Computational ligand design in enantio- and diastereoselective ynamide [5+2] cycloisomerization

Transition metals can catalyse the stereoselective synthesis of cyclic organic molecules in a highly atom-efficient process called cycloisomerization. Many diastereoselective (substrate stereocontrol), and enantioselective (catalyst stereocontrol) cycloisomerizations have been developed. However, asymmetric cycloisomerizations where a chiral catalyst specifies the stereochemical outcome of the cyclization of a single enantiomer substrate--regardless of its inherent preference--are unknown. Here we show how a combined theoretical and experimental approach enables the design of a highly reactive rhodium catalyst for the stereoselective cycloisomerization of ynamide-vinylcyclopropanes to [5.3.0]-azabicycles. We first establish highly diastereoselective cycloisomerizations using an achiral catalyst, and then explore phosphoramidite-complexed rhodium catalysts in the enantioselective variant, where theoretical investigations uncover an unexpected reaction pathway in which the electronic structure of the phosphoramidite dramatically influences reaction rate and enantioselectivity. A marked enhancement of both is observed using the optimal theory-designed ligand, which enables double stereodifferentiating cycloisomerizations in both matched and mismatched catalyst-substrate settings.

Cascade polycyclizations in natural product synthesis

Cascade (domino) reactions have an unparalleled ability to generate molecular complexity from relatively simple starting materials; these transformations are particularly appealing when multiple rings are forged during this process.

Combining cycloisomerization with trienamine catalysis: a regiochemically flexible enantio- and diastereoselective synthesis of hexahydroindoles

The synthesis of polysubstituted hexahydroindoles through trienamine-organocatalyzed cycloadditions of pyrrolidinyl dienals, prepared by palladium-catalyzed cycloisomerization, is reported.

Reducing call-to-needle times: the critical role of pre-hospital thrombolysis

BACKGROUND

Current guidelines recommend that patients with acute myocardial infarction should receive thrombolysis within 60 min of seeking professional help.

AIM

To compare current rates of pre-hospital thrombolysis in Grampian with historical data, and assess the effect of pre-hospital thrombolysis on the proportion of patients achieving 'call-to-needle' times within national guidelines.

DESIGN

Prospective audit.

METHODS

Data were collected on all patients (n=535) admitted to the coronary care unit and thrombolysed, either in hospital or in the community from July 2000 to June 2002, using standardized forms.

RESULTS

One hundred and thirty-three patients (25%) received pre-hospital thrombolysis and 402 (75%) received in-hospital thrombolysis. This compares with a 19% (195/1046) pre-hospital thrombolysis rate in the mid-1990s (p=0.005). Median 'call-to-needle' times were 45 min for pre-hospital thrombolysis and 105 min for patients who received in-hospital thrombolysis (p < 0.001). Only 24% (96/396) of patients receiving in-hospital thrombolysis were treated within the recommended guideline, vs. 79% (88/111) of pre-hospital thrombolysis patients (p <0.001).

DISCUSSION

Pre-hospital thrombolysis rates in Grampian are increasing. Administration of thrombolysis in the community greatly increases the proportion of patients achieving a 'call-to-needle' time of 60 min, with a median time saving of approximately 1 h.

Outcomes of a randomized community-level HIV prevention intervention for women living in 18 low-income housing developments

OBJECTIVES

Women in impoverished inner-city neighborhoods are at high risk for contracting HIV. A randomized, multisite community-level HIV prevention trial was undertaken with women living in 18 low-income housing developments in 5 US cities.

METHODS

Baseline and 12-month follow-up population risk characteristics were assessed by surveying 690 women at both time points. In the 9 intervention condition housing developments, a community-level intervention was undertaken that included HIV risk reduction workshops and community HIV prevention events implemented by women who were popular opinion leaders among their peers.

RESULTS

The proportion of women in the intervention developments who had any unprotected intercourse in the past 2 months declined from 50% to 37.6%, and the percentage of women's acts of intercourse protected by condoms increased from 30.2% to 47.2%. Among women exposed to intervention activities, the mean frequency of unprotected acts of intercourse in the past 2 months tended to be lower at follow-up (mean = 4.0) than at baseline (mean = 6.0). These changes were corroborated by changes in other risk indicators.

CONCLUSIONS

Community-level interventions that involve and engage women in neighborhood-based HIV prevention activities can bring about reductions in high-risk sexual behaviors.

Comparative efficacy and safety of ondansetron, droperidol, and metoclopramide for preventing postoperative nausea and vomiting: a meta-analysis

Postoperative nausea and vomiting are important causes of morbidity after anesthesia and surgery. We performed a meta-analysis of published, randomized, controlled trials to determine the relative efficacy and safety of ondansetron, droperidol, and metoclopramide for the prevention of postoperative nausea and vomiting. We performed a literature search of English references using both the MEDLINE database and a manual search. Double-blinded, randomized, controlled trials comparing the efficiency of the prophylactic administration of ondansetron, droperidol, and/or metoclopramide therapy during general anesthesia were included. A total of 58 studies were identified, of which 4 were excluded for methodological concerns. For each comparison of drugs, a pooled odds ratio (OR) with a 95% CI was calculated using a random effects model. Ondansetron (pooled OR 0.43, 95% CI 0.31, 0.61; P < 0.001) and droperidol (pooled OR 0.68, 95% CI 0.54, 0.85; P < 0.001) were more effective than metoclopramide in preventing vomiting. Ondansetron was more effective than droperidol in preventing vomiting in children (pooled OR 0.49; P = 0.004), but they were equally effective in adults (pooled OR 0.87; P = 0.45). The overall risk of adverse effects was not different among drug combinations. We conclude that ondansetron and droperidol are more effective than metoclopramide in reducing postoperative vomiting.

IMPLICATIONS

We performed a systematic review of published, randomized, controlled trials to determine the relative efficacy and safety of ondansetron, droperidol, and metoclopramide for preventing postoperative nausea and vomiting. Ondansetron and droperidol were more effective than metoclopramide in reducing postoperative vomiting. The overall risk of adverse effects did not differ.

Hyperinsulinemia produces cardiac vagal withdrawal and nonuniform sympathetic activation in normal subjects

The exact mechanisms for the decrease in R-R interval (RRI) during acute physiological hyperinsulinemia with euglycemia are unknown. Power spectral analysis of RRI and microneurographic recordings of muscle sympathetic nerve activity (MSNA) in 16 normal subjects provided markers of autonomic control during 90-min hyperinsulinemic/euglycemic clamps. By infusing propranolol and insulin (n = 6 subjects), we also explored the contribution of heightened cardiac sympathetic activity to the insulin-induced decrease in RRI. Slight decreases in RRI (P < 0.001) induced by sevenfold increases in plasma insulin could not be suppressed by propranolol. Insulin increased MSNA by more than twofold (P < 0.001), decreased the high-frequency variability of RRI (P < 0.01), but did not affect the absolute low-frequency variability of RRI. These results suggest that reductions in cardiac vagal tone and modulation contribute at least in part to the reduction in RRI during hyperinsulinemia. Moreover, more than twofold increases in MSNA occurring concurrently with a slight and not purely sympathetically mediated tachycardia suggest regionally nonuniform increases in sympathetic activity during hyperinsulinemia in humans.

