Attenuated forearm vasodilator response to atrial natriuretic factor in the elderly

Dysregulation of pulsatility in aging IV. Pulsatile signaling and cardiovascular aging: functions and regulation of natriuretic peptide signaling

Atrial and brain natriuretic peptides (ANP and BNP) are cardiac hormones connecting heart and kidney and playing a key role in hydromineral and hemodynamic homeostasis. In contrast with the renin-angiotensin-aldosterone system, circulating ANP and BNP are not temporally related with rapid eye movement (REM)-nonREM sleep cycles, autonomic activity, or blood pressure. Cardiac natriuretic peptides are secreted in a pulsatile manner, with short periods of 20-48min, in normal as well as in pathological conditions. The frequency of pulses seems to be unchanged with aging, whereas the absolute amplitude of the oscillations seems to increase, most likely as a result of an increase in the plasma hormone levels observed in elderly. Enhanced cardiac secretion and decreased degradation partly explain the higher ANP and BNP concentrations observed in elderly. Despite higher levels, the natriuretic system seems to loose efficiency at the renal site in elderly. This more probably relies on reduced target organ responsivity and not on deeply altered hormone secretion. Here we review the impact of aging on the renal effects of the natriuretic peptides, and point out the lack of knowledge on the precise interactions between the ultradian rhythms of the systems involved in salt and water balance in elderly. Additional studies focusing on potential age-induced alterations of the intracellular signaling pathway are now needed.

Factors that affect calorie-sensitive and calorie-insensitive reduction in blood pressure during short-term calorie restriction in overweight hypertensive women

This study was performed to elucidate the factors that affect the reduction in blood pressure produced by calorie restriction in overweight women with essential hypertension. Fifty-one subjects were admitted to the metabolic ward of the hospital. After being fed a standard diet (6.3 to 8.4 MJ/d) for 2 weeks, the calorie-restricted group (n=34) was fed a low-calorie diet (1.9 MJ/d) for an additional 2 weeks. The calorie-nonrestricted group (n=17) was fed the standard diet for 4 weeks. Sodium and potassium intake was kept constant, as was the level of exercise activity. The calorie-restricted group was subdivided into "calorie-sensitive" and "calorie-insensitive" groups based on an average 5 mm Hg reduction in mean blood pressure during the low-calorie diet. The mean age was 51+/-6 years (mean+/-SD) in the calorie-sensitive group (n=16), which was significantly lower than the mean age of 61+/-6 years in the calorie-insensitive group (n=18). Multiple regression analysis indicated that age and change in body weight exhibited significant correlations with blood pressure reduction produced by calorie restriction among 17 parameters. Findings suggest that age can predict the extent of blood pressure reduction that would be obtained during 2 weeks of calorie restriction in overweight hypertensive women. The reduction in blood pressure may be related in part to the amount of weight loss.

Effect of atrial natriuretic factor on skin microcirculation versus skeletal muscle blood flow

The response of the skin microcirculation and of forearm skeletal muscle blood flow to infusion of alpha-human (99-126) atrial natriuretic factor (ANF) into the brachial artery was investigated in 15 young (18-25 years) healthy volunteers in a double-blind, randomized, placebo-controlled study. The forearm blood flow (FBF) was measured with venous occlusion plethysmography, and the skin flux was measured by using laser Doppler fluxmetry (LDF). Dose-response curves were made using increasing dosages of ANF: 1, 10, and 100 ng/min/dl forearm volume. The FBF showed a significant, dose-dependent increase during ANF infusion, averaging 107 + 22% during the highest ANF dosage, as compared with -5 +/- 9% during placebo (p < 0.001). For the LDF, these numbers were 34 +/- 21 and -6 +/- 10%, respectively (NS). In two subgroups of subjects, the effect of ANF on microvascular reactivity was assessed by registering the vasoconstrictor response to cold exposure (n = 7) and the vasodilator response to arterial occlusion (n = 7). ANF did not change the microvascular response to these stimuli. ANF induces a dose-dependent increase in skeletal muscle BF without a relevant response in the skin microcirculation. ANF does not play an important role in the regulation of skin perfusion.

Age-related changes in vascular responses: a review

Normal aging is associated with different changes in the cardiovascular system that lead to an increase in pathological processes, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. The vascular alterations consist of changes in the function and structure of the arteries, and increasing vascular stiffness, mainly when atherosclerosis is present, whose incidence is increased with age. The arteries accumulate lipids, collagen, and minerals. Cerebral perfusion may be reduced in the elderly, mainly regional cerebral blood flow, which leads to a deterioration of mental and physical functions. The degree of deterioration is increased when aging is associated with hypertension. Aging alters endothelial cells, which play an important role in vascular tone regulation. Such a process tends to reduce endothelium-dependent relaxations, and clearly reduces the vasodilation elicited by beta-adrenoceptor agonists. The contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium and angiotensin are barely affected with aging, whereas those elicited by noradrenaline or endothelin are usually reduced. However, plasma noradrenaline levels are increased with age, mainly due to a reduction in the sensitivity of presynaptic alpha 2-adrenoceptors and also of noradrenaline uptake. Sodium pump activity, that controls cellular ionic homeostasis, may be altered depending on animal species. Finally, vascular Ca2+ regulation appears to be altered and the extracellular Ca2+ dependence of contractile responses elicited by agonists is increased, which justifies the enhanced sensitivity to Ca2+ antagonists in senescence.

Comparison of cyclic guanosine monophosphate response to infusion of atrial natriuretic peptide in young and elderly subjects

OBJECTIVE

To compare the sensitivity to atrial natriuretic peptide (ANP) in young and elderly subjects.

DESIGN

Double-blind, random-order, placebo-controlled study using two different rates of ANP infusion.

SUBJECTS

Eight healthy young (23 +/- 3 years, mean +/- SD) and eight healthy elderly (76 +/- 4 years) subjects recruited from the general population.

MEASUREMENT

Plasma cyclic guanosine monophosphate (cGMP, the second messenger of ANP) levels reflecting the sensitivity of biologically active ANP receptors.

RESULTS

Baseline ANP levels were higher and rose to a greater extent in the elderly both during low- (0.25 microgram/min) and high-dose (2.0 micrograms/min) infusion of ANP. Plasma levels of cGMP rose in proportion to the increase in ANP. When the rise in cGMP levels was related to the increase in ANP levels (expressed as nmol/L per 100 pg/mL ANP increase), no difference was found between young and elderly subjects.

CONCLUSION

The ability of elderly subjects to increase cGMP in response to exogenous ANP is similar to that of young subjects. This may reflect a similar sensitivity of the target organs towards ANP. However, because of lower clearance in the elderly, a similar dose of ANP results in a greater elevation of ANP and cGMP levels and hence induces a greater effect.