Regeneration of endothelial cells after balloon denudation of the rabbit carotid artery and changes in responsiveness

The Aging Vasculature: Glucose Tolerance, Hypoglycemia and the Role of the Serum Response Factor

The fastest growing demographic in the U.S. at the present time is those aged 65 years and older. Accompanying advancing age are a myriad of physiological changes in which reserve capacity is diminished and homeostatic control attenuates. One facet of homeostatic control lost with advancing age is glucose tolerance. Nowhere is this more accentuated than in the high proportion of older Americans who are diabetic. Coupled with advancing age, diabetes predisposes affected subjects to the onset and progression of cardiovascular disease (CVD). In the treatment of type 2 diabetes, hypoglycemic episodes are a frequent clinical manifestation, which often result in more severe pathological outcomes compared to those observed in cases of insulin resistance, including premature appearance of biomarkers of senescence. Unfortunately, molecular mechanisms of hypoglycemia remain unclear and the subject of much debate. In this review, the molecular basis of the aging vasculature (endothelium) and how glycemic flux drives the appearance of cardiovascular lesions and injury are discussed. Further, we review the potential role of the serum response factor (SRF) in driving glycemic flux-related cellular signaling through its association with various proteins.

Optimizing endothelial nitric oxide activity may slow endothelial aging

The capacity of vascular endothelium to generate bioactive nitric oxide (NO) decreases with advancing age, even in healthy subjects with a relatively benign risk factor profile; this phenomenon may reflect decreased expression of NO synthase, as well as increased production of superoxide, and evidently contributes importantly to the increased vascular risk associated with aging. Studies with cultured endothelial cells suggest that the rate of endothelial aging is determined primarily by the rate of cell turnover and the associated progressive shortening of telomeres; endothelial cells transfected with the catalytic subunit of telomerase--which preserves a youthful telomere length--do not show a reduction in NO synthase expression after numerous doublings, in contrast to the marked reduction observed in control cells. Also consistent with this view is the fact that, following balloon denudation of arteries, the regenerated endothelium makes less NO. In the vasculature of adults, the rate of endothelial cell mitosis is evidently a reflection of the rate of endothelial cell apoptosis. Numerous cell culture studies demonstrate that physiological levels of NO protect endothelial cells from apoptosis induced by a wide range of noxious stimuli--including vascular risk factors such as oxidized LDL, angiotensin II, and hyperglycemia. In the human vasculature, endothelial cells with disproportionately short telomeres are found capping atheromatous lesions and in atheroma-prone areas where blood flow is turbulent; these findings evidently reflect increased endothelial cell turnover in regions where NO bioactivity is relatively weak. It can be deduced that lifelong adherence to an "endotheliophilic lifestyle" that optimizes vascular NO production, while minimizing that of superoxide, will literally slow the rate of aging of vascular endothelium, such that, at any given advanced age, the optimal functional capacity of the vascular endothelium will be superior to that of age-matched controls. These considerations underline the desirability of actively promoting vascular health in younger and middle-aged individuals in whom risk for vascular events may still be quite low. The impact of lifelong caloric restriction on endothelial aging requires further study, preferably in primates.

Endogenous nitric oxide synthase inhibitors in endothelial cells, endothelin-1 within the vessel wall, and intimal hyperplasia in perimenopausal human uterine arteries

The present experiments were designed to investigate the ability to produce nitric oxide, concentrations of N(G)-monomethyl-L-arginine (L-NMMA), and asymmetric N(G), N(G)-dimethyl-L-arginine (ADMA) in endothelial cells, endothelin-1 within the vessel wall, and the degree of intimal hyperplasia (intima/media ratio) in perimenopausal human uterine arteries. According to the tentative classification based on basal cyclic GMP levels, 16 arteries could be grouped into groups I and II consisting of eight each. Net production of the nucleotide was significantly higher in group I than that in group II. Concentration of L-NMMA plus ADMA and endothelin-1 content were significantly higher in group II. All specimens from group I were histologically normal, whereas mild to severe intimal hyperplasia was observed in group II specimens. Although considerable individual variations were detectable in the intima/media ratio, L-NMMA plus ADMA and endothelin-1 (n = 35 each), there were significant and positive correlations between three parameters, indicating that intimal hyperplasia became greater as L-NMMA plus ADMA and endothelin-1 were increased. These results suggest that endogenous nitric oxide synthase inhibitors in endothelial cells and endothelin-1 within the vessel wall are important markers of intimal hyperplasia.