Hyperglycemia without hyperinsulinemia produces both sympathetic neural activation and vasodilation in normal humans

To explore the effects of the acute induction of hyperglycemia on sympathetic activity and vascular function we studied eight normal control subjects (28 +/- 3 years of age). Muscle sympathetic nerve activity (MSNA) and forearm vascular resistance (FVR) were measured before (5.4 +/- 0.2 mmol/L) and during systemic infusion of 20% dextrose with octreotide (250 microg/h) and low dose insulin (4 mU x m(-2) x min(-1)) with 60 min of hyperglycemia (venous plasma glucose, 12.5 +/- 0.6 mmol/L). To control for the effects of hyperosmolarity and volume infusion subjects returned for two control studies with equal volume 20% mannitol and 0.2% saline infusions instead of dextrose infusion. The increase in MSNA during hyperglycemia (178 +/- 48 units) was significantly greater than the increase during mannitol (69 +/- 46 units, p < 0.001) or during 0.2% saline (28 +/- 28 units, p < 0.001). The decreases in FVR after 60 min of hyperglycemia (20 +/- 4 units, p = 0.002) and mannitol (13 +/- 4 units, p = 0.033) were significantly greater than the decrease during saline (0.1 +/- 4 units). The changes in FVR during hyperglycemia and mannitol did not differ. Acute hyperglycemia causes sympathoexcitation and peripheral vasodilation. The vascular effect may be mediated by increased osmolar load.

Sympathetic nerve activity and insulin sensitivity in normotensive offspring of hypertensive parents

Insulin resistance and elevated sympathetic nerve activity (SNA) are observed in young borderline hypertensive humans. A positive family history of hypertension (FH) is a strong risk factor for developing hypertension. To assess whether insulin resistance and increased sympathetic tone precede the onset of hypertension, we studied 17 young adults with and 17 without a documented family history of hypertension. Subjects were matched for age (33+/-0.4 years in FH positive and 32+/-0.5 years in FH negative; mean+/-SE) and body mass index (BMI, 25+/-1 kg/m2 in both FH positive and FH negative subjects). We measured blood pressure (BP), heart rate (HR), muscle sympathetic nerve activity (MSNA, microneurography), forearm blood flow, and insulin sensitivity (total glucose uptake determined by an euglycemic/hyperinsulinemic clamp using stable isotope tracer infusion), and calculated forearm vascular resistance (FVR). Mean BP and HR were similar in both groups (86+/-3 mm Hg and 61+/-2 beats/min, and 85+/-2 mm Hg and 62 +/-2 beats/min, respectively, in FH positive and negative respectively, P = ns). Baseline MSNA (24 +/-3 bursts/min in FH positive v 20+/-3 bursts/min in FH negative, P = ns) and total glucose uptake [0.104+/-0.014 mg/(kg x min x microU insulin/mL) in FH positive v 0.095+/-0.014 mg/(kg xmin x microU insulin/mL) in FH negative, P = ns] did not differ between the groups. Sympathetic and vascular responses to insulin were also similar in both groups. The increase in MSNA was 10+/-2 bursts/ min in FH positive and 10+/-1 bursts/min in FH negative, P = ns. Thus, age- and weight-matched offspring with and without a FH of hypertension did not vary in MSNA or insulin sensitivity. These findings suggest that in the absence of obesity and high arterial pressure, a FH of hypertension may not be accompanied by decreased insulin sensitivity or increased MSNA.

Microneurographically determined muscle sympathetic nerve activity levels are reproducible in insulin-dependent diabetes mellitus

Our objective was to determine whether microneurographically determined muscle sympathetic nerve activity (MSNA) levels are equally reproducible in control and insulin-dependent diabetes mellitus (IDDM) subjects. We used a retrospective review of MSNA levels in 14 IDDM and 16 control subjects who had at least two microneurographic studies in the last 8 years in our laboratory. Results showed mean MSNA levels were lower in IDDM (9.2+/-1.2 bursts/min) than in control subjects (16.8+/-1.7 bursts/min) (p<0.002) but mean within individual MSNA coefficients (IDDM: 47+/-8%; controls 30+/-5%) and ranges of variation (IDDM: 6.6+/-1.9; controls: 7.5+/-1.9 bursts/min) did not differ between IDDM and control subjects. Thus, microneurographically determined MSNA levels are equally reproducible in IDDM and controls subjects. These results confirm and substantiate our previous findings of diminished MSNA in IDDM subjects.

Pulmonary blood flow redistribution with low levels of positive end-expiratory pressure

BACKGROUND

Recent studies have questioned the importance of the gravitational model of pulmonary perfusion. Because low levels of positive end-expiratory pressure (PEEP) are commonly used during anesthesia, the authors studied the distribution of pulmonary blood flow with low levels of PEEP using a high spatial resolution technique. They hypothesized that if hydrostatic factors were important in the distribution of pulmonary blood flow, PEEP would redistribute flow to more dependent lung regions.

METHODS

The effects of zero cm H2O PEEP and 5 cm H2O PEEP on pulmonary gas exchange were studied using the multiple inert gas elimination technique; the distribution of pulmonary blood flow, using fluorescent-labeled microspheres, was also investigated in mechanically ventilated, pentobarbital-anesthetized dogs. The lungs were removed, cleared of blood, dried at total lung capacity, and then cubed to obtain approximately 1,000 small pieces of lung (approximately 1.7 cm3).

RESULTS

Positive end-expiratory pressure increased the partial pressure of oxygen by 6 +/- 2 mmHg (P < 0.05) and reduced all measures of ventilation and perfusion heterogeneity (P < 0.05). By reducing flow to nondependent ventral lung regions and increasing flow to dependent dorsal lung regions, PEEP increased (P < 0.05) the dorsal-to-ventral gradient. Redistribution of blood flow with PEEP accounted for 7 +/- 3%, whereas structural factors accounted for 93 +/- 3% of the total variance in blood flow.

CONCLUSIONS

The increase in dependent-to-nondependent gradient with PEEP is partially consistent with the gravitationally based lung zone model. However, the results emphasize the greater importance of anatomic factors in determining the distribution of pulmonary blood flow.

Frequency response characteristics of sympathetically mediated vasomotor waves in humans

In a recent study, we demonstrated that transmission from peripheral sympathetic nerves to vascular smooth muscles is strongest in the frequency band from 0.2 to 0.5 Hz in conscious rats. In contrast, sympathetic modulation of vasomotor tone in humans is suggested to be reflected in the power spectrum of arterial blood pressure in a frequency range centered around approximately 0.1 Hz. Therefore, we addressed whether frequency response characteristics of sympathetic transmission from peripheral sympathetic nerves to vascular smooth muscles in humans differ from those in rats. In 12 male subjects, skin-sympathetic fibers of the left median nerve were electrically stimulated via microneurography needles with stimulation frequencies ranging from 0.01 to 0.5 Hz. Simultaneously, blood flow in the innervated skin area at the palm of the ipsilateral hand was recorded by a laser-Doppler device. The skin blood flow in the same area of the contralateral hand was recorded as a control. Median nerve stimulation produced transient decreases in skin blood flow in the ipsilateral hand. At frequencies ranging from 0.025 to 0.10 Hz, median nerve stimulation evoked high-power peaks at the same frequencies in the skin blood flow power spectra of the ipsilateral but not of the contralateral hand. The greatest responses were found in the frequency range from 0.075 to 0.10 Hz. Therefore, these data indicate that the transmission from peripheral sympathetic nerves to cutaneous vascular smooth muscles in humans is slower than in rats. In addition, the frequency range believed to be most important in sympathetic modulation of vasomotor activity in humans corresponds to the frequency band of the greatest response of cutaneous vascular smooth muscle contraction to sympathetic nerve stimulation.

