Intracavernosal injections of vascular endothelial growth factor protects endothelial dependent corpora cavernosal smooth muscle relaxation in the hypercholesterolemic rabbit: a preliminary study

Atherosclerosis is a major risk factor for erectile dysfunction, and loss of endothelium-dependent vasodilation appears early in the development of this disorder. Nitric oxide (NO) appears to he the principle mediator of erectile function and is generated in part by the sinusoidal endothelium. Vascular endothelial growth factor (VEGF) is an angiogenic growth factor and an endothelial cell-specific mitogen and the actions of VEGF are coupled to NO. In this preliminary study, we investigated whether VEGF could be used to protect endothelial dependent cavernosal relaxation from the atherosclerotic injury induced by a hypercholesterolemic diet. Two groups of New Zealand white adult male rabbits received a 1% cholesterol diet for four weeks, and two groups consumed normal rabbit chow. Half of the rabbits consuming the 1% cholesterol diet received weekly penile injections of 0.3 mg VEGF (n = 8), and half injections of normal saline (n = 8), Rabbits fed normal chow followed a similar protocol, half received weekly penile injections of 0.3 mg VEGF (n = 6) and half were given weekly penile injections of normal saline (n = 6). Isometric tension studies (with norepinephrine, acetylcholine, sodium nitroprusside and histamine) were performed on isolated strips of corpora cavernosa, The degree of corporal smooth muscle relaxation in response to ACH and SNP administration was recorded and compared. Significant elevation in serum total cholesterol levels occurred in rabbits receiving 4 weeks of the 1% cholesterol diet (727 +/- 75.6 mg/dl vs 38.7 +/- 5.53 mg/dl) P < 0.01. There were no significant differences in cavernosal contraction in any group, while cavernosal smooth muscle from rabbits on normal chow retained the ability to relax in response to ACH and SNP in tissue bath. The hypercholesterolemic rabbits receiving VEGF had a significantly higher maximal per-cent relaxation to ACH (111 +/- 28.9) compared to the hypercholesterolemic rabbits that received NS (77 +/- 23.1, P < 0.001). This difference in percent maximal relaxation to SNP was also present for hypercholesterolemic/VEGF rabbits (129.4 +/- 24) versus the hypercholesterolemic/NS rabbits (115.0 +/- 18, P = 0.033), In conclusion, intracavernosal injections of VEGF appear to protect corporal endothelium from hypercholesterolemia induced injury, thus preserving endothelial dependent corporal smooth muscle relaxation in hypercholesterolemic rabbit.