Plasma catecholamines and cardiac, renal and peripheral vascular adrenoceptor-mediated responses in different age groups of normal and hypertensive subjects

Extra- and intracranial blood flow regulation during the cold pressor test: influence of age

We determined how the extra- and intracranial circulations respond to generalized sympathetic activation evoked by a cold pressor test (CPT) and whether this is affected by healthy aging. Ten young [23 ± 2 yr (means ± SD)] and nine older (66 ± 3 yr) individuals performed a 3-min CPT by immersing the left foot into 0.8 ± 0.3°C water. Common carotid artery (CCA) and internal carotid artery (ICA) diameter, velocity, and flow were simultaneously measured (duplex ultrasound) along with middle cerebral artery and posterior cerebral artery mean blood velocity (MCAv_mean and PCAv_mean) and cardiorespiratory variables. The increases in heart rate (~6 beats/min) and mean arterial blood pressure (~14 mmHg) were similar in young and older groups during the CPT (P < 0.01 vs. baseline). In the young group, the CPT elicited an ~5% increase in CCA diameter (P < 0.01 vs. baseline) and a tendency for an increase in CCA flow (~12%, P = 0.08); in contrast, both diameter and flow remained unchanged in the older group. Although ICA diameter was not changed during the CPT in either group, ICA flow increased (~8%, P = 0.02) during the first minute of the CPT in both groups. Whereas the CPT elicited an increase in MCAv_mean and PCAv_mean in the young group (by ~20 and ~10%, respectively, P < 0.01 vs. baseline), these intracranial velocities were unchanged in the older group. Collectively, during the CPT, these findings suggest a differential mechanism(s) of regulation between the ICA compared with the CCA in young individuals and a blunting of the CCA and intracranial responses in older individuals.NEW & NOTEWORTHY Sympathetic activation evoked by a cold pressor test elicits heterogeneous extra- and intracranial blood vessel responses in young individuals that may serve an important protective role. The extra- and intracranial responses to the cold pressor test are blunted in older individuals.

Cardiac phenylethanolamine N-methyltransferase: localization and regulation of gene expression in the spontaneously hypertensive rat

Phenylethanolamine N-methyltransferase (PNMT) is the terminal enzyme in the catecholamine biosynthetic pathway responsible for adrenaline biosynthesis. Adrenaline is involved in the sympathetic control of blood pressure; it augments cardiac function by increasing stroke volume and cardiac output. Genetic mapping studies have linked the PNMT gene to hypertension. This study examined the expression of cardiac PNMT and changes in its transcriptional regulators in the spontaneously hypertensive (SHR) and wild type Wistar-Kyoto (WKY) rats. SHR exhibit elevated levels of corticosterone, and lower levels of the cytokine IL-1β, revealing systemic differences between SHR and WKY. PNMT mRNA was significantly increased in all chambers of the heart in the SHR, with the greatest increase in the right atrium. Transcriptional regulators of the PNMT promoter show elevated expression of Egr-1, Sp1, AP-2, and GR mRNA in all chambers of the SHR heart, while protein levels of Sp1, Egr-1, and GR were elevated only in the right atrium. Interestingly, only AP-2 protein-DNA binding was increased, suggesting it may be a key regulator of cardiac PNMT in SHR. This study provides the first insights into the molecular mechanisms involved in the dysregulation of cardiac PNMT in a genetic model of hypertension.

G protein-coupled receptor kinase 2 expression and activity are associated with blood pressure in black Americans

Hypertension occurs with higher prevalence and morbidity in black Americans compared with other groups. Alterations in the signal transduction pathways of 7-transmembrane spanning receptors are found in hypertensive patients. G protein-coupled receptor kinases (GRKs) play an important role in regulating this receptor signaling. The 2 most abundantly expressed GRKs in the cardiovascular system are GRK2 and GRK5, and each has unique substrates. Understanding changes in expression may give us insight into activated receptors in the pathophysiological progression of hypertension. In heart failure and white hypertensives, increased GRK2 expression arises because of neurohormonal stimulation of particular receptors. GRK2 subsequently desensitizes specific receptors, including beta-adrenergic receptors. In blood pressure control, beta-adrenergic receptor desensitization could lead to increased blood pressure. GRK2 and GRK5 mRNA were evaluated in lymphocytes of black Americans via quantitative real-time PCR. GRK2 mRNA expression directly correlated with systolic blood pressure and norepinephrine levels. GRK2 was elevated >30% among those with systolic blood pressure > or =130 mm Hg. No significant correlation between GRK5 mRNA expression and blood pressure or catecholamines was observed. Diabetic status, age, sex, and body mass index were also compared with GRK2 expression using univariate and multivariate analyses. GRK2 protein expression was elevated 2-fold in subjects with higher blood pressure, and GRK activity was increased >40%. Our data suggest that GRK2, but not GRK5, is correlated with increasing blood pressure in black Americans. Understanding the receptors stimulated by increased neurohormonal activation may give insight into the pathophysiology of hypertension in this at-risk population.