Accelerated intimal hyperplasia and increased endogenous inhibitors for NO synthesis in rabbits with alloxan-induced hyperglycaemia

1. We examined whether endogenous inhibitors of NO synthesis are involved in the augmentation of intimal hyperplasia in rabbits with hyperglycaemia induced by alloxan. 2. Four weeks after the endothelial denudation of carotid artery which had been performed 12 weeks after alloxan, the intimal hyperplasia was greatly augmented with hyperglycaemia. The degree of hyperplasia was assessed using three different parameters of histopathological findings as well as changes in luminal area and intima: media ratio. 3. There were positive and significant correlations between intima:media ratio, plasma glucose, and concentrations of N(G)-monomethyl-L-arginine (L-NMMA) and N(G), N(G)-dimethyl-L-arginine (ADMA) in endothelial cells, that is, the intima:media ratio became greater as plasma glucose and endothelial L-NMMA and ADMA were increased. Furthermore, endothelial L-NMMA and ADMA were increased in proportion to the increase in plasma glucose. 4. In contrast, there were inverse and significant correlations between cyclic GMP production by carotid artery strips with endothelium and plasma glucose, between cyclic GMP production and endothelial L-NMMA and ADMA, and between the intima:media ratio and cyclic GMP production. 5. Exogenously applied L-NMMA and ADMA inhibited cyclic GMP production in a concentration-dependent manner. IC50 values were determined to be 12.1 microM for the former and 26.2 microM for the latter. The cyclic GMP production was abolished after the deliberate removal of endothelium from the artery strips. 6. These results suggest that the augmentation of intimal hyperplasia with hyperglycaemia is closely related to increased accumulation of L-NMMA and ADMA with hyperglycaemia, which would result in an accelerated reduction in NO production/release by endothelial cells.

Loss of arterial dilation in the reendothelialized area of the flow-loaded rat common carotid artery

We have investigated regenerated endothelial cells and their possible contribution to arterial dilation in response to increased blood flow in rat common carotid artery (CCA). After endothelial denudation using a balloon catheter in the left CCA, an arteriovenous shunt was constructed between the left CCA and the left external jugular vein at 20 mm distal from the orifice in the denuded group. Animals that were given the arteriovenous shunt without denudation were used to form the nondenuded group. The blood flow rate in the left CCA was increased by sixfold after operation in the denuded group. We observed that endothelial cells were gradually regenerated from the orifice to the distal area and that the reendothelialized area after 4 to 8 weeks was approximately one third of the left CCA (5.31 +/- 1.49 mm at 4 weeks, 5.47 +/- 1.56 mm at 8 weeks). In the reendothelialized area of the left CCA after 4 to 8 weeks, the lumen diameter was significantly smaller than that of the nondenuded group and showed no significant difference from age-matched nonsurgical animals. The intimal and medial thickening, which would result in arterial stenosis in the reendothelialized area, was not observed in the denuded group, although the denuded control showed significant intimal thickening. From these results, we conclude that regenerated endothelial cells reduce intimal thickening but do not respond to increased blood flow to dilate the artery.

The effects of L-arginine on neointimal formation and vascular function following balloon injury in heritable hyperlipidaemic rabbits

OBJECTIVE

The aims of this study were to determine the morphological and functional consequences of balloon angioplasty of the left subclavian artery of Froxfield heritable hyperlipidaemic (FHHL) rabbits and the influence of oral L-arginine therapy on these changes.

METHODS

Sixteen-week-old FHHL rabbits were subjected to balloon injury of the left subclavian artery under halothane anaesthesia. Control rabbits (n = 7) were given free access to food and normal tap water. L-Arginine-treated rabbits were given L-arginine (5 g.l-1 in the drinking water for 2 days prior to angioplasty and then for either 2 weeks (n = 7) or 4 weeks (n = 7) after surgery. All rabbits were euthanised 28-30 days after surgery and blood and tissue removed for quantification of neointimal size and determination of endothelial function using isolated vessel tension studies. The ability of the endothelium to prevent platelet aggregation was determined by challenging a vessel ring with carbachol when incorporated into a whole blood sample in which platelet aggregation was induced with collagen.

