Endothelium-modulated proliferation of medial smooth muscle cells: influence of angiotensin II and converting enzyme inhibition

Exercise intensity modulates capillary perfusion in correspondence with ACE I/D modulated serum angiotensin II levels

During exercise the renin-angiotensin system is stimulated. We hypothesized that the increase in serum angiotensin II (AngII) levels after exercise is dependent on exercise intensity and duration and secondly that people with the ACE-II genotype will show a higher increase in AngII serum levels. We also assumed that perfusion of upper limbs is transiently reduced with maximal cycling exercise and that subjects with the ACE-II compared to the ACE-ID/DD genotype will have a higher capillary perfusion due to lower AngII levels. Ten healthy subjects completed a maximal exercise test, a 12-min exercise test at ventilatory threshold and a 3-min test at the respiratory compensation point. AngII serum levels and capillary recruitment of the skin in the third finger were measured before and after exercise and breath-by-breath gas exchange during exercise was assessed. Baseline levels of AngII levels were lower prior to the 3-min test which took place on average 5 days after the last exercise. A two-fold increase compared to baseline levels was found for AngII only immediately after the 3-min test and not after the maximal exercise test and 12-min of exercise. Subjects without the I allele showed a decrease in AngII values after the maximal test in contrast to subjects with the ACE-II/ID genotype. Subjects with the ACE-II genotype had a 1.8 times significant higher capillary perfusion in the finger after exercise. A trend was observed for a 34.3% decreased capillary recruitment in the ACE-ID/DD genotype after exercise. We conclude that the rise in AngII after exercise is intensity dependent and that variability in serum AngII and capillary perfusion is related to the ACE I/D polymorphism.

Angiotensin I-converting enzyme activity and vascular sensitivity to angiotensin I in rat injured carotid artery

We used a vasoreactivity assay to examine the functional significance of angiotensin I-converting enzyme overexpression in smooth muscle cells after vascular injury. Rat carotid arteries isolated at days 2 to 14 after in vivo endothelial denudation were compared with the contralateral freshly denuded (control) vessels. Arterial rings were constricted ex vivo with angiotensin I in the absence or presence of the angiotensin I-converting enzyme inhibitors captopril (300 nM and 3 microM) or perindoprilate (1 nM). Angiotensin I-converting enzyme activity was determined by cleavage of the chromogenic substrate Hip-His-Leu. Angiotensin I-converting enzyme activity in injured arteries was increased (2-fold) at day 7 only after vascular injury. Contractions to angiotensin I were unaffected after injury. Inhibition by captopril and perindoprilate of angiotensin I-induced contractions was significantly less potent in injured arteries at day 7 as compared to control vessels. Mechanical removal of neointimal smooth muscle cells normalized the inhibition by captopril in injured arteries at day 7. Captopril did not affect angiotensin II-induced contractions. Thus, upregulation of angiotensin I-converting enzyme after arterial injury confers resistance to angiotensin I-converting enzyme inhibitors.

ACE inhibition and fibroblast growth factor in cultured human vascular smooth muscle

The effects of the angiotensin converting enzyme (ACE) inhibitor, enalaprilat, and basic fibroblast growth factor (bFGF) on DNA synthesis and expression of ACE mRNA were examined in human vascular smooth muscle cells cultured from saphenous vein and internal mammary artery. DNA synthesis was estimated using 3H-thymidine uptake, and ACE mRNA was estimated by rt-PCR. Enalaprilat (0.125 microg/ml, 48 h) decreased 3H-thymidine uptake to 66+/-12% (SE) of the control without enalaprilat (p < 0.05). Basic FGF (10 ng/ml, 24 h) increased uptake by 41 +/- 12% (p < 0.05) while enalaprilat pretreatment (24 h) decreased uptake to 56 +/- 12% of this augmented value (p < 0.025). Basic FGF increased ACE mRNA, a process that was time dependent with an approximately 50% increase after 24 h exposure. Pre-exposure to enalaprilat (24 h) before bFGF reduced ACE mRNA to approximately 50% of that found in the presence of bFGF alone. The results indicate that ACE mRNA is present in human vascular smooth muscle cells and that exposure to an ACE inhibitor reduces DNA synthesis. Basic FGF stimulates DNA synthesis and ACE mRNA expression, and both of these effects are reduced by an ACE inhibitor. The results are consistent with the effects of bFGF being exerted through, or alternatively in concert with, angiotensin II. Further, they suggest that ACE inhibition can reduce the activity of the renin-angiotensin system by inhibiting the production of ACE, or at least the expression of ACE mRNA, in addition to producing enzyme inhibition at the ACE level.

Proteoglycan production by vascular smooth muscle cells from resistance arteries of hypertensive rats

Extracellular matrix (ECM) modifications in the vascular wall contribute to the narrowing of arteries in hypertension. Because direct evidence for the role of proteoglycans (PGs) in the pathological process of resistance-sized arteries has not already been demonstrated, we examined the effect of growth factors on secreted and membrane-bound PG synthesis by cultured mesenteric vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and Wistar rats. After 48 hours of stimulation with angiotensin II (Ang II), platelet-derived growth factor (PDGF-BB), and 10% fetal calf serum (FCS) or 0.1% FCS as control, PG synthesis (in dpm/ng DNA) was evaluated in the medium (M-ECM) and in the cell layer (P-ECM) by a double-isotopic label method with both [(3)H]-glucosamine and [(35)S]-sodium sulfate, which are incorporated into all complex carbohydrates or only into sulfated disaccharides, respectively. VSMC from SHR displayed a significantly lower level of synthesis of M-ECM [(3)H]-PGs than those of Wistar rats in all the experimental groups, including the control group (0. 1% FCS), but no differences in M-ECM [(35)S] uptake were found in any case. In the P-ECM, Ang II was the only factor that produced a lesser effect on [(3)H]-glucosamine and a greater effect on [(35)S]-sodium sulfate uptakes in VSMC from SHR than from Wistar rats. The most prominent change seen in VSMC from SHR was an increased sulfation, assessed by [(35)S]/[(3)H] ratio, in nonstimulated cells and in response to 10% FCS and Ang II but not to PDGF-BB compared with VSMC from Wistar rats. These data indicate the existence of changes in PG modulation in the resistance vessels of SHR, which suggests that PGs may contribute to the development of structural and functional modifications in hypertensive states.