Heart rate variability before and after treatment with electroconvulsive therapy

It has been suggested that depression may be associated with decreased parasympathetic activity. Based on this work, we tested the hypothesis that treatment of depression with electroconvulsive therapy (ECT) would result in a relative increase in cardiac vagal (parasympathetic) activity. Changes in respiratory sinus arrhythmia, a marker of cardiac parasympathetic activity, were examined in nine patients with depressive episodes before and after ECT using spectral analysis. Hamilton Depression Rating Scale scores decreased significantly. In terms of the heart rate measures, RR interval tended to decrease and the amplitude of respiratory sinus arrhythmia decreased significantly following the course of ECT. This reduction in respiratory sinus arrhythmia contributed to the overall decrease in RR interval variability. Additionally, the magnitude of symptom improvement as measured by the Hamilton Scale correlated with the decrease in amplitude of the respiratory sinus arrhythmia. We report that treatment of depression with ECT was associated with a relative decrease in parasympathetic activity, in contrast to our initial hypothesis of a relative increase. This finding may not be related to the ECT per se but rather to the resolution of depression, as there was a significant correlation between the decrease in Hamilton Depression Rating Scale scores and decrease in parasympathetic activity. Further work is necessary to better understand the autonomic changes associated with depressive illness and the clinical risks and benefits associated with various treatment modalities.

Contrasting autonomic and hemodynamic effects of insulin in healthy elderly versus young subjects

Acute increases in plasma insulin produce both sympathoexcitation and vasodilation in normal young adults. Aging is associated with insulin resistance and may alter the sympathetic or the vascular responses to insulin. Therefore, we assessed sympathetic and vascular responses to acute physiological increases in plasma insulin levels in 10 healthy, normotensive elderly (65+/-2 years) and 12 normal young (27+/-1 years) subjects matched for body mass index (25+/-1 kg/m2 in both groups). We measured muscle sympathetic nerve activity (microneurography), FBF (plethysmography), heart rate, and blood pressure and calculated forearm vascular resistance and insulin sensitivity (M value) during a 90-minute hyperinsulinemic/euglycemic clamp. M values were 4.3+/-0.4 mg x kg(-1) x min(-1) in the elderly and 8.4+/-1.4 mg x kg(-1) x min(-1) in the young subjects (P<.05). Baseline muscle sympathetic nerve activity was higher in the elderly subjects (33+/-3 versus 15+/-2 bursts per minute, P<.05); however, the absolute and percent increases in muscle sympathetic nerve activity were smaller in the elderly than in the young subjects (+10+/-1 versus +15+/-1 bursts per minute, or +37+/-11% versus +110+/-16%, P<.05). Forearm vascular resistance decreased with insulin from 46+/-2 to 31+/-3 units in the young but increased with insulin in the elderly subjects from 37+/-3 to 47+/-7 units (P<.05). Heart rate increased in young but not in elderly subjects. Insulin did not change blood pressure in either group. In conclusion, as opposed to vasodilation in young adults, insulin caused vasoconstriction in healthy elderly individuals. The failure of the vasodilator action of insulin in the elderly may permit even modest insulin-induced sympathoexcitation to elicit vasoconstriction. We speculate that the vasoconstrictor response to insulin may further potentiate insulin resistance in the elderly.

Hypoglycemic symptom variation is related to epinephrine and not peripheral muscle sympathetic nerve response

Hypoglycemic unawareness may be due to diminished adrenal and/or peripheral sympathochromaffin responses to hypoglycemia. To determine whether hypoglycemic symptom awareness is more closely related to adrenal or nonadrenal sympathetic activity, we studied the relationship between symptoms and the epinephrine, norepinephrine, and muscle sympathetic nerve activity (MSNA) responses to hypoglycemia in ten IDDM and ten control subjects. MSNA was measured continuously using microneurography during hyperinsulinemic (720 pmol m-2 min-1), glucose clamp with 60 min of euglycemia, 30 min of hypoglycemia, and 30 min of recovery. Subjects were asked to rate a series of symptoms every 10 min during the last 30 min of each period and were unaware of their plasma glucose concentration. MSNA increased significantly in both groups during insulin clamp (p < 0.05) and further increased during hypoglycemia (p < 0.01). Both epinephrine and norepinephrine levels significantly increased during hypoglycemia (p < 0.02). The increase in adrenergic symptom responses during hypoglycemia positively correlated with epinephrine (r = 0.75, p < 0.01), but not with MSNA in the control subjects. A similar near significant relationship for epinephrine was seen in IDDM subjects (r = 0.65, p = 0.056). No significant predictors were found for neuroglycopenic or cholinergic symptoms. Thus, the variation in hypoglycemic symptoms is not related to the MSNA response to hypoglycemia. Adrenergic symptom variation is due to differences in adrenal epinephrine secretion.

African-American homeless and low-income housed mothers: comparison of parenting practices

The child-rearing practices of homeless and low-income housed mothers of preschool children in Head Start were compared. Overall, homeless mothers provided less learning and academic stimulation, less variety in social and cultural experiences, less warmth and affection, and a less positive physical environment for their children than did housed mothers. Mothers in both living arrangements provided more language stimulation to daughters than to sons. Implications of the findings for working with homeless families are discussed.

Tonic chemoreflex activation does not contribute to elevated muscle sympathetic nerve activity in heart failure

BACKGROUND

Sympathetic activation in heart failure may be due to an increase in sympathetic excitatory influences or to a decrease in inhibitory signals to the brain stem. Chemoreflex sensitivity may be increased in patients with heart failure. The present study tested the hypothesis that tonic activation of excitatory chemoreceptor afferents contributes to the elevated sympathetic activity in heart failure.

METHODS AND RESULTS

We recorded sympathetic nerve activity to muscle circulation from the peroneal nerve of 12 chronic heart failure patients while the patients were breathing room air and during deactivation of the chemoreceptors while the patients were breathing a 100% O2 gas mixture. All patients except 2 were in class III of the New York Heart Association functional classification. Left ventricular ejection fraction defined by radionuclide ventriculography was 24 +/- 2% (mean +/- SE). We also obtained measurements of resting sympathetic nerve activity in 9 healthy control subjects to document that sympathetic nerve activity was elevated in heart failure subjects. Resting sympathetic nerve activity was 59 +/- 5 bursts/min in heart failure patients versus 36 +/- 4 bursts/min in control subjects (P < .01). In heart failure patients, oxygen administration increased oxygen saturation from 94 +/- 0.9% to 99 +/- 0.3% (P < .0001). This increase in oxygen saturation did not affect resting muscle sympathetic nerve activity (798 +/- 122 U/min while patients breathed room air and 824 +/- 35 U/min during 100% O2 breathing) or blood pressure.

CONCLUSIONS

Increased efferent sympathetic activity to muscle circulation in patients with heart failure is not explained by tonic activation of excitatory chemoreflex afferents.

