[Efficacy and feasibility of catheter-based adrenal ablation on Cushing's syndrome associated hypertension]

Objective: To explore the value of catheter-based adrenal ablation in treating Cushing's syndrome (CS)-associated hypertension. Methods: A clinical study was conducted in patients with CS, who received catheter-based adrenal ablation between March 2018 and July 2023 in Daping Hospital. Parameters monitored were blood pressure (outpatient and 24-hour ambulatory), body weight, clinical characteristics, serum cortisol and adrenocorticotropic hormone (ACTH) at 8 am, 24-hour urinary free cortisol (24 h UFC), fasting blood glucose and postoperative complications. Procedure effectiveness was defined as blood pressure returning to normal levels (systolic blood pressure<140 mmHg (1 mmHg=0.133 kPa) and diastolic blood pressure<90 mmHg), cortisol and 24 h UFC returning to normal and improvement of clinical characteristics. The parameters were monitored during follow up in the outpatient department at 1, 3, 6, and 12 months after catheter-based adrenal ablation. Results: A total of 12 patients (aged (40.0±13.2) years) were reviewed. There were 5 males, with 5 cases of adenoma and 7 with hyperplasia from imaging studies. Catheter-based adrenal ablation was successful in all without interruption or surgical conversion. No postoperative complication including bleeding, puncture site infection, adrenal artery rupture or adrenal bleeding was observed. The mean follow up was 28 months. Compared to baseline values, body weight declined to (59.48±11.65) kg from (64.81±10.75) kg (P=0.008), fasting blood glucose declined to (4.54±0.83) mmol from (5.53±0.99) mmol (P=0.044), outpatient systolic blood pressure declined to (128±21) mmHg from (140±19) mmHg (P=0.005), diastolic blood pressure declined to (78±10) mmHg from (86±11) mmHg (P=0.041), and the mean ambulatory daytime diastolic blood pressure declined to (79±12) mmHg from (89±8) mmHg (P=0.034). Catheter-based adrenal ablation in 8 patients was defined as effective with their 24 h UFC significantly reduced after the procedure (1 338.41±448.06) mmol/L from (633.66±315.94) mmol/L, P=0.011). The change of 24 h UFC between the effective treatment group and ineffective group was statistically significant (P=0.020). The postoperative systolic blood pressure in the treated adenoma group was significantly lower than those of hyperplasia group (112±13) mmHg vs. (139±20) mmHg, P=0.026). Conclusions: For patients with CS-associated hypertension who are unwilling or unable to undergo surgical treatment, catheter-based adrenal ablation could improve the blood pressure and cortisol level. Catheter-based adrenal ablation could be a safe, effective, and minimally invasive therapy. However, our results still need to be validated in further large-scale studies.

[Challenges and countermeasures of schistosomiasis control in Hunan Province in the new era]

This paper describes the current epidemic characteristics and endemic status of schistosomiasis, analyzes the main challenges of schistosomiasis control and proposes the emphasis and interventions for future schistosomiasis control activities in Hunan Province, so as to provide insights into the elimination of schistosomiasis in Hunan Province.

[Implications, spiritual characteristics and practical significance of Chinese schistosomiasis control culture]

The culture of schistosomiasis control is specific in the history of Chinese culture. Broadly speaking, the culture of schistosomiasis control is a summary of specific social mood, social consciousness and material culture created by Chinese populations during the progress of schistosomiasis control since the founding of the People's Republic of China. Narrowly speaking, the culture of schistosomiasis control is the spiritual culture that is jointly created and nurtured by schistosomiasis control workers since the founding of the People's Republic of China. The spiritual features of Chinese schistosomiasis control culture are characterized by the patriotism and care about the people, the matter-to-fact attitude, the pioneering and enterprising spirit, and the spirit of sacrifice and dedication. The ultimate goal of the research on the culture of schistosomiasis control is to facilitate the achievement of the strategic goal of Healthy China 2030 as scheduled, accelerate the progress towards elimination of schistosomiasis, and to promote the sustainable development of schistosomiasis control in China.

