Effects of short-term administration of sublingual nifedipine on coronary arterial wall elastic properties: evaluation by intravascular ultrasound

EFFECT OF MAGNESIUM ON MECHANICAL PROPERTIES OF PRESSURIZED MESENTERIC SMALL ARTERIES FROM OLD AND ADULT RATS

The purpose of the present study was to determine the effects of magnesium (Mg) on the mechanical properties of resistance arteries in adult and old rats. Studies were performed in adult (17 weeks) and old (104 weeks) male Wistar rats. The vasodilatory response and the passive mechanical properties of the wall of isolated perfused and pressurized arterial segments of mesenteric small arteries were investigated after Mg and verapamil application, both known for their calcium antagonistic properties. Mesenteric resistance arteries from old rats exhibited an outward hypertrophic remodelling, with enlargment of the lumen, thickening of the media and enlarged media cross-sectional area. The vasodilatory response induced by the application of increasing extracellular concentrations of Mg and verapamil was significantly smaller in preconstricted mesenteric arteries of old rats than in those of adult rats. Incremental distensibility in response to increasing intravascular pressures did not change. However, the stress-strain curve was shifted to the left in pressurized mesenteric arteries from old rats, indicating arterial wall stiffness. Verapamil (3 micro mol/L) did not modify the stress-strain curves in either adult or aged rats. However, Mg (4.8 mmol/L) significantly shifted the curve to the right in mesenteric arteries from adult rats and, to a greater degree, in those from old rats. Although Mg-induced vasodilatation is impaired in aged rats, increased Mg concentration improved the mechanics of pressurized mesenteric resistance arteries. The fact that Mg decreases arterial stiffness in arteries from old rats suggests that Mg has a beneficial effect on age-related changes to the vascular wall.

Effects of a slow-release nifedipine on 24-hour ambulatory blood pressure and ischemic changes on 24-hour ambulatory electrocardiogram in patients with severe coronary artery disease

Calcium antagonists have long been used as first-line drugs for hypertension and angina. However, deleterious effects have also been reported in patients treated with calcium antagonists. Thus, we evaluated the effect of a slow-release twice-daily formulation of nifedipine in 10 patients with severe coronary artery disease. Twenty-four-hour ambulatory electrocardiography (AECG) and blood pressure monitoring (ABPM) were performed simultaneously to detect any association between ischemic episodes on the ECG and changes in blood pressure (BP) and heart rate with and without nifedipine. Increased oxygen demand due to an increased systolic BP and heart rate was associated with ischemic episodes without nifedipine, while those with nifedipine were accompanied by a fall in diastolic BP and a rapid increase in heart rate. This slow-release twice-daily formulation of nifedipine may induce myocardial ischemia through a heart-rate increase and a decrease in coronary blood flow due to lower diastolic BP in patients with severe coronary artery disease. A once-daily formulation of nifedipine might be of great value for such patients.

Effects of troglitazone on collagen accumulation and distensibility of aortic wall in prestage of non-insulin-dependent diabetes mellitus of Otsuka Long-Evans Tokushima Fatty rats

We investigated the effect of troglitazone (TG) on aortic distensibility and histopathology at the preclinical stage in the non-insulin-dependent diabetes mellitus (NIDDM) model. Twenty male diabetic and 20 male nondiabetic rats were each divided into two groups: treated-DM, untreated-DM, treated-nonDM, and untreated-nonDM. TG (0.2%) was mixed in chow in the treated groups. From age 5 to 15 weeks, fast blood glucose and insulin were monitored. At 15 weeks, oral glucose tolerance test results, aortic wall histopathology, and collagen content were studied, and intravascular ultrasound images and aortic pressure were recorded. Aortic diameter was measured during the cardiac cycle, and the stiffness parameter beta was calculated. Blood glucose (mg/dl) 2 h after loading in treated-DM (139+/-20) was normalized (untreated-DM, 188+/-27; p<0.05). Insulin concentration (ng/ml) in treated-DM (3.2+/-0.4) was lower than that in untreated-DM (8.1+/-1.5; p<0.01). At 15 weeks, beta in untreated-DM (2.4+/-0.8) was larger than those in untreated-nonDM (1.5+/-0.4; p<0.0001) and in treated-DM (1.9+/-0.4, p = 0.0081). Aortic wall collagen (mg/g dry weight) increased in untreated-DM (32.8+/-3.3) as compared with treated-DM (28.1+/-3.8; p = 0.048). Histomorphometry showed decreased medial area (mm2) in treated-DM (0.55+/-0.05) compared with untreated-DM (0.78+/-0.12; p<0.0001). This study suggests that TG may prevent metabolic abnormalities and the deterioration of aortic distensibility at an early prediabetic stage.