Exercise-induced shear stress is associated with changes in plasma von Willebrand factor in older humans

Shear stress is the frictional force of blood against the endothelium, a stimulus for endothelial activation and the release of von Willebrand factor (vWF). This study tested the hypothesis that the increase in shear stress associated with exercise correlates with plasma vWF. Young (n = 14, 25.7 +/- 5.4 years) and older (n = 13, 65.6 +/- 10.7 years) individuals participated in 30 min of dynamic handgrip exercise at a moderate intensity. Brachial artery diameter and blood flow were measured using ultrasound Doppler and blood samples were collected before, immediately after, and following 30 min of recovery from exercise with plasma levels of vWF. Plasma levels of vWF increased (P < 0.05) by 6 +/- 2% in young individuals and 4 +/- 1% in older individuals immediately after exercise. The change in plasma vWF was linearly correlated with the increase in shear stress during exercise in older individuals (post-exercise: r = 0.78, 30 min recovery: r = 0.77, P < 0.01), but no association was found in the young individuals. These changes in plasma levels of vWF in humans suggest that aging influences endothelial activation and hemostasis.

Plasma epinephrine levels in hypertension and across gender and ethnicity

Epinephrine (E) infusions raise blood pressure and there is an excess incidence of hypertension among males and blacks. However, reports of E levels by ethnicity, gender, and blood pressure status are inconsistent. Insensitive assays, variability in plasma E levels within individuals, and the small size of most studies have contributed to these conflicting reports. We measured plasma E levels in a large diverse sample of subjects, using a highly sensitive assay. A total of 361 individuals participated in the study: 61% were men and 39% women, 74% were normotensive and 26% hypertensive, 59% were white and 41% were black. Except for difference in blood pressure and body mass index between the normotensives and hypertensives, subjects had similar baseline characteristics and took no antihypertensive medications for at least five days prior to sampling. All blood samples were collected after resting for a least 30 minutes following the insertion of an indwelling i.v. catheter. Catecholamine levels were determined using a radioenzymatic assay (assay sensitivities for E and norepinephrine were 6 pg/ml and 10 pg/ml, respectively). An ethnicity by gender interaction was found (F(1,315) = 5.126, p = .024). Subsequent analysis revealed that white women had significantly lower basal plasma E levels than white men (p <0.001) and black women (p = 0.036). There were no significant differences in E levels between black men and women or between white men and black men. Uncorrected E levels were lower in normotensive than hypertensive subjects (p = .009) but this difference was not significant when corrected for body mass index (BMI). Uncorrected norepinephrine levels were higher in women than men (p = .03) but the difference was no longer significant when corrected for BMI. Plasma E levels were significantly lower among white women than men or black women. In contrast to prior studies, E levels were lower in hypertensives, but this may reflect obesity among hypertensives.

Age, hypertension, and cardiac responses to beta-agonist in humans

OBJECTIVES

To evaluate the effects of hypertension on heart rate and left ventricular responses to beta-agonist in young and older subjects, as well as the modulating effect of the arterial baroreflex on these responses.

METHODS

Isoproterenol (INN, isoprenaline) alone was infused in 14 young normotensive subjects (mean age, 30 +/- 2 years), 18 older normotensive subjects (mean age, 60 +/- 2 years), 11 young hypertensive subjects (mean age, 36 +/- 1 years), and 17 older hypertensive subjects (mean age, 59 +/- 1 years); isoproterenol combined with ganglionic blockade (trimethaphan [INN, trimetaphan]) was administered to eight young normotensive subjects and eight young hypertensive subjects. Isoproterenol was infused at three to four incremental rates, each rate for 8 minutes. Left ventricular responses were assessed by echocardiography.

RESULTS

Isoproterenol caused similar increases in heart rate in all four groups. With ganglionic blockade, heart rate responses were enhanced but were similar in the young normotensive and hypertensive subjects. In young subjects, hypertension did not affect left ventricular responses to isoproterenol alone, whereas older hypertensive subjects showed some blunting of left ventricular responses compared with older normotensive subjects. With ganglionic blockade, young hypertensive subjects also showed mild blunting of left ventricular responses.