RESULTS

Balloon injury in non-treated rabbits resulted in the development of marked intimal hyperplasia (18.8[3.6]% of the area within the internal elastic lamina) while endothelial function remained intact. Maximum responses to carbachol and calcimycin were, respectively, a 66.6[14.7]% and 46.9[12.9]% relaxation of 5HT-induced tone, compared to 58.0[3.2]% and 39.8[9.4]% in non-injured vessels. Maximum contractile responses to 5HT and KCl were unaffected by injury. L-Arginine therapy alone had no effect on the vasodilator function of the endothelium, but reduced the endothelium-dependent inhibition of platelet aggregation (68.4[7.8] vs 109[10]% of the maximum extent of platelet aggregation in non-treated and 2-week L-arginine-treated non-injured vessels, respectively). L-Arginine significantly reduced the extent of neointimal formation (7.2[3.9]% of the area within the IEL; P < 0.05 vs. non-treated group). However, L-arginine significantly attenuated the relaxant responses to both carbachol (26.5[10.4]% and 31.4[9.4]% for 2- and 4-week L-arginine groups) and calcimycin (38.7[15.4]% and 16.4[10.7]%) in the injured artery (P < 0.05 compared to non-treated controls).

CONCLUSIONS

L-Arginine reduces neointimal formation following balloon catheter injury in heritable hypercholesterolaemic rabbits, which is consistent with previous findings in normocholesterolaemic models. However, in the presence of hypercholesterolaemia, L-arginine has a detrimental effect on endothelial function following injury. This may be a consequence of the presence of lipids in the vascular wall on nitric oxide synthase activity.

Effect of nicotine on the intimal hyperplasia after endothelial removal of the rabbit carotid artery

1. The present experiments were designed to investigate the effect of long-term oral nicotine (10 mg/200 ml/kg/day for 7 weeks) on the intimal hyperplasia after endothelial removal of the rabbit carotid artery. 2. The plasma concentrations of nicotine were determined to be 11.7-12.5 ng/ml during the term of administration and corresponded to the plasma levels in human smokers. 3. Six weeks after the endothelial removal, light microscopy revealed a marked intimal hyperplasia. Administration of nicotine tended to accelerate the intimal hyperplasia, which was estimated by comparing the histological findings, DNA content and wet weight of the vessel wall. 4. Acetylcholine- and A23187-induced endothelium-dependent relaxations were greatly impaired in the hyperplastic artery strips. The impairment of relaxations tended to be accelerated in the nicotine group. Sodium nitroprusside-induced relaxation was not different between the control and the hyperplastic artery strips and remained unaffected in the nicotine group. 5. The concentrations of endogenous nitric oxide (NO) synthesis inhibitors, NG-monomethyl-L-arginine (L-NMMA) and asymmetrical NG,NG-dimethyl-L-arginine (ADMA) were significantly more increased in the regenerated endothelial cells compared with those in the control endothelial cells. The concentrations of L-NMMA and ADMA in the regenerated endothelial cells were significantly increased by as much as 1.3 x 10(-6) and 5.6 x 10(-7) M, respectively, in the nicotine group. 6. Immunoreactive endothelin-1 was significantly increased in the hyperplastic vessel wall (2.4 times that of the control) in 6 weeks. Administration of nicotine tended to increase the level. 7. It seems possible to assume from these results that, although, under the present experimental conditions, nicotine exhibited a tendency to accelerate the intimal hyperplasia after endothelial removal, the longer exposure to nicotine or a higher dose of the agent or both would significantly accelerate the intimal hyperplasia through the enhanced impairment of endothelium-derived relaxing factor/ NO production, which might be brought about by the enhanced increases in L-NMMA and ADMA concentrations, and the enhanced increase in endothelin-1 in the vessel wall.

