Nitric oxide synthases are involved in the modulation of cardiovascular adaptation in hemorrhaged rats

Nitric oxide has been implicated in the cardiovascular adaptation to hemorrhagic shock. Our aim was to study the potential role of nitric oxide synthases (NOS) in the cardiovascular response in hemorrhagic hypotension produced experimentally in anesthetized rats.

Groups of animals (n = 14, per group): (a) normotensive; (b) hypovolemic (20% blood loss); (c) normotensive and pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME); (d) hypovolemic and pretreatment with L-NAME.

L-NAME restored the hypotension induced by hemorrhage. Blood loss decreased heart rate in the first stage increasing at 60 and 120 min. L-NAME blunted this effect. Right atria and left ventricle histochemical NOS activities increased at 60 and 120 min (atria 8% and 24%, respectively; ventricle 21% and 45%, respectively). This activity increased 17% in smooth muscle at 120 min. Heart endothelial NOS protein levels increased in heart at 60 min being attenuated at 120 min. Inducible NOS protein levels raised significantly in right atria, left ventricle and aorta at 120 min.

Hemorrhagic shock induced a time-dependent and specific NOS activation modulating cardiovascular function. The inhibition of nitric oxide system appears to prevent the acceleration of heart rate during late phases after acute hypovolemic state induced by blood loss.