CONCLUSION

These results show that, in humans, hypertension does not lead to a decrease in chronotropic responses to infusion of the beta-agonist isoproterenol and causes only a modest decrease in left ventricular responses.

Effect of age on bronchodilator response in acute severe asthma treatment

STUDY OBJECTIVES

This study was designed to evaluate the effects of age on bronchodilator response to salbutamol in patients with acute severe asthma in the emergency department.

SUBJECTS AND METHODS

Sixty-four sequential patients (mean age, 34.2+/-10.7 years) with acute asthma were enrolled in the trial. Using age as a major criterion, we divided the sample in two groups: the young one (age < or = 35 years, n=30) and the older (> 35 years, n=34). All patients were treated with salbutamol delivered with metered-dose inhaler into a spacer device, in a dose of four puffs every 10 min (100 microg per actuation) during 3 h.

RESULTS

Mean FEV1 improved significantly over baseline values for both groups (p=0.001). At final disposition, the mean percent of predicted FEV1 was 55.1+/-16.3% in the young group and 58.0+/-20.9% in the older group. There were no significant differences between both groups for FEV1 percent response at any point studied. A significant increase in heart rate over baseline was seen in the older group (p=0.001). Older patients also presented a higher incidence in nausea and tremor. Young and older patients with acute asthma achieved equivalent bronchodilation response to salbutamol.

CONCLUSIONS

We concluded that age is not a predictor of response to beta-agonists.

Cardiac chronotropic responsiveness to beta-adrenoceptor stimulation is not reduced in the elderly

OBJECTIVES

This study evaluated cardiac beta-adrenoceptor responsiveness in the elderly.

BACKGROUND

The hypothesis of reduced cardiac beta-adrenoceptor responsiveness in the elderly is based on a smaller increase in heart rate after administration of isoproterenol, a nonselective beta 1- and beta 2-adrenoceptor agonist. By means of dobutamine-stress-echocardiography we were able to retest the hypothesis more accurately because dobutamine is a relatively selective beta 1-adrenoceptor agonist with weak beta 2- and alpha-adrenoceptor stimulant activity that prevents baroreflex-mediated changes in heart rate.

METHODS

After administration of stepwise incremental infusions of dobutamine, we measured heart rate and blood pressure responses in 360 patients who had no beta-adrenergic blocking agent therapy and no side effects during the stress test. For each patient we calculated the dose of dobutamine required to increase heart rate by 50% of the maximal heart rate during the highest dose of dobutamine.

RESULTS

No relation was found between age and sensitivity to dobutamine (n = 293). Power analysis revealed that this negative finding was not the result of inadequate sample size. In contrast to the prevailing hypothesis, an increased heart rate response to dobutamine was found even in a subgroup of "healthy" elderly subjects (i.e., those without concomitant disease or acute myocardial ischemia, n = 67) that was not related to changes in blood pressure during stress. However, in subjects with acute ischemia (n = 109), smokers (n = 151) or patients with a history of a previous myocardial infarction (n = 148), dobutamine sensitivity was reduced in the elderly despite a diminished change in systolic blood pressure with advanced age during dobutamine infusion. This phenomenon could be explained by a decrease in efferent cardiac baroreflex sensitivity, as has been observed during acute myocardial ischemia. There were no age-related differences in plasma concentrations of dobutamine.

CONCLUSIONS

No evidence for reduced beta-adrenoceptor responsiveness to dobutamine was found in "healthy" elderly subjects.

Age-related modifications in neural cardiovascular control

Integrated cardiovascular responses to a range of different stimuli, as well as the overall, spontaneously occurring variability in blood pressure and heart rate, undergo complex changes with aging. A general trend is that homeostatic control mechanisms lose part of their ability to modulate heart rate and to buffer the concomitant blood pressure variations; the two phenomena are possibly linked by a cause-effect relationship. A detailed analysis of the age-related changes in the major reflex systems reveals a clear-cut impairment in arterial baroreceptor control of the heart rate, but much less pronounced changes in its control of blood pressure, on the other hand, both the hemodynamic and humoral components of the cardiopulmonary reflex appear to be markedly attenuated. The experimental evidence of the mechanisms underlying these changes is still largely incomplete, and it appears that the gaps will have to be filled by a systematic, detailed analysis, i.e., that no generalizations or extrapolations will be possible. Indeed, the data available so far indicate that the age-related alterations are highly non-uniform, some functions undergoing a definite impairment but others being much better preserved and some being even enhanced; thus aging is by no means associated with a generalized decline in cardiovascular functions and should instead be viewed as a complex, highly selective process. These peculiar biological features of the aging phenomena merit further investigation in both the cardiovascular and the other organ systems, in order to verify the possibility that currently unrecognized homeostatic potentials in the elderly subject may be exploited to advance his/her clinical management in health and disease.

