The influence of physical activity on the variability of ambulatory blood pressure

The aim of this study was to assess the contribution of physical activity levels to blood pressure (BP) variability, and to assess the effect age, gender, body mass index, and use of antihypertensive medications on this relationship. We simultaneously monitored 24-h ambulatory BP by automated recorder and activity by actigraphy in 431 patients. Mean activity scores for the 5, 10, 15, and 20 min preceding each BP measurement were calculated, and BP and heart rate were related to these variables using linear mixed model regression. Various patient characteristics were added to the mixed model as covariates. Patients were heterogeneous in age (48 +/- 13 years), sex (49% men), and average 24-h BP (132/81 +/- 15/10 mm Hg). Mean daytime activity level was 44 +/- 15 U. During the daytime, systolic BP (r = 0.33), diastolic BP (r = 0.29), and heart rate (r = 0.42) correlated best with the average activity for the 15 min preceding each measurement (P < .001). Variance was very high, with activity explaining from 0% to 62% of BP variability for different individuals. Men and the obese had a greater reactivity of systolic BP to activity; older patients and those on antihypertensive therapy had a lower reactivity of heart rate. Blood pressure level is significantly associated with physical activity, but the percentage of variance of BP explained by physical activity varies greatly between individuals. Correlation is strongest between BP and average activity integrated over the previous 15 min. Much of the variance in blood pressure remains unexplained.

Nocturnal blood pressure dipping: a consequence of diurnal physical activity blipping?

This study was designed to describe the interaction between physical activity (PA), quantified objectively by electronic activity monitors, and ambulatory blood pressure (ABP), and to test the hypothesis that modifying daily PA can effect significant changes in the diurnal variation in blood pressure and may result in altered dipping/nondipping status of an individual. Initially, 70 individuals underwent simultaneous ABP and electronic activity monitoring (actigraph devices manufactured by Gaewihler Electronics, Switzerland) over a 24-h period. Then, in a prospective study, the dipping/nondipping status of 43 subjects was assessed using ABP recorded over two 24-h periods of differing activity levels. Of the 70 subjects (age 49 +/- 11 years, 42 male) the diurnal variation in systolic blood pressure (20 +/- 12%, step-up from night [120 +/- 12 mm Hg] to day [144 +/- 13 mm Hg]) and diurnal variation in PA score (increment from sleep, 44 +/- 17 units) correlated significantly (R2 = 0.29; P < .05). Of the 43 subjects who underwent ABP monitoring on a more active day, four had a nondipping BP profile; 12 of these same 43 subjects had a nondipping BP profile when monitored on a less active day (chi2 = 4.9; P < .05). These results provide a quantitative description of the contribution of PA, including the sleep/awake status, to blood pressure variation in a group of normotensive and hypertensive individuals. The magnitude of this effect underscores the importance of interpreting 24-h ABP data only in the presence of adequately quantified activity data.

Electronic activity-monitor-derived sleeping and awake times and diurnal variation of blood pressure

BACKGROUND

Results of a number of studies have indicated that target-organ damage is more pronounced in non-dippers, those in whom the blood pressure falls by less than 10% with the onset of sleep, than it is in dippers with comparable clinic blood pressures. However, the standard use of arbitrarily defined daytime and night-time periods, rather than precise estimates of sleeping time and awake time, could limit the accuracy of estimates of diurnal variation of blood pressure and hence of dipping status.

DESIGN AND METHODS

In this study of 102 consecutive patients undergoing ambulatory blood pressure monitoring we compared activity-derived estimates of sleeping and awake blood pressures using electronic activity monitoring and diary records with estimates determined using pre-defined day and night-time periods. The dipping/non-dipping status of each subject was assessed using these three different techniques for defining the awake/asleep time periods.

RESULTS

The sleeping/awake times based on the activity monitor, diary and default data were 2356 h+/-55 min/0754 h+/-50 min, 2326 h+/-61 min/0722 h+/-72 min and 2300 h and 0700 h respectively. The percentage systolic/diastolic falls in blood pressure were 18+/-6/18+/-7% with six non-dippers (activity-monitor-derived data), 16+/-6/17+/-8% and 12 non-dippers (diary data) and 13+/-7/15+/-7% and 21 non-dippers (using the pre-set daytime and night-time periods).

DISCUSSION

Results of this study demonstrate that the extent of the diurnal variation in blood pressure (and hence dipping status) can differ depending on the technique used to define periods of wakefulness and sleep.

Dopamine: a role in the pathogenesis and treatment of hypertension

The catecholamine dopamine (DA), activates two distinct classes of DA-specific receptors in the cardiovascular system and kidney--each capable of influencing systemic blood pressure. D1 receptors on vascular smooth muscle cells mediate vasodilation, while on renal tubular cells they modulate sodium excretion. D2 receptors on pre-synaptic nerve terminals influence noradrenaline release and, consequently, heart rate and vascular resistance. Activation of both, by low dose DA lowers blood pressure. While DA also binds to alpha- and beta-adrenoceptors, selective agonists at both DA receptor classes have been studied in the treatment of hypertension. An unfavourable side-effect profile (largely nausea and orthostasis) have precluded wide use of D2 agonists. In contrast, the D1 selective agonist fenoldopam has been licensed for the parenteral treatment of severe hypertension. Apart from inducing systemic vasodilation it induces a diuresis and natriuresis, enhanced renal blood flow, and a small increment in glomerular filtration rate. Evidence is emerging that abnormalities in DA production, or in signal transduction of the D1 receptor in renal proximal tubules, may result in salt retention and high blood pressure in some humans and in several animal models of hypertension.

Physical activity level is an independent predictor of the diurnal variation in blood pressure

OBJECTIVE

The aim of this study was to define the relationship between physical activity and the magnitude of the percentage fall in blood pressure at night (nocturnal dip).

METHODS

We simultaneously monitored 24-h ambulatory blood pressure and measured physical activity by actigraphy in 434 patients. Blood pressure was measured every 20 min; the actigraph integrated an activity score every 10 s. Mean daytime and night-time activity were calculated from mean scores for the 15 min preceding each blood pressure measurement. Nocturnal dip in systolic and diastolic blood pressure (SBP and DBP) were regressed on mean (log-transformed) daytime activity. Mean night-time activity, age, gender, smoking status, body mass index (BMI) and clinic blood pressure were added into a multiple linear regression.

RESULTS

The patient group was heterogeneous in age, gender and mean 24-h blood pressure. Mean daytime activity level was significantly and positively associated with the magnitude of the nocturnal dip in both SBP and DBP. Increased night-time activity was significantly associated with a smaller nocturnal dip. Older patients had a smaller nocturnal dip per log unit daytime activity. Nocturnal dip in SBP was greater in males, and smaller in those taking antihypertensive medications. Smoking, BMI and clinical blood pressure level were not associated with the extent of the nocturnal dip after adjustment for other factors.