[Endemic situation of schistosomiasis in Hunan Province in 2019]

OBJECTIVE

To analyze the endemic situation of schistosomiasis in Hunan Province in 2019, so as to provide insights into the achievement of transmission interruption of schistosomiasis in the province in 2020.

METHODS

The data pertaining to Schistosoma japonicum infections in humans and livestock and snail status were captured from Hunan Province in 2019 and analyzed.

RESULTS

Schistosomiasis was endemic in 281 townships (towns) from 41 counties (districts) of 6 cities in Hunan Province by the end of 2019. A total of 991 900 persons received blood testing in Hunan Province in 2019, and 22 773 were positive for the blood testing, with sero-prevalence of 2.30%. All stool examinations were negative in 22 933 individuals detected. The high sero-prevalence was seen in Nanxian County, Anxiang County and Ziyang District. Currently, there were 5 034 cases with advanced schistosomiasis detected in Hunan Province, and they were predominantly identified in Yuanjiang City, Heshan District and Yueyang County. There were 44 963 bovines fenced in schistosomiasis-endemic villages in Hunan Province in 2019, which were predominantly distributed in Yuanjiang City, Hanshou County and Ziyang District, and no positives were detected in 1 996 bovines receiving blood testing or 20 684 bovines receiving stool examinations. In 2019, there were snail habitats of 1.73 billion m² found in Hunan Province, which were mainly found in Yuanjiang City, Hanshou County and Yueyang County.

CONCLUSIONS

The endemic situation of schistosomiasis further decreases in Hunan Province in 2019; however, there is still a risk of schistosomiasis transmission in local areas of the province.

[Application of the exponential smoothing model and ARIMA model in prediction of the endemic situation of schistosomiasis in Hunan Province]

OBJECTIVE

To predict the changes in the prevalence of Schistosoma japonicum infections in humans and livestock in Hunan Province using the exponential smoothing model and the ARIMA model.

METHODS

The data pertaining to S. japonicum infections in humans and livestock in Hunan Province from 1957 to 2015 were collected, and the exponential smoothing model and the ARIMA model were created using the software Eviews and PASW Statistics 18.0. In addition, the effectiveness of these two models for the prediction of S. japonicum infections in humans and livestock in Hunan Province from 2016 to 2018 was evaluated.

RESULTS

The exponential smoothing model and the ARIMA model had a high goodness of fit for prediction of S. japonicum infections in humans and livestock in Hunan Province from 1957 to 2015. There was a linear trend in the prevalence of S. japonicum infections in humans and livestock in Hunan Province from 1957 to 2015. The prevalence of S. japonicum infections in humans predicted with the Brown's linear trend and the prevalence of S. japonicum infections in livestock predicted with the Holt's linear trend in Hunan Province from 2016 to 2018 fitted better the actual data than the ARIMA model; however, prediction of the ARIMA model indicated that the endemic situation of schistosomiasis remained at a low level in Hunan Province.

CONCLUSIONS

At a low epidemic level, development of highly sensitive tools for monitoring schistosomiasis is urgently needed in Hunan Province to fit the current endemic situation, and the schistosomiasis control measures should be intensified to consolidate the control achievements.

[Survey of the capacity building of the county-level schistosomiasis diagnosis network laboratory in Hunan Province]

OBJECTIVE

To examine the construction and operation of the schistosomiasis diagnostic network platform in Hunan Province, so as to provide insights into the improvements of the schistosomiasis diagnostic network laboratory system in the province.

METHODS

According to the criteria and requirements for the construction of the county-level schistosomiasis diagnostic network laboratory in China, the establishment and operation of the laboratory were assessed using self-assessment and field review in national schistosomiasis surveillance sites of Hunan Province.