Effect of age on bronchodilator response

STUDY OBJECTIVE

Our objective was to compare the differential effects of age and drug type on bronchodilator response.

DESIGN

The design was an unblinded, randomized crossover study.

SETTING

An ambulatory pulmonary drug study unit was the setting.

PATIENTS

Nineteen young (18 to 25 yr) and 17 elderly (greater than 65 yr) stable asthmatic subjects were studied.

INTERVENTIONS AND MEASUREMENTS

Albuterol or ipratropium was given on two separate mornings using an MDI with extender. Subjects inhaled two puffs initially and then one puff every 30 min to a total of six puffs. Pulmonary function, blood pressure, and pulse were measured at baseline and every 30 min for 3 h.

RESULTS

All subjects had a greater than 15 percent increase in FEV1 with one or both drugs. More patients responded to albuterol than to ipratropium in both age groups. The maximum percentage of change from baseline was greater (p less than 0.05) with albuterol (mean, 40.1 percent in young and 60.5 percent in old) than with ipratropium (21.2 percent in young; 31.2 percent in old) in both groups. These differences remain significant after correction for baseline differences using area-under-the-curve analysis of the percent of maximum improvement; however, the differences between age groups for the same drug were not statistically significant by either index of change. There were also no differences between drugs or between age groups for time (or number of puffs) to reach maximum improvement (mean, 2.0 to 2.2 h for albuterol and 1.6 to 1.7 h for ipratropium). The changes in FVC and FEF25-75% were similar to FEV1. Changes in blood pressure and pulse were not significant. Three subjects stopped therapy with albuterol with side effects.

CONCLUSIONS

Both drugs are effective bronchodilators in young and old asthmatic subjects, but albuterol results in a greater magnitude of response in both age groups. Age is not a predictor of response to either drug.

Catecholamine-induced lipolysis in adipose tissue of the elderly

Age-dependent alterations in the effects of catecholamines on lipolysis were investigated in 25 young (21-35 yr) and 10 elderly (58-72 yr) healthy, nonobese subjects using isolated adipocytes obtained from abdominal subcutaneous tissue. Basal lipolysis was not affected by aging, while the rate of catecholamine-stimulated lipolysis was reduced by 50% in the elderly subjects (P less than 0.005). To elucidate the mechanisms behind this phenomenon lipolysis was stimulated with agents that act at well-defined steps in the lipolytic cascade, from the receptor down to the final step: the activation of the protein kinase/hormone-sensitive lipase complex. All agents stimulated lipolysis at a 50% lower rate in elderly as compared with young subjects (P less than 0.05 or less). However, half-maximum effective concentrations of the lipolytic agents were similar in both groups. The antilipolytic effects of alpha 2-adrenoceptor agonists were also the same in young and old subjects. Moreover, the stoichiometric properties of the beta- and alpha 2-receptors did not change with increasing age. In vivo studies performed on the same individuals likewise demonstrated an impaired lipolytic responsiveness, with 50% lower plasma glycerol concentrations during exercise in the elderly subjects (P less than 0.05), in spite of a normal rise in plasma norepinephrine. The plasma glycerol levels correlated strongly to the glycerol release caused by catecholamine-stimulated lipolysis in vitro in both young and elderly subjects (r = 0.8-0.9, P less than 0.001). In conclusion, a decreased activation of the hormone-sensitive lipase complex appears to be the mechanism underlying a blunted lipolytic response of fat cells to catecholamine stimulation in elderly subjects. This finding may, explain the age-dependent decreased lipolytic response to exercise in vivo.

