Endothelium-dependent basilar and aortic vascular responses in normotensive and coarctation hypertensive rats

The responsiveness of acetylcholine (ACh), nitroglycerin (NG) and norepinephrine (NE) (aorta only) in both basilar arteries (BA) and thoracic aortic (TA) rings from coarctation hypertensive rats (CHR) were studied and compared to their sham-operated normotensive control rats (SNR). The effects of these agents were also evaluated in TA or BA with and without endothelium from naive normotensive rats (NNR). Blood pressure (BP) and plasma renin activity (PRA) of CHR were significantly higher than their time-matched SNR. Endothelium removal from TA of NNR significantly enhanced NE and NG sensitivity and reduced the maximum ACh relaxation. Removal of BA endothelium of NNR abolished ACh-induced relaxation but had no effect on NG-induced relaxation. In BA from CHR at any stage of hypertension studied, the sensitivity and maximum relaxation induced by ACh or NG were not significantly different than their respective time-matched SNR. ACh sensitivity of TA did not change in 1 Day CHR but decreased in 4 and 14 Day CHR. NG sensitivity increased, did not change and decreased in 1, 4 and 14 Day CHR, respectively. NE sensitivity increased in all stages of hypertension. These data suggest that in coarctation-induced hypertension there is a complex progression of events in TA which is modulated by different mechanisms as evidenced by the changes in the effects of NE, ACh and NG at various stages of hypertension. The results also suggest that the vascular endothelium of TA but not of BA may provide an acute protective mechanism to counteract the imbalance created by the increased sensitivity of smooth muscle cells to contractile agonists in the early stage of hypertension. However, persistent hypertension appears to override this mechanism.