RESULTS

A total of 41 county-level schistosomiasis diagnostic network laboratories were built in national schistosomiasis surveillance sites of Hunan Province, and 36 met the requirements for the construction of the national schistosomiasis diagnostic network laboratory in China, which were approved for inclusion in the province-level schistosomiasis diagnostic network laboratory. During the six inter-laboratory comparisons performed by the national schistosomiasis diagnostic reference center of China, full consistency was achieved by 3 county-level schistosomiasis diagnostic network laboratories in Hunan Province, and the coincidence rates for re-review of serological and pathogenic detection samples were 98.40% and 100%, respectively.

CONCLUSIONS

The county-level schistosomiasis diagnostic network laboratory system has been preliminarily built and under effective operation in Hunan Province; however, the building capability remains to be improved.

Cu fractions, mobility and bioavailability in soil-wheat system after Cu-enriched livestock manure applications

Fertilization of crops with livestock manure (LM) is a common waste disposal option, but repeated application of LM containing high concentrations of heavy metals such as Cu could lead to crop toxicity and environmental risk. To examine the Cu availability and uptake by wheat in a Mollisol affected by Cu-enriched LM, pot experiments were conducted. LM (376 mg kg⁻¹ Cu originally) was spiked with different concentrations of Cu (0, 100, 200, 400, 600 and 800 mg kg⁻¹ soil, added as CuSO⁴) to simulate soil Cu contamination by LM application. The results indicated that Cu was predominately distributed in organic bound fraction, while the most drastic increase was found in reducible fraction. Acid-extractable fraction played a more important role than other fractions in controlling the mobility and bioavailability of Cu. DTPA-extractable Cu may overestimate the Cu bioavailability since DTPA solution could extract soluble and part of stable forms. The application of LM at 1% level significantly decline the Cu mobility, but that at 3% level exhibited the opposite effect. Although the quantities of Cu in wheat was very low compared with the accumulation in soil, Cu concentrations in roots increased evidently from 12 to 533 mg kg⁻¹ and that in aerial parts were in a narrow range from 12.1 to 32.7 mg kg⁻¹, indicating the more sensitivity of roots to the Cu toxicity. The Cu concentrations in grains after 3% manure application did not approach the threshold for Cu toxicity (< 20mg kg⁻¹) even at higher Cu addition rates.

Chromosome mapping of five differently expressed miRNAs in porcine skeletal muscle development (Brief Report)

Abstract. MicroRNAs (miRNAs) are a class of short, non-coding regulatory RNAs, which are approximately 22 nucleotides in length. Typically, miRNAs negatively regulate gene expression by binding with the 3' untranslated region (UTR) of its regulatory target mRNAs. MicroRNAs are known to play diverse roles in fundamental biological processes, such as proliferation, differentiation and apoptosis (Bartel 2004, 2009). It has been reported that miR-1, miR-133, miR-181 and miR-206 play important roles in skeletal muscle proliferation and hypertrophy (Callis et al. 2007, McCarthy -Esser 2007). We have detected porcine miRNA expression profiles during different stage of skeletal muscle development and a total of 140 miRNAs were differentially expressed (HUANG et al. 2008). In this study, we mapped five differentially expressed miRNAs (mir-29c, mir-103-1, mir-127, mir-193b and mir-218-1) using the radiation hybrid (IMpRH) panel (YERLE et al. 1998).

Effect of Schistosoma japonicum infection on serum testosterone levels in mice

OBJECTIVE

To determine the effect of Schistosoma japonicum infection on the testoterone level in the sera from male C57BL/6 mice.

METHODS

Radioimmunoassay was used to examine testosterone levels in sera of 9 male mice experimentally infected with Schistosoma japonicum.

RESULTS

The serum testosterone levels reduced significantly in all experimentally infected animals 45 days after infection, as compared with the uninfected controls.

CONCLUSION

Infection with Schistosoma japonicum decreases testosterone levels in the mouse host.

