Insulin does not reduce forearm alpha-vasoreactivity in obese hypertensive or lean normotensive men

Evidence supports the hypothesis that an impaired capacity of insulin to antagonize norepinephrine-induced vasoconstriction increases alpha-adrenergic tone in overweight young men with insulin resistance and mild hypertension. Therefore, the effects of regionally infused insulin at 100 microU/mL on forearm blood flow (milliliters per deciliter per minute) and responses to norepinephrine were measured in seven obese hypertensive and eight lean normotensive men younger than 45 years old. The obese hypertensive men were hyperinsulinemic and insulin resistant compared with the normotensive men, as evidenced by abnormal values for fasting insulin (15.5 +/- 1.6 versus 7.2 +/- 0.8 microU/mL, P < .001), the insulin area under the curve in response to a 2-hour oral glucose tolerance test (12.0 +/- 1.5 versus 6.7 +/- 1.1 mU x min/dL, P < .01), and the disappearance rate of glucose during a 15-minute insulin tolerance test (2.7 +/- 0.3 versus 4.1 +/- 0.3 mg%/min, P < .05). The logarithm of the norepinephrine EC50 was not significantly different in obese hypertensive men (mean, 95% confidence interval: -8.15, -8.42 to -7.87) versus lean normotensive men (-7.91, -8.23 to -7.59). The 2-hour regional insulin infusion at 100 microU/mL did not significantly alter the EC50 for norepinephrine in either group. Insulin at this concentration induced significant and similar increases of forearm blood flow in the hypertensive and normotensive groups (1.7 +/- 0.4 versus 1.7 +/- 0.6 mL/100 mL per minute, P = NS). At approximately 100 microU/mL, insulin does not antagonize norepinephrine-induced vasoconstriction in the forearm circulation of either obese hypertensive or lean normotensive men.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved baroreflex sensitivity in elderly hypertensives on lisinopril is not explained by blood pressure reduction alone

OBJECTIVE

The major goals of this study were to determine whether lisinopril and nifedipine lowered blood pressure and improved carotid baroreflexes in older hypertensives.

DESIGN

The effects of lisinopril at 10-40 mg/day versus nifedipine gastrointestinal therapeutic system (GITS) at 30-90 mg/day on blood pressure and baroreflex sensitivity were studied after 3 weeks each on (1) single-blind placebo, (2) double-blind assignment to either lisinopril or nifedipine, (3) single-blind placebo, and (4) crossover to double-blind lisinopril or nifedipine. Measurements at the end of the four phases included 24-h blood pressure using the Accutracker, laboratory hemodynamics with the Dinamap and impedance cardiography, baroreflex sensitivity with the pneumatic neck chamber, and plasma samples for neurohumoral and metabolic activity.

PATIENTS

Thirteen patients aged 55 years or older (mean +/- SEM 65 +/- 1 years) with mild-to-moderate hypertension completed the study.

MAIN OUTCOME MEASURES

The primary data for analysis across the four study phases included ambulatory blood pressure values, laboratory hemodynamics, and baroreflex sensitivity.

RESULTS

Compared with the preceding placebo, lisinopril and nifedipine lowered 24-h blood pressure significantly. In the laboratory, the effects of both compounds on blood pressure, cardiac output, calculated total systemic resistance, and the stroke volume-pulse pressure relationship, an index of arterial compliance, were similar. Lisinopril was associated with a relative increase in the standing systolic blood pressure compared with nifedipine (P < 0.05). This coincided with an enhanced heart-rate (R-R interval) response to neck pressure, which also decreased carotid transmural pressure, with lisinopril versus nifedipine (P < 0.05).

CONCLUSIONS

Lisinopril and nifedipine were both effective as monotherapy for controlling blood pressure in these elderly patients. Despite similar effects on blood pressure and systemic hemodynamics, baroreflex sensitivity in response to a reduction in carotid transmural pressure was greater with lisinopril than with nifedipine.