Alpha 2-receptor-mediated vasoconstriction in patients with congestive heart failure

alpha 2-Adrenoceptors exist postsynaptically to subserve vasoconstriction and presynaptically to modulate norepinephrine release into the synaptic cleft. Because adrenoceptors may down-regulate in response to chronic stimulation, we investigated the activity of alpha 2-receptor-mediated vasoconstriction in patients with congestive heart failure, who had increased levels of plasma norepinephrine. We used the isolated forearm model and intra-arterial infusions of subsystemic doses of yohimbine, a specific alpha 2-blocker, in 11 patients with heart failure and in 15 normal subjects. Yohimbine produced a dose-related increase in forearm blood flow and decrease in forearm vascular resistance. These findings were consistent with a direct vasodilator effect mediated by blockade of the postsynaptic alpha 2-vascular receptor. Furthermore, the vasodilator responses in patients with heart failure were similar to the normal subjects in terms of the percent increase in forearm blood flow, the dose-response relation, and the fractional response to hyperemia and phentolamine; thus, alpha 2-receptor-mediated vasoconstriction is neither enhanced nor down-regulated in heart failure. In addition, in patients with heart failure and in normal subjects, yohimbine produced an increase in the forearm venous norepinephrine concentration, consistent with an inhibition of the presynaptic alpha 2-receptor resulting in an augmented release of norepinephrine into the synaptic cleft. Thus, these data suggest that the postsynaptic alpha 2-receptor is an important mediator of vasoconstriction in patients with heart failure. Despite chronic elevations in plasma norepinephrine in patients with heart failure, alpha 2-receptor mechanisms subserving vasoconstriction and inhibition of norepinephrine release into the synaptic cleft are still functional in heart failure.

Effect of increasing age on adrenergic control of heart rate in the rat

To determine if decreased cardiac rate with increasing age in Fischer-344 rats was due to changes in the heart itself, in adrenergic nerves innervating the heart or in both, we studied heart rate in vivo and in vitro, and atrial and ventricular pacemaker activity in vitro following atrioventricular block, in control and in chemically sympathectomized rats [pretreated with 6-hydroxydopamine (6-OHDA), 20 mg/kg, s.c., 24 h prior to testing] at ages 1 to 28 months. With increasing age, heart rate (bpm) in vivo decreased from 440 +/- 12 to 385 +/- 10 in the control and from 403 +/- 20 to 318 +/- 11 in 6-OHDA pretreated rats; heart rate in vitro decreased from 353 +/- 9 to 243 +/- 8 in the control, and from 346 +/- 15 to 214 +/- 18 in 6-OHDA pretreated rats; the atrial rate (AR) decreased from 304 +/- 9 to 210 +/- 8 in the control and from 288 +/- 13 to 161 +/- 32 in 6-OHDA pretreated rats while the ventricular pacemaker rate (VR) decreased from 121 +/- 8 to 92 +/- 5 in the control, and from 100 +/- 14 to 70 +/- 7 in 6-OHDA pretreated rats. With age, AR decreased to a greater extent than VR and 6-OHDA had a greater effect in decreasing AR than VR. Using cardiac rate as a measure, it appears that with age changes in the pacemakers of the heart themselves (postjunctional) as well as in the adrenergic nerve endings innervating the heart (prejunctional) contribute to decreased cardiac rate and pacemaker activity in older rats.

The neurobiology of aging: does it predispose to depression?

This review examines the various research approaches undertaken to investigate possible central nervous system correlates of major depressive illness and relates findings from these studies to the alterations in central nervous system and neuroendocrine function that normally accompany aging in humans. The topics reviewed include: epidemiology of depression and suicide in the elderly; monoamine theories of depression; neuroendocrine disturbances in depression; and imaging studies.

Ageing and alpha 1 adrenoceptors in the iris

This study was undertaken to determine if the age related decrease in pupil size is attributable to altered sympathetic adrenoceptor responsiveness. Log dose response curves using the selective alpha 1 agonist phenylephrine and antagonist thymoxamine showed that there is no difference in alpha 1 adrenoceptor sensitivity in the elderly and the young. Therefore age related miosis is not caused by an alteration in alpha 1 receptors with age.

Alpha-adrenoceptor responsiveness in the aged rat

The effects of ageing on vascular alpha 1- and alpha 2-adrenoceptors were examined using anaesthetised and pithed young (3-7 months) and old (21-24 months) Sprague-Dawley rats. In pithed animals, the pressor and cardioinhibitory effects of the alpha 2-adrenoceptor agonist xylazine were significantly reduced in old animals (8- and 6-fold shift), but the pressor effects of the alpha 1-adrenoceptor agonist amidephrine were not significantly altered by ageing. In anaesthetised rats, the pressor response to the mixed alpha-adrenoceptor agonist noradrenaline (NA) was not significantly altered, and the pressor potency of the alpha 1-adrenoceptor agonist amidephrine was only slightly reduced (1.7-fold shift) in old animals. In the presence of cocaine (1 mg kg-1) the pressor potency of NA was markedly reduced (13-fold shift) in old animals. In the presence of prazosin (1 mg kg-1) to eliminate alpha 1-adrenoceptor-mediated responses, the pressor potency of NA was markedly reduced in old as animals as compared to young animals (16-fold shift). The neuronal uptake blocker cocaine (1 mg kg-1) significantly potentiated the pressor response to NA only in young. In summary, we have found a reduced alpha 2-adrenoceptor-mediated pressor and cardioinhibitory responsiveness and a reduced neuronal uptake of NA in old animals with little change in alpha 1-adrenoceptor-mediated vascular responsiveness.