Increased vascular adrenergic vasoconstriction and decreased vasodilation in blacks. Additive mechanisms leading to enhanced vascular reactivity

Blood pressure reactivity is enhanced in young black subjects through mechanisms that are poorly understood. We compared alpha-adrenergic-mediated vasoconstrictor and ss-adrenergic vasodilator sensitivity and their relation to sympathetic activity in blacks and whites. Ten healthy black (age, 29.9+/-2.4 years) and 10 white (age, 28.3+/-1.9 years) men were studied. Forearm blood flow was measured with strain-gauge plethysmography after the intrabrachial artery administration of phenylephrine (1.25 to 20 microgram/min) and isoproterenol (60 and 400 ng/min) after application of lower-body negative pressure and after a cold pressor test. Forearm and systemic norepinephrine spillover were measured with a radioisotope dilution technique. alpha-Adrenergic vasoconstriction was markedly increased (ANOVA P=0.008) and ss-adrenergic vasodilation decreased (ANOVA P=0.02) in blacks. Phenylephrine (10 microgram/min) decreased forearm blood flow by 58.0+/-2.5% in blacks but only by 26.6+/-6.0% in whites (P<0.001). Vasoconstrictor response to endogenous norepinephrine, stimulated by a cold pressor test, resulted in a higher forearm vascular resistance in blacks than in whites (107.3+/-13 versus 64.8+/-13 mm Hg. mL(-)(1). 100 mL(-)(1), P=0.03). There were no significant ethnic differences in basal or stimulated forearm or systemic norepinephrine spillover. Increased vasoconstrictor and decreased vasodilator responses in blacks were not correlated. Increased sympathetically mediated vascular tone caused by enhanced vasoconstriction and attenuated vasodilation, effects that would be additive, and not increased sympathetic activity could enhance vascular reactivity and may play a role in the pathogenesis of hypertension in blacks.

Basal and stimulated sympathetic responses after epinephrine: no evidence of augmented responses

Delayed facilitation of norepinephrine release through the action of epinephrine (NE) at presynaptic beta-adrenoceptors has been postulated to account for the delayed hemodynamic effects of epinephrine and to be a mechanism causally related to the development of hypertension. To determine whether a short-term increase in epinephrine concentrations resulted in subsequent facilitation of sympathetic responses, 9 healthy subjects (age, 21+/-0.9 years) were studied at rest and during physiological stress on 2 occasions when they received an infusion of either saline or epinephrine (20 ng/kg per minute) in random order. Heart rate, blood pressure, forearm blood flow, epinephrine concentrations, and NE spillover were measured at rest, during mental stress (Stroop test), and during a cold pressor test. Measurements were performed before, during the 1-hour infusion of epinephrine or placebo, and 1 hour after the infusion. A radioisotope dilution method was used to measure NE spillover. Hemodynamic measurements and NE spillover were increased during the infusion of epinephrine, but 1 hour after discontinuation of epinephrine there was no significant augmentation of hemodynamic or sympathetic responses. NE spillover 1 hour after saline or epinephrine infusion was similar (0.85+/-0.2 versus 0. 87+/-0.2 microg/min; P=0.92). In addition, there was no delayed facilitation of stress-induced hemodynamic or NE responses after epinephrine. These findings do not support the hypothesis that epinephrine results in delayed facilitation of NE release.

Angiotensin II mediates systemic rebound hypertension after cessation of prostacyclin infusion in sheep

Prostacyclin (or epoprostenol), an arachidonic acid metabolite, is an effective treatment for patients with primary pulmonary hypertension. Interruption of chronic prostacyclin infusion can result in recurrent symptoms of dyspnea and fatigue. The etiology of this phenomenon is unknown. We hypothesized that sympathoadrenal activation could lead to increased vascular tone after abrupt termination of the infusion. To evaluate this effect, we monitored six chronically instrumented, awake sheep during and after infusion of prostacyclin. Prostacyclin decreased mean arterial pressure (MAP) by 14% and increased cardiac output by 33%. After the infusion ceased, MAP rebounded 23% above baseline, and cardiac output decreased by 28% from peak values within 10 min. We were unable to demonstrate an increase in norepinephrine levels after cessation of prostacyclin, nor did alpha-adrenergic blockade affect postinfusion hemodynamics. However, plasma renin activity increased >10-fold at peak infusion and remained elevated for up to 2 h after discontinuation of prostacyclin. Coinfusion of the angiotensin II-receptor antagonist L-158,809 resulted in complete abrogation of the postcessation rise in MAP. We conclude that renin-angiotensin system activation is primarily responsible for systemic hypertension occurring after abrupt cessation of prostacyclin infusion in sheep and that angiotensin II receptor blockade prevents this response. Our data do not support a role for sympathetic nervous system activation in the systemic pressor response after prostacyclin infusion.

