Renin and sympathetic nervous system responsiveness to adrenergic stimuli in essential hypertension

Physiological reactivity to acute mental stress in essential hypertension-a systematic review

Objective

Exaggerated physiological reactions to acute mental stress (AMS) are associated with hypertension (development) and have been proposed to play an important role in mediating the cardiovascular disease risk with hypertension. A variety of studies compared physiological reactivity to AMS between essential hypertensive (HT) and normotensive (NT) individuals. However, a systematic review of studies across stress-reactive physiological systems including intermediate biological risk factors for cardiovascular diseases is lacking.

Methods

We conducted a systematic literature search (PubMed) for original articles and short reports, published in English language in peer-reviewed journals in November and December 2022. We targeted studies comparing the reactivity between essential HT and NT to AMS in terms of cognitive tasks, public speaking tasks, or the combination of both, in at least one of the predefined stress-reactive physiological systems.

Results

We included a total of 58 publications. The majority of studies investigated physiological reactivity to mental stressors of mild or moderate intensity. Whereas HT seem to exhibit increased reactivity in response to mild or moderate AMS only under certain conditions (i.e., in response to mild mental stressors with specific characteristics, in an early hyperkinetic stage of HT, or with respect to certain stress systems), increased physiological reactivity in HT as compared to NT to AMS of strong intensity was observed across all investigated stress-reactive physiological systems.

Conclusion

Overall, this systematic review supports the proposed and expected generalized physiological hyperreactivity to AMS with essential hypertension, in particular to strong mental stress. Moreover, we discuss potential underlying mechanisms and highlight open questions for future research of importance for the comprehensive understanding of the observed hyperreactivity to AMS in essential hypertension.

Therapeutic potential of angiotensin II receptor antagonists

The circulating renin-angiotensin system plays an important role in cardiovascular homeostasis. More importantly, the local tissue renin angiotensin plays a pivotal role in cell growth and remodelling of cardiomyocytes and on the peripheral arterial vasculature. In addition, the renin angiotensin system is related to apoptosis, control of baroreflex and autonomic responses, vascular remodelling and regulation of coagulation, inflammation and oxidation. The cardioprotective and vascular protective effects of the angiotensin receptive blockade appears to be related to selective blockade of the angiotensin II (A-II) Type I (AT(1)) receptors. However, there is now growing evidence showing that some of the effects of AT-II receptor blockers (ARBs) are related to the activation of the kinin pathways. This paper will review some of the recent mechanisms related to the cardiovascular effects of angiotensin and more specifically of ARBs. This paper will present the novel data on the role of ARB in the development of atherosclerosis, vascular remodelling, coagulation balance and autonomic regulation. Finally, the role of ARBs, used alone or in combination with ACE inhibitor in patients with heart failure, will be discussed.

Neuroendocrine and cardiovascular stress reactivity in middle-aged normotensive adults with parental history of cardiovascular disease

Neuroendocrine and cardiovascular stress reactivity was studied in healthy middle-aged individuals whose parental history included essential hypertension and/or myocardial infarction and a control group without parental history of cardiovascular disease. All subjects completed a rest session (1 hour) and a stress session (1 hour). The stress session included behavioral (mirror image tracing, mental arithmetic, and the Stroop color word conflict test) and physical stressors (the cold pressor test and isometric exercise). Systolic and diastolic blood pressures and heart rate were recorded at baseline before and during all stressors. Specimens for determination of urinary catecholamines and cortisol were sampled after the rest and stress sessions respectively. Generally, a parental history of hypertension but not of myocardial infarction influenced neuroendocrine and cardiovascular stress reactivity. A family history of hypertension was associated with exaggerated epinephrine, norepinephrine, and cortisol excretion during stress and with enhanced heart-rate reactivity to behavioral (mental arithmetic and mirror image tracing) but not to physical stressors (isometric exercise or the cold pressor test). We conclude that individuals with a family history of hypertension tend to display exaggerated cardiovascular and neuroendocrine reactivity to stress.

