Endothelium-dependent control of vascular tone: effects of age, hypertension and lipids

Supplementation with l-arginine and nitrates vs age and individual physiological reactivity

Ageing is a natural ontogenetic phenomenon that entails a decrease in the adaptive capacity of the organism, as a result of which the body becomes less adaptable to stressful conditions. Nitrate and nitrite enter the body from exogenous sources and from nitrification of ammonia nitrogen by intestinal microorganisms. This review considers the mechanisms of action of l-arginine, a known inducer of nitric oxide (NO) biosynthesis, and nitrates as supplements in the processes of ageing and aggravated stress states, in which mechanisms of individual physiological reactivity play an important role. This approach can be used as an element of individual therapy or prevention of premature ageing processes depending on the different levels of initial reactivity of the functional systems. A search was performed of the PubMed, Scopus, and Google Scholar databases (n = 181 articles) and the author's own research (n = 4) up to May 5, 2023. The review presents analyses of data on targeted treatment of NO generation by supplementation with l-arginine or nitrates, which is a promising means for prevention of hypoxic conditions frequently accompanying pathological processes in an ageing organism. The review clarifies the role of the individual state of physiological reactivity, using the example of individuals with a high predominance of cholinergic regulatory mechanisms who already have a significant reserve of adaptive capacity. In studies of the predominance of adrenergic influences, a poorly trained organism as well as an elderly organism correspond to low resistance, which is an additional factor of damage at increased energy expenditure.

CONCLUSION

It is suggested that the role of NO synthesis from supplementation of dietary nitrates and nitrites increases with age rather than from oxygen-dependent biosynthetic reactions from l-arginine supplementation.

Comparing cerebrovascular reactivity measured using BOLD and cerebral blood flow MRI: The effect of basal vascular tension on vasodilatory and vasoconstrictive reactivity

Cerebrovascular reactivity (CVR) is an important metric of cerebrovascular health. While the BOLD fMRI method in conjunction with carbon-dioxide (CO2) based vascular manipulation has been the most commonly used, the BOLD signal is not a direct measure of vascular changes, and the use of arterial-spin labeling (ASL) cerebral blood flow (CBF) imaging is increasingly advocated. Nonetheless, given the differing dependencies of BOLD and CBF on vascular baseline conditions and the diverse CO2 manipulation types currently used in the literature, knowledge of potential biases introduced by each technique is critical for the interpretation of CVR measurements. In this work, we use simultaneous BOLD-CBF acquisitions during both vasodilatory (hypercapnic) and vasoconstrictive (hypocapnic) stimuli to measure CVR. We further imposed different levels of baseline vascular tension by inducing hypercapnic and hypocapnic baselines, separately from normocapnia by 4mmHg. We saw significant and diverse dependencies on vascular stimulus and baseline condition in both BOLD and CBF CVR measurements: (i) BOLD-based CVR is more sensitive to basal vascular tension than CBF-based CVR; (ii) the use of a combination of vasodilatory and vasoconstrictive stimuli maximizes the sensitivity of CBF-based CVR to vascular tension changes; (iii) the BOLD and CBF vascular response delays are both significantly lengthened at predilated baseline. As vascular tension can often be altered by potential pathology, our findings are important considerations when interpreting CVR measurements in health and disease.

Study of the intima-media thickening in carotid arteries of healthy elderly with high blood pressure and elderly with high blood pressure and dyslipidemia

OBJECTIVE

The objective of this study was to assess the mean intima-media thickening of carotid arteries of elderly subjects, and its relationship with age, anthropometric measurements, high systolic blood pressure and dyslipidemia.

METHODS

In this investigation, 129 subjects were enrolled between 1995 and 1998, age ranging from 29 to 94 years. They were assigned to one of 4 groups, including 2 control groups (group I, of healthy younger subjects; group II of healthy elderly subjects). Groups III and IV included those who presented with isolated systolic hypertension (ISH), and ISH and dyslipidemia, respectively. All subjects were submitted to a medical interview, lab tests with measurement of cholesterol levels, electrocardiogram, and carotid ultrasound. The ultrasound included measurement of the intima-media thickening (IMT) of the carotid arteries, the right carotid artery (RCA) and left carotid artery (LCA), and assessment of the presence of plaques. Blood fat and glucose were measured by a standard method. The results were compared among the groups through statistical tests. The tests employed were: Chi-Square, Pearson's and Likelihood Ratio, Student's t, Mann-Whitney; ANOVA followed by Tukey's test, Kruskal-Wallis nonparametric test, and test for multiple comparisons and Odds Ratio determination (OR).