Aging and the cardiovascular system

What has preceded has been largely a listing of contradictory data: what follows is an attempt to gleam a pattern from all of this. In general, responsiveness is either reduced or unchanged by aging; reduced responsiveness has been demonstrated most frequently for cardiac beta-adrenoreceptors, cardiac muscarinic receptors, vascular beta-adrenoreceptors and vascular alpha 2-adrenoreceptors. A reduced ability of the amine uptake system has been demonstrated in some but not all studies: any reduction in re-uptake would tend to potentiate the effects of NA and counteract the reduced receptor responsiveness (or vice versa). This may explain why the most consistent cardiovascular alteration reported in the elderly is an increased plasma NA. While there are clinical reports that beta-blockers and converting enzyme inhibitors are less effective in elderly hypertensives at lowering blood pressure, this may reflect more the pathological development of hypertension with time rather than a true aging phenomenon. Overall, it appears that resting function of the cardiovascular system is near normal in the aged, but since the mode of control is somewhat altered, in particular with a blunted baroreflex, perturbations in the system produced by drugs may cause a higher incidence of adverse effects.

Beta-blocking effect and pharmacokinetics of pindolol in young and elderly hypertensive patients

The pharmacokinetics and beta-blocking effect of pindolol has been compared in 20 patients with essential hypertension (WHO Stage I), 10 below 25 years of age and 10 older than 60 years. Each patient received pindolol 10 mg p.o. once a day for 5 days. The area under the curve (AUC) of pindolol was larger in the old than in the young patients both on the first (p less than 0.05) and the fifth (p less than 0.01) days. The AUC of pindolol was 14% higher on the fifth day compared to the first day in the elderly group, indicating minor accumulation at steady-state. There was no change in AUC in the young patients. Endogenous creatinine clearance was lower in the old (80 +/- 9 ml/min) than in the young patients (150 +/- 45 ml/min). The beta-blocking effect did not differ between the groups at 2 h after administration of pindolol on Days 1 or 5. However, 24 h after the first and fifth doses approximately 60% of the beta-blockade persisted in the old group whereas 17 and 19% of the beta-blockade, respectively, persisted in the young group; the difference between the groups was statistically significant (p less than 0.01). The most probable explanation for the more sustained beta-blocking effect in the elderly is the physiologically decrease in renal function, which results in a more sustained plasma level of pindolol in those patients.

The effect of aging on alpha-adrenoceptors and their responses in rabbits

The effects of age on alpha-adrenoceptor responses, sensitivity and number were studied in rabbits aged from 1 to 36 months. Three types of investigation were carried out: conscious animal studies, isolated tissue studies and radioligand binding studies. Specific [3H]-prazosin binding decreased with age in both spleen and heart suggesting that the number of alpha 1-receptors declined at least in the tissues studied. The specific binding of [3H]-clonidine to spleen membranes and [3H]-yohimbine to platelets was not affected by age. In vitro responsiveness to alpha-adrenoceptor agonists decreased with age in abdominal aorta and renal artery, while the affinity of adrenoceptors for prazosin (pA2) was not altered. The decrease may be non-specific as responses to potassium were also altered. No change in alpha 2-adrenoceptor mediated platelet aggregation was observed. No change in pressor or depressor responses to full adrenoceptor agonists or to antagonists was observed in vivo. However, responses to clonidine, which is a partial agonist at alpha 1-adrenoceptors, were decreased. While aging influenced alpha-adrenoceptor subtypes differently, there was no direct relation between functional changes and number of receptors.