CONCLUSIONS

Daytime and night-time physical activity levels are independently and significantly predictive of the magnitude of the nocturnal dip in blood pressure. Variation in activity may confound interpretation of 24-h ambulatory blood pressure monitoring, and contribute to the poor reproducibility of dipper status.

Ambulatory blood pressure monitoring: which arm?

To determine the effects of routinely selecting the nondominant arm for ambulatory blood pressure monitoring (ABPM) on estimates of patients' blood pressure (BP) and to evaluate the practise of using manual BP from one arm and ambulatory BP from the other on the estimation of white coat effect (WCE), an observational study was conducted in 10 volunteers, exhibiting an interarm resting clinic systolic BP (SBP) difference > or =10 mm Hg. The main outcome measures were: (i) average ambulatory SBP measured on right and left arm simultaneously during 24 h, and (ii) estimate of WCE derived, by current practise, as the difference between the referral clinic BP (the higher of the manual readings from both arms) and ambulatory non-dominant arm BP, contrasted with the WCE calculated as the difference between clinic and ambulatory readings from the same arm (the arm with the higher manual readings). The supine referral clinic SBP was 16+/-6 mm Hg higher in the right compared with the left arm. Average 24 h ambulatory SBP was 6+/-7 mm Hg higher in the right arm (range +17 to -3 mm Hg), P = 0.025. Diastolic BP measurements mirrored the systolic findings. One-third of the WCE, estimated by current practise, could be attributed to inconsistency in the choice of arm for BP measurement. Thus, inconsistency in the selection of arms for BP measurement, by different techniques, may confound estimation of patients' cardiovascular morbidity risk.

Short- and long-term outcome of total parathyroidectomy with immediate autografting versus subtotal parathyroidectomy in patients with end-stage renal disease

A retrospective study was performed in 36 patients with end-stage renal disease (ESRD) comparing total parathyroidectomy followed by immediate autografting into the forearm (total PTX + IA) with parathyroidectomy (subtotal PTX) over a five-year period. Twenty-eight patients underwent subtotal PTX and 8 had total PTX + IA. The two surgical methods were evaluated with respect to preoperative severity of hyperparathyroidism, perioperative morbidity, and the incidence of recurrent hyperparathyroidism. Eleven patients in total (30.6%) developed recurrent hyperparathyroidism; 2/8 (25%) in the total PTX + IA group compared to 9/28 (32.1%) in the subtotal PTX group (p = 0.699). The median time to recurrence was longer in the total PTX + IA group (39 vs. 16 months), and the median long-term postoperative PTH value was lower (81 vs. 199 ng/l), but these differences did not reach statistical significance. In conclusion, the incidence of recurrent hyperparathyroidism is high regardless of surgical modality. However, total PTX + IA may produce more favorable results with respect to median postoperative PTH level and time to recurrence.

The design of a prospective study of Pravastatin in the Elderly at Risk (PROSPER). PROSPER Study Group. PROspective Study of Pravastatin in the Elderly at Risk

The PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) is a randomized, double-blind, placebo-controlled trial designed to test the hypothesis that treatment with pravastatin will diminish risk of subsequent major vascular events in a cohort of men and women (70 to 82 years old) with preexisting vascular disease or significant risk of developing this condition. Five thousand eight hundred four men and women in addition to receiving advice on diet and smoking, have been randomized equally to treatment with 40 mg pravastatin/day or matching placebo in 3 centers (Cork, Ireland, Glasgow, Scotland, and Leiden, The Netherlands). Following an average 3.5-year intervention period, a primary assessment will be made of the influence of this therapy on major vascular events (a combination of coronary heart disease, death, nonfatal myocardial infarction, and fatal and nonfatal stroke). A number of additional analyses will also be conducted on the individual components of the primary end point, on men, on women, and on subjects with and without previous evidence of vascular disease. Finally, an assessment will be made of the effects of treatment on cognitive function, disability, hospitalization or institutionalization, vascular mortality, and all-cause mortality.

Biochemical characterization of a Dictyostelium myosin II heavy-chain phosphatase that promotes filament assembly

In Dictyostelium cells, myosin II is found as cytosolic nonassembled monomers and cytoskeletal bipolar filaments. It is thought that the phosphorylation state of three threonine residues in the tail of myosin II heavy chain regulates the molecular motor's assembly state and localization. Phosphorylation of the myosin heavy chain at threonine residues 1823, 1833 and 2029 is responsible for maintaining myosin in the nonassembled state, and subsequent dephosphorylation of these residues is a prerequisite for assembly into the cytoskeleton. We report here the characterization of myosin heavy-chain phosphatase activities in Dictyostelium utilizing myosin II phosphorylated by myosin heavy-chain kinase A as a substrate. One of the myosin heavy-chain phosphatase activities was identified as protein phosphatase 2A and the purified holoenzyme was composed of a 37-kDa catalytic subunit, a 65-kDa A subunit and a 55-kDa B subunit. The protein phosphatase 2A holoenzyme displays two orders of magnitude higher activity towards myosin phosphorylated on the heavy chains than it does towards myosin phosphorylated on the regulatory light chains, consistent with a role in the control of filament assembly. The purified myosin heavy-chain phosphatase activity promotes bipolar filament assembly in vitro via dephosphorylation of the myosin heavy chain. This system should provide a valuable model for studying the regulation and localization of protein phosphatase 2A in the context of cytoskeletal reorganization.

Molecular characterization and immunolocalization of Dictyostelium discoideum protein phosphatase 2A

Protein phosphatase 2A (PP2A) was previously purified from Dictyostelium and biochemically characterized. The purified PP2A holoenzyme was composed of a 37 kDa catalytic 'C-subunit', a 65 kDa 'A-subunit' and a 55 kDa 'B-subunit'. We report here the characterization of the genes encoding the Dictyostelium PP2A subunits as well as the immunolocalization of the PP2A subunits in Dictyostelium. The cDNAs encoding the B- and C-subunits were isolated from a Dictyostelium library and the deduced amino acid sequences reveal strong conservation with the mammalian PP2A homologues. Southern blot analysis suggests that each of the PP2A subunit genes is present in a single copy. The PP2A subunits were localized mainly to the cytosol in Dictyostelium cells. However, immunofluorescence confocal microscopy demonstrates that the B-subunit of PP2A is highly enriched in centrosomes, suggesting a potential role for this PP2A regulatory subunit in the centrosomal function.