Strategic service quality management for health care

Quality management has become one of the most important and most debated topics within the service sector. This is especially true for health care, as the controversy rages on how the existing American system should be restructured. Health care reform aimed at reducing costs and ensuring access to all Americans cannot be allowed to jeopardize the quality of care. As such, total quality management (TQM) has become a vital ingredient to strategic planning within the health care domain. At the heart of any such quality improvement effort is the issue of measurement. TQM cannot be effectively utilized as a competitive weapon unless quality can be accurately defined, measured, evaluated, and monitored over time. Through such analysis a hospital can elect how to expend its limited resources toward those quality improvement projects which will impact customer perceptions of service quality the most. Thus, the purpose of this report is to establish a framework by which to approach the issue of quality measurement, delineate the various components of quality that exist in health care, and explore how these elements affect one another. We propose that the issue of quality measurement in health care be approached as an integration of service quality attributes common to other service organizations and technical quality attributes unique to health care. We hope that this research will serve as a first step toward the synthesis of the various quality attributes inherent in the health care domain and encourage other researchers to address the interactions of the various quality attributes.

Insulin increases forearm vascular resistance in obese, insulin-resistant hypertensives

OBJECTIVE

To determine whether acutely lowering insulin levels with somatostatin in obese, insulin-resistant hypertensive individuals reduces arterial pressure and forearm vascular resistance; and whether these changes are reversed by restoring insulin levels during continuing somatostatin infusion.

SUBJECTS

Subjects were 11 obese (body mass index 36 +/- 4 kg/m2) insulin-resistant, hypertensive men (systolic/diastolic blood pressures 153 +/- 6/94 +/- 2 mmHg, aged 51 +/- 7 years, fasting insulin level 17 +/- 8 mU/l).

METHODS

Arterial pressure, forearm blood flow and vascular resistance were measured during 2 h of somatostatin infusion and during 2h of somatostatin plus insulin infusion (hyperinsulinemic or euglycemic clamp).

RESULTS

Somatostatin infusion decreased plasma insulin levels from 17 +/- 2 to <3 mU/l. Insulin infusion raised plasma insulin levels to 86 +/- 7 mU/l. The forearm vascular resistance decreased significantly during somatostatin infusion and increased significantly during infusion of somatostatin plus insulin. Somatostatin also caused small but significant reductions in arterial pressure whereas insulin infusion during somatostatin infusion increased arterial pressure. Control experiments in six obese hypertensives indicated that the changes in forearm vascular resistance (but not in arterial pressure) were caused neither by time nor by vehicle. Control studies in six young normotensives indicated that somatostatin does not block the vasodilator response to insulin previously demonstrated in this group.

CONCLUSIONS

The present results suggest that insulin causes forearm vasoconstriction in obese, insulin-resistant hypertensive humans.

Measuring service quality at the University of Texas M.D. Anderson Cancer Center

Evaluates the service quality of four clinics at the University of Texas M.D. Anderson Cancer Center using a questionnaire methodology. The SERVQUAL instrument was administered to patients of the Medical Breast, Leukemia, Medical Gastroenterology and Bone Marrow Aspiration clinics. Results show that, according to the service gap methodology of comparing expectations and perceptions, across all four clinics the issues of billing accuracy and waiting times are deemed by patients as significant problems. In comparing the individual clinics, the Medical Gastroenterology and Leukemia clinics are best performers and the Medical Breast clinic is the worst. However, these differences in performance are due to differences in patients' expectations of service quality, rather than differences in perceptions. Concludes that customer expectations can have a strong impact on a firm's evaluation of its service quality.

Dissociation of sympathoexcitatory and vasodilator actions of modestly elevated plasma insulin levels

OBJECTIVE

To determine sympathetic and vascular responses to modest increases in plasma insulin level.

BACKGROUND

Most studies of sympathetic and vascular actions of insulin have evaluated high plasma insulin levels ( > 50 microU/ml). Those levels increase sympathetic nerve activity but also cause vasodilation. Hypertension and obesity are associated with only modestly elevated fasting insulin levels.

METHODS

We investigated the effects of a 90 min low-dose hyperinsulinemic euglycemic clamp on muscle sympathetic nerve activity (microneurography), forearm vascular resistance (plethysmography), heart rate, blood pressure and central venous pressure. Insulin and vehicle sessions were performed in 12 normal subjects.

RESULTS

Plasma insulin levels were elevated from values of 10 +/- 2 in the fasting state to 25 +/- 3 microU/ml during insulin infusion. Insulin levels did not change during vehicle administration. Muscle sympathetic nerve activity increased from 16 +/- 2 to 25 +/- 3 burst/min during the insulin session and did not change during vehicle administration. In contrast to muscle sympathetic nerve activity, forearm vascular resistance did not change during insulin administration (from 50 +/- 3 to 51 +/- 4 U). Forearm vascular resistance tended to fall during vehicle administration (from 45 +/- 2 to 37 +/- 3 U). There were no changes in heart rate, blood pressure and central venous pressure that could be attributed to insulin.

CONCLUSIONS

Modest elevations of plasma insulin levels produce sympathetic activation similar to that caused by high levels, but, in contrast to high levels modest elevations in plasma insulin level do not decrease forearm vascular resistance. The present findings suggest a dissociation between sympathoexcitatory and vascular actions of insulin at low plasma levels.

Genetic factors determine the blood pressure response to insulin resistance and hyperinsulinemia: a call to refocus the insulin hypothesis of hypertension

We have briefly reviewed the controversy regarding the role of insulin resistance and hyperinsulinemia in the pathogenesis of hypertension in an attempt to emphasize the evidence in support of this concept. In so doing, we have highlighted the concept that genetic factors may determine sensitivity or resistance to the hypertensive effects of insulin resistance and hyperinsulinemia. We hope that this idea will help to reconcile seemingly conflicting evidence on this hypothesis and will focus future research.

Renal sympathetic nerve activity is increased in obese Zucker rats

A low level of sympathetic nerve activity (SNA) to brown adipose tissue has been found in genetically obese Zucker rats and may promote obesity through decreased thermogenesis. In contrast, acquired obesity is reportedly associated with increased SNA. To determine whether low SNA levels in obese Zucker rats extend to the kidney, we compared baseline levels of renal SNA in obese and lean conscious unrestrained Zucker rats fed for 2 weeks on low salt (0.4% NaCl) and high salt (8.0% NaCl) diets. Baseline renal SNA was calculated from multifiber recordings obtained before death under conscious, resting conditions and after death. Body weight averaged 490 +/- 12 g (mean +/- SEM) in obese rats (n = 17) and 339 +/- 7 g in lean rats (n = 19). Mean arterial pressure did not differ in obese and lean Zucker rats fed the low salt diet. However, on the high salt diet, mean arterial pressure was significantly higher in obese rats (n = 8) than in lean rats (n = 9) (113 +/- 3 and 101 +/- 3 mm Hg, respectively; P < .05). Baseline renal SNA was approximately 2 to 2.5 times higher (P < .05) in obese rats than in lean rats in all groups. These studies suggest that obese Zucker rats have heightened levels of SNA to the kidney in contrast to reduced SNA to brown adipose tissue.

Muscle sympathetic nerve activity is higher in intensively versus conventionally treated IDDM subjects

OBJECTIVE

To determine whether poor long-term glycemic control may play a role in the lower muscle sympathetic nerve activity (MSNA) levels in insulin-dependent diabetes mellitus (IDDM).

