Effects of bacterial endotoxin on the contraction and relaxation responses of the rabbit cavernous smooth muscles

We evaluated effects of bacterial endotoxin during septicemia on contraction and relaxation responses of cavernous smooth muscles in rabbits.

We performed isometric tension studies with norepinephrine (NE), endothelium-dependent and endothelium-independent vasodilators, and nonadrenergic noncholinergic (NANC)-selective electrical field stimulation on the muscle strips of control and endotoxin (lipopolysaccharide; LPS)-treated rabbits. To determine reversibility of the LPS effects on the cavernous smooth muscle, the contraction and relaxation studies were repeated after resting the strips for 1 day at 4C. We also investigated the effect of the nonspecific nitric oxide synthase (NOS) inhibitor (NW-nitro-L-arginine methyl ester; L-NAME) and the selective immunologic NOS inhibitor (aminoguanidine) on reactivity of the strips to NE and acetylcholine.

Contractile response to NE was significantly (p <0.01) reduced in the cavernous smooth muscles from the systemically and locally LPS-treated rabbits, compared with control group. Both aminoguanidine and L-NAME markedly improved the diminished contraction of the strips. Relaxation response to endothelium-dependent agonists (acetylcholine and bradykinin) was significantly (p <0.05) decreased in the LPS-treated groups, compared with the control group but not to endothelium-independent vasodilators (papaverine and verapamil) and NANC-selective electrical field stimulation. L-NAME completely inhibited the relaxation response to acetylcholine in the control and LPS-treated groups but aminoguanidine did not. The impaired contraction and relaxation of the strips was completely restored after resting for 1 day.

Bacterial endotoxin may cause non-endothelial overproduction of NO and inhibition of endothelium-derived NO production, which may contribute to impairment of contraction and relaxation of rabbit cavernous smooth muscles.