Opioid antagonist modulation of ischaemia-induced ventricular arrhythmias: a peripheral mechanism

Ventricular arrhythmias are an important cause of death after myocardial ischaemia. Animal studies have generated conflicting data on the potentiating or attenuating effects of opioid agonists and antagonists on cardiac rhythm during acute myocardial ischaemia and coronary artery reperfusion. Whether these effects of opioid antagonists are mediated by central or peripheral nervous system mechanisms remains unclear. We examined (a) the effects of peripheral opioid receptor blockade on ischaemia-induced arrhythmia by using methylnaltrexone (MNTX), a novel quaternary derivative of naltrexone (NTX) that does not cross the blood-brain barrier, and (b) whether MNTX would modulate morphine effects during acute coronary artery ligation and reperfusion in the rabbit. The incidence and severity of cardiac arrhythmias were assessed during 40 min of coronary artery occlusion and reperfusion and summarised in an arrhythmia score (AS). MNTX reduced the incidence of ventricular fibrillation (VF) and arrhythmia score during coronary artery occlusion when compared with vehicle (p < 0.05). Naltrexone reduced the incidence of VF (p < 0.05). Although morphine alone had no significant effects, its coadministration blunted the antiarrhythmic properties of MNTX. The data suggest that blockade of opiate receptors outside the central nervous system may protect against ischaemia-induced arrhythmias.

A comparison of the effects of tramadol and morphine on gastric emptying in man

In a previous study using an electrical bioimpedance technique and the paracetamol absorption test, we demonstrated that 0.09 mg.kg-1 of morphine delayed gastric emptying in healthy human volunteers. The aim of this study was to investigate whether analgesic doses of tramadol would cause a delay in gastric emptying similar to conventional opioids. Using the same volunteers and techniques as in our previous study, placebo or tramadol (1 mg.kg-1) was given in a randomised, double-blinded, cross-over placebo-controlled study. Gastric emptying was measured concurrently by a noninvasive epigastric bioimpedance technique and by the paracetamol absorption test. After the ingestion of 500 ml of deionised water plus paracetamol 1.5 g, the mean (SEM) time taken for gastric volume to decrease to 50% (t0.5) was recorded. No difference in gastric emptying rates (t0.5) between placebo, 7.7 (1 min), and tramadol, 9.5 (2 min), was noted. In our previous study, morphine prolonged t0.5 to 21 (3) min (p < 0.03). The maximum concentration and area under the curve of serum paracetamol concentrations following morphine were significantly different from placebo (p < 0.05) and tramadol (p < 0.05). We conclude that tramadol at a dose of 1 mg.kg-1 does not delay gastric emptying in humans.

Opioid-induced delay in gastric emptying: a peripheral mechanism in humans

BACKGROUND

Opioids delay gastric emptying, which in turn may increase the risk of vomiting and pulmonary aspiration. Naloxone reverses this opiate action on gastric emptying, but it is not known whether this effect in humans is mediated by central or peripheral opiate antagonism. The importance of peripheral opioid receptor antagonism in modulating opioid-induced delay in gastric emptying was evaluated using methylnaltrexone, a quaternary derivative of the opiate antagonist naltrexone, which does not cross the blood-brain barrier.

METHODS

In a randomized, double-blind, crossover placebo-controlled study, 11 healthy volunteers were given either placebo (saline), 0.09 mg/kg morphine, or 0.09 mg/kg morphine plus 0.3 mg/kg methylnaltrexone on three separate occasions before ingesting 500 ml deionized water. The rate of gastric emptying was measured by two methods: a noninvasive epigastric bioimpedance technique and the acetaminophen absorption test.

RESULTS

The epigastric bioimpedance technique was sufficiently sensitive to detect opioid-induced changes in the rate of gastric emptying. The mean +/- SD time taken for the gastric volume to decrease to 50% (t0.5) after placebo was 5.5 +/- 2.1 min. Morphine prolonged gastric emptying to (t0.5) of 21 +/- 9.0 min (P < 0.03). Methylnaltrexone given concomitantly with morphine reversed the morphine-induced delay in gastric emptying to a t0.5 of 7.4 +/- 3.0 (P < 0.04). Maximum concentrations and area under the concentration curve from 0 to 90 min of serum acetaminophen concentrations after morphine were significantly different from placebo and morphine administered concomitantly with methylnaltrexone (P < 0.05). No difference in maximum concentration or area under the concentration curve from 0 to 90 min was noted between placebo and methylnaltrexone coadministered with morphine.

CONCLUSIONS

The attenuation of morphine-induced delay in gastric emptying by methylnaltrexone suggests that the opioid effect is mediated outside the central nervous system. Methylnaltrexone may have the potential to decrease the side effects of opioid medications, which are mediated peripherally, while maintaining the central analgesia effect of the opioid.

Supervised drug administration in patients with refractory hypertension unmasking noncompliance

Noncompliance with medication is common, particularly in asymptomatic conditions such as hypertension that require long-term treatment, and is often unsuspected. We describe two patients with refractory hypertension in whom noncompliance was confirmed by a precipitous fall in blood pressure when antihypertensive medications were given under direct supervision.

Mapping of the novel protein kinase catalytic domain of Dictyostelium myosin II heavy chain kinase A

Myosin heavy chain kinase A (MHCK A) in Dictyostelium was identified as a biochemical activity that phosphorylates threonine residues in the myosin II tail domain and regulates myosin filament assembly. The catalytic domain of MHCK A has now been mapped through the functional characterization of a series of MHCK A truncation mutants expressed in Escherichia coli. A recombinant protein comprising the central nonrepetitive domain of MHCK A (residues 552-841) was isolated in a soluble form and shown to phosphorylate Dictyostelium myosin II, myelin basic protein, and a synthetic peptide substrate. The functionally mapped catalytic domain of MHCK A shows no detectable sequence similarity to known classes of eukaryotic protein kinases but shares substantial sequence similarity with a transcribed Caenorhabditis elegans gene and with the mammalian elongation factor-2 kinase (calcium/calmodulin-dependent protein kinase III). We suggest that MHCK A represents the prototype for a novel, widely occurring protein kinase family.

Factors confounding assessment of ambulatory blood pressure monitors, studied during formal evaluation of the Tycos Quiet-Trak

The credibility of studies assessing ambulatory blood pressure monitoring (ABPM) devices will be enhanced by minimizing opportunities to manipulate the outcome through biased selection of patient volunteers, and by insuring that participants are representative of the target patient population. While subjecting the Welch Allyn Quiet-Trak to the British Hypertension Society (BHS) protocol, we examined the extent to which certain candidate characteristics might influence device assessment. The Quiet-Trak achieved an A grade overall. During its field testing, daytime physical activity measured with a wrist-mounted, piezoelectric accelerometer, influenced significantly the rate of measurement rejection. The tertiles of subjects with highest and lowest levels of daytime physical activity (64 +/- 16 and 35 +/- 10 activity units; P < .001) exhibited significantly different measurement rejection rates (10 +/- 3 and 3 +/- 2 daytime rejects; P < .001)). Most rejected readings occurred during episodes of high physical activity. During static evaluation (Phase V), the level of systolic BP influenced the accuracy of diastolic BP estimation; above 190 mm Hg systolic BP, estimates of diastolic BP differed significantly from manual measurements. Subjects' age and arm circumference influenced neither field nor static evaluation. Retrospective comparison of the study subjects with 120 consecutive ABPM clinic attenders revealed (1) that participants in field testing were younger, had lower BP but were equally active compared with clinic patients; and (2) that Phase V participants exhibited higher systolic (155 +/- 42 v 135 +/- 15 mm Hg; P < .001) but similar diastolic BP levels compared to controls. The reliability of ABPM validation protocols would be enhanced by: (a) incorporation of objective measurement of physical activity during field testing, demonstrating normal levels of activity; (b) requiring that field testing be conducted in representative patients rather than normal volunteers; and (c) a greater focus in both static and field testing on those levels of blood pressure that are relevant in clinical practice.