Attenuated inhibition of adrenergic contraction by nitric oxide in injured guinea pig femoral artery

The present study aimed to examine the altered modulation of adrenergic contraction by nitric oxide and sensory neuropeptides in balloon-injured muscular artery. A guinea pig femoral artery (GPFA) was injured by a newly developed silastic microballoon catheter. The contralateral GPFA served as the control. The studied GPFAs consisted of six groups; control (C) and injured (I) GPFA, isolated at 0 days, and 2 and 8 weeks after injury (C0, I0, C2, I2, C8, and I8). Isometric tension was measured in the presence of indomethacin (10(-5) M), to exclude effects of cyclooxygenase-generated eicosanoids. Endothelial removal with the catheter was confirmed by histological examination. In each group, except for 10, NG-nitro-I-arginine methyl ester (L-NAME, 10(-6) M) induced significant augmentation of perivascular nerve stimulation (PNS)-evoked adrenergic contraction, which was blocked by L-arginine (3 x 10(-4) M). The degree of L-NAME augmentation in I8 was significantly smaller than that in C8 and I2. Capsaicin (10(-6) M) did not significantly affect PNS-contraction in any group, indicating that there was no sensory neuropeptide involvement in this contraction. In I8, acetylcholine (10(-6) M)-induced relaxation after noradrenaline (10(-5) M)-precontraction was significantly smaller than that seen in the other groups, except for I0, which was lacking in acetylcholine-induced relaxation. Histologically, injured GPFAs showed progressive intimal thickening. The present findings thus showed attenuated nitric oxide-mediated inhibition of adrenergic contraction, accompanying intimal thickening, in balloon-injured muscular artery, 8 weeks after injury.

Intimal hyperplasia in human uterine arteries accompanied by impaired synergism between prostaglandin I2 and nitric oxide

1. The present experiments were designed to investigate the mechanisms causing intimal hyperplasia in connection with the impaired synergism between prostaglandin I2 (PGI2) and nitric oxide (NO) in human uterine arteries (UAs). 2. In order to assess the magnitude of intimal hyperplasia, the intima:media ratio (%) was estimated with the aid of an image analyser. Human UAs were classified into two groups, I and II on the basis of the ratio and the degree of elastin deposition of histologically normal specimens. The intima:media ratio in group II was determined to be 38.9 +/- 7.7% (n = 6), which was significantly (P < 0.01) higher than that in group I (16.5 +/- 1.5%, n = 7). Less deposition of elastin was found in group I than in group II. 3. The relaxation activities of iloprost (IP) as a stable analogue of PGI2 and sodium nitroprusside (SNP) as a NO donor were not different between the two groups. When the minimum concentrations (Cmin) of IP and SNP in producing relaxation were applied together to the UA strips, these compounds interacted synergistically in group I. The observed relaxation (48.7 +/- 8.8%, n = 7) in this group was significantly (P < 0.01) greater than the predicted value of 18.8 +/- 3.1% (n = 7) (the mathematical sum of the relaxations caused by IP and SNP alone). By contrast, these agents interacted in an additive manner in group II. The observed relaxation (20.8 +/- 9.5%, n = 6) was not significantly different from the predicted value (18.6 +/- 2.4%, n = 6) in this group. 4. During the relaxation produced by the addition of IP and SNP alone or in combination, the changes in cyclic nucleotides (cyclic AMP and cyclic GMP) contents (pmol mg-1 protein) were assayed. When IP and SNP at Cmin were applied together to the UA strips, these compounds interacted synergistically in increasing cyclic nucleotides in group I. The observed net increase in the content was determined to be 1.46 +/- 0.30 (P < 0.05 vs. the predicted value of 0.67 +/- 0.12) in this group (n = 7). By contrast, the observed net increase (0.40 +/- 0.07, n = 6) did not exceed the predicted value (0.65 +/- 0.07, n = 6) in group II. 5. These results suggest that the formation of intimal hyperplasia in group II may be closely related to the impaired synergism between PGI2 and NO in the human UAs.

Immunohistochemical detection of Ki-67 in replicative smooth muscle cells of rabbit carotid arteries after balloon denudation

BACKGROUND AND PURPOSE

Ki-67 immunohistochemistry has been shown to be useful for paraffin sections from human species after wet heating. We applied Ki-67 immunohistochemistry to rabbit arteries after balloon denudation and compared the results with proliferating cell nuclear antigen (PCNA) immunohistochemistry.

METHODS

Monoclonal antibodies MIB-1 for Ki-67 and PC-10 for PCNA were used to detect replicative smooth muscle cells in rabbit carotid arteries during a period of 4 weeks after balloon endothelial denudation.