Effects of enalapril on the hyperinsulinemic response to severe salt restriction in obese young men with mild systemic hypertension

Hypertension in obese patients is associated with hyperinsulinemia and salt sensitivity. Very low salt diets may exacerbate hyperinsulinemia, perhaps by activating the renin-angiotensin system. Therefore, the effects of a low salt diet alone and with enalapril on blood pressure and the insulin response to an oral glucose tolerance test were studied in 9 obese (body mass index 35 +/- 2 kg/m2) men with mild hypertension. Measurements were first obtained after a 2-week high-salt (20 mEq/day sodium diet+eleven 1 g salt tablets per day) baseline period. The same measurements were repeated after 2 weeks on a low salt diet (20 mEq/day) and after 2 weeks on low salt diet with enalapril in random sequence. The insulin area under the curve increased from 12.8 +/- 3.0 mU-min/dl during high salt to 16.6 +/- 3.2 mU-min/dl (p < 0.001). Plasma renin activity also increased with salt restriction from 1.4 +/- 0.2 to 3.0 +/- 0.5 ng/ml/hour, p = 0.01. With addition of enalapril to the low sodium chloride diet, the insulin area under the curve (14.5 +/- 2.6 mU-min/dl) was not significantly different from that during the high sodium chloride phase. Mean blood pressure in the laboratory was 105 +/- 1 mm Hg with high salt versus 99 +/- 1 mm Hg with low salt, p < 0.05. Addition of enalapril to the low-salt diet reduced mean blood pressure to 87 +/- 1 mm Hg (p < 0.01 vs low salt), largely by reducing total systemic resistance (p < 0.05). Salt restriction decreases laboratory BP while raising insulin levels in obese men with mild hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased prevalence of abnormal signal-averaged electrocardiograms in older patients who have hypertension with low diastolic blood pressure

Greater mortality in hypertensive patients with the lowest diastolic blood pressure (DBP) values has been reported and may be partially explained by more fatal arrhythmias. The records of 135 patients were reviewed to determine whether the prevalence of an abnormal signal-averaged electrocardiogram (SAECG+), a risk marker for ventricular arrhythmias, was greater in patients who have hypertension with DBP < 85 mm Hg. SAECG+ was present in 31 (39%) of 80 patients with hypertension and 13 (24%) of 55 subjects with normotension p < 0.05. Hypertensive patients were more likely than normotensive subjects to have left ventricular hypertrophy (LVH, p = 0.01) and LV dysfunction (p < 0.01). In multivariate analysis only age and systolic dysfunction emerged as significant predictors of SAECG+. Among 68 hypertensive patients and for whom recent DBP data were available, SAECG+ was present in 18 of 37 with DBP < 85 mm Hg (group 1), 1 of 12 with DBP 85 to 94 mm Hg (group 2, p < 0.05 vs group 1), and 4 of 19 with DBP > 95 mm Hg (group 3, p < 0.05 vs group 1, p = 0.08 vs group 2). There were no significant differences between the three groups of hypertensive patients for coronary artery disease, LVH, systolic dysfunction, or left-sided cardiac chamber enlargement. Multivariate analysis in hypertensive patients indicated that age and DBP were each independently predictive of SAECG+, whereas the indexes of heart disease were not. Within group 1, those with SAECG+ were significantly older (68 +/- 1 vs 59 +/- 1 years, p < 0.01) and more likely to have LVH (p < 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men

There is a widespread interest in fish oil as a dietary supplement and possible nonpharmacologic adjunct in the treatment of hypertension. The effect of dietary fish oil on blood pressure is controversial and the effect on systemic hemodynamics and regional vascular reactivity in humans is unknown. To address these questions, a double-blind, placebo-controlled, crossover study on the effect of dietary fish oil substitution was performed during a carefully controlled diet in 8 normotensive men. Systemic hemodynamics and the forearm vascular response to intrabrachial artery infusions of norepinephrine, phentolamine and angiotensin II were obtained. Compared with a safflower oil placebo, dietary fish oil had no effect on cardiac output (6.42 +/- 0.38 vs 6.87 +/- 0.28 liters/min, p = not significant) or 24-hour blood pressure (122/68 +/- 3/3 vs 122/68 +/- 3/2 mm Hg, p = not significant). The vascular response to norepinephrine and phentolamine was unchanged. Fish oil, however, significantly (p < 0.05) reduced forearm vascular resistance responses to angiotensin II. These changes were associated with a reduction in plasma triglycerides (64 +/- 9 vs 39 +/- 4 mg/dl, p = 0.02) and an increase in plasma eicosapentaenoic acid levels (0.51 +/- 0.25 vs 1.72 +/- 0.35 microM, p < 0.05). Substitution of a moderate dose of fish oil for fat in a "Western diet" selectively attenuates the vascular response to angiotensin independently of changes in alpha-adrenergic vasoconstriction or systemic hemodynamics.