Prostacyclin and thromboxane levels in pleural space fluid during cardiopulmonary bypass

Prostaglandins exhibit a variety of cardiovascular actions that may affect the hemodynamic recovery of the ischemic myocardium after cardiopulmonary bypass. We have observed a decrease in the mean arterial pressure on autotransfusion of the accumulated pleural cavity fluid during operation. One aim of this study was to determine the concentrations of prostacyclin and thromboxane A2 in the pleural cavity fluid by measuring their stable metabolites, 6-keto-PGF1 alpha and thromboxane B2, respectively, in 8 consecutive patients undergoing myocardial revascularization, and to compare them with the arterial levels. A second aim was to quantify the hemodynamic effect of the pleural cavity fluid during operation. The concentration of 6-keto-PGF1 alpha in the pleural cavity fluid was significantly higher than the arterial concentration (mean, 21.6 +/- 18.2 ng/mL; p < 0.01). The concentration of thromboxane B2 was also raised compared with the arterial concentration (mean, 3.62 +/- 5.96 ng/mL; p < 0.2). The percentage fall in the mean arterial pressure was 29.7% +/- 8.86% (p < 0.02), which was transient and lasted 1 to 3.5 minutes. The hemoglobin concentration, potassium level, and pH were also measured. This study shows that the pleural cavity fluid during cardiac operations contains significant amounts of endogenous prostacyclin. Considering the potential benefit of prostacyclin on the recovering myocardium, we believe that this fluid should be transfused as a volume replacement, keeping in mind the transient phase of hemodynamic instability.

Differential effects of chronic oral antihypertensive therapies on systemic arterial circulation and ventricular energetics in African-American patients

BACKGROUND

A comprehensive evaluation of arterial load characteristics and left ventricular energetics in systemic hypertension has been limited by the need for invasive techniques to access instantaneous aortic pressure and flow. As a consequence of this methodological limitation, no data exist on the effects of long-term antihypertensive therapy on global arterial impedance properties and indexes of myocardial oxygen consumption (MVO2). Using recently validated noninvasive techniques, we compared in hypertensive patients the effects of chronic oral treatment with ramipril, nifedipine, and atenolol on arterial impedance and mechanical power dissipation as well as indexes of MVO2.

METHODS AND RESULTS

Sixteen African-American subjects with systemic hypertension were studied with a randomized, double-blind, crossover protocol. Instantaneous central aortic pressure and flow, from which arterial load characteristics can be derived, were estimated from calibrated subclavian pulse tracings (SPTs) and continuous-wave aortic Doppler velocity in conjunction with two-dimensional (2D) echocardiographic measurements of the aortic annulus, respectively. To derive ventricular wall stress and indexes of MVO2, left ventricular short- (M-mode) and long-axis (2D echo) images were acquired simultaneously with SPTs. Data were collected at the end of a 2-week washout period (predrug control) and after 6 weeks of treatment with each agent. Although all three agents reduced diastolic blood pressure to the same extent, different effects on mean and systolic pressures and vascular impedance properties were noted. Nifedipine reduced total peripheral resistance (TPR; 1744 +/- 398 versus 1290 +/- 215 dyne-s/cm5) and increased arterial compliance (ACL; 1.234 +/- 0.253 versus 1.776 +/- 0.415 mL/mm Hg). This improvement in arterial compliance was not entirely accounted for by the reduction in distending pressure. Ramipril also decreased TPR (1740 +/- 292 versus 1437 +/- 290 dyne-s/cm5) and increased ACL (1.214 +/- 0.190 versus 1.569 +/- 0.424 mL/mm Hg), but with this agent, the change in arterial compliance was explained solely on the basis of a reduction in distending pressure. Atenolol, in contrast, did not affect either TPR or ACL. In agreement with the compliance results, nifedipine and ramipril significantly lowered the first two harmonics of the impedance spectrum, but atenolol did not. None of these agents resulted in a significant change in characteristic impedance or in the relative amplitude of the reflected pressure wave. Total vascular mechanical power and percent of oscillatory power remained unaltered with all antihypertensive treatments. Only ramipril and nifedipine reduced the integral of both meridional and circumferential systolic wall stresses, indicating that MVO2 per beat was reduced with these agents. Stress-time index, a measure of MVO2 per unit time, decreased significantly with ramipril but not with nifedipine because of an increase in heart rate noted in 10 of 16 patients (mean increase, 10 beats per minute). Thus, a reduction in MVO2 coupled with unchanged total vascular mechanical power suggests improved efficiency of ventriculoarterial coupling with ramipril and with nifedipine in the subset of patients in whom heart rate remained unchanged. In contrast, there was no evidence of a reduction in wall stress, stress integral, or stress-time index with atenolol.

CONCLUSIONS

The noninvasive methodology used in this study constitutes a new tool for serial and simultaneous evaluation of arterial hemodynamics and left ventricular energetics in systemic hypertension. In this study, we demonstrate the differential effects of chronic antihypertensive therapies on systemic arterial circulation and indexes of MVO2 in African-American subjects. Consideration of drug-induced differential responses of arterial load and indexes of MVO2 with each drug may provide a more physiological approach to the treatment of systemic hypertension in indivi

The dual-specificity CLK kinase induces neuronal differentiation of PC12 cells

CLK is a dual-specificity protein kinase capable of phosphorylating serine, threonine, and tyrosine residues. We have investigated the action of CLK by establishing stable PC12 cell lines capable of inducibly expressing CLK. Expression of CLK in stably transfected PC12 cells mimicked a number of nerve growth factor (NGF)-dependent events, including the morphological differentiation of these cells and the elaboration of neurites. Moreover, CLK expression enhanced the rate of NGF-mediated neurite outgrowth of these cells, indicating that CLK expression and NGF treatment activate similar signal transduction pathways. CLK expression, unlike NGF, was not able to promote PC12 cell survival in serum-free media, demonstrating that CLK only partially recapitulated the actions of NGF on these cells and that the biochemical pathways necessary for morphological differentiation can be stimulated without also stimulating those necessary for survival. Induction of CLK expression also resulted in the selective activation of protein kinases that are components of growth factor-stimulated signal transduction cascades, including ERK1, ERK2, pp90RSK, and S6PKII. Induction of CLK expression, however, did not stimulate pp70S6K or Fos kinase, two NGF-sensitive protein kinases. These data indicate that CLK action mediates the morphological differentiation of these cells through its capacity to independently stimulate signal transduction pathways normally employed by NGF.