RESULTS

We demonstrated clear immunoreactivities for Ki-67 in paraffin sections of rabbit arteries after hydrated autoclaving. Ki-67-positive smooth muscle cells appeared throughout the thickened intima 1 week after endothelial denudation. At 2 weeks, Ki-67-positive cells were confined to the surface layer of the intima. PCNA-positive cells appeared in almost the same location by 2 weeks after endothelial denudation but were significantly greater in number than Ki-67-positive cells. PCNA-positive cells remained in the surface layer of the intima 4 weeks after endothelial denudation, while Ki-67-positive cells had almost disappeared from the intima.

CONCLUSIONS

Our results indicate that Ki-67 immunohistochemistry using MIB-1 monoclonal antibody provides a powerful tool, even in rabbit species, for the detection of replicative smooth muscle cells during the repair of arterial injury and that it detects replicative cells more accurately than PCNA immunohistochemistry.

Accelerated endothelial regeneration and intimal hyperplasia following a repeated denudation of rabbit carotid arteries: morphological and immunohistochemical studies

1. We compared endothelial regeneration and intimal thickening after endothelial denudation between normal and sclerotic carotid arteries (CA). Endothelial denudation of the right CA of rabbits formed intimal thickening covered with regenerated endothelial cells (EC) in 6 weeks, which was considered as the sclerosis model. Both CA were then denuded. Morphological and immunohistochemical studies using antibodies for proliferating cell nuclear antigen (PCNA), von Willebrand factor and macrophages were performed. 2. Regeneration of EC were observed 24 h after denudation on both CA, but completed earlier in the double-denuded right CA. The density of EC in both CA increased after regeneration and gradually decreased afterwards. 3. After a single denudation on the left CA, PCNA-positive cells clearly appeared in 24 h, markedly increased in 72 h both in the intima and media, then greatly decreased in 4 and 6 weeks. 4. After a double denudation of the right CA, enhancement of the intimal hyperplasia was observed. PCNA-positive cells markedly increased in 1 week and remained significantly increased in 6 weeks both in the intima and the media. 5. We concluded from these results that the repeated endothelial denudation caused more sustained proliferation of smooth muscle cells which led to an enhancement of the intimal hyperplasia.

Accumulation of endogenous inhibitors for nitric oxide synthesis and decreased content of L-arginine in regenerated endothelial cells

1. We examined regeneration of endothelial cells (ECs), neointima formation, decreased endothelium-dependent relaxation (EDR) and changes in the contents of L-arginine, NG-monomethyl-L-arginine (L-NMMA), asymmetrical NG, NG-dimethylarginine (ADMA) and symmetrical NG,NG-dimethylarginine (SDMA) in the regenerated ECs, 6 weeks after balloon denudation of the rabbit carotid artery. 2. Regeneration of ECs was completed in 6 weeks and a significant neointima formation accompanied by the decreased EDR was observed. 3. L-NMMA and ADMA contents in the regenerated ECs (23.5 +/- 4.3 and 21.2 +/- 2.0 pmol mg-1 DNA, respectively) were significantly (P < 0.05 and P < 0.01) higher than those in the control ECs (8.8 +/- 3.0 and 7.4 +/- 1.9 pmol mg-1 DNA, respectively), whereas L-arginine was significantly (P < 0.005) decreased in the regenerated ECs (31,470 +/- 1,050 pmol mg-1 DNA) as compared to that in the control ECs (47,870 +/- 1,890 pmol mg-1 DNA). SDMA content was below the assay limits. 4. L-NMMA and ADMA, but not SDMA, inhibited the EDR induced by acetylcholine in a concentration-dependent manner. The inhibition with L-NMMA and ADMA was prevented by an addition of L-arginine, but not by D-arginine. 5. These results suggest that the accumulation of endogenous inhibitors for nitric oxide synthesis and decreased L-arginine content are associated with decreased NO production/release from regenerated ECs and neointima formation.