Cyclooxygenase products do not modulate angiotensin II-induced contractions of human chorionic plate arteries

OBJECTIVE

This study sought to determine whether cyclooxygenase products modulate angiotensin II-induced contractions of human placental arteries.

STUDY DESIGN

Ring segments of chorionic plate arteries (3 to 5 mm inner diameter) were obtained after normal vaginal deliveries. Active force in response to 10(-6) mol/L angiotensin II or 10(-4) mol/L arachidonic acid was measured in the presence or absence of 10(-6) mol/L indomethacin to inhibit cyclooxygenase. The response of K+ contracted arteries to the stable prostacyclin analog iloprost was also tested to determine whether prostacyclin relaxes these vessels. Statistical differences were assessed by analysis of variance, Wilcoxon sign rank test, or Student t test with Bonferroni correction for multiple comparisons.

RESULTS

Successive applications of angiotensin II produced significantly less contraction than the original dose (angiotensin II tachyphylaxis). Angiotensin II tachyphylaxis was unaffected by indomethacin. Arachidonic acid caused an indomethacin-sensitive contraction and iloprost failed to relax the arteries.

CONCLUSIONS

These results suggest that cyclooxygenase products do not mediate angiotensin II tachyphylaxis in these vessels.

NaCl induces differential changes of regional vascular reactivity in salt-sensitive versus salt-resistant men

The objective of our study was to determine the structural or functional factors which increase forearm vascular resistance (FAVR) during a high NaCl diet in salt-sensitive (SS) volunteers. We studied the effects of 20 v 200 mEq/day NaCl diets on FAVR responses to norepinephrine (NE), angiotensin II (AII), nitroprusside, verapamil, and ischemia in 27 men. Twelve men had supine mean arterial pressure (MAP) on high NaCl which was greater than or equal to 5% above MAP on low NaCl and were consequently labeled SS. Eleven subjects had lower MAP on the high NaCl diet and were classified salt-resistant (SR). Basal FAVR was greater in SS (P less than .005) and unchanged in SR subjects on high (v low) NaCl. FAVR responses to NE and nitroprusside were not different between the two diets within either the SS or SR subgroups. FAVR responses to AII decreased during high NaCl in the SR (P less than .01), but not in the SS subset. The response to phentolamine and verapamil increased in SS (P less than or equal to .05) and tended to decrease in SR subjects (P less than .15) during high NaCl. In contrast, the vasodilator response to ischemia was impaired in the SS (P = .02) and enhanced in the SR (P = .02) group on high v low NaCl. Enhanced alpha-adrenergic and Ca2+ channel (verapamil)-dependent vascular tone probably contribute to the greater baseline FAVR in SS subjects on high NaCl. Failure to decrease vasoconstrictor responses to AII may indirectly contribute to their maladjustment of FAVR.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurohumoral, hemodynamic and microvascular changes as mechanisms of insulin resistance in hypertension: a provocative but partial picture