The use of ambulatory blood pressure monitoring in the evaluation of racial differences in blood pressure

Ethnic differences in 24h blood pressure profiles exist, and 24h ambulatory blood pressure monitoring shows that blacks have a higher nocturnal blood pressure associated with a small diurnal change in pressure. Studies in adolescents suggest that these diurnal differences antedate adulthood. Nocturnal blood pressure may be independently important in the pathogenesis of left ventricular hypertrophy.

Ethnic differences in circadian hemodynamic profile

Since the introduction of 24-h ambulatory blood pressure monitoring (ABPM), some studies, although not all, have suggested the presence of a blunted nocturnal blood pressure decline in black versus white subjects, a difference that may help explain the higher incidence of target organ damage in blacks. To better define ethnic differences in diurnal hemodynamic profiles, we studied ABPM recordings from 275 black (55.6% women) and 246 white (43.1% women) previously untreated subjects, with a similar age distribution (from 20 to 79 years) and a wide range of systolic (100-230 mm Hg) and diastolic (50-130 mm Hg) blood pressures. Average clinic systolic (diastolic) blood pressures were higher in black v white men by 10.2 (7.3) mm Hg; P = .04 (P = .004), with a similar trend in women (P = NS). On ABPM, blacks had higher average values, a difference that was greater during sleep (9.4 mm Hg for systolic blood pressure) than while awake (4.7 mm Hg; P = .003). Average diurnal change in systolic blood pressure (awake minus sleep values) was 13.1 +/- 0.7 v 18.0 +/- 0.6 mm Hg for blacks v whites (P < .001). There was a strong negative correlation between baseline (ie, sleep) blood pressure and the diurnal change (r = -0.58; P < .001), but at each given level, blacks had a lower daytime increment/nocturnal fall (P = .02). Results for diastolic blood pressure and heart rate were similar. The data suggest that the smaller diurnal change in blacks may be related in part to their higher blood pressure levels, but that there is an additional, independent effect of race. This results in a greater 24-h blood pressure load in blacks than whites for each given clinic (daytime) value, and may help explain differences in target organ damage. Future studies investigating the effects of blood pressure on target organs in different populations should consider diurnal profiles in addition to clinic blood pressure.

Fenoldopam mesylate versus sodium nitroprusside in the acute management of severe systemic hypertension

Thirty-three patients with severe systemic hypertension defined as a diastolic blood pressure (DBP) > or = 120 mm Hg were randomized in a single-blind fashion to be treated with either intravenous fenoldopam mesylate (FNP) or sodium nitroprusside (NTP). Fenoldopam mesylate and NTP infusion rates began at 0.1 microgram/kg/minute and 0.5 microgram/kg/minute, respectively and were titrated to achieve a goal DBP of between 95 and 110 mm Hg; or a reduction of at least 40 mm Hg if the baseline DBP was > 150 mm Hg. Fenoldopam mesylate (n = 15) reduced blood pressure from 217/145 +/- 6/5 to 187/112 +/- 6/3 mm Hg (P < .001) at an average infusion rate of 0.5 +/- 0.1 microgram/kg/minute. The average time to achieve goal DBP with FNP was 1.5 +/- 1.4 hours. Nitroprusside (n = 18) reduced blood pressure from 210/136 +/- 5/2 to 172/103 +/- 6/2 mm Hg (P < .001) at an average infusion rate of 1.2 +/- .24 micrograms/kg/minute. Nitroprusside response time averaged 2 +/- 2.5 hours. There was no significant difference between the magnitude of effect seen with either FNP or NTP; nor was there any difference observed in the adverse effect rates of the two agents. Fenoldopam mesylate and NTP demonstrate similar overall efficacy in the treatment of severe systemic hypertension.

Identification and characterization of a nerve growth factor-stimulated mitogen-activated protein kinase activator in PC12 cells

Nerve growth factor treatment of PC12 cells results in the rapid activation of MAP kinases. These enzymes are activated through interaction with a protein "activator." The mitogen-activated protein (MAP) kinase activator has been partially purified by ion exchange and gel filtration chromatography. The activator has an apparent molecular mass of 50-60 kDa. The MAP kinase activator is rapidly generated in response to nerve growth factor (NGF) and can be detected within 30 s of exposure, reaching maximal levels within 2 min and then declining to near basal levels by 15-20 min. The activation of MAP kinase is dependent upon the time of incubation with the activator and on activator concentration. The MAP kinase activator is itself a protein kinase that phosphorylates MAP kinases and mediates their activation. The NGF-stimulated MAP kinase activator phosphorylates MAP kinase on serine, threonine, and tyrosine residues, establishing this enzyme as dual specific kinase. The MAP kinase activator is itself a phosphoprotein whose phosphorylation on tyrosine residues is stimulated upon NGF treatment of the cells. The enzyme activity of MAP kinase activator is abolished by treatment with both the tyrosine-specific phosphatase PTP-1 and the serine/threonine-specific phosphatase PP2A. The activator is produced in response to NGF, epidermal growth factor, and fibroblast growth factor. The protein kinase inhibitor K252a selectively inhibits the ability of NGF to generate MAP kinase activator activity. These data suggest that the upstream events governing MAP kinase activation involve the regulated phosphorylation of dual specificity MAP kinase activator as an immediate consequence of receptor activation.

Comparison of two noninvasive screening tests for renovascular hypertension

OBJECTIVE

To compare and contrast the diagnostic accuracy rates of two newer noninvasive screening tests for renovascular hypertension, the most common curable cause of secondary hypertension.

PATIENTS AND METHODS

One hundred fifty patients, thought to have a high probability of renovascular hypertension by established clinical criteria, underwent both the captopril challenge test and the renal scintigram with angiotensin-converting enzyme inhibitor, while on their usual antihypertensive regimen except angiotensin-converting enzyme inhibitors. If the result of either test was abnormal, angiography was undertaken, followed immediately by angioplasty (if a stenosis was found) or by renal vein renin determinations. Patients whose blood pressures were lower 6 to 12 weeks after a revascularization procedure (surgery or angioplasty) were diagnosed as having renovascular hypertension.

RESULTS

Of the 150 patients, 100 underwent angiography, and 59 had renal artery stenosis. Of 53 patients who had surgery (n = 21) or angioplasty (n = 32), 51 had lowered blood pressures compared with before the procedure. Sensitivity and specificity of the tests were as follows: renal scintigram with angiotensin-converting enzyme inhibitor: 92% and 91% (all patients) and 92% and 80% (only patients with angiograms); captopril challenge test: 76% and 82% (all patients) and 76% and 58% (only patients with angiograms). Little difference in accuracy rates was observed in subgroup analyses in patients with chronic renal impairment, previous diuretic or beta-blocker therapy, or bilateral renal artery stenosis.

