A. Coronary microvascular response to serotonin demonstrates a relaxation response prior to cardiopulmonary bypass. After bypass the microvessels switched to a strong contraction response. After addition of a 5-HT1B receptor blocker (SB224289) the post bypass contraction response was significantly diminished. (* pre- to post-bypass p< 0.001) (+ post-bypass to post-bypass + antagonist p< 0.001).
B. Microvascular response to serotonin in the presence of the PLC inhibitor, Quinacrine and PLA2 inhibitor, U73122, prior to CP-CPB. (Quinacrine to 5HT alone p= 0.17 and U73122 to 5HT alone p= 0.38). Post-CP-CPB microvessels subjected to Quinacrine yielded a significant reduction in the contractile response as compared to the post-CP-CPB response with 5HT alone (* p< 0.001). The contractile response was not significantly changed when U73122 was applied to post-CP-CPB microvessels as compared to 5HT alone (p= 0.58).