RESEARCH DESIGN AND METHODS

Intraneural electrodes were used to record MSNA from the peroneal nerve at baseline and during euglycemic insulin infusion (120 mU.m-2.min-1) in 16 IDDM subjects enrolled in the Diabetes Control and Complications Trial (DCCT), 8 intensively treated (HbA1c 7.1 +/- 1.2%) and 8 conventionally treated (HbA1c 9.0 +/- 1.5%; P < 0.05).

RESULTS

Fasting plasma glucose levels tended to be higher at baseline in the conventionally treated group (11.3 +/- 1.7 mmol/l) than in the intensively treated group (7.4 +/- 1.1 mmol/l, P < 0.1), but did not differ during insulin infusion (conventional, 5.0 +/- 0.3 mmol/l; intensive, 5.1 +/- 0.4 mmol/l). Plasma free insulin levels did not differ between groups either before or during insulin infusion. The intensively treated group had significantly high MSNA levels than the conventionally treated group both in the fasting state (16.2 +/-2.7 vs 10.5 +/- 4.4 bursts/min, P < 0.05 and during insulin infusion with euglycemia (27.8 +/- 2.1 vs 17.5 +/- 5.2 bursts/min.

CONCLUSIONS

MSNA levels in intensively treated IDDM subject are higher than in conventionally treated subjects. These results suggest that improved long-term glycemic control is associated with increased sympathetic neural outflow to muscle. The mechanism for this effect remains unclear.

Mechanisms of insulin action on sympathetic nerve activity

Insulin resistance and hyperinsulinemia may contribute to the development of arterial hypertension. Although insulin may elevate arterial pressure, in part, through activation of the sympathetic nervous system, the sites and mechanisms of insulin-induced sympathetic excitation remain uncertain. While sympathoexcitation during insulin may be mediated by the baroreflex, or by modulation of norepinephrine release from sympathetic nerve endings, it has been shown repeatedly that insulin increases sympathetic outflow by actions on the central nervous system. Previous studies employing norepinephrine turnover have suggested that insulin causes sympathoexcitation by acting in the hypothalamus. Recent experiments from our laboratory involving direct measurements of regional sympathetic nerve activity have provided further evidence that insulin acts in the central nervous system. For example, administration of insulin into the third cerebralventricle increased lumbar but not renal or adrenal sympathetic nerve activity in normotensive rats. Interestingly, this pattern of regional sympathetic nerve responses to central neural administration of insulin is similar to that seen with systemic administration of insulin. Further, lesions of the anteroventral third ventricle hypothalamic (AV3V) region abolished increases in sympathetic activity to systemic administration of insulin with euglycemic clamp, suggesting that AV3V-related structures are critical for insulin-induced elevations in sympathetic outflow.

Measuring service quality at a university health clinic

Describes research undertaken to assess the quality of service provided by a public university health clinic. The SERVQUAL instrument was administered to patients of the University of Houston Health Center in order to evaluate customer perceptions of service quality. The results of this study are currently being incorporated into the clinic's strategic planning process, specifically with respect to future resource allocation towards quality improvement projects.

Three-state thermodynamic analysis of the denaturation of staphylococcal nuclease mutants

Using microcalorimetry, we found an equilibrium intermediate state during the denaturation of the wild-type and five mutant staphylococcal nuclease proteins: V66L, V66W, G88V, D77A, and E75V. The presence of two distinct heat absorption peaks allowed direct measurement of the enthalpy differences between the native, intermediate, and denatured states. Conditions of low pH and high NaCl concentration facilitated observation of the intermediate, or I-state. We propose to consider the nuclease protein as composed of two subdomains, divided along the active-site cleft. The structure of the I-state apparently consists mainly of the folded beta-barrel subdomain, as does that of a nuclease fragment protein [Shortle, D., & Abeygunawardana, C. (1993) Structure 1, 121-134]. The cooperativity of folding of the subdomains is maintained by electrostatic bonds across the active-site cleft. Removal of these bonds by the mutation D77A or E75V results in decooperation of the protein's structure and a three-state mechanism of denaturation at pH 7.0. The origins of differences in the enthalpy change of denaturation and in the m value of guanidinium chloride-induced denaturation with mutant nucleases are discussed in terms of this three-state mechanism.

Hypoglycemia increases muscle sympathetic nerve activity in IDDM and control subjects

OBJECTIVE

The relationship between the increase in adrenomedullary catecholamine secretion and the sympathetic response to hypoglycemia is not well understood in humans. To explore this relationship more closely, we directly muscle sympathetic nerve activity (MSNA) in control subjects and in insulin-dependent diabetes mellitus (IDDM) subjects without clinically evident diabetic complications.

RESEARCH DESIGN AND METHODS

Twelve IDDM subjects (22.5 +/- 3.9 years of age, diabetes duration of 9.8 +/- 8.3 years) and 12 age-matched control subjects were studied. MSNA was measured during insulin infusion (720 pM.m-2.min-1) with 30-min periods of 1) euglycemia, 2) hypoglycemia (target plasma glucose, 2.8 mM), and 3) recovery. The effect of increased insulin dose (1,440 pM.m-2.min-1) was studied in six subjects in each group, and the effect of prolonged hypoglycemia (1 h) was studied in five IDDM subjects and four control subjects.

RESULTS

MSNA levels increased in IDDM and control subjects, 31 +/- 8 and 29 +/- 6%, respectively, above euglycemia during hypoglycemia and returned to euglycemic levels during recovery. MSNA levels during hypoglycemia were lower in IDDM subjects than in control subjects (26 +/- 3 vs. 35 +/- 2 bursts/min, P < 0.01). Importantly, no relationships were found between the MSNA and epinephrine responses to hypoglycemia in either group. Increasing the insulin infusion rate did not alter the MSNA response to hypoglycemia. During prolonged hypoglycemia, MSNA remained elevated above euglycemic levels throughout hypoglycemia.

CONCLUSIONS

These results demonstrate that insulin-induced hypoglycemia increases muscle sympathetic neural outflow in IDDM and control subjects. The lack of correlation between the MSNA and epinephrine responses to hypoglycemia indicates that the adrenomedullary and peripheral sympathetic responses to hypoglycemia are independently mediated.

Recruitment of family physicians in rural practice

We report the results of a study to find out how rural family physicians choose their practice location--information that could allow physicians and practices to be more appropriately and easily matched. We interviewed rural family physicians who completed a Minnesota residency in 1990 or 1991 to determine what factors influenced their final practice selection. The survey revealed that partners in practice are physicians' greatest concern, followed by geographic location, recreational activities, call schedule, and opportunities for spouse and children. Despite numerous available practice options, it was difficult for physicians to find practices and communities that met the majority of their personal, professional, and familial needs. This study suggests a need for a physician placement network that would increase retention and help ease the current health care provider shortage in rural Minnesota.

Thermodynamics of staphylococcal nuclease denaturation. I. The acid-denatured state

Using high-sensitivity differential scanning calorimetry, we reexamined the thermodynamics of denaturation of staphylococcal nuclease. The denaturational changes in enthalpy and heat capacity were found to be functions of both temperature and pH. The denatured state of staphylococcal nuclease at pH 8.0 and high temperature has a heat capacity consistent with a fully unfolded protein completely exposed to solvent. At lower pH values, however, the heat capacity of the denatured state is lower, resulting in a lower delta Cp and delta H for the denaturation reaction. The acid-denatured protein can thus be distinguished from a completely unfolded protein by a defined difference in enthalpy and heat capacity. Comparison of circular dichroism spectra suggests that the low heat capacity of the acid-denatured protein does not result from residual helical secondary structure. The enthalpy and heat capacity changes of denaturation of a less stable mutant nuclease support the observed dependence of delta H on pH.