Selective inhibition of myosin phosphorylation and tension of hyperplastic arteries by the kinase inhibitor HA1077

To examine possible alterations in myosin light chain phosphorylation in hyperplastic arteries, rabbit strips from right hyperplastic and left normal control carotid arteries were used for experiments 6 weeks after the ballooning procedure. When the hyperplastic artery was stimulated with various concentrations of K+ (10, 20, 30, 40 and 60 mM), the maximal tension in response to each concentration was significantly higher (P < 0.05) than that in the control artery. The maximal extent of myosin light chain phosphorylation induced by 60 mM K+ in the hyperplastic artery was also significantly higher than that in the control (55.1 +/- 4.1 vs. 45.1 +/- 3.2%, mean +/- S.D.). However, the [Ca2+]i response to elevated K+ in hyperplastic arteries was much the same as that in control arteries, when measured with fura-PE3. HA1077 (1-5-(isoquinolinesulfonyl)-homopiperazine), a protein kinase inhibitor, was about 3-5 times more effective in inhibiting the tension and myosin light chain phosphorylation induced by 60 mM K+ in the hyperplastic artery than in the control artery. Nifedipine inhibited the tension and myosin light chain phosphorylation to the same extent in control and hyperplastic arteries. Thus, an alteration of the myosin light chain phosphorylation system, but not an alteration of Ca2+ mobilization, may be involved in the enhanced contraction of the hyperplastic artery. The enhanced phosphorylation of myosin light chain may be sensitive to HA1077.

Role of endothelium in the human uterine arteries during normal menstrual cycle

1. The present experiments were designed to investigate the role of endothelium in the human uterine arteries during the normal menstrual cycle. 2. Acetylcholine (ACh) produced a concentration-dependent relaxation response during the higher level of plasma 17 beta-oestradiol (E2) (follicular and luteal phases, E2 = 131.9 +/- 15.9 pg ml-1, n = 13; group I). However, the agent did not produce a definite relaxation, but produced a slight contraction during the ovulatory and menstruation phases (E2 = 19.8 +/- 2.9 pg mg-1, n = 5; group II). During the follicular and luteal phases (E2 = 181.1 +/- 9.0 pg ml-1, n = 6), ACh produced a slight contraction, but not relaxation in 6 cases (group III). Relaxation in response to A23187 in group II was not different from that in group I, while it was significantly (P < 0.05 and P < 0.005) reduced in group III. Sodium nitroprusside (SNP)-induced relaxation was similar in the three groups. 3. Correlation between the maximum response to ACh and the plasma E2 was highly significant (gamma = 0.8142, P < 0.001) in 18 cases of groups I and II, but not in all 24 cases including group III (gamma = 0.1183, NS). 4. Relaxations in response to ACh in group I or A23187 in all groups were abolished after removal of the endothelium. In group I, ACh- and A23187-induced relaxations were greatly inhibited by methylene blue or NG-nitro-L-arginine (L-NOARG) and partially inhibited by indomethacin. None of these treatments except for methylene blue modified the SNP-induced relaxation, which was significantly inhibited by methylene blue.5. The A23187-induced relaxation was hardly affected by methylene blue or L-NOARG in group III,but was partially inhibited by these agents in group II. The effect of indomethacin in inhibiting the A23187 induced-relaxation was most potent (58.9%) in group III and least (16.9%) in group I.6. There were no histological changes in 14 cases out of 18 (groups I and II), but very slight intimal thickening was observed in 4 cases in group I. On the other hand, severe intimal thickening was observed in all 6 cases in group III.7. These results indicate that, in human uterine artery strips, ACh and A23187 cause endothelium dependent relaxations, which are mediated mainly through EDRF/NO in group I, mainly prostacyclin(PGI2) in group III, or both in group II. It is suggested that lack of the production/release of EDRF/NO and/or of interaction between EDRF/NO and PGI2 might play a role in the formation of intimal thickening in human uterine arteries.

Beneficial effect of SPM-5185, a cysteine-containing nitric oxide donor, in rat carotid artery intimal injury

