Smooth muscle myosin heavy chains occur in 2 isoforms, SMA (slow) and SMB (fast). We hypothesized that the SMB isoform is predominant in the faster-contracting rat vena cava compared to thoracic aorta. We compared the time to half maximal contraction in response to a maximal concentration of endothelin-1 (ET-1; 100 nM), potassium chloride (KCl; 100 mM) and norepinephrine (NE; 10 µM). The time to half maximal contraction was shorter in the vena cava compared to aorta (aorta: ET-1 = 235.8 ± 13.8 s, KCl = 140.0 ± 33.3 s, NE = 19.8 ± 2.7 s; vena cava: ET-1 = 121.8 ± 15.6 s, KCl = 49.5 ± 6.7 s, NE = 9.0 ± 3.3 s). Reverse-transcription polymerase chain reaction supported the greater expression of SMB in the vena cava compared to aorta. SMB was expressed to a greater extent than SMA in the vessel wall of the vena cava. Western analysis determined that expression of SMB, relative to total smooth muscle myosin heavy chains, was 12.5 ± 4.9-fold higher in the vena cava compared to aorta, while SMA was 4.9 ± 1.2-fold higher in the aorta than vena cava. Thus, the SMB isoform is the predominant form expressed in rat veins, providing one possible mechanism for the faster response of veins to vasoconstrictors.

Oxidative stress plays an important pathophysiological role in the development of cardiovascular diseases. The imbalance of pro and antioxidant factors, defining oxidative stress, occurs when production of reactive oxygen species (ROS) by generators (NADPH oxidase, xanthine oxidase, uncoupled NO synthase, lipoxygenases, cyclooxygenases or the mitochondrial electron transport chain) overcomes cellular protection provided by defense systems (superoxide dismutase, catalase, glutathione and nonenzymatic scavengers). Our laboratory is researching the role of veins in the development of hypertension. We investigated ROS generation and some of its major determinants in venous and arterial blood vessels from normal rats. The superior mesenteric vein (SMV) and artery (SMA), as well as the inferior vena cava (VC) and the thoracic aorta (Ao) were compared in terms of their basal superoxide production relative to tissue weight, using a lucigenin chemiluminiscence based assay. In both cases, the vein generated more superoxide than its arterial counterpart (VC = 210 ± 42% Ao; SMV = 267 ± 48% SMA). Western analysis of homogenates from rat VC and Ao revealed that xanthine oxidase expression was significantly increased in the VC compared to the Ao (280 ± 31%), as well as catalase expression (VC = 135 ± 11% Ao) while p47phox had decreased expression in the VC compared to Ao (70 ± 11%). No significant change was observed for eNOS, RAC1 and Cu Zn SOD. These data suggest that veins differ from arteries with respect to ROS metabolism. However, the molecular mechanisms behind the different ROS handling by venous and arterial vascular tissue have yet to be uncovered.