Norepinephrine release in the human forearm: effects of epinephrine

It has been postulated that delayed facilitation of norepinephrine release by epinephrine is causally related to the development of hypertension. It has been proposed that a brief increase in epinephrine concentrations results in the uptake of epinephrine into the sympathetic nerve terminal. Subsequent rerelease of epinephrine stimulates presynaptic beta-adrenergic receptors, resulting in a prolonged increase in plasma norepinephrine (NE) concentrations, with amplified sympathetic responses and vasoconstriction. To determine whether such epinephrine-induced, delayed facilitation of NE release occurs in a vascular bed draining resistance vessels and, if it occurs, whether that facilitation differs in hypertension, we used a radioisotope dilution method to measure unstimulated and isoproterenol-stimulated forearm NE spillover before, during, and after a 50 ng/min infusion of epinephrine for 30 minutes directly into the brachial artery. No delayed facilitatory effects of epinephrine on forearm NE spillover were observed in either 6 normotensive (NT) or 8 borderline hypertensive (BHT) subjects (NT unstimulated forearm NE spillover preepinephrine 1.79+/-0.41 ng/min versus postepinephrine 2.36+/-0.65 ng/min, P=.38; BHT preepinephrine 2.24+/-0.70 ng/min versus postepinephrine 1.93+/-0.46 ng/min, P=.51; NT isoproterenol-stimulated forearm NE spillover preepinephrine 4.61+/-1.01 ng/min versus postepinephrine 4.4+/-0.98 ng/min, P=.9; BHT preepinephrine 4.04+/-1.36 ng/min versus postepinephrine 4.69+/-1.49 ng/min P=.5). We conclude that the short-term local infusion of epinephrine does not have a delayed facilitatory effect on forearm NE spillover in NT or BHT subjects. Therefore, the prolonged increase in NE concentrations after epinephrine infusion previously shown systemically, and not seen locally in the forearm, suggests that the delayed facilitatory response to epinephrine may occur in other organs.

Sympathoinhibitory response to clonidine is blunted in patients with heart failure

To determine whether alpha2-adrenergic-mediated sympathoinhibition was altered in chronic heart failure, sympathoinhibitory sensitivity was assessed using the alpha2-adrenergic agonist clonidine in 7 patients with heart failure and in 10 healthy control subjects. Basal norepinephrine spillover was significantly higher in patients with heart failure (1.3+/-0.3 microg/min) than in control subjects (0.7+/-0.1 microg/min, P=.05). Compared with control subjects, the decrement in norepinephrine spillover to cumulative doses of clonidine (1, 2, and 3 microg/kg administered intravenously) was significantly less in patients with heart failure (P<.05). Blood pressure also tended to decrease less in patients with heart failure (P=.06). The doses of clonidine required to produce a 10% decrease in blood pressure and a 25% decrease in norepinephrine spillover were significantly higher in heart failure (P<.01 and P=.05, respectively). Thus, although clonidine lowers norepinephrine spillover significantly in patients with heart failure, such patients are less sensitive to clonidine than healthy control subjects. This difference in sensitivity suggests that doses of clonidine provide effective sympathoinhibition will need to be selected for studies that will evaluate the potential therapeutic effect of clonidine in heart failure.