Alteration in aortic wall stiffness and accumulation of collagen during the prediabetic stage of type II diabetes mellitus in rats

Aortic damage during the prediabetic stage of diabetes mellitus (DM) was investigated in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II DM. In 30 OLETF and 30 nonDM rats, an oral glucose tolerance test was performed at 10, 20 and 30 weeks of age. At 15 and 30 weeks, intravascular ultrasound images and aortic pressure were recorded and the stiffness parameter beta was calculated. The aortic walls were excised at 5, 15 and 30 weeks for histopathology and the measurement of hydroxyproline. At 10 weeks, blood glucose (mg/dl) and insulin concentrations (ng/ml) of the OLETF rats (2h; 168+/-30 and 0.82+/-0.15) were significantly high (nonDM: 118+/-15; p = 0.02 and 0.16+/-0.64; p = 0.003). At the prediabetic stage (15 weeks), beta in the OLETF rats (2.5+/-0.9) was larger than in nonDM rats (1.4+/-0.4; p = 0.0006), and the collagen (hydroxyproline) content/dry weight (mg/g) of the aortic wall was significantly higher in OLETF (33.5+/-3.1) than in nonDM rats (28.7+/-3.5; p<.05). Histopathological examination showed that from 15 weeks of age the medial wall thickness increased gradually. In the prediabetic stage, collagen accumulation may contribute to impairment of aortic wall stiffness in the OLETF rats, which would accelerate the aging process in the aortic wall.

Neurogenic regulation of basal tone of coronary artery with mild atherosclerosis in humans: observation using two-dimensional intravascular ultrasound

The purpose of this study was to assess the role of the autonomic nervous system in the regulation of basal coronary artery tone in normal and atherosclerotic plaque segments by using intravascular ultrasound in humans. In each of 21 patients, a short-axis image at one site of coronary artery was imaged by means of a 3.2F, 30-MHz intravascular ultrasound before and after intracoronary administration of 2 mg isosorbide dinitrate (ISDN). The authors identified the perimeters of the vessel wall segments with normal or atherosclerotic plaque on ultrasound images and evaluated the basal tone in each segment as a percent increase in each perimeter produced by ISDN. Using heart rate variability analysis for 512 seconds recorded immediately before ISDN administration, they evaluated cardiac sympathetic and vagal activities at rest as the integrated power of fast Fourier transform (FFT) spectrum for the low-frequency (LF: 0.04 to 0.15 Hz), and high-frequency (HF: 0.15 to 0.4 Hz) components, respectively. Of 29 segments examined by ultrasound, 16 were normal and 13 were atherosclerotic plaque. In all 29 segments, ISDN produced an increase in the perimeter of the vessel wall. At the normal 16 segments, the increase in perimeter by ISDN exhibited a significant correlation to the power of HF (r = 0.749, p = 0.0008) but no significant correlation to LF. At 13 plaque segments, however, no significant correlation between the response to ISDN and autonomic nerve activity was observed. In conclusion, the basal tone of normal coronary arterial wall segment is closely related to parasympathetic nerve, whereas the relation is impaired in mild atherosclerotic segments.