Plasma and myocardial catecholamine levels in young and aged rats during halothane anesthesia

Plasma and heart tissue catecholamines were measured in young (4-month) and aged (28-month) Sprague Dawley rats under unanesthetized conditions and following the induction of halothane anesthesia. Arterial blood pressure, blood gases, plasma and heart tissue norepinephrine, epinephrine and dopamine concentrations were measured in separate groups of unanesthetized and halothane anesthetized rats. Young and aged rats were tested under equal anesthetic levels and blood halothane concentrations were measured using gas chromatography. Aged rats required significantly less halothane to maintain anesthesia compared to young animals (7.25 +/- 1.43 vs. 14.91 +/- 0.93 mg/dL, p less than 0.05). Cardiovascular parameters were similar in young vs. aged rats under unanesthetized conditions, but blood pressure decreased significantly more in aged than in young rats during halothane anesthesia (43% vs. 17%, p less than 0.05). Heart tissue catecholamines were not different between young and aged and did not change during halothane anesthesia. Plasma norepinephrine concentrations were consistently elevated in aged vs. young rats under both unanesthetized and anesthetized test conditions, but there was no significant change in these levels from the unanesthetized to the anesthetized state. Results suggest that increased catecholamine levels in aged animals may be necessary to maintain a normal cardiovascular state under unanesthetized conditions and that catecholamines do not increase during the hypotensive state produced by halothane anesthesia in spite of marked hypotension.

Effect of a new calcium antagonist, tiapamil, in hypertension of the elderly

The antihypertensive effect of a single oral dose of tiapamil (450 mg) and placebo were compared in a single blind randomized cross-over study in 10 71-86 year old hypertensive patients. Blood pressure (BP) and heart rate (HR) were recorded every 15 min for 12 h by an automatic device. Tiapamil led to a decrease in mean daytime systolic (SBP) and diastolic (DBP) BP from 171 +/- 12/98 +/- 10 mm Hg to 159 +/- 11/90 +/- 9 mm Hg (P less than 0.001) without significant variation in HR. Thereafter patients received tiapamil 450 twice daily; by the seventh day of treatment mean daytime SBP and DBP were 155 +/- 13/85 +/- 14 mm Hg (P less than 0.001 vs placebo). The hourly mean values of SBP recorded for 8/12 h (first tiapamil day) and 10/12 h (seventh tiapamil day) were significantly lower than the corresponding values after placebo. We conclude that tiapamil in the elderly exerts a sustained antihypertensive effect lasting 12 h or more, with only minor variations in HR. This effect predominates on systolic pressure and is significant from the first dose.

Age and cardiovascular response adaptation. Determinants of an antihypertensive treatment concept primarily based on beta-blockers and calcium entry blockers

The patient's age has great impact on the development of hypertension, its duration, and severity. In patients with essential hypertension, sympathetic cardiovascular control changes from an early phase with increased beta-adrenoceptor-mediated responses, e.g., cardiac output and renin, into a later phase where these responses are blunted and alpha-adrenoceptor-mediated vasoconstriction prevails, associated with higher intracellular free sodium and calcium concentration. This pathophysiological view of essential hypertension has its corollary in the pharmacotherapeutic approach. Younger patients, who often have high renin levels, respond better to monotherapy with a beta-blocker or with a converting-enzyme inhibitor. Older patients, who often have low renin levels, respond less well to beta-blockers but particularly well to calcium entry blockers as an alternative to diuretics. Therefore, beta-blockers and calcium entry blockers form new cornerstones for antihypertensive treatment and strategy, with the potential of cardioprotection.

Studies of the mechanisms underlying impairment of beta-adrenoceptor-mediated effects in human hypertension

To investigate the impairment of beta-adrenoceptor responsiveness in human hypertension, we evaluated the effect of an oral salt load (400 mEq/day of NaCl for 7 days) on plasma catecholamine concentrations and beta-adrenoceptor-mediated effects in 11 young patients with mild essential hypertension. Responses of heart rate and plasma cAMP to isoproterenol administration were used as indices of beta-adrenoceptor responsiveness. Salt loading induced a significant reduction in the dose of isoproterenol required to raise the heart rate by 25 bpm (CD25) (from 7.6 +/- 1.5 to 5.3 +/- 0.9 micrograms, p less than 0.05) and an increase in the slopes of the regression lines for heart rate changes and isoproterenol doses (delta HR/IS) (from 3.3 +/- 0.6 to 4.7 +/- 0.7, p less than 0.05) and for plasma cyclic AMP (cAMP) level changes and isoproterenol doses (delta cAMP/IS) (from 0.3 +/- 0.06 to 1.4 +/- 0.3, p less than 0.05). After salt loading there was a significant reduction in plasma catecholamine concentrations with a significant relationship between changes in upright plasma epinephrine levels and changes in CD25 (r = 0.904, p less than 0.01) and in the slopes for delta HR/IS (r = 0.983, p less than 0.001) and delta cAMP/IS (r = 0.922, p less than 0.001). These results support the hypothesis that the impairment of beta-adrenoceptor sensitivity observed in human hypertension is associated with a beta-adrenoceptor overstimulation due to chronically elevated adrenergic tone.