Psychophysiological theories on sympathetic nervous system reactivity in the development of essential hypertension

Psychophysiological theories on the development of essential hypertension are reviewed and evaluated. Two interconnected theories that relate behavior to essential hypertension and account for individual differences in susceptibility to disease are the "hyperreactivity" theory and "the symptom specificity" theory. The "hyperreactivity" theory identifies individual differences in autonomic nervous system reactivity as the pathophysiological mechanism and the "symptom specificity" theory suggests that inflexible, stereotypical responding increases the risk to develop hypertension. Based on a literature review, these theories are examined. There exist both case/control and prospective studies on autonomic nervous system reactivity and the development of hypertension. It is concluded that a neurogenically mediated hyperreactivity to stress is a precursor and not an effect of hypertension. Tasks that call for active but not passive coping efforts are more efficient elicitors of reactivity differences between those at high and low risk to develop hypertension in case/control studies. In prospective studies, active tasks may also have a predictive advantage over passive with respect to blood pressure development. In the early phase of hypertension, an increased cardiovascular reactivity is accompanied by increased neuroendocrine activation. In the later phase, heightened reactivity is confined to the cardiovascular system. This does not prove but is consistent with the notion that transient episodes of increased cardiac output translate into essential hypertension by causing vascular hypertrophy. Case/control studies suggest that an increased "symptom specificity", with stereotypical responding across multiple stressors, is independent of cardiovascular reactivity and a precursor of hypertension. The literature lacks prospective studies on the clinical relevance of stereotypical responding. It is suggested that the presence of both hyperreactivity and symptom specificity in a single individual increases the risk to develop essential hypertension.

Tilt test in essential hypertension. Differential responses in heart rate and vascular resistance

Changes in hemodynamic parameters following 50-degree head-up tilt were studied in a population of 56 men, including 35 subjects with sustained essential hypertension and 21 age-matched normotensive controls. The increase in heart rate following tilt was similar in groups and exhibited the same reduction in response with age. The increase in vascular resistance following tilt was strongly and positively correlated with both age and baseline vascular resistance. The latter finding was observed mainly in hypertensive subjects. The study provided evidence that differentiated responses of heart rate and vascular resistance may be observed following orthostasis. In both normal and hypertensive subjects, the age dependence of heart rate response possibly reflected differences in baroreceptor reflex control of parasympathetic and sympathetic activity. In hypertensive subjects, the vascular response was amplified with age and baseline vascular resistance, suggesting a role for structural changes of the vessels in the increased vascular response.

Mechanisms of elevated blood pressure in human essential hypertension

This review of the mechanisms of elevation of blood pressure in human essential hypertension first focuses on individual mechanisms and their interrelations. The authors then try to identify those forms of essential hypertension in which the major determinants are known. When the most significant processes associated with elevated blood pressure in individual patients are understood, a rational approach to therapy can be undertaken even though the ultimate cause of the disorder is not understood.

Effect of beta-adrenergic blockade on circulating catecholamines and dopamine-beta-hydroxylase activity during exercise in normal subjects

We investigated the effects of beta-adrenergic blockade with propranolol (P) on circulating catecholamines at rest and during isometric and dynamic exercise. By means of a radioenzymatic assay, we measured plasma norepinephrine (NE) and epinephrine (E) concentrations in nine normal, sedentary men, aged 22 to 34 years. Measurements were made during resting conditions, at 3 minutes of 30% maximal isometric handgrip exercise (IHE), and during submaximal and maximal dynamic treadmill exercise. Measurements were repeated one week later after the subjects received P in doses ranging from 40 to 80 mg four times a day (plasma P levels at the time of exercise ranged from 96 to 303 ng/ml with a mean of 178 ng/ml). We also measured serum dopamine-beta-hydroxylase (DBH) activity to detect changes in chronic sympathetic tone. Changes in NE from rest to exercise were significant (p less than 0.01) at all exercise loads with or without P. Changes in E from rest to exercise were significant (p less than 0.01) at all exercise loads with or without P except for submaximal dynamic exercise during the control study (p greater than 0.05). For NE, there were no significant differences between the control and P values either at rest or during any form of exercise. For E, there were no significant changes between the control and p values at rest or at maximal dynamic exercise, although there were mild increases (p less than 0.05) with IHE and submaximal dynamic exercise. DBH activity increased significantly (p less than 0.01) from rest to exercise for all exercise points with and without P, but there were no significant differences between the control and p values either at rest or during any form of exercise. In conclusion, we have demonstrated that competitive blockade of beta-adrenergic receptors at the tissue level does not alter neural release of NE or DBH and has little effect on adrenal release of E.

Cardiovascular reactivity in mild hypertension

Blood pressure and heart rate were monitored in 18 mild hypertensives and 18 normotensive controls matched for age and sex during rest, isometric exercise, carbon dioxide rebreathing, cold pressor test, head-up tilt, radiant heat, head-back tilt and mental arithmetic. Blood pressure and heart rate were higher in the hypertensive than in the normotensive group at rest. During the instructions prior to the mental arithmetic and head-back tilt tests, heart rate increased more in the hypertensive than in the normotensive group while during mental arithmetic performance, blood pressure levels increased more in hypertensives than in normotensive controls. Diastolic blood pressure levels increased more in hypertensives during head-up tilt. In all other conditions, cardiovascular responses were similar in both groups. The results support the view that the sympathetic nervous system contributes to hypertension since the cardiovasculature of mild hypertensives was hyperreactive during tests where sympathetic activity was likely to predominate.

