Expression of inducible nitric oxide synthase (iNOS) within the ventrolateral medulla in rats following transient middle cerebral artery occlusion and reperfusion

Abstract

Majority of stroke cases are due to ischemia in regions supplied by the middle cerebral artery (MCA). We reported that cardiovascular responses during static muscle contractions are attenuated following a transient MCA occlusion (MCAO), and involved differential expression of neuronal nitric oxide synthase (nNOS) protein within the rostral (RVLM) and caudal ventrolateral medulla (CVLM). In this study, we compared cardiovascular responses and inducible NOS (iNOS) protein expression within the left and right sides of both RVLM and CVLM in sham‐operated rats, and in rats with a 90‐minute left‐sided MCAO followed by 24 hour reperfusion. Pressor responses during static muscle contractions were attenuated in MCAO rats when compared to sham rats. Also, iNOS expression within the left RVLM was augmented when compared to the right RVLM in MCAO rats, and to both RVLM quadrants in sham rats. Conversely, compared to sham rats and the right CVLM of MCAO rats, iNOS expression was significantly attenuated in the left CVLM quadrant in left‐sided MCAO rats. Thus, the attenuated pressor response during muscle contraction in MCAO rats is partly due to overexpression and attenuation of iNOS protein within the ipsilateral RVLM and CVLM, respectively. Results demonstrate that differential expression of iNOS protein within the medulla mediates cardiovascular responses during static exercise in pathophysiological conditions.