Blunted blood pressure response to central sympathoinhibition in normotensive blacks: increased importance of nonsympathetic factors in blood pressure maintenance in blacks

Enhanced sympathetic reactivity may predispose blacks to the development of hypertension and may occur because of increased sympathetic stimulation and/or attenuated sympathoinhibition. A potential site for such attenuated sympathetic inhibition may be at the level of central alpha2-adrenergic receptors, which play an important role in the feedback inhibition of norepinephrine release. We used cumulative doses (1, 2, and 3 microg/kg I.V.) of the centrally acting alpha2-adrenergic agonist clonidine to measure the sensitivity of alpha2-adrenoceptor-mediated sympathoinhibition and the resultant hypotensive response in 8 normotensive blacks and 10 normotensive whites. Sympathetic activity was determined by radioisotope dilution methodology. Basal norepinephrine spillover was similar in blacks (0.80+/-0.14 microg/min) and whites (0.73+/-0.19 microg/min, P=NS) and after clonidine decreased significantly in both blacks (0.21+/-0.07 microg/min, P<.0001) and whites (0.24+/-0.06 microg/min, P<.0001), with no difference between the groups (P=NS). Despite this similar degree of sympathoinhibition, the hypotensive response to clonidine was markedly blunted in blacks, such that mean arterial pressure decreased by only 10% in blacks but by 21% in whites (P<.0001). The smaller blood pressure decrement after clonidine in normotensive blacks, in the face of an equal degree of sympathoinhibition, suggests that even when sympathetic tone is decreased to the same level in blacks and whites, normotensive blacks have less reduction in blood pressure than whites, implying that nonadrenergic mechanisms contribute more to blood pressure maintenance in blacks than whites. Whether a similar interethnic difference in response to sympathoinhibition occurs in hypertensive patients is as yet unknown.

Angiotensin converting enzyme inhibition and sympathetic activity in healthy subjects

BACKGROUND

One suggested mechanism for the reduction in mortality rates resulting from the use of angiotensin converting enzyme inhibitors in congestive heart failure is the inhibition of the angiotensin II-mediated norepinephrine release. Direct evidence for this mechanism is lacking in humans.

SUBJECTS AND METHODS

We examined the effects of captopril, 25 mg three times a day, or matched placebo for 7 days on sympathetic activity during a 10 mEq/day sodium diet in seven healthy male subjects aged 30 +/- 3 (SEM) years. A tritiated norepinephrine radioisotope dilution technique was used to measure sympathetic activity, both at rest and during isometric handgrip exercise.

RESULTS

Captopril blunted the increase in mean arterial pressure during isometric handgrip exercise (placebo, from 81 +/- 4 to 112 +/- 2 mm Hg; captopril, from 78 +/- 3 to 101 +/- 2 mm Hg; p < 0.01). However, the increase in systemic norepinephrine spillover during isometric handgrip exercise was not blunted by captopril. Captopril had no effect on resting mean arterial pressure or systemic norepinephrine spillover.

CONCLUSIONS

Captopril did not attenuate baseline or static exercise-stimulated sympathetic activity in healthy subjects. These findings would indicate that angiotensin converting enzyme inhibition does not decrease sympathetic activity at rest or during the stimulus of isometric handgrip exercise.

Triazolam pharmacokinetics and pharmacodynamics in Caucasians and Southern Asians: ethnicity and CYP3A activity

A threefold higher area under the plasma drug concentration-time curve (AUC) of nifedipine, a substrate of cytochrome P4503A (CYP3A), has been shown in Southern Asians when compared with Caucasians. To determine if these differences are specific to nifedipine or apply to other substrates of CYP3A, we examined the pharmacokinetics and pharmacodynamics of 0.375 mg triazolam, another substrate of CYP3A, in eight healthy Caucasians and eight healthy Southern Asians in a double-blind placebo-controlled study. When compared with Caucasians, Southern Asians achieved higher maximum plasma concentration (Cmax) (8.0 +/- 2.6 vs 4.8 +/- 1.9 ng ml-1; the 95% confidence interval (CI) of the mean difference was 0.76 to 5.7; P < 0.01) and had a shorter time to reach maximal concentration (tmax) (45 min (range 30-75) vs 90 min (range 60-145); the 95% CI of the mean difference was -69 to -20; P < 0.002). Triazolam AUC, clearance and partial metabolic clearance did not