The pressure from the expanding penis compresses the veins (blood vessels that drain the blood out of the penis) in the tunica albuginea, helping to trap the blood in the corpora cavernosa, thereby sustaining erection. Erection is reversed when cGMP levels in the corpora cavernosa fall, causing the smooth muscles of the corpora cavernosa to contract, stopping the inflow of blood and opening veins that drain blood away from the penis. The levels of the cGMP in the corpora cavernosa fall because it is destroyed by an enzyme called phosphodiesterase type 5 (PDE5) Footnotes ?1 Abbreviations: PDE, phosphodiesterase; cAMP, adenosine 3?5?-cyclic monophosphate; cGMP, guanosine 3?5?-cyclic monophosphate; GAF, cyclic GMP, adenylyl cyclase, FhlA; CaM, calmodulin; PK, protein kinase; PKA, cAMP-dependent protein kinase; PKG, cGMP-dependent protein kinase; CNS, central nervous system; ANP, atrial natriuretic peptide; NO, nitric oxide; PDP, 9-(6-phenyl-2-oxohex-3-yl)-2-(3,4-dimethoxybenzyl)-purin-6-one; BAY 60-7750, 2-(3,4-dimethoxybenzyl)-7-[(1R)-1-hydroxyethyl]-4-phenylbutyl]-5-methylimidazo[5,1-f] [1,2,4]triazin-4(3H)-one; PI3K, phosphatidylinositol 3-kinase; IGF1, insulin-like growth factor 1; OPC-33450, 6-[3-[3-cyclooctyl-3-[(1R*,2R*)-2-hydroxycyclohexyl]ureido]-propoxy]-2(1H)-quinolinone; UCR, upstream conserved region; CRE, cAMP-responsive element-binding protein; RACK, receptor for activated C-kinase 1; AKAP, A-kinase anchoring proteins; ERK, extracellular signal-regulated kinase; BRL 50481, 3-(N,N-dimethylsulfonamido)-4-methyl-nitrobenzene; PAS, Period, Arnt, and Sim; IBMX, 3-isobutyl-1-methylxanthine; BAY 73-6691, 1-(2-chlorophenyl)-6-[(2R)-3,3,3-trifluoro-2-methylpropyl]-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidine-4-one. where to buy viagra safely real viagra online without prescription Pelvic Trauma, Surgery, Radiation Therapy generic viagra here real viagra online without prescription
