OBJECTIVETo determine whether recombinant adeno-associated virus-mediated overexpression of hCGRP in the corpus cavernosum can affect the continuous production of hCGRP in the penile tissue and enhance erectile responses in STZ-induced diabetic rats.

METHODSDiabetes mellitus was induced by a single intraperitoneal injection of 60 mg/kg streptozotocin in male SD rats. VssHGCMV-hCGRP, VssCMV-GFP and rAAV solution were injected into the corporal cavernosum of STZ-induced diabetic rats, respectively. The corporal tissue was obtained from groups of 8 rats on day 5 post-injection, and the expressions of CGRP and GFP in cavernosal tissue were detected using immunohistochemistry and laser scanning confocal microscopy, respectively. Cavemosal tissue cAMP and cGMP levels were measured using radioimmunoassay. On day 5 post-injection, intracavernous pressure induced by electrostimulation of penile dorsal nerves was measured and recorded with a biological signal processing system in each group rat.

RESULTSrAAV transduction efficiency of GFP reporter gene was measured by laser scanning confocal microscopy and was observed in the penile tissue, especially in the corporal cavernosum and the vessel 5 days after transfection with VssCMV-GFP. Immunohistochemistry showed that the CGRP increased in the corporal cavernosum. In addition, both cAMP and cGMP levels in the corpora cavernosa transfected with VssHGCMV-hCGRP were significantly increased, compared with controls [(48.4 +/- 6.5) nmol/L and (21.2 +/- 13.6) nmol/L vs (16.7 +/- 2.5) nmol/L and (0.42 +/- 0.12) nmol/L, respectively]. More importantly, 5 days after administration of VssHGCMV-hCGRP,a significant increase was observed in the erectile response to penile dorsal nerve stimulation in the diabetic rat [(60.5 +/- 4.5) mm Hg vs (22. 3 +/- 1.3) mm Hg].

CONCLUSIONSThis results demonstrate that rAAV-mediated transfer of the CGRP gene can increase production of endogenous CGRP, cAMP and cGMP in corpora cavernosa of STZ-induced diabetic rats. Moreover, overexpression of CGRP enhances ICP and the erectile response to penile dorsal nerve stimulation in the diabetic rat.