Thermodynamics of staphylococcal nuclease denaturation. II. The A-state

Staphylococcal nuclease, at low pH and in the presence of high salt concentrations, has previously been proposed to exist in a partially folded or molten globule form called the "A-state" (Fink et al., 1993, Protein Sci 2:1155-1160). We have found that the A-state of nuclease at pH 2.1 in the presence of moderate to high salt concentrations and at low temperature exists in a substantially folded form structurally more similar to a native state. The A-state has the far-UV circular dichroism spectra characteristic of the native protein, which indicates that it has a large degree of secondary structure. Upon heating, the A-state denatures with a sigmoidal change in far-UV ellipticity and an observable peak in a differential scanning calorimeter trace, indicating that it is thermodynamically distinct from the denatured state. Three different mutations in a residue normally buried in the protein's core stabilize or destabilize the A-state in the same way as they affect the denaturation of the native state. The A-state must, therefore, contain at least some tertiary packing of side chains. Unlike the native state, which shows cold denaturation at low temperatures, the A-state is most stable at temperatures below 0 degrees C.

Muscle sympathetic nerve activity in response to glucose ingestion. Impact of plasma insulin and body fat

Carbohydrate intake stimulates sympathetic nervous system activity in lean subjects, whereas in obese subjects, the results have been inconsistent. The aim of this study was to directly measure sympathetic neural outflow to skeletal muscle in response to a 75-g oral glucose tolerance test (OGTT) in 15 Pima Indian and 16 Caucasian men, matched for body fat and age, but covering a large range of body weight (57-113 kg) and body fat (4-41%). Fasting muscle sympathetic nerve activity (MSNA) correlated positively with body fat (r = 0.73; P = 0.001) in Caucasians but not in Pima Indians, whereas the increase in MSNA during the OGTT correlated negatively with the percentage of body fat (r = -0.38, P = 0.03) independently of race. In each subject, the increase in MSNA over time correlated positively with the increase in plasma insulin levels, but the slopes of these relationships were inversely related to the percentage of body fat (r = -0.52, P = 0.003) independently of race. In conclusion, obesity is associated with a higher fasting sympathetic neural outflow to muscle but a blunted increase in response to an oral glucose load despite a larger increase in plasma insulin levels. This blunted response may represent another feature of the obesity/insulin resistance syndrome.

Effects of fludrocortisone on sympathetic nerve activity in humans

Fludrocortisone reduces plasma norepinephrine in healthy humans, but forearm vascular and pressor responses to norepinephrine are potentiated. The effects of fludrocortisone on sympathetic nerve activity in healthy humans are not known. To investigate these effects we evaluated muscle sympathetic nerve activity, heart rate, and arterial pressure in 11 healthy volunteers during three protocols: (1) before and on day 7 of fludrocortisone (0.4 mg/d) treatment with ad libitum diet (n = 6); (2) before and on day 7 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 7); and (3) before and on day 2 of fludrocortisone (0.4 mg/d) or placebo with a 150 mmol/24 h (mEq/24 h) sodium diet (n = 4). Placebo did not alter any parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced sympathetic nervous activity. A potential mechanism predisposing to body weight gain

The sympathetic nervous system is recognized to play a role in the etiology of animal and possibly human obesity through its impact on energy expenditure and/or food intake. We, therefore, measured fasting muscle sympathetic nerve activity (MSNA) in the peroneal nerve and its relationship with energy expenditure and body composition in 25 relatively lean Pima Indian males (means +/- SD; 26 +/- 6 yr, 82 +/- 19 kg, 28 +/- 10% body fat) and 19 Caucasian males (29 +/- 5 yr, 81 +/- 13 kg, 24 +/- 9% body fat). 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate were measured in a respiratory chamber, whereas body composition was estimated by hydrodensitometry. Pima Indians had lower MSNA than Caucasians (23 +/- 6 vs 33 +/- 10 bursts/min, P = 0.0007). MSNA was significantly related to percent body fat in Caucasians (r = 0.55, P = 0.01) but not in Pimas. MSNA also correlated with energy expenditure adjusted for fat-free mass, fat mass, and age in Caucasians (r = 0.51, P = 0.03; r = 0.54, P = 0.02; and r = 0.53, P = 0.02 for adjusted 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate, respectively) but not in Pima Indians. In conclusion, the activity of the sympathetic nervous system is a determinant of energy expenditure in Caucasians. Individuals with low resting MSNA may be at risk for body weight gain resulting from a lower metabolic rate. A low resting MSNA and the lack of impact of MSNA on metabolic rate might play a role in the etiology of obesity in Pima Indians.

Muscle sympathetic nerve activity is reduced in IDDM before overt autonomic neuropathy

Studies of heart-rate variability have demonstrated that abnormal cardiac parasympathetic activity in individuals with IDDM precedes the development of other signs or symptoms of diabetic autonomic neuropathy. To determine whether IDDM patients have impaired sympathetic activity compared with normal control subjects before the onset of overt neuropathy, we directly recorded MSNA. We also examined the effects of changes in plasma glucose and insulin on sympathetic function in each group. MSNA was recorded by using microneurographic techniques in 10 IDDM patients without clinically evident diabetic complications and 10 control subjects. MSNA was compared during a 15-min fasting baseline period and during insulin infusion (120 mU.m-2.min-1) with 30 min of euglycemia. A cold pressor test was performed at the end of euglycemia. Power spectral analysis of 24-h RR variability was used to assess cardiac autonomic function. IDDM patients had lower MSNA than control subjects at baseline (8 +/- 1 vs. 18 +/- 3 burst/min, P < 0.02). MSNA increased in both groups with insulin infusion (P < 0.01) but remained lower in IDDM patients (20 +/- 3 vs. 28 +/- 3 burst/min, P < 0.01). In the IDDM group, we found no relationships between MSNA and plasma glucose, insulin, or HbA1c concentrations. BP levels did not differ at rest or during insulin. Heart-rate variability and the MSNA response to cold pressor testing in IDDM patients did not differ from those in healthy control subjects. IDDM patients had reduced MSNA at rest and in response to insulin. The lower MSNA is not attributable to differences in plasma glucose or insulin, but, rather, is most likely an early manifestation of diabetic autonomic neuropathy that precedes impaired cardiac parasympathetic control.

Sympathetic neural mechanisms in human hypertension

This review discusses the role of the sympathetic nervous system in the pathogenesis and maintenance of human hypertension. Three points are emphasized: first, there are mechanisms by which the sympathetic nervous system can contribute to the long-term regulation of vascular resistance and arterial pressure in addition to the moment-to-moment regulation of arterial pressure; second, the microneurographic method for direct intraneural recording of sympathetic nerve activity in humans has provided mounting evidence for increased sympathetic neural activity in human essential and renovascular hypertension; and third, there are both peripheral reflex and humoral mechanisms that may contribute to sympathetic overactivity in human hypertension.