Prospective study of predictive factors determining borderline hypertensive individuals who develop sustained hypertension: prognostic value of increased diastolic orthostatic blood pressure tilt-test response and subsequent weight gain

Repeat hemodynamic determinations in supine and tilting positions were performed in 23 young men with borderline hypertension (HBP). The mean duration of follow-up was 48 months. During the study 11 patients had no change in hemodynamic parameters (group II), while 12 patients exhibited significant increase in systolic (p less than 0.001) and mean (p less than 0.01) arterial pressures (BP) and in body weight (p less than 0.05) (group I). In this latter group, the initial hemodynamic pattern included supine elevations in cardiac output (CO) and heart rate (HR) and significant increase in diastolic orthostatic BP. After follow-up, the group I primary supine increases in CO and HR were followed by secondary supine increases in total peripheral resistance (p less than 0.01) and systolic (p less than 0.001) and mean (p less than 0.01) BP with lower CO (p less than 0.05) and HR (p less than 0.001). In addition, it was shown during long-term follow-up in group I patients that : (1) the increase in systolic BP per unit age was negatively correlated with initial age (p less than 0.001), (2) the increase in BP was positively correlated with weight gain (p less than 0.05), and (3) the diastolic orthostatic hypertension disappeared. This study provides evidence that, in patients with borderline HBP having supine elevations of CO and HR, the subsequent development of sustained HBP can be expected, with follow-up observation of lower supine HR and disappearance of diastolic orthostatic hypertension accompanied by rapid weight gain.

Effect of beta-adrenergic receptor blockade with propranolol on the response of plasma catecholamines and renin activity to upright tilting in normal subjects

1 Relationship between plasma catecholamines (measured as noradrenaline and adrenaline) and plasma renin activity (PRA) were examined at rest and during passive head-up tilting for 30 min in nine normal subjects, before and after treatment with propranolol 160 mg daily for 7 days. 2 Noradrenaline (NA) and adrenaline (A) increased substantially after tilting for 15 min. There were no changes in PRA. After 30 min tilting, NA remained elevated, whereas A had returned to resting levels. A significant increase in PRA was apparent at 30 min. Pulse rate and diastolic blood pressure increased progressively during tilting. Systolic pressure did not change. 3 Treatment with propranolol reduced pulse rate and systolic blood pressure at rest and during tilting. Resting catecholamine concentrations and the response of NA to tilting were unaffected. In contrast, treatment prolonged the A response leading to significantly higher levels after 30 min tilting. Propranolol reduced PRA in six of the nine subjects and prevented the increase with tilting observed before treatment.

Changes in blood pressure, heart rate, and sympathetic activity on abrupt withdrawal of tiamenidine (HOE 440) in essential hypertension

A limitation of clonidine therapy is the syndrome of rebound hypertension and sympathetic overactivity after withdrawal. Ten patients, four male, six female, aged 28--64 years, with essential hypertension, were treated for one year with an imidazoline derivative, tiamenidine. Blood pressure fell from an average of 178/108 mm Hg pretreatment to 152/86 mm Hg after 1 year. Tiamenidine was then withdrawn in hospital, replaced by identical placebo under single blind conditions and observations made over 96 h. The study was interrupted in five patients (4 patients within 36 h) because blood pressure rose to greater than 30 mm Hg (systolic) or greater than 20 mm Hg (diastolic) above pretreatment values. For the group, blood pressure was maximal at 194/112 mm Hg, 18 h post withdrawal, significantly higher than pretreatment (p less than 0.005). Headache, tremor, flushing and insomnia were noted. Saliva production rose 100% at 24 h. Plasma noradrenaline rose within 24 h with an accompanying rise in urinary metanephrine and catecholamine excretion. Tiamenidine appears to share with other imidazolines rebound cardiovascular and autonomic effects following abrupt withdrawal.

Plasma angiotensin II and the control of diabetes mellitus

Plasma angiotensin II was measured in twenty patients with poorly controlled non-ketotic diabetes mellitus, and again when blood glucose control improved. Plasma angiotensin II fell significantly improved control, both when patients were supine and fasting overnight, and when studied after 4 h ambulation. The change occurred with improved short-term and longer-term control. It is concluded that the degree of blood glucose control is important when assessing the renin-angiotensin system in diabetic patients.