Hyperinsulinemia and insulin resistance are largely explained by upper body obesity in hypertension. However, non-obese hypertensive patients have similar metabolic defects. Thus, neurohumoral, hemodynamic, and microvascular abnormalities which occur in the development of hypertension may contribute to insulin resistance independent of obesity. Sympathetic drive and vascular alpha-tone are increased in young, predominantly overweight patients with borderline-mild hypertension. The importance of increased neurogenic tone, especially the alpha-adrenergic component, is emphasized by evidence that alpha 1-receptor antagonists virtually normalize insulin metabolism in hypertensive patients. Patients with mild hypertension have elevated forearm vascular resistance which could theoretically contribute to insulin resistance by impairing muscle perfusion. However, blood flow is normal at baseline and maximal dilation. Similarly, overweight young men have hyperinsulinemia, despite higher basal forearm blood flow and a normal vasodilator reserve. Thus, insulin resistance is not uniformly determined by basal blood flow or flow reserve. However, defects in regional flow distribution or in dynamic flow responses may alter insulin action. Microvascular rarefaction may contribute to insulin resistance in hypertensive patients by increasing diffusion distance for insulin to sites of action. The independent role of capillary density is unknown, since it correlates with muscle fiber type. Furthermore, in the absence of significant kinetic differences for insulin's multiple actions in skeletal muscle, structural vascular abnormalities would likely cause global defects rather than specific abnormalities in non-oxidative glucose disposal. Theories linking neurohumoral, hemodynamic and microvascular abnormalities in hypertension to insulin resistance are intriguing but unproven. Since insulin resistance has important implications in human disease, further research on mechanisms of this resistance is important.

Salt loads raise plasma fatty acids and lower insulin

Some fatty acids are potent inhibitors of angiotensin binding and aldosterone production in adrenal glomerulosa cells and thereby may be involved in regulating salt and water balance. To study the possible regulation of fatty acids by salt, we measured the levels of unesterified fatty acids in plasma from patients subjected to extremes of dietary salt intake and saline infusion. Insulin and catecholamines, two known regulators of plasma fatty acids, also were measured. Infusion of 2 l saline over 4 hours caused the levels of most unesterified fatty acids to rise. Total unesterified fatty acids rose 60-100%. A high salt diet caused a smaller rise in total unesterified fatty acids (approximately 33%). In both instances, oleic and palmitoleic acids showed the greatest proportionate increases, whereas stearic acid was relatively unaffected. When salt loads were administered by either intravenous or dietary routes, plasma insulin levels fell by approximately 50%. Plasma norepinephrine increased after saline infusion but not during a high salt diet. Postsaline levels of fatty acids correlated inversely with postsaline levels of aldosterone, supporting a possible role for fatty acids as physiological regulators of the adrenal glomerulosa. A rise in plasma fatty acids and fall in insulin in response to salt loads could act in concert to increase sodium excretion, constituting a physiological mechanism contributing to salt and water balance.

Neurohumoral and metabolic effects of short-term dietary NaCl restriction in men. Relationship to salt-sensitivity status

Published observations suggest that not everyone benefits from severe dietary NaCl restriction, since blood pressure responses appear heterogeneous and adverse metabolic effects may occur. We studied the cardiovascular, neurohumoral, and metabolic effects of 7 day periods of 20 v 200 mEq/day NaCl diets in 27 men. Twelve subjects were salt sensitive (SS), defined as mean intraarterial pressure (MAP, mm Hg) during high NaCl greater than or equal to 5% above MAP on low NaCl. Eleven subjects were salt resistant (SR), defined as MAP during the low NaCl phase greater than or equal to MAP during the high NaCl phase. The SR subset had a tendency to greater neurohumoral activity, assessed by changes in mean values for plasma norepinephrine (NE, P = .12) and plasma renin activity (PRA, P less than .001) on the low v high NaCl diet. In SR subjects the low v high NaCl diet also raised mean values for creatinine (P = .03), uric acid (P = .001), and low density cholesterol (LDL-C, P = .03), but not fasting insulin (P = .15). In SS subjects, the low v high NaCl diet did not raise NE (P = .35), although the PRA was greater (P = .002). Among SS subjects, mean values for uric acid (P = .005) and insulin (P = .02) were greater during the low v high NaCl phase, while creatinine (P = .15) and LDL-C (P = .67) were not different. The data suggest that severe, short-term NaCl restriction can be undesirable, especially in SR subjects, since potentially adverse neurohumoral and metabolic changes are not counterbalanced by the benefits of a lower MAP.