CONCLUSIONS

In selected, treated patients with a high probability of renovascular hypertension, the renal scintigram with angiotensin-converting enzyme inhibitor was a more accurate noninvasive screening test than the captopril challenge test. Noninvasive screening tests for renovascular hypertension can help to identify patients who should undergo angiography and often predict success after revascularization.

Low predictive value of positive Osler manoeuvre for diagnosing pseudohypertension

Pseudohypertension is a condition where indirectly determined BP (e.g. via sphygmomanometry) significantly overestimates actual intraarterial pressure. A patient who has a palpable, although pulseless, radial artery while the blood pressure cuff is inflated above systolic pressure, has a positive 'Osler sign'. This 'Osler manoeuvre' has been reported to predict the presence of pseudohypertension. To evaluate its importance in diagnosing pseudohypertension, 19 hypertensive patients deemed Osler-positive by at least two observers were studied. BP was determined indirectly using a stethoscope and mercury sphygmomanometer. Intraarterial pressure was determined by a brachial artery catheter-transducer-monitoring system. For both pressure-measurement techniques and each patient, six readings were averaged to give a single systolic and diastolic value. Mean arterial pressure was calculated as diastolic pressure plus one-third the pulse pressure. Pseudohypertension was defined as a sphygmomanometric mean pressure that exceeded intraarterial mean pressure by > or = 10 mmHg. In this group of 19 Osler-positive patients, stethoscope-sphygmomanometry underestimated systolic and overestimated diastolic intraarterial pressure. For mean pressure, sphygmomanometry was > or = 10 mmHg higher than intraarterial in two patients and > or = 10 mmHg lower than intraarterial in three patients. Thus, while two patients had pseudohypertension, three could be considered to have pseudohypotension, defined as a condition where indirect blood pressure significantly underestimates intraarterial pressure. Accordingly, a positive Osler manoeuvre did not reliably predict the presence of pseudohypertension in this population.

Diurnal blood pressure variability and physical activity measured electronically and by diary

In order for 24 h ambulatory blood pressure monitoring (ABPM) to be useful in clinical decision making, it is necessary to quantify ambient physical activity and to develop appropriate norms of ambulatory pressure for different levels of activity. The present study has compared the predictive value of physical activity determined by an electronic activity monitor or a written diary, for concomitantly recorded blood pressure during ABPM in healthy normotensive subjects. Each subject wore four activity monitors, on the right and left wrists, on the left ankle and at the waist, respectively. Linear regression analysis was performed for each subject to determine the correlation between ABPM data (systolic and diastolic blood pressure and heart rate) and activity data (obtained from diaries and the four monitors). Significant differences in the degree of correlation were found for both the location of the activity monitor and the time (1/2, 2, 5, 10, 15, and 30 min preceding blood pressure measurement) over which activity was averaged (P < .05 by two-way analysis of variance). The best correlation was obtained with the activity monitor worn on the dominant wrist, and when activity was averaged over 2 to 10 min preceding blood pressure determination, accounting for 18 to 69% (mean 36 +/- 5%) of systolic blood pressure variation. Diaries performed similarly in these well-motivated subjects. It is concluded that because of the significant interaction between activity and blood pressure, ABPM data should be interpreted only in the light of concomitant activity data.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiographic changes during acute treatment of hypertensive emergencies with sodium nitroprusside or fenoldopam

BACKGROUND

Electrocardiograms are routinely obtained before and during the acute treatment of hypertensive emergencies, usually to rule out "ischemic changes." Despite a few anecdotal reports of electrocardiographic changes, little is known about the incidence and significance of such changes, or their relationship to the treatment used.

METHODS

We prospectively analyzed 12-lead electrocardiograms from 21 patients admitted for hypertensive emergencies (average blood pressure, 222 +/- 4/140 +/- 3 mm Hg). Patients were randomly assigned to treatment with sodium nitroprusside (n = 11) or the dopamine receptor agonist fenoldopam mesylate (n = 10). Electrocardiograms were obtained at baseline and within 30 minutes of reaching goal blood pressure (diastolic blood pressure, 100 to 110 mm Hg).

RESULTS

There was no significant effect of either drug treatment on PR interval, QRS duration, QT interval, or R-wave amplitude, and no major ST-segment changes were noted. During treatment with either drug, the average T-wave amplitude decreased in all leads except aVR. New T-wave inversions in lead V4 occurred in two and four patients after fenoldopam and nitroprusside treatment, respectively. There were no clinically apparent episodes of myocardial ischemia in any patient.

CONCLUSIONS

Even in the absence of obvious myocardial ischemia, a decrease in T-wave amplitude, including T-wave inversion, occurs commonly during acute blood pressure reduction in hypertensive emergencies, an observation that may be explained by the accompanying acute changes in cardiac chamber volumes.

Selecting optimum antihypertensive therapy: indications for choosing a calcium channel blocker

In choosing the optimum antihypertensive agent for an individual patient, various factors should be considered. Demographic characteristics (e.g., age, gender, race) and the circadian pattern of blood pressure elevation may influence the response to therapy. Concomitant therapy for coexisting medical disorders must be evaluated for possible drug interactions. Calcium channel blockers, which can be used in any age group, may be particularly useful in hypertensive patients with certain concurrent conditions (e.g., coronary artery disease, migraine, or gastrointestinal motility disorders). Life-style, including occupation and leisure-time activities, may contraindicate the use of certain drugs in a particular patient. It also may be necessary to consider the economic status of the patient, particularly in the elderly, who often have limited disposable income. Since to a great extent successful therapeutic management of hypertension depends on patient compliance, reduced frequency of dosing (i.e., once or twice daily) is desirable. The clustering of morbid events in the hours immediately following awakening highlights the need for therapy that provides 24-hour control, thereby ensuring adequate pharmacodynamic effects during that crucial period. The challenge is to select the most appropriate first-line agent (diuretic, beta blocker, calcium channel blocker, or angiotensin-converting enzyme inhibitor) for a particular patient.

Blood pressure and fitness for work

A survey was carried out to determine whether physicians in Occupational Medicine exclude job applicants because of hypertension and to examine the critical blood pressure cut-off values they apply. The survey sampled 116 respondents, members of the American Occupational Medical Association, Central States. Of these, 33 (28%) reported excluding hypertensives from work permanently, as the policy of one or more of the companies they serve. Another 78 physicians (68%) reported excluding hypertensives permanently on their own initiative when there was no company policy. The critical determining diastolic pressure varied from 90 to greater than 130 mm Hg; 22 respondents (19%) excluded individuals with mild hypertension. The results demonstrate that blood pressure is frequently used as a criterion for employment. Additionally, the level of blood pressure precluding work is arbitrary and variable. There is a need for consensus on appropriate guidelines to preclude inappropriate discrimination against hypertensive job applicants.

