure and a shorter latency period at 6 months than at 1 month (p<0.001, p<0.001, respectively).
CONCLUSION
These data suggest that IGF-I and TGF-beta 2, may play a key role in regeneration of NOS-containing nerve fibers in the dorsal and intracavernosal nerves, and eNOS increases temporarily in the intracavernosum involving VEGF189 after unilateral cavernosal nerve injury.