Comparative effects of overweight on cardiovascular risk in younger versus older men

The relation of age and body mass index (BMI) to atherosclerosis risk factors was examined in 357 men. Older (greater than or equal to 45 years) men had higher (p less than 0.01) systolic and diastolic blood pressures, fasting cholesterol and glucose, and 1-hour glucose and insulin levels. Fasting insulin and triglyceride levels were not significantly different between the 2 age groups. Although older men (n = 170) had greater values for several risk factors, overweight (BMI greater than 25.5 kg/m2) increased risk factors more in men younger than 45 years (n = 187). In younger men, those with higher BMIs had a greater prevalence, respectively, of blood pressure greater than 140/90 mm Hg (35.2 vs 11.2%, p less than 0.0001), cholesterol greater than 200 mg/dl (53.5 vs 29.3%, p less than 0.001), fasting triglycerides greater than 150 mg/dl (38.0 vs 10.3%, p less than 0.0001), 1-hour glucose greater than 160 mg/dl (15.5 vs 5.2%, p less than 0.05), fasting insulin greater than 11 microU/ml (28.2 vs 5.2%, p less than 0.0001), and 1-hour insulin greater than 110 microU/ml (28.2 vs 9.5%, p less than 0.001). In contrast, among older men, the prevalence of elevated blood pressure, cholesterol, triglycerides and glucose values was not significantly greater in the subgroup with high BMI. However, elevations of fasting (19.6 vs 6.4%, p less than 0.05) and 1-hour insulin (29.3 vs 11.5%, p less than 0.01) values were more common among older men with higher BMIs.(ABSTRACT TRUNCATED AT 250 WORDS)

Sensitization of human alpha 1- and alpha 2-adrenergic venous responses by guanadrel sulfate

The alpha 1- and alpha 2-adrenergic venoconstriction in dorsal hand veins of normal subjects was determined by infusion of phenylephrine or clonidine. Oral administration of prazosin reduced the constriction response to phenylephrine but not to clonidine. Subjects were treated for 3 weeks in a randomized crossover design with placebo or guanadrel sulfate. Guanadrel reduced sympathetic tone (i.e., plasma norepinephrine and norepinephrine release rate), whereas venous responses to phenylephrine and clonidine were both augmented during guanadrel treatment. The effect on phenylephrine responses was primarily attributable to a decrease in the median effective concentration with a small increase in maximum response. Clonidine showed a markedly increased maximum response with a small increase in the median effective concentration. Platelet alpha 2-adrenergic receptors increased slightly but there was no change in the amount of platelet pertussis toxin substrate during guanadrel treatment. Thus reduction in sympathetic tone in normal young men results in increased venous responses to both alpha 1- and alpha 2-agonists.

Artefacts in measurement of blood pressure and lack of target organ involvement in the assessment of patients with treatment-resistant hypertension

OBJECTIVE

To determine the relative importance of factors known to cause therapy-resistant hypertension, and to derive an efficient approach to the evaluation of this problem in clinical practice.

DESIGN

Consecutive sample.

SETTING

University hospital hypertension clinic and clinical research center.

PATIENTS

Fifteen patients referred for management of refractory hypertension and found to have a seated diastolic blood pressure greater than 95 mm Hg while taking a standard dose of hydrochlorothiazide, propranolol, and hydralazine or its equivalent for at least 4 weeks.

MEASUREMENTS AND MAIN RESULTS

Seven patients (group 1) had normal, resting mean intra-arterial blood pressure (mean pressure less than 107 mm Hg) and eight had elevated pressure (group 2). Patients in group 1 had minimal or not target organ involvement whereas those in group 2 had higher minimum vascular resistance by forearm plethysmography and greater interventricular septal wall thickness. Factors contributing to resistant hypertension, particularly in group 1, were "office hypertension" (clinic systolic blood pressure at least 20 mm Hg higher than home systolic blood pressure), pseudohypertension (cuff diastolic blood pressure at least 15 mm Hg higher than simultaneously determined intra-arterial pressure), and "cuff-inflation hypertension" (intra-arterial diastolic blood pressure rise of at least 15 mm Hg during cuff inflation).

CONCLUSION

Home blood pressure monitoring and echocardiography are recommended as initial steps in the evaluation of patients with resistant hypertension. Intra-arterial blood pressure measurement is particularly helpful in patients with resistant hypertension who do not have office hypertension yet have normal septal thickness on echocardiography.

