(A) Constitutive (endothelial) nitric oxide synthase (NOS), (B) protein kinase G (PKG) activity, and (C) phosphodiesterase type 5 (PDE5) activity, in control, BM-SS, and BM-SS mice treated with sildenafil. BM-SS mice penes had a significant (*P<0.05) reduction in constitutive (endothelial) NOS, PDE5, and PKG activities compared to control animals. After chronic PDE5 inhibitor therapy with sildenafil, constitutive NOS and PDE5 activities were similar to values from control mice penes. PKG activity was significantly increased (**P<0.05) to values greater than both control and SS BMT mice penes. N=6 in each group.