Diurnal blood pressure variation and cardiac mass in American blacks and whites and South African blacks

American blacks exhibit higher nocturnal blood pressure than American whites with similar daytime pressure. To determine whether this represents a true racial difference, as opposed to a consequence of different environmental factors, we measured ambulatory blood pressure, cardiac left ventricular mass, and urinary electrolyte excretion in 22 South African blacks (15 women, aged 36 +/- 12 years) and age, sex, and daytime mean pressure-matched American blacks and whites. While all three groups exhibited similar daytime blood pressure, American blacks displayed significantly higher nighttime mean blood pressure. Both African blacks and American whites experienced the same fall in nighttime blood pressure. Left ventricular mass index was highest in American blacks and lowest in South African blacks. Urine sodium excretion was similar in all groups, but both black populations excreted significantly less potassium than American whites. The data suggest that the differences in diurnal blood pressure rhythm between American blacks and whites do not represent a true racial difference, but more likely are environmental in origin. Furthermore, since both black populations had similar cation excretion rates, yet differed in blood pressure pattern and cardiac mass, divergence in dietary sodium or potassium intake cannot explain the ethnic group differences in the United States.

5-Hydroxytryptamine receptor activity of the dopamine receptor agonist fenoldopam in canine tracheal smooth muscle

Fenoldopam is a new vasodilator undergoing clinical trials for the treatment of hypertensive emergencies. Its pharmacologic effects result from activation of vascular dopamine-1 receptors. In canine tracheal smooth muscle strips, fenoldopam caused a concentration- and calcium-dependent increase in tension, which was not antagonized by atropine, indomethacin or the dopamine-1 receptor antagonist, SCH 23390. The EC50 (1.89 x 10(-6) M) exceeded that of serotonin or acetylcholine (8.38 x 10(-8) and 8.25 x 10(-8) M, respectively). Maximum tension was similar for fenoldopam and serotonin (11.6 +/- 1.5 g, n = 7 and 13.8 +/- 0.8 g, n = 24; P greater than .2) and considerably greater for acetylcholine (20.5 +/- 1.3 g, n = 14; P less than .005). The serotonin antagonists ketanserin and methysergide reversed completely the effect of fenoldopam (5 x 10(-7) M) with IC50 values of 2.5 x 10(-9) and 2.7 x 10(-9) M, respectively. Phentolamine, rauwolscine and chlorpheniramine were also effective, but they were less potent (IC50 values 6.6 x 10(-8), 1.0 x 10(-7) and 1.7 x 10(-7) M, respectively). By contrast, only very high concentrations (IC50, 5.3 x 10(-5) M) of terazosin produced an inhibition of fenoldopam-induced tension increases. The effect of antagonists could be overcome by increasing the fenoldopam concentration. Experiments performed on strips precontracted with serotonin (5 x 10(-8) M) revealed a very similar order of potency for the five antagonists. The addition of serotonin did not increase the tension produced by supramaximal concentrations of fenoldopam (and vice-versa), whereas acetylcholine increased tension further.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal blood pressure variation: differences among disparate ethnic groups

We examined the possibility that excess cardiovascular morbidity in American blacks compared with whites might be partly the result of differences in diurnal blood pressure variation. Urban American blacks have higher night-time blood pressures and show a smaller increase in blood pressure during the waking day than whites. This difference is associated with a higher cardiac mass in the blacks and occurs despite similar duration and quality of sleep in blacks and whites. Both groups show similar levels of sympatho-adrenal activity at night, but the diurnal increase is smaller in blacks, paralleling the smaller increase in blood pressure. In Africa blacks show a diurnal pressure pattern similar to American whites. Disparities in cation consumption do not explain the differences in blood pressure variation between these groups.

A double-blind, randomized, placebo-controlled comparison of the metabolic effects of low-dose hydrochlorothiazide and indapamide

To compare the metabolic effects of indapamide (I) and hydrochlorothiazide (HCTZ) at equivalent hypotensive doses, 11 hypertensive patients (5 male, 8 black, aged 56 +/- 8 yr--mean +/- SEM) having serum uric acid concentrations greater than 8.0 mg/dL while receiving previous therapy with thiazides, received 28-day courses of placebo, indapamide (2.5 mg/d), and HCTZ (25 mg/d) in randomized, double-blind, double-crossover design. Supine and standing blood pressures, weight, pulse rates and sera were obtained after each 28 day period. Blood pressures and weights were lowered (P less than .001 and 0.01, respectively) equally by the diuretics: supine blood pressures fell from 168 +/- 4/104 +/- 2 (placebo) to 153 +/- 4/93 +/- 2 (HCTZ) and 155 +/- 4/94 +/- 2 mm Hg (I); standing blood pressures (after 2 minutes upright) also decreased: 171 +/- 5/104 +/- 2 (placebo) to 156 +/- 5/93 +/- 2 (HCTZ) and 157 +/- 4/94 +/- 2 mm Hg (I). There was a statistically significant difference (P less than .05) across treatments by analysis of variance in both uric acid and potassium concentrations: serum urate (in mg/dL) was lowest with placebo (7.1 +/- 0.3), and rose to 8.3 +/- 0.2 with HCTZ (P less than .001 compared with placebo by paired t test), and 8.1 +/- 0.2 with I (P less than .005 vs. placebo). The urate concentration with I was significantly lower than that with HCTZ (P less than .02), but the magnitude of the difference was small (0.2 mg/dL).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of diuretic therapy on the clonidine suppression test

Moduretic has been reported to inhibit the suppression of plasma norepinephrine (NE) levels by the alpha 2 adrenoceptor agonist, clonidine. To determine whether plasma volume reduction by hydrochlorothiazide (HCTZ) or antagonism of Na+/H+ exchange by amiloride (the constituents of Moduretic) is responsible, the authors performed a modified clonidine suppression test (CST) in nine normal volunteers (aged 25 +/- 2 years), pretreated for 1 week with HCTZ 50 mg daily, amiloride 10 mg daily, or placebo, in a randomized, double-blind, crossover study. Baseline characteristics were identical on all study days, except serum [K+] and weight, which were lowest on HCTZ (3.6 +/- 0.2 mEq/L and 78.7 +/- 2.5 kg), compared with amiloride (4.2 +/- 0.1 mEq/L and 79.9 +/- 2.4 kg) and placebo (4.0 +/- 0.1 mEq/L and 80.2 +/- 2.7 kg, P less than .05). Oral clonidine (0.3 mg) produced a reduction in mean blood pressure by about 20%. Plasma norepinephrine levels were similar in patients receiving placebo, HCTZ, and amiloride (205 +/- 18, 272 +/- 40 and 277 +/- 44 pg/mL, P greater than .20), and decreased significantly during CST. The maximal reduction for each subject averaged 72.7 +/- 12.4%, 87.9 +/- 3.8%, and 82.9 +/- 5.7% for placebo, HCTZ, and amiloride. Clonidine also produced a four to seven-fold increase in plasma growth hormone levels, reduced salivary flow by about 75%, and increased the level of sedation. There were no differences among the three pretreatment regimens in the effects of clonidine, indicating that diuretic therapy does not need to be systematically discontinued in patients undergoing CST.