Plasma noradrenaline concentration in hypertensive and normotensive forty-year-old individuals: relationship to plasma renin concentration

Forty-year-old individuals with labile and with mild sustained essential hypertension, identified during a survey of a population born in 1936, were investigated. None had ever received antihypertensive treatment. In thirty-three individuals (26 M, 7F) with diastolic blood pressure (DBP) greater than or equal to 95 mmHg at the very first examination and in thirty-one (14 M, 17 F) randomly selected normotensive controls plasma noradrenaline concentration (PNAC) was measured at rest supine. In twenty-two patients (16 M, 6 F), with sustained diastolic hypertension (diastolic blood pressure greater than or equal to 95 mmHg on at least three different occasions) and in twenty-four (14 M, 10 F) normotensive controls PNAC and plasma renin concentration (PRC) were measured supine at rest and again 2 h after furosemide and ambulation. Basal and acutely stimulated values for PNAC and PRC were identical in hypertensive and normotensive individuals. A close correlation between PNAC and PRC after acute stimulation (r = 0.77, P < 0.001) as well as between the absolute changes from resting to acutely stimulated values (r = 0.72, P < 0.001) were found in the hypertensive individuals. It is concluded that sympathetic nerve activity, as defined from measurements of plasma noradrenaline concentration, is similar in young patients with mild hypertension and in normotensive controls. We propose that the discrepancies found in the literature might be related to a lack of comparability between hypertensive and normotensive individuals studied, as far as the source of study populations is concerned.

Echocardiographic dimensions in borderline and sustained hypertension

Echocardiographic dimensions and hemodynamic indexes were determined in 42 patients with borderline hypertension and in 22 with sustained hypertension and the results were compared with findings in 33 normal subjects. In patients with borderline hypertension the thickness of the interventricular septum (IVS) was significantly increased (P less than 0.001), whereas the posterior wall PW) thickness remained within normal range. The IVS/PW ratio was significantly elevated (P less than 0.001) and was correlated negatively with the cardiac index (P less than 0.01) and positively with the preejection period (P less than 0.01). In patients with sustained hypertension a symmetric cardiac hypertrophy was observed, and there was a significant positive correlation between the IVS/PW ratio and diastolic pressure (P less than 0.05). The study suggested that (1) in sustained hypertension the symmetric cardiac hypertrophy was secondary to a progressive increase in pressure load, whereas (2) in borderline hypertension the asymmetric cardiac hypertrophy could not be directly related to the level of blood pressure and was probably associated with abnormalities of the sympathetic nervous system.

[Plasma renin activity, plasma volume extracellular fluid volume and cardiac output in essential hypertension (author's transl)]

The plasma renin activity (PRA), the plasma volume (PV), the extracellular fluid volume (ECV), the cardiac output and the peripheral vascular resistance (TPR) were determined in 51 patients (14 women, 37 men) with essential hypertension of varying severity. The following findings were achieved: 1. In 9 of the 51 patients with essential hypertension (approximately 18%) a low and non-sensitive PRA was detected. 2. PV, ECV, cardiac output and the calculated peripheral vascular resistance of the essential hypertensive patients with low and non-sensitive PRA did not differ significantly from those of the essential hypertensive patients with normal or elevated PRA. 3. The hypertensive patients with low and nonsensitive PRA had the highest average arterial pressure. From these findings it can be concluded that the essential hypertensive patients with low PRA are not an homogeneous group. It is assumed that in a subgroup the elevated blood pressure may be the cause of the renin suppression.

Alterations in the responses of the sympathetic nervous system and renin in borderline hypertension

We investigated the effect of stimuli activate the sympathetic nervous system on plasma catecholamines, renin activity, urinary metanephrine and normetanephrine, and various hemodynamic parameters in normal subjects (NIs) and borderline hypertensive (BH) subjects. No differences were observed in sympathetic nervous system activity or renin activity when the subjects were in the resting state on a 150 mEq sodium diet. However, the BH group exhibited greater responses in terms of plasma catecholamines and plasma renin activity in response to sodium deprivation and treadmill exercise. Although hemodynamic differences in the cold pressor test and handgrip exercise did not emerge, the radio of atrial size decrement to venous tone increment during the Valsalva maneuver was significantly reduced in the BH group. The investigations suggest that in the basal state, BH subjects have appropriate levels of activation of the sympathetic and renin systems for a normal level of pressure but that perturbations of pressure and volume factors lead to unmasking of abnormalities in regulation of both systems. The data are also consistent with the suggestion that venous compliance is reduced in these patients.