RESULTS

In this investigation, a positive association was observed between aging and IMT. In relation to systolic hypertension, a significant association was observed with IMT (IMT-RCA p = 0.0034; IMT-LCAp = 0.0196; IMT-RLCAp = 0.0299), and with the presence of plaques (PlaqueR p = 0.0110; PlaqueL p = 0.0294; PlaqueRL p = 0.0040).

CONCLUSION

This investigation evidenced the important role of aging in IMT, and of systolic hypertension in the IMT and presence of plaque. However, further studies are needed for a better understanding of the actual role of risk factors in aging.

L-NAME hypertension alters endothelial and smooth muscle function in rat aorta. Prevention by trandolapril and verapamil

Nitric oxide is an important regulator of vascular function and blood pressure. Chronic administration of nitric oxide inhibitors provides a new model of hypertension with pronounced target organ damage. We investigated the effects of oral treatment with N omega-nitro-L-arginine methyl ester (L-NAME) for 6 weeks on vascular reactivity of the aorta in Wistar-Kyoto rats. Certain rats received verapamil or trandolapril in addition to L-NAME. Systolic blood pressure increased in the L-NAME group (by approximately or equal to 80 mm Hg systolic) but not in controls or rats treated with verapamil or trandolapril. Isometric tension changes of aortic rings were recorded. Endothelium-dependent relaxations to acetylcholine were reduced in the L-NAME group (58 +/- 6% versus 104 +/- 1% in placebo, P < .05) but were normalized by treatment with verapamil or trandolapril. In contrast, endothelium-independent relaxations to sodium nitroprusside were not significantly reduced in L-NAME hypertension but were slightly enhanced by trandolapril therapy (P < .05) in the L-NAME group only. In quiescent rings, acetylcholine caused endothelium-dependent contractions in particular after in vitro incubation with L-NAME. These contractions tended to be enhanced in L-NAME hypertension (23 +/- 4% versus 14 +/- 3% in the placebo group; P = NS) and were significantly reduced after treatment with verapamil or trandolapril (P < .05). Concentrations to norepinephrine and angiotensin I and II were unaffected by L-NAME hypertension, whereas those to endothelin-1 were reduced (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary alpha 1-constrictor tone during renovascular hypertension

BACKGROUND

A coronary alpha 1-adrenergic constrictor tone exists under conditions associated with increased sympathetic stimulation but not during resting conditions in the normal heart. During renovascular hypertension, elevated circulating angiotensin II may enhance sympathetic stimulation of the heart, even at rest. This study tested the hypothesis that an alpha 1-adrenergic constrictor tone imposes limitations on coronary blood flow in resting dogs after development of renovascular hypertension, exacerbates coronary alpha-constrictor tone during exercise, and increases coronary vascular adrenergic responsiveness.

METHODS AND RESULTS

Left circumflex blood flow velocity (CFV), aortic pressure (AoP), and heart rate (HR) were examined in five quietly resting dogs during control conditions and after selective alpha 1-adrenergic blockade using an intracoronary injection of 0.5 mg prazosin. In the normotensive state, AoP was 87 +/- 7 mm Hg (mean +/- SD), HR was 105 +/- 25 beats per minute, and CFV was 28 +/- 6 cm/s. These parameters were not affected by alpha 1-adrenergic blockade. During submaximal exercise, removal of an alpha 1-adrenergic constrictor resulted in a 14 +/- 4% increase in CFV (P < .05). Two weeks after development of renovascular hypertension induced by stenosis of the left renal artery, mean AoP was 114 +/- 7 mm Hg (P < .05 versus normotensive state), HR was 111 +/- 28 beats per minute, and CFV was 21 +/- 8 cm/s. In contrast to the normotensive state, alpha 1-adrenergic blockade caused a 28 +/- 6% increase in CFV at rest (P < .05) and a 27 +/- 13% increase in CFV during exercise in the hypertensive state (P < .05 versus exercise before blockade and versus normotensive state). This resting coronary constrictor tone was associated with enhanced vasoconstrictor responsiveness to norepinephrine and phenylephrine.

CONCLUSIONS

It appears that renovascular hypertension results in a significant coronary alpha 1-adrenergic constrictor tone in the resting dog and an enhanced constrictor tone during exercise.