Neurogenic mechanisms initiating essential hypertension

Evidence for increased sympathetic drive, as assessed both by measurements of plasma norepinephrine and by studies of tritiated norepinephrine kinetics, is most frequently obtained in young hypertensive patients. During the initial phases of hypertension, the increased sympathetic drive may persistently elevate arterial pressure through effects on the heart, the blood vessels, and the kidneys. In some patients, signs of a hyperkinetic circulation--including elevated heart rate and, less often, high cardiac output--predominate. In others, elevated vascular resistance, reflecting increased alpha-adrenergic tone, is the principal hemodynamic aberration. Even in patients with high cardiac output, a relative increase of vascular alpha-adrenergic tone accounts for their higher blood pressure. Increased sympathetic drive to the kidneys diminishes the efficiency of pressure diuresis, which is designed to restore normal arterial pressure. Although increased plasma norepinephrine levels are not consistently observed among older hypertensive patients compared with age-matched controls, neurogenic hypertension is not only a temporary event. In fact, tachycardia, which is neutrogenically mediated, doubles the risk of sustained hypertension later in life. The precise sequence of events in the transition from a principally neurogenic hypertension early in life to a predominantly nonneurogenic hypertension later in life is not known, although it likely includes decreased beta-receptor sensitivity with consequently reduced tachycardia and beta-mediated vasodilation. Functional diminution in endothelium-dependent vasodilation may augment sensitivity to vasoconstrictors such as norepinephrine and serotonin. Moreover, structural vascular changes nonspecifically enhance vascular reactivity to all vasoactive compounds and may provide a more permanent basis for altered pressure diuresis. Thus, hypertension initiated predominantly by neurogenic mechanisms could be sustained later without excessive sympathetic drive.

Increased beta-adrenergic tone enhances arterial compliance in hyperkinetic borderline hypertension

Arterial compliance, assessed by the stroke volume-pulse pressure relationship, was measured in 32 patients with a high cardiac output together with borderline hypertension and 26 control subjects with normokinetic borderline hypertension. Measurements were obtained in the supine position both before and after 0.2 mg/kg intravenous propranolol. Baseline arterial compliance was significantly greater in the hyperkinetic group (P less than 0.01). The inter-group difference was no longer significant after the administration of propranolol, since compliance tended to increase in the normokinetic group and decrease in the hyperkinetic group. Therefore, disparities in vascular beta-adrenergic tone between hyperkinetic and normokinetic borderline hypertensive patients probably contribute to group differences in arterial compliance.

Regional hemodynamic abnormalities in overweight men. Focus on alpha-adrenergic vascular responses

Blood pressure, forearm hemodynamic data, and red blood cell (RBC) cation transport measurements were obtained in 27 men with body mass indexes (BMI) greater than 26.6 kg/m2 and 21 men with BMI less than 26.6 kg/m2. Subjects with higher BMI had significantly higher systolic and diastolic pressure measured both noninvasively and invasively, P less than .02-.001. Baseline forearm blood flow (FABF) was substantially higher in the heavier subjects, P less than .02, whereas forearm vascular resistance (FAVR) levels were not different, P greater than .10. Despite the higher baseline forearm blood flow, the high BMI group displayed a greater rise in flow, P less than .01, in response to a regional phentolamine infusion, an index of vascular alpha-tone. Results of multiple regression analysis suggested that overweight was indirectly correlated with vascular alpha-tone via a relationship with arterial plasma norepinephrine concentration, a marker of sympathetic drive, and bumetanide-sensitive RBC Na+-K+ cotransport activity. These data indicate that in overweight men (1) higher FABF is not fully counter-balanced by lower FAVR; (2) increased vascular alpha-tone contributes to the altered flow-resistance relationship and thereby to the elevated blood pressure; and (3) greater sympathetic drive and Na+-K+ cotransport activity may explain the elevated vascular alpha-tone.