Racial differences in pressure, volume and renin interrelationships in essential hypertension

The interrelationships of arterial pressure, plasma volume (PV), and plasma renin activity were studied in 152 consecutive male patients with uncomplicated essential hypertension. Of these, 22 (17 white and 5 black) subjects had normal plasma volumes and because of the small number were not included in the analysis of results. The remaining 130 (35 black and 95 white) patients were classified as having either expanded or contracted plasma volume. A higher percentage of black (43%) than white (21%) subjects were volume expanded (PV > 19 ml/cm) and a lower percentage of blacks (57%) than whites (79%) were volume contracted (PV < 17 ml/cm). There was not significant difference in mean arterial pressure and plasma renin activity between the volume expanded and contracted black patients. In contrast, the white patients with contracted plasma volume had significantly higher arterial pressures (p < 0.05) and plasma renin activity (p < 0.001) than those with expanded plasma volume. More blacks than whites had low plasma renin activity and did not manifest the inverse relationship of plasma renin activity to plasma volume as did the whites. These data confirm and extend previous observations that the relationship between plasma volume and plasma renin activity (PRA) in the male patient with essential hypertension seems to differ between the black and white race. Efforts to explain the low PRA in black patients might be best directed toward those patients with suppressed PRA and with contracted intravascular volume.

Clinical and physiological significance of borderline hypertension at youth

Marginal blood pressure elevation at youth is widely prevalent. Clinically such patients represent a dilemma, since they are at highest risk to develop hypertension and its sequelae, but the risk is not sufficiently strong to mandate antihypertensive medication. The decision as to whether to treat will depend on the presence of other risk factors for hypertension. Multiple and complex pathophysiologic abnormalities have been described in borderline hypertension. A better understanding of the relationship of some of these abnormalities to the development of hypertension is needed.

Mild high-renin essential hypertension. Neurogenic human hypertension?

To determine whether the elevated plasma renin activity in some cases of mild essential hypertension expresses sympathetic-nervous-system over-activity, we compared indexes of sympathetic activity in 16 patients with mild high-renin essential hypertension, 15 hypertensive patients with normal plasma renin activity and 20 normal subjects. Patients with elevated activity exhibited a raised plasma norepinephrine concentration (P less than 0.05), a greater fall in cardiac output with cardiac beta-adrenergic blockade by intravenous propranolol (P less than 0.01), reduction in total peripheral vascular resistance with alpha-adrenergic blockade produced by intravenous phentolamine (P less than 0.01), and reduction to normal of blood pressure by "total" autonomic blockade (atropine, propranolol and phentolamine). On psychometric testing, patients with high-renin hypertension, but not those with normal plasma renin activity, exhibited suppressed hostility (P less than 0.01), a behavioral pattern linked to increased sympathetic activity. The hypertension in these patients with high renin activity is neurogenic and possibly psychosomatic in origin.

[Interrelations between blood pressure, blood volume, plasma renin and urinary catecholamines during beta-blockade in essential hypertension (author's transl)]

Studies in 55 patients with benign essential hypertension showed that the beta-blockers bufuralol (22 patients) and propranolol (33 patients) at a dose ratio of 1:4, possess comparable antihypertensive efficacy despite different properties regarding intrinsic sympathomimetic activity. Beta-blocker-monotherapy normalized blood pressure ( less than 140/90 mm Hg) in one fourth of the patients. Body weight and plasma and blood volumes remained unchanged during beta-blockade of four to six weeks duration, the mean plasma potassium was slightly increased. The inhibition of plasma renin activity (PRA) was more pronounced with propranolol (-69%) than with bufuralol (-47%). Wirth both beta-blockers decreases in blood pressure correlated inversely with pre-treatment PRA (p less than 0.05). Propranolol-induced changes in blood pressure correlated also with associated changes in PRA (p less than 0.005); in contrast, no such relationship was observed with bufuralol. The blood pressure effects of bufuralol, however, correlated significantly with changes in urinary noradrenaline excretion (r=0.41; p less than 0.05). Patient sub-groups with low, normal or high pre-treatment PRA in the average showed a comparable pattern of pre-treatment noradrenaline excretion and patients with normal renin levels exreted more adrenaline than those with low renin levels (p less than 0.001). These data are consistent with the concept that in untreated essential hypertension PRA may be an index of adrenergic activiity, the latter representing an important determinant of blood pressure response to beta-blockade. The blood pressure lowering effects of bufuralol in benign essential hypertension seem to be independent of renin and may be related, at least partly, to diminished free peripheral noradrenaline levels.