A signal-averaging technique for the analysis of human muscle sympathetic nerve activity

We present a signal-averaging technique for analysis of human muscle sympathetic nerve activity (SNA). Nerve traffic was averaged by coupling signal acquisition to electrocardiographic R waves. The amplitude of the averaged waveform was multiplied by the number of R waves sampled to provide a measure of SNA in arbitrary units. This was compared with SNA measured by manual digitization of hard-copy records. In nine volunteers, SNA was increased or decreased with stepwise infusions of nitroprusside or phenylephrine: there were 10 5-min periods of data in each subject. Across all subjects, the correlation between manual and signal-averaged measures of SNA was excellent during both nitroprusside (r = 0.98) and phenylephrine infusions (r = 0.91) and the slopes of the regression lines were near unity. In three periods of data collection, electrical artifacts were added randomly at frequencies of 0.5 and 0.07 Hz during playback of the signal into the computer. Signal-averaged estimates of SNA were unaffected by artifacts. This technique provides reliable observer-independent measures of SNA.

Insulin increases sympathetic activity but not blood pressure in borderline hypertensive humans

We have previously demonstrated that physiological hyperinsulinemia in normotensive humans increases sympathetic nerve activity but not arterial pressure since it also causes skeletal muscle vasodilation. However, in the presence of insulin resistance and/or hypertension, insulin may cause exaggerated sympathetic activation or impaired vasodilation and thus elevate arterial pressure. This study sought to determine if insulin causes a pressor response in borderline hypertensive humans by producing exaggerated increases in sympathetic neural outflow or impaired vasodilation. We recorded muscle sympathetic nerve activity (microneurography, peroneal nerve), forearm blood flow, heart rate, and blood pressure in 13 borderline hypertensive subjects during a 1-hour insulin infusion (38 microunits/m2/min) while holding blood glucose constant. Plasma insulin rose from 12 +/- 3 microunits/ml (mean +/- SEM) during control to 73 +/- 7 microunits/ml during insulin infusion and fell to 9 +/- 2 microunits/ml 2 hours after insulin infusion was stopped. Muscle sympathetic nerve activity, which averaged 25 +/- 2 bursts per minute in control, increased significantly during insulin infusion (+9 bursts per minute) and remained elevated 1.5 hours into recovery (+7 bursts per minute, p less than 0.001). Despite increased muscle sympathetic nerve activity, there were significant (p less than 0.001) increases in forearm blood flow and decreases in forearm vascular resistance during insulin infusion. Further, systolic and diastolic pressures fell approximately 3 and 6 mm Hg, respectively, during insulin infusion (p less than 0.01). This study suggests that acute physiological increases in plasma insulin elevate sympathetic neural outflow in borderline hypertensive humans but produce vasodilation and do not elevate arterial pressure.

Correlation of endomyocardial biopsy findings with autopsy findings in human cardiac allografts

To determine the reliability of endomyocardial biopsies in the detection of rejection, we took biopsy specimens from 22 autopsied human cardiac allografts by direct visualization. Five specimens were taken from each of four sites: left ventricular free wall, left ventricular septum, right ventricular free wall, and right ventricular septum. The findings in individual biopsy specimens and the summed diagnosis in the five biopsy specimens from each site were graded for rejection by a grading system similar to the Billingham criteria. Grading of the five specimens from each site also was done using criteria recommended by the International Society for Heart and Lung Transplantation. These findings were compared with the rejection grade determined by examination of large tissue sections from the autopsied hearts, used as the standard. Overall, X-Y correlation for single-specimen grading had an r value of 0.792. Grading based on five biopsy specimens from all sites using the modified Billingham criteria grading scheme had an r value of 0.845; the r value was 0.857 for the new grading system. Specificity of findings was high for all grades. Sensitivity of findings, however, was dramatically less for grades 1, 2, and 3. Predictive values for these grades also were less for grades 1, 2, and 3, but to a lesser degree than sensitivity. No difference in detection of rejection was found from specimens taken from different areas of the heart. We conclude that a significant number of hearts with middle grades of rejection may be underestimated by routine biopsies. The criteria for grading of the International Society for Heart and Lung Transplantation had a slight advantage over a more traditional grading system.

Hyperinsulinemia produces both sympathetic neural activation and vasodilation in normal humans

Hyperinsulinemia may contribute to hypertension by increasing sympathetic activity and vascular resistance. We sought to determine if insulin increases central sympathetic neural outflow and vascular resistance in humans. We recorded muscle sympathetic nerve activity (MSNA; microneurography, peroneal nerve), forearm blood flow (plethysmography), heart rate, and blood pressure in 14 normotensive males during 1-h infusions of low (38 mU/m2/min) and high (76 mU/m2/min) doses of insulin while holding blood glucose constant. Plasma insulin rose from 8 +/- 1 microU/ml during control, to 72 +/- 8 and 144 +/- 13 microU/ml during the low and high insulin doses, respectively, and fell to 15 +/- 6 microU/ml 1 h after insulin infusion was stopped. MSNA, which averaged 21.5 +/- 1.5 bursts/min in control, increased significantly (P less than 0.001) during both the low and high doses of insulin (+/- 5.4 and +/- 9.3 bursts/min, respectively) and further increased during 1-h recovery (+15.2 bursts/min). Plasma norepinephrine levels (119 +/- 19 pg/ml during control) rose during both low (258 +/- 25; P less than 0.02) and high (285 +/- 95; P less than 0.01) doses of insulin and recovery (316 +/- 23; P less than 0.01). Plasma epinephrine levels did not change during insulin infusion. Despite the increased MSNA and plasma norepinephrine, there were significant (P less than 0.001) increases in forearm blood flow and decreases in forearm vascular resistance during both doses of insulin. Systolic pressure did not change significantly during infusion of insulin and diastolic pressure fell approximately 4-5 mmHg (P less than 0.01). This study suggests that acute increases in plasma insulin within the physiological range elevate sympathetic neural outflow but produce forearm vasodilation and do not elevate arterial pressure in normal humans.

Mental stress increases sympathetic nerve activity during sustained baroreceptor stimulation in humans

Muscle sympathetic nerve activity (MSNA) in humans is regulated in part by arterial baroreceptors. However, although mental stress increases blood pressure, it also increases MSNA. This suggests that baroreceptor control of MSNA is altered during mental stress. In nine healthy men (age range, 20-26 years), we recorded heart rate, blood pressure, and efferent MSNA (peroneal nerve, microneurography) during a 4-minute mental arithmetic task performed both before and during infusion of phenylephrine sufficient to markedly suppress resting MSNA. Before phenylephrine, mental stress significantly increased mean blood pressure (p less than 0.01), heart rate (p less than 0.01), and MSNA (from 18.5 +/- 3.2 to 24.8 +/- 3.5 bursts/min, p less than 0.001). Phenylephrine infusion increased resting mean blood pressure (from 84.0 +/- 2.6 to 90.0 +/- 2.7 mm Hg, p less than 0.01) and decreased resting heart rate (from 65.6 +/- 1.7 to 55.6 +/- 2.0 beats/min, p less than 0.01). Resting MSNA decreased dramatically during phenylephrine (from 18.5 +/- 3.2 to 3.3 +/- 1.3 bursts/min, p less than 0.01). During phenylephrine, mental stress again significantly (p less than 0.01) increased mean blood pressure, heart rate, and MSNA (from 3.1 +/- 1.4 to 10.9 +/- 1.8 bursts/min). The magnitude of stress-induced increases in MSNA and heart rate were comparable before and during phenylephrine infusion despite the greater elevation in diastolic pressure during stress plus phenylephrine. The present study demonstrates that mental stress produces sympathoexcitatory and pressor responses even during sustained stimulation of arterial baroreceptors.

