Increased Cyclic Guanosine Monophosphate Synthesis and Calcium Entry Blockade Account for the Relaxant Activity of the Nitric Oxide-Independent Soluble Guanylyl Cyclase Stimulator BAY 41-2272 in the Rabbit Penile Urethra

Objectives: To study the direct relaxant activity of 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]pyrimidin-4-ylamine (BAY 41-2272) in the rabbit penile urethra and to investigate its modulatory effect on nitric oxide (NO)-mediated responses. Methods: Urothelium-intact (U+) and denuded (U-) rings were mounted in 10-mL organ baths for isometric force recording. Intracellular cyclic guanosine monophosphate (cGMP) levels were quantified with specific kits. Results: BAY 41-2272 (0.0001 to 10 μmol/L) caused relaxation of urethral rings contracted with phenylephrine (10 μmol/L), with higher potency (P <0.01) in U+ (pEC₅₀ 7.77 ± 0.09) compared with U- (pEC₅₀ 6.84 ± 0.19) preparations. The NO synthesis inhibitor N^ω-nitro-L-arginine methyl ester (100 μmol/L) or the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one (ODQ) (10 μmol/L) had no effect on BAY 41-2272 responses in U+ or U- rings. The phosphodiesterase-5 inhibitor vardenafil (0.1 μmol/L) potentiated the relaxant effects of BAY 41-2272 in both U+ (10-fold) and U- (sevenfold) tissues. Ca²⁺-induced contractions in K⁺ depolarized rings were significantly attenuated by BAY 41-2272 (1 μmol/L) in an ODQ-insensitive manner. BAY 41-2272 (0.03-0.3 μmol/L) increased the amplitude and duration of electrical field stimulation-induced relaxations (1 to 32 Hz), as well as those evoked by the NO donor glyceryl trinitrate (0.0001 to 10 μmol/L). BAY 41-2272 induced ODQ-resistant increases in cGMP levels above baseline (approximately twofold) in both U+ and U- rings. Conclusions: BAY 41-2272 relaxes penile urethra in a synergic fashion with NO. Targeting soluble guanylate cyclase with BAY 41-2272 may represent a new therapy in the management of voiding disturbances associated with impaired NO-cGMP signaling.