Renin, aldosterone and arterial pressure responses to acute beta-adrenergic receptor blockage in hypertensive patients

The effect of acute (intravenous) beta-adrenergic blockade with propranolol or pindolol on arterial pressure (BP), plasma renin activity (PRA), and plasma concentration of aldosterone (PA) was evaluated in 20 essential hypertensive men. BP, PRA and PA were determined during continuous recumbency over-night (8 p.m. to 6 a.m.) every 30 min. Two groups of patients were observed. Patients of group 1 exhibited a characteristic day-night rhythm of PRA with low values before midnight and large increases early in the morning. Conversely, no rhythm and very low PRA values were observed in patients of group II. BP was higher in group II than in group I. In group I following intravenous propranolol or pindolol, BP fell within minutes and levels as well as rhythms of PRA were converted to those of group II without treatment. In group II day-night profiles of PRA and BP remained unchanged. Rhythm and concentration of PA in the two groups were not influenced by either drug. In 4 patients of group I infusion of angiotensin II inhibitor did not lower BP. The observations suggest that in the two groups dissimilarities in rhythms of PRA as well as in BP responses to beta-blockade may reflect differences in neuro-adrenergic tone.

Suppression of sympathetic nervous function in low-renin essential hypertension

Study of general haemodynamics in 15 patients with low-renin essential hypertension showed haemodynamic and pathophysiological heterogeneity. However, there was suppression of sympathetic nervous system function in all low-renin patients, regardless of haemodynamic pattern. Subnormal sympathetic nervous activity was manifested by a low normal mean plasma-noradrenaline concentration at rest, diminished noradrenaline responsiveness to postural stimulation, and a reduced blood-pressure response to the indirectly acting sympathomimetic amine tyramine. It is proposed that the syndrome of low-renin essential hypertension is of diverse aetiology, but with secondary sympathetic nervous system underactivity as a feature common to the various forms. The low plasma-renin activity is probably an expression of defective sympathetic nervous system stimulation of renin release.

Acute and long-term studies of the mechanisms of action of beta-blocking drugs in lowering blood pressure

The antihypertensive effect of intravenous (acute) and oral (long-term) beta-adrenergic blockade with propranolol or pindolol was evaluated in 46 male patients with either borderline (group I; 23 patients) or sustained (group II; 23 patients) essential hypertension. Arterial pressure, plasma renin activity and plasma concentration of aldosterone were determined during continuous recumbency overnight every 30 minutes before and after treatment. Patients of group I exhibited a marked variation of their recumbent plasma renin activity with relatively low values before midnight and large increases early in the morning. In contrast, low plasma renin activity values and only minimal fluctuations in renin were observed in patients of group II. Plasma renin activity had a consistent relationship with blood pressure both after acute (r = 0.79) and long-term (r = 0.4) beta-blockade. In four patients of group I, who had high plasma renin activity and had responded to intravenous propranolol, infusion of angiotensin II inhibitor did not lower pressure. In group I following beta-blockade, day-night profiles of renin were similar to those observed in group II before treatment. Thus in this latter subgroup, low renin profiles might reflect reduced beta-adrenergic activity. Acute as well as long-term beta-blockade consistently eliminated the day-night rhythm of plasma renin activity, but it did not change rhythm of plasma concentration of aldosterone. Plasma concentration of aldosterone was lower in group II but appeared to be inappropriately high relative to renin levels. These observations suggest that in hypertensive patients classified according to blood pressure and recumbent plasma renin activity profiles a significant relationship exists between changes in plasma renin activity and arterial pressure responses. Thus, patients with high renin levels respond better to treatment than patients with low renin levels. We conclude that in the patients studied, sympathetic nervous system activity mainly determined renin levels as well as antihypertensive effectiveness of the beta-blocking drugs.

Control of renin release: a review of experimental evidence and clinical implications

Present knowledge of the mechanisms regulating release of renin is reviewed with particular emphasis on neural factors. Evidence is given for a direct effect of renal innervation on beta adrenergic receptors in juxtaglomerular cells, and for the involvement of reflex release of renin in conditions such as tilting and acute salt depletion. Participation of neural and nonneural mechanisms of control is also shown to occur in other conditions, such as aortic constriction and hemorrhage. The view is held that neural sympathetic factors might explain some of the renin disturbances found in essential hypertension. First, in patients with high renin hypertension part of the hypertension is renin-dependent, and these pressor levels of renin seem to be neurally induced since they can commonly be suppressed by beta adrenoreceptor blocking agents. Second, the hypothesis is presented that patients with low renin hypertension, at least those who have no volume disturbance, have a blunted sympathetic control of renin release. Therefore a sufficiently precise test of sympathetic activity, and possibly of body fluid volumes, should be associated with renin profiles for a better understanding of the pathophysiology of arterial hypertension and as a better guide to therapeutic management. Indeed, most of the available antihypertensive drugs act on sympathetic activity, body fluid volume or renin, and this multifaceted profile would provide more rational guidelines for treatment.