Effect of dietary potassium on blood pressure, renal function, muscle sympathetic nerve activity, and forearm vascular resistance and flow in normotensive and borderline hypertensive humans

We evaluated the effect of a low potassium diet on blood pressure in normotensive (NT) and in borderline hypertensive subjects (BHT). There were 11 BHT men (age, 24.6 +/- 1.2 years) and 10 NT men (age, 23.5 +/- 1.0 years). Subjects were studied while on both low potassium, high sodium (30 meq/day, 400 meq/day) diets and high potassium, high sodium (100 meq/day, 400 meq/day) diets, each taken for 6 days. During the low potassium diet, daytime ambulatory systolic blood pressure increased in both NT (123 +/- 5 mm Hg, low potassium, vs. 116 +/- 4 mm Hg, high potassium, p less than 0.01) and BHT groups (134 +/- 3, low potassium, vs. 124 +/- 3, high potassium, p less than 0.001). Mean blood pressure was not different in NT during the two diets but was significantly higher during the low potassium diet in BHT subjects (97 +/- 2 mm Hg low potassium, vs. 92 +/- 1 mm Hg, high potassium, p less than 0.05) without change in heart rate in BHT subjects during the two diets. Low potassium diet increased the postural rise in diastolic blood pressure when subjects changed from the supine position to quiet standing (standing diastolic blood pressure for NT: low potassium, 79 +/- 2 mm Hg vs. high potassium, 72 +/- 2 mm Hg; for BHT: low potassium, 89 +/- 2 mm Hg vs. high potassium diet, 83 +/- 2 mm Hg, p less than 0.01). The effects of low potassium diet on blood pressure were not related to marked changes in renal hemodynamics, in plasma renin activity, in aldosterone, or in norepinephrine, nor to increases in forearm vascular resistance or in muscle sympathetic nerve activity. In fact, muscle sympathetic nerve activity decreased in the BHT group during low potassium compared with high potassium diets (p less than 0.001) and did not change in the NT group. Sympathetic nerve activity was also higher in BHT compared with the NT group during high potassium and low potassium diets, p less than 0.001. In the NT group, the low potassium diet was associated with lower hematocrit levels, weight gain, and increased 24 hour urinary calcium levels. After the low potassium diet, serum potassium fell in both groups, and serum phosphorus fell significantly in the BHT group.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscle relaxants change myocardial metabolism in patients with ischemic heart disease during high-dose fentanyl anesthesia

Although not unanimously accepted, high-dose fentanyl anesthesia has been associated with hemodynamic stability and little derangement of myocardial oxygen balance. This apparent inconsistency inspired us to investigate the effects on cardiac function and myocardial metabolism of stepwise increasing doses of fentanyl, accumulating to 15, 30, and 50 micrograms.kg-1, with the least possible interference from other drugs. Subjects were unpremedicated patients with ischemic cardiac disease scheduled for coronary artery bypass grafting or major vascular surgery. In an initial study employing succinylcholine for muscle relaxation, we found that heart rate (HR), coronary sinus blood flow (CSF) and coronary vascular resistance (CVR) remained unchanged, while systemic arterial pressure (SBP), rate-pressure product (RPP), coronary perfusion pressure (CPP) and left ventricular work (LVW) decreased. Myocardial uptake of oxygen (MVO2) and free fatty acids (FFA) both decreased in a dose-dependent manner. Arterial lactate concentration and myocardial lactate uptake both increased. These findings opposed the postinduction myocardial ischemia noted by some other investigators. In most of these studies pancuronium bromide had been used for muscle relaxation. Since the latter agent has been claimed to increase cardiac work, a second group of correspondingly diseased patients was studied in which succinylcholine was replaced by pancuronium bromide. In this group HR, RPP, CSF and MVO2 all increased at the lowest dose of fentanyl and HR additionally also at 30 micrograms.kg-1. The cardiac index was higher in the pancuronium group at the lowest and middle dose steps of fentanyl. Lactate uptake decreased with higher doses of fentanyl and relative myocardial lactate extraction declined.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated sympathetic nerve activity in borderline hypertensive humans. Evidence from direct intraneural recordings

Reports of elevated plasma catecholamine levels and augmented responses to autonomic blockade suggest increased sympathetic tone in borderline hypertension. It is not known if this reflects greater sympathetic neural outflow. We directly recorded muscle sympathetic nerve activity (microneurography) in 15 normotensive and 12 borderline hypertensive age-matched men to determine whether borderline hypertensive individuals have elevated sympathetic nerve activity. Supine heart rate, blood pressure, plasma norepinephrine, and efferent muscle sympathetic nerve activity (peroneal nerve) were measured after 6 days of both low and high dietary sodium intake (10 and 400 meq sodium/24 hr). Sympathetic nerve activity was elevated significantly in borderline hypertensive individuals on both low (37 +/- 1 in borderline hypertensive individuals vs. 29 +/- 1 bursts/min in normotensive individuals; p less than 0.01) and high (25 + 1 in borderline hypertensive individuals vs. 16 +/- 1 bursts/min in normotensive individuals; p less than 0.01) sodium diets. The borderline hypertensive group had higher systolic (p less than 0.01) and diastolic (p less than 0.05) blood pressures independent of sodium intake. Across both groups, high sodium intake reduced muscle sympathetic nerve activity (p less than 0.001), plasma norepinephrine (p less than 0.001), diastolic blood pressure (p less than 0.02), heart rate (p less than 0.002), and increased weight (p less than 0.005). A significant (p less than 0.05) group-by-diet interaction was observed for plasma norepinephrine levels. Specifically, compared with the normotensive group, plasma norepinephrine levels in the borderline hypertensive group tended to be higher on low sodium diet (p = 0.08) and lower on high sodium diet (p = 0.23).(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-mediated and reflex changes in large peripheral artery tone in humans

Studies of peripheral blood vessels in humans have focused primarily on regulation of blood flow and vascular resistance, which are thought to reflect small vessel caliber. Recent studies in animals have identified flow-mediated and neurogenic changes in large artery diameter. This study tested for flow-mediated dilatation and reflex constriction of the brachial artery in humans. A dual-crystal pulsed Doppler system was used to measure brachial artery diameter and blood flow proximal to the antecubital fossa. To test for flow-mediated dilatation, flow through the brachial artery was altered by an occluding cuff placed on the forearm distal to the site of brachial artery flow and diameter measurement. Control blood flow was 123 +/- 20 ml/min, and brachial artery diameter was 4.74 +/- 0.17 mm (mean +/- SEM). By inflating the distal occluding cuff (distal circulatory arrest), flow was reduced through the brachial artery to 21 +/- 5 ml/min (p less than 0.005), and brachial artery diameter was reduced to 4.35 +/- 0.20 mm (p less than 0.001). By deflating the distal occluding cuff after 10 minutes (reactive hyperemia), brachial artery flow was increased to 358 +/- 55 ml/min (p less than 0.001), and diameter was increased to 5.6 +/- 0.19 mm (p less than 0.001). These interventions did not change systemic arterial pressure and, as measured in three subjects, caused only small changes in local brachial artery distending pressure. Thus, both increased and decreased brachial artery blood flow produced significant changes in brachial artery diameter without altering arterial distending pressure. These data provide evidence for flow-mediated dilatation in humans.(ABSTRACT TRUNCATED AT 250 WORDS)