Sustained saline-induced secretion of atrial natriuretic hormone is not maintained by atrial stretch

To determine the relationship between changes in right and left atrial pressures and changes in plasma levels of immunoreactive atrial natriuretic hormone (ANH), 11 normal men were studied during rapid infusion of 1 L 150 mmol/L NaCl. Right atrial pressure, pulmonary capillary wedge pressure, and peripheral plasma ANH levels were measured serially for 30 min in 6 men and for 90 min in 5 men. There were significant increases in right atrial pressure at 15 and 30 min [4.8 +/- 0.4 (+/- SE) vs. 8.9 +/- 0.3 and 6.5 +/- 0.4 mm Hg; P less than 0.001] and in pulmonary capillary wedge pressure at the same time intervals [8.5 +/- 0.6 vs. 13.6 +/- 0.8 (P less than 0.001) and 10.6 +/- 0.6 mm Hg (P less than 0.01)]. Plasma ANH increased significantly at 30 min (11.5 +/- 2.4 vs. 20.6 +/- 3.0 pmol/L; P less than 0.001). Regression analysis revealed no correlation between the increase in plasma ANH at 30 min and the increase in either right atrial or pulmonary capillary wedge pressure at 15 min (r = 0.46; P = 0.16 for right atrial pressure; r = 0.02; P = 0.96 for pulmonary capillary wedge pressure). In the 5 men studied for 90 min, right atrial and pulmonary capillary wedge pressures returned to basal values by 45 min. In contrast, plasma ANH levels remained significantly elevated at all sampling times from 30-90 min (P less than 0.001); the peak value occurred at 75 min. We conclude that ANH secretion persists after saline infusion and that the cause of this prolonged secretion is not atrial stretch.

Erythrocyte water, Na+-K+ cotransport, and forearm vascular function in humans

We examined the relationships between erythrocyte (RBC) composition (Na+, K+, and water content) and ouabain-insensitive transports (Na+-K+ cotransport, Li+-Na+ countertransport) and forearm vascular hemodynamics under standardized basal conditions and during vasoconstriction (intra-arterial infusion of graded doses of norepinephrine and angiotensin II) and vasodilation (intra-arterial phentolamine and postischemic exercise). RBC water content correlated positively and significantly (r = 0.53, p = 0.001) with minimum forearm vascular resistance, a measure of vascular structural change, and negatively with maximal forearm blood flow (r = -0.55, p less than 0.001). Similar correlations with forearm vascular resistance and blood flow were observed under all experimental conditions. RBC Na+-K+ cotransport correlated positively and significantly (r = 0.43, p = 0.01) with the change in forearm blood flow produced by phentolamine, a functional measure of alpha-adrenergic tone, and was as strong an independent predictor of phentolamine-induced blood flow change as was arterial norepinephrine concentration. RBC Na+-K+ cotransport was also significantly positively correlated with residual forearm blood flow and resistance after phentolamine administration, where nonadrenergic influences predominate. RBC water correlated negatively with Li+-Na+ countertransport (r = -0.33, p less than 0.05) and Na+-K+ cotransport (r = -0.44, p less than 0.01). We propose that RBC water is a marker for a vascular structural property that contributes to vascular reactivity. RBC Na+-K+ cotransport seems to relate most strongly to the sympathetically mediated control of forearm blood flow and may also be linked to the intrinsic myogenic tone of the forearm vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)

Red blood cell Li+-Na+ countertransport, Na+-K+ cotransport, and the hemodynamics of hypertension

Red blood cell Li+-Na+ countertransport and Na+-K+ cotransport activities, home blood pressure, invasive systemic hemodynamics, and limb venous compliance were measured in 65 white men (23 normotensive, 22 borderline hypertensive, and 20 mild essential hypertensive subjects). Li+-Na+ countertransport activity was positively and significantly correlated with subject-determined home systolic blood pressure (r = 0.31, p less than 0.02) and with directly measured systolic (r = 0.29, p less than 0.02) and diastolic (r = 0.27, p less than 0.03) blood pressures in the hemodynamic laboratory, independent of potential confounding variables. Analysis of the hemodynamic determinants of blood pressure revealed a significant positive correlation of countertransport with vascular resistance (r = 0.30, p less than 0.02) but not with cardiac output or cardiac index. High red blood cell Na+-K+ cotransport activity was not independently associated with hypertension or with a characteristic hemodynamic pattern but was related to decreased venous compliance. Red blood cell Li+-Na+ countertransport deserves further study as a marker for the genetic substrate of human essential hypertension. Red cell Na+-K+ cotransport may be altered secondarily by factors related to high blood pressure and seems to be a valid marker for abnormalities of the venous system in hypertension.