Long term treatment of moderate hypertension with penbutolol (Hoe 893d). II. Effect on the response of plasma catecholamines and plasma renin activity to insulin-induced hypoglycemia

The effect of insulin-induced hypoglycemia on the blood levels of catecholamines and renin activity has been studied in five patients with moderate hypertension before and after treatment for 3 - 8 months with penbutolol (PEN) 20 - 30 mg twice daily. Penbutolol caused no change in fasting blood glucose level. Insulin o.1 IU per kg body weight i.v. reduced blood glucose concentration by approximately 50 per cent after 30 - 45 min, both before and during treatment with penbutolol. Hypoglycemia prior to medication was accompanied by a marked increase in the production of adrenaline and a minor increase of noradrenaline in all five patients. During treatment the response of adrenaline to hypoglycemia was reduced in four patients and the data was inconclusive in one. Basal renin activity was rather low in three patients, within the normal range in one and relatively high in one. Before penbutolol the hypoglycemia-induced increase in catecholamine production caused no change in plasma renin activity in the three patients with low basal levels, whereas a marked increase was observed in the other two. During medication plasma renin activity remained unchanged on induction of hypoglycemia regardless of the catecholamine response. Despite the marked increase in plasma adrenaline following insulin-induced hypoglycemia, no statistically significant increase in pulse rate was recorded.

Contrasting effects of hypoglycemia on plasma renin activity and cyclic adenosine 3',5'-monophosphate (cyclic AMP) in low renin and normal renin essential hypertension

Insulin-induced hypoglycemia previously has been shown to provoke a beta-adrenergic response that normally results in an increase in plasma renin activity (PRA). In our study, hypoglycemia induced definite increases in PRA in a group of five patients with normal renin essential hypertension but failed to do so in a group of six patients with low renin essential hypertension. In both groups, plasma cyclic adenosine 3',5'-monophosphate (cyclic AMP; cAMP) increased more than 2-fold during hypoglycemia, but the response in the low renin group was significantly less than that previously observed in normal subjects under the same conditions. Plasma cortisol increased to an equal extent in both groups of hypertensive patients during hypoglycemia. Infusion of the phosphodiesterase inhibitor, theophylline, resulted in definite increases of PRA in patients with normal renin hypertension but not in patients with low renin hypertension. Because changes in the level of plasma cAMP during hypoglycemia have been thought to reflect adrenal catecholamine release, our finding of a blunted increase in plasma cAMP during hypoglycemia in patients with low renin hypertension may suggest that there is a generalized alteration in adrenergic responsiveness in this condition.

[Diurnal variation in the urinary excretion of vanilmandelic acid and aldosterone in normal and hypertensive persons (author's transl)]

The excretion of creatinine, VMA, and aldosterone was measured in the urine of 14 normal and 25 persons with stable essential hypertension during a day time (7.00-23.00 hrs) and a night time (23.00-7.00 hrs) period. Excretion of VMA and aldosterone per hour in the two groups was lower during the night period than during the day. No significant difference existed between the excretion values of both groups. Night/day rations for the excretion of VMA and of aldosterone respectively, per mg of creatinine excreted were calculated for each subject. In the normal group the night/day ratios of aldosterone excretion showed a significant correlation to the corresponding ratios of VMA excretion; such correlation was not found in the hypertensive group. The fact that a correlation was observed in the normal group is compatible with the hypothesis that catecholamines are involved in the regulation of the renin-angiotensin-aldosterone system. Lack of correlation in the group of hypertensive does not as yet allow any conclusions. In two patients with primary hyperaldosteronism, the aldosterone excretion during the night was relatively more elevated than in the day.

Relation of renin status to neurogenic vascular resistance in borderline hypertension

The relation of renin-angiotensin status to general hemodynamics and to neurogenic vascular resistance was studied in patients with border-line hypertension. Plasma renin activity during standing was referred to a standard renin-urinary sodium nomogram derived from 18 normal subjects. Among 22 patients with borderline hypertension the renin level was high in 8, low in 4 and within normal limits in the remaining 10. In patients with borderline hypertension and high or normal levels of plasma renin activity, the blood pressure elevation was due to increased total peripheral vascular resistance. In contrast, in patients with low renin borderline hypertension, total peripheral resistance was not significantly elevated; the blood pressure elevation reflected a cardiac index 12 percent higher than that in normal subjects. The neurogenic contribution to total peripheral vascular resistance was assessed by studying the effects of alpha adrenergic blockade with phentolamine, after prior autonomic blockade of the heart with atropine (0.04 mg/kg body weight) and propranolol (0.2 mg/kg). Phentolamine (15 mg) produced an immediate reduction in total peripheral resistance of 12.0 +/- 6.7 percent in patients with high renin borderline hypertension (P less than 0.01) but no change in normal subjects or those with borderline hypertension and normal or low renin levels. Normalization of the blood pressure followed "total" autonomic blockade with atropine, propranolol or phentolamine only in patients with high renin borderline hypertension. It is concluded from these preliminary data that in high renin borderline hypertension the blood pressure elevation is sustained by neurogenic mechanisms. The elevated renin level in these patients is probably an expression of increased sympathetic nervous activity. Although the elevated plasma renin level may possibly be contributing to the generation of higher sympathetic tone, or data do not support a direct role of circulating angiotensin in the maintenance of the elevated vascular resistance.