Long-term preservation of renal function in hypertensive heart transplant recipients treated with enalapril and a diuretic

Hypertension and progressive deterioration in renal function are commonly seen in heart transplant recipients treated for the long term with cyclosporine. Because angiotensin converting enzyme inhibitors have been associated with amelioration of renal dysfunction in some patients with hypertension and preexisting mild-moderate kidney failure, we treated nine hypertensive recipients of orthotopic heart transplants with enalapril (11 +/- 2 mg/day) and furosemide (62 +/- 15 mg/day) for 23 +/- 4 months. Most of the enalapril dose was given at bedtime, which minimized nocturnal and early morning hypertension. In addition to controlling blood pressure (154 +/- 6/100 +/- 2 mm Hg before enalapril vs 120 +/- 5/81 +/- 2 mm Hg currently; p less than 0.001 for both systolic and diastolic blood pressures by paired t test), there has been no increase in serum creatinine level over 684 +/- 102 days of follow-up (1.88 +/- 0.20 mg/dl before enalapril vs 1.81 +/- 0.17 mg/dl currently; p greater than 0.70). This is unlikely to be caused by the reduction in daily cyclosporine dose (492 +/- 60 mg/day before enalapril to 305 +/- 47 mg/day currently) because there were no significant changes in mean blood cyclosporine level (which has been maintained between 100 and 500 ng/ml). Treatment of hypertension with enalapril and a diuretic after heart transplantation may help prevent or delay the impairment of renal function often seen during prolonged cyclosporine therapy.

Intraocular pressure increases with fenoldopam, but not nitroprusside, in hypertensive humans

Fenoldopam mesylate stimulates adenyl cyclase in porcine ocular trabecular meshwork and raises intraocular pressure in humans. To clarify whether this results from direct activation of the dopamine-1 receptor or indirectly from baroreflex sympathetic stimulation after blood pressure reduction, intraocular pressure was measured in 14 patients with accelerated/malignant hypertension, randomized between intravenous fenoldopam or sodium nitroprusside. Intraocular pressure was measured with a Perkins tonometer, before and at the twentieth minute of each dose increment. In seven patients with a mean blood pressure of 232/131 mm Hg treated with fenoldopam, intraocular pressure increased in a dose-dependent fashion, from 16 +/- 1 to 20 +/- 2 mm Hg (p less than 0.005). In contrast, seven patients with a mean blood pressure of 225/134 mm Hg treated with sodium nitroprusside exhibited no change in intraocular pressure (15 +/- 1 versus 14 +/- 1 mm Hg) despite similar blood pressure reduction. Increases in heart rate were not significantly different. Rates of urinary excretion of norepinephrine plus epinephrine increased significantly relative to baseline (p less than 0.05) but were not different between groups. These data suggest that the increase in intraocular pressure with fenoldopam results from specific activation of the dopamine-1 receptor and is not caused by baroreflex sympathetic stimulation. Because dopamine-1 receptors may modulate intraocular pressure, dopamine-1 receptor blockers might be useful therapy for glaucoma.

Selective role of dopamine in the natriuresis produced by iso-osmotic saline infusion

Endogenous dopamine (DA) selectively contributes to the natriuresis (UNaV) produced by infusion and dietary consumption of sodium chloride. The present study in anesthetized rats determined whether DA has a role in the natriuresis produced by small (2.0 +/- 0.11% increase in body weight) and large (17.9 +/- 0.58% increase in body weight) increments in extracellular fluid volume with iso-osmotic saline. Small volume expansion increased urine flow (V) by 59 +/- 15%, UNaV by 155 +/- 31%, and dopamine excretion by 25 +/- 9%. DA1-receptor blockade with SCH 23390 (SCH, 1.0 microgram/kg/min), attenuated the natriuresis; an increase in UNaV of only 69 +/- 15%. Large volume expansion increased V by 1,026 +/- 215% and UNaV by 2,735 +/- 899%, without affecting dopamine excretion. Increments in V and UNaV were unaffected by increasing doses of SCH (1.0 microgram/kg/min; 10 micrograms/kg/min; and 50 micrograms/kg bolus, followed by 10 micrograms/kg/min). Adequacy of DA1-receptor blockade was demonstrated by the fact that SCH (1.0 microgram/kg/min) attenuated the natriuresis produced by the DA1-receptor agonist, fenoldopam (0.1 micrograms/kg/min ia). We conclude that endogenous DA contributes to the natriuresis produced by small, but not large, increases in extracellular fluid volume with iso-osmotic saline.

Equivalent antihypertensive effects of combination therapy using diuretic + calcium antagonist compared with diuretic + ACE inhibitor

To test the hypothesis that the combination of a calcium antagonist and diuretic is less effective in lowering BP than the combination of ACE inhibitor plus diuretic, we compared two groups of patients. The first was a group of 157 consecutive patients (32% male, 90% black, aged 57 +/- 1 years) in whom the only change in therapy was the addition or deletion of either a calcium antagonist or diuretic. Each patient served as his/her own control, with a follow-up time of 41 +/- 4 days. The BP responses of this group were compared with those of another group of 170 consecutive patients (33% male, 85% black, aged 55 +/- 1 years), who had had the addition or deletion of an ACE inhibitor or diuretic some 32 +/- 2 days previously. As there were no statistically significant differences either between drugs within the classes or between the addition or deletion of a drug, the BP results were pooled. Combination therapy with calcium antagonist + diuretic was associated with a 13.4 +/- 1.7/5.4 +/- 0.9 mmHg drop in supine BP; the ACE inhibitor + diuretic combination lowered supine BP by 12.3 +/- 1.6/8.0 +/- 0.9 mmHg compared with monotherapy (all P less than 0.001 by paired t-test). The effects on standing BP were similar: calcium antagonist + diuretic, 13.2 +/- 1.9/5.6 +/- 0.9 mmHg; and ACE inhibitor + diuretic, 12.3 +/- 1.5/7.0 +/- 0.9 mmHg (all P less than 0.001). There were no significant differences in BP responses between the calcium antagonist + diuretic and ACE inhibitor + diuretic combinations. These data indicate that, regardless of the order of addition or subtraction, the combination of calcium antagonist + diuretic was more effective in lowering BP than either agent used alone, and that the combination of calcium antagonist + diuretic was as effective as the ACE inhibitor + diuretic combination.