Mechanism of augmented alpha 2 adrenergic receptor contraction in aorta from chronic nitric oxide synthase inhibited hypertensive rats

Hypertension effects 25% of Western adults and increases risk of cardiovascular disease. Endothelium-denuded aortic rings from rats made hypertensive with NOS inhibition contract more to α₂-adrenoreceptor (AR) stimulation. We hypothesized that upregulation of α₂-AR contractile signaling pathways augment contraction in chronic NOS-inhibited hypertensive rat aorta. To evaluate this hypothesis, we assessed the contribution of tyrosine kinases, RhoA/ROK, and PKC to α₂-AR vascular contraction in normotensive (NR) and NOS-inhibited hypertensive rats (LHR).; The first specific aim was to evaluate the contribution of tyrosine kinases to α₂-AR contraction. We hypothesized that one or more tyrosine kinases augment α₂-AR contraction in LHR arteries by increasing intracellular calcium. Tyrosine kinase inhibition attenuated UK14304 contraction of aortic rings, but did not alter UK14304 augmentation of contraction in ionomycin-permeabilized aorta, suggesting α₂-AR-stimulated tyrosine kinases regulate intracellular calcium concentration.; The second specific aim was to determine the contribution of RhoA and ROK to α₂-AR contraction. We hypothesized that increased RhoA/ROK activity enhances α₂-AR vasoreactivity in LHR aorta. ROK inhibition attenuated UK14304 contraction more in NR rings than in LHR rings. Additionally, relaxation to SNAP and Y-27632 in denuded ionomycin-permeabilized rings was greater in NR than in LHR. These studies indicate α₂ -AR contraction depends on ROK activity, but more in NR than LHR aorta.; The third specific aim was to determine the contribution of PKC and PI3K to α₂-AR contraction. We hypothesized that enhanced PKC activity or a change in PKC isoform augments α₂-AR contraction in LHR aorta. PKC and PI3K inhibition reduced UK14304 contraction in both NR and LHR aorta. Additionally, PI3K inhibition attenuated UK14304-stimulated PKC activity. However, calcium-dependent PKC inhibition only attenuated CaCl ₂ and α₂-AR contraction in LHR aorta, suggesting that PI3K-dependent PKCα augments calcium sensitivity and α₂-AR reactivity in LHR aorta.; These data suggest that the α₂-AR contractile pathway has two parts. The first is tyrosine kinase-dependent and regulates calcium entry. The second is ROK- and PKC-dependent, regulates calcium sensitivity, and is augmented in NOS inhibition hypertension. PKCα contributed to CaCl₂ and α₂-AR contraction in LHR only. Together, these data lead us to conclude that PKCα-dependent calcium sensitivity augments α₂-AR contractility in LHR aorta.