Autonomic nervous cardiovascular regulation in borderline hypertension

Borderline hypertension attracts investigative interest since it is an early predictor of established hypertension and its sequelae. This condition offers the opportunity of studying arterial hypertension at its inception, before the development of secondary pressure-related changes. A number of abnormalities of the circulation have been described in borderline hypertension. The peripheral resistance is either elevated or inappropriately adjusted to the prevailing increased cardiac output and blood flow. Cardiac output, heart rate and stroke volume are elevated in a proportion of patients. Decreased plasma volume, enhanced pressor responsiveness and elevated plasma renin activity have also been noted. All these changes could hypothetically be explained by a neurogenic mechanism. Although the experimental evidence supporting a neurogenic origin of borderline hypertension is incomplete and often indirect, most findings point toward an abnormal autonomic control of the circulation in this disorder. It is postulated that in a subgroup of patients with borderline hypertension a neurogenic mechanism is in fact operative. There is a need for further characterization of this category of borderline hypertension and for description of its natural history, particularly in relation to the possible subsequent development of essential hypertension.

Antihypertensive beta blocking action as related to renin and age: a pharmacologic tool to identify pathogenetic mechanisms in essential hypertension

Three hundred fifteen patients with essential hypertension were classified according to low (18 percent), normal (59 percent) or high (23 percent) renin-sodium index. The proportion of patients with low renin hypertension progressively increased with increasing age and blood pressure, there being no difference between the sexes. Two high renin groups emerged: a younger group with early moderate hypertension, and an older group with severe hypertension consequent to possibly ischemic renal disease. Long-term beta blocking monotherapy in 137 patients resulted in a reduction of idastolic pressure to 95 mm Hg or less in 65 percent: 85 percent in those with high and 73 percent in those with normal renin activity; pressure was reduced to this level in only 1 of 24 patients (4 percent) with a low renin index. Antihypertensive efficacy was also related to age, since diastolic pressure was normalized in 80 percent of patients under age 40 years, in 50 percent of those aged 40 to 60 years, but in only 20 percent of those over age 60 years. Age may heolp in patient selection but is no substitute for the more reliable renin index, especially in patients over age 40 years, or with high pressure. Using studiew with propranolol as a standard, similar renin responses were obtained with two cardioselective beta1 type blocking drugs, atenolol and metoprolol, as well as with two nonselective beta2+1 receptor antagonists, LL21945 exhibiting prolonged receptor affinity and oxprenolol in slow release form. These long-acting drugs, which proved effective in single daily doses, could be of value in improving patient compliance...

Control plasma renin activity and changes in sympathetic tone as determinants of minoxidil-induced increase in plasma renin activity

A study was made of the possible mechanism(s) underlying minoxidil-induced increase in plasma renin activity (PRA). 10 patients with essential hypertension were treated with minoxidil and subsequently with a combination of minoxidil plus propranolol. Minoxidil lowered mean arterial pressure 31.6 plus or minus 3.3 mm Hg, mean plus or minus SEM. There was an associated increase in both PRA, 6.26 plus or minus 2.43 NG/ML/H, and heart rate, 21.4 plus or minus 2.7 beats/min. The changes in PRA and heart rate were positively correlated, r, 0.79. Addition of propranolol reduced mean arterial pressure by a further 10.1 plus or minus 1.5 mm Hg and returned heart rate to control levels. Propranolol reduced PRA significantly but not to control levels. Control PRA positively correlated with PRA on minoxidil, r, 0.97, and with PRA on minoxidil plus propranolol, r, 0.98. We conclude that control PRA is a major determinant of change in PRA with minoxidil. Minoxidil increased PRA by at least two mechanisms: (a) an adrenergic mechanism closely related to change in heart rate and blocked by propranolol, and (b) a mechanism(s) not sensitive to propranolol and possibly related to decrease in renal perfusion pressure.