We studied the effects of an organic nitric oxide (NO) donor SPM-5185 in a rat carotid artery intimal injury model. Seven days after injury, the two end segments of the injured carotid arteries were studied for endothelial release of NO, and the middle segments were used for histological measurement of the intimal-to-medial (I/M) ratio and scanning electron microscopy of the luminal surface. The NO donor SPM-5185 or its non-NO-donating control compound SPM-5267 were infused intravenously at 30 micrograms/d. Full vasorelaxant responses of rat carotid arterial rings were obtained with the endothelium-dependent vasodilators acetylcholine (ACh), A23187, and the endothelium-independent vasodilator acidified NaNO2 in sham-operated control rings. Impaired relaxation occurred with 10 mumol/L ACh and 1 mumol/L A23187 in injured rings but not in rings infused with SPM-5185 for 7 days. Relaxation to 100 mumol/L acidified NaNO2 was not significantly different among any of the groups, indicating a normal vascular smooth muscle response after intimal injury. Morphometric analysis of injured carotid arteries given vehicle and SPM-5267 showed marked intimal thickening with an average I/M ratio of 0.78 +/- 0.03 and 0.74 +/- 0.05, respectively. SPM-5185 markedly attenuated intimal thickening, resulting in an I/M ratio of 0.13 +/- 0.03 (P < .01 from vehicle), representing an approximately 82% inhibition of intimal thickening. SPM-5185 infusion resulted in accelerated regeneration of endothelial cells on the intimal surface at 7 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the responses of isolated rings of rabbit left carotid artery. A potential protocol for the assessment of pathologically induced functional changes

Studies on such injury processes as atherosclerosis, angioplasty, and restenosis, have shown an impairment of relaxations mediated by endothelium-derived relaxing factor (EDRF). Increasingly, the rabbit carotid artery is being used as the vessel of choice in such studies, but a definite protocol for the assessment of endothelial dysfunction or denudation has not been developed. Using isolated carotid artery rings, we have obtained reproducible dose-response curves in endothelially intact and denuded vessels from normally fed rabbits to a variety of vasoconstrictors and endothelium-dependent and -independent vasodilators. Endothelium-dependent vasodilators (acetylcholine (1 x 10(-8)-1 x 10(-6) M), carbachol (1 x 10(-8)-5 x 10(-6) M), substance P (0.01-100 nM), and A23187 (1 x 10(-8)-1 x 10(-7) M) relaxed the arteries in a concentration-dependent manner but produced no relaxation in denuded vessels. Endothelium-independent nitric oxide (NO) donors [Sin-1 (1 x 10(-8)-1 x 10(-6) M)] and sodium nitroprusside (1 x 10(-8)-1 x 10(-6) M)) relaxed both intact and denuded vessels to a similar degree (slight augmentation of the relaxation induced in denuded vessels was not significant), demonstrating that denuded vessels did not have an impaired reactivity to NO. Concentration response curves to the vasoconstrictors [5-HT (1 x 10(-7)-1 x 10(-4) M) and KCl (15-60 mM)] were produced in intact vessels and it was shown that similar contraction was produced by 1 x 10(-6) M 5-HT in intact and denuded vessels. This indicated that the vessels retained contractile ability following denudation.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of intimal thickening after endothelial removal by a nonpeptide angiotensin II receptor antagonist, losartan

1. The present experiments were designed to investigate the role of local angiotensin II receptors in the myointimal proliferative response of the vascular wall after endothelial removal, by use of a novel, nonpeptide, angiotensin II receptor antagonist, losartan. 2. When administered 1 week before endothelial removal from the rabbit carotid artery and then continuously until animals were killed 6 weeks later, losartan in a dose of 10 mg kg-1 daily, p.o. had no significant effects on the carotid blood flow (CBF), mean arterial blood pressure (MBP) and heart rate (HR). 3. A full endothelial lining with increased density of regenerated endothelial cells was observed 6 weeks after the endothelial removal. These changes were unaffected by treatment with losartan. 4. Six weeks after endothelial removal, acetylcholine (ACh)- and adenosine diphosphate (ADP)-induced relaxations were greatly reduced though endothelial cells had regenerated. The reduction of the relaxations to these agonists were significantly restored by chronic treatment with losartan. The endothelial-independent, sodium nitroprusside (SNP)-induced relaxation remained unaffected in all groups. 5. There were no differences in the noradrenaline (NA)- and endothelin-1 (ET-1)-induced contractions of the carotid artery strips between vehicle and losartan-treated groups. In contrast, the contractile response of the strips to angiotensin II was significantly decreased in the losartan group, indicating the specific antagonism by chronic losartan against the angiotensin II receptor. 6. Six weeks after endothelial removal, marked myointimal proliferation resulting from new accumulation of proliferating smooth muscle cells and connective tissue was observed in the vehicle group. Losartan treatment greatly suppressed the myointimal proliferative response.7. These results suggest that the local angiotensin II receptors play a role in the myointimal proliferativeresponse of the vascular wall to removal of the endothelium.