Decreased venous distensibility and reduced renin responsiveness in hypertension

Abnormalities of renin release and of venous distensibility have been described in essential hypertension. We have postulated that decreased venous distensibility could contribute to the blunted renin response to upright posture in hypertension. Stiffer veins might prevent venous pooling in the lower extremities, which in turn might affect the stretch on cardiopulmonary mechanoreceptors, thereby influencing the reflex release of renin. We investigated this hypothesis in the present study of 47 patients with mild hypertension and 26 (male) healthy volunteers of similar age and race. To induce isolated changes in the stretch of cardiopulmonary mechanoreceptors, systemic hemodynamics were measured before and after thigh cuff inflation at 60 mm Hg for 30 minutes. Cardiac output was determined by dye dilution. Before the intervention, variable thigh cuff pressures were used to measure venous pressure volume with mercury-in-Silastic strain gauge plethysmography. Venous distensibility was diminished in hypertension, as evidenced by a shift in the calf venous volume/pressure curve toward the pressure axis. During the 30-minute experiment, the hypertensive subjects had less blood pooling in their legs in response to thigh cuff inflation, as compared with the control subjects. The hemodynamic and renin responses reflected this diminished effect of thigh cuff inflation on venous return. The smaller increase of renin in the hypertensive group was associated with a smaller fall in the stroke index and right atrial pressure; the reflex rise in the heart rate was also decreased. By pooling blood in the lower extremities, thigh cuff inflation simulates upright posture. It is customary to classify the renin status of hypertensive patients according to the renin response to upright posture.(ABSTRACT TRUNCATED AT 250 WORDS)

Anger and anxiety in borderline hypertension

Psychologic studies of hypertension have usually focused on the relationship of anger and anxiety to clinic or laboratory blood pressure (BP). Yet, average blood pressure outside of the clinic has proven to be a more important predictor of hypertensive complications. In this study, we have isolated two groups of borderline hypertensives--one group that maintained high blood pressure outside of the clinic and another whose average BP returned to normal at home. All 33 subjects were given psychometric instruments for measuring various components of anger and anxiety: Spielberger's State-Trait Personality Inventory, the Anger Expression Scale, and the State Anger Reaction Scale. The high home BP group reported greater intensity of anger, although they suppressed their expression of anger to a greater extent. The groups did not differ in anxiety. Also, blood pressure variability was not different between the two groups. It is suggested that the psychologic differences found in the group of higher-risk borderline hypertensives may, through autonomic arousal, contribute to the later development of established hypertension.

Role of cardiovascular receptors on the neural regulation of renin release in normal men

Although factors influencing renin release have been studied extensively, one facet of renin release remains controversial, namely, neural regulation by arterial high-pressure receptors and cardiopulmonary low-pressure receptors. We therefore designed four studies to investigate systematically the separate and combined effects of unloading (decreased stretch) high- and low-pressure receptors on renin release in normal men. Selective unloading of cardiopulmonary receptors was induced by impeding the venous return with tourniquets around the thighs. A predominant unloading of arterial (carotid) baroreceptors was elicited with upright posture and simultaneously preventing the venous pooling in the legs. Unloading of both high- and low-pressure receptors was achieved by both upright standing and tilting. During postural experiments to predominantly unload arterial baroreceptors, the heart rate increased and the veins constricted, but renin failed to increase. The postural increase of renin occurred only if we allowed venous pooling in the legs. Selective unloading of cardiopulmonary receptors elicited substantial increases of renin. When both the cardiopulmonary and arterial baroreceptors were unloaded, renin increased more than with isolated unloading of cardiopulmonary receptors. We conclude that: 1) in intact humans it is possible to demonstrate an independent role of cardiopulmonary receptors in the control of renin release; 2) there Is evidence for interaction between the two receptor systems in renin control; but 3) an independent role for arterial baroreceptors in the control of renin release could not be demonstrated under the conditions of this experiment.