Effects of atenolol and hydrochlorothiazide on blood pressure and plasma catecholamines in essential hypertension

The antihypertensive effects of atenolol and hydrochlorothiazide were compared with placebo in a randomized, double-blind crossover study, with the blood pressure responses related to sympathetic nervous system activity. Twelve patients with essential hypertension were given atenolol (100 mg), hydrochlorothiazide (50 mg), and placebo as single daily doses, each for 6 weeks. Mean supine, standing, and post-exercise blood pressures (mm Hg) on atenolol (155/94, 152/95, 177/93, respectively) and hydrochlorothiazide (154/99, 150/103, 172/96) were lower (p less than 0.01) than corresponding placebo values (172/109, 166/113, 204/111) at 6 weeks. The role of the sympathetic nervous system in the antihypertensive actions of atenolol and hydrochlorothiazide was examined. The supine plasma norepinephrine on placebo was used as an index of sympathetic activity to categorize each patient's "adrenergic status." The six "hyperadrenergic" patients with high resting norepinephrine values (mean, 302 pg/ml) exhibited a greater (p = 0.05) decrease in BP (-30/-20 mm Hg) on atenolol compared with the BP fall of -9/-11 mm Hg observed in the lower norepinephrine group (mean, 211 pg/ml). Resting plasma norepinephrine values did not predict the BP fall on hydrochlorothiazide. The "adrenergic status" of each patient as measured by the plasma norepinephrine concentration tended to be relatively constant regardless of therapy or the state of activity. In this study, atenolol was an effective antihypertensive agent comparable to hydrochlorothiazide in potency. Adrenergic status tended to predict the BP response to atenolol and was a relatively constant feature of the patients in all treatment phases.

Alpha-adrenoceptors, adrenaline, and exaggerated vasoconstrictor response to stress in essential hypertension

Stressful sympathetic stimulation by cold pressor test in patients with essential hypertension results in an exaggerated response of the already elevated plasma adrenaline, heart rate, blood pressure, and alpha-adrenoceptor-mediated vasoconstriction when compared with normotensive subjects. The stress-induced increase in adrenaline was correlated with the attendant increase in blood pressure. The stress-induced reduction in forearm flow was reversed during infusion of the postjunctional alpha 1-adrenoceptor blocker prazosin. Therefore, enhanced responses to sympathetic stress, as reflected and perhaps caused by an exaggerated rise in plasma adrenaline, may contribute to an increased alpha 1-adrenoceptor-mediated vasoconstriction in essential hypertension.

Plasma catecholamines and essential hypertension. An analytical review

Of 78 comparative studies of plasma catecholamines in patients with essential hypertension and in normotensive controls, most reported higher catecholamine levels in the hypertensives, although only about 40% of the studies were positive (reporting statistically significant hypertensive-normotensive differences). Although there was dramatic variability in catecholamine values within and across studies, virtually all studies of norepinephrine in young, consistently hypertensive patients were positive. The likelihood that a study was positive with respect to norepinephrine was independent of the likelihood with respect to epinephrine, so that total catecholamine values, or else the sum of norepinephrine plus epinephrine, differentiated hypertensives from normotensives to a greater extent than levels of either substance alone. The preponderance of literature on the subject supports the hypothesis that increased plasma catecholamine concentrations occur in some patients with essential hypertension. Elevated plasma norepinephrine in relatively young, established hypertensive patients is consistent with a pathophysiologic role for increased sympathetic neural activity in this subgroup.

Enhanced alpha-adrenoreceptor-mediated vasoconstriction in essential hypertension

Forearm blood flow (FAF) has been determined using venous occlusion plethysmography in 24 patients with essential hypertension (EHT) and in 16 age-matched normotensive subjects (NT) under basal resting conditions, following nonspecific vasodilatation with sodium nitroprusside and after intraarterial infusion of the postjunctional alpha-blocking drug, prazosin. Under basal conditions, FAF was significantly higher in EHT than in NT. Infusion of sodium nitroprusside produced a similar absolute increase in FAF in both groups, whereas postjunctional alpha-blockade with prazosin led to a significantly greater increase in FAF in EHT than in NT. A positive correlation was found between plasma epinephrine concentration and prazosin-induced FAF in EHT but not in NT. These results suggest an enhanced postjunctional alpha-adrenoreceptor-mediated vasoconstrictor component in established EHT.