Hindlimb unweighting decreases ecNOS gene expression and endothelium-dependent dilation in rat soleus feed arteries

We tested the hypothesis that hindlimb unweighting (HLU) and the associated reduction in soleus muscle blood flow causes decreased expression of endot helial cell nitric oxide synthase (ecNOS) mRNA and protein and attenuated e ndothelium-dependent vasodilator responses in rat soleus feed arteries (SFA ). Male Sprague-Dawley rats were exposed to HLU (n = 12) or cage control (C on; n = 12) conditions for 14 days; At the end of this period, SFA were iso lated, removed, and cannulated with two glass micropipettes for examination of vasodilator responses or frozen for analysis of ecNOS mRNA and protein expression; RT-PCR of RNA from single SFA was used to measure ecNOS mRNA, a nd immunoblots on single SFAs were used to measure ecNOS protein content. R esults revealed that both ecNOS mRNA and ecNOS protein expression were lowe r in SFA from HLU rats. Dilation to increased intraluminal flow was attenua ted in SFA from HLU rats (Con: 88 +/- 8% vs. HLU: 53 +/- 8%) as was maximal vasodilation to acetylcholine (10(-9)-10(-4) M; Con: 88 +/- 5% vs. HLU: 73 +/- 5%). Sensitivity to the endothelium-independent vasodilator sodium nit roprusside (10(-10)-10(-4) M) was enhanced by HLU (EC50: Con: 4.46 x 10(-7) M vs. HLU: 5.00 x 10(-8) M). Collectively, these data indicate that the ch ronic reduction in soleus blood flow associated with the reduced physical a ctivity during HLU results in reduced expression of ecNOS mRNA and protein in SFA and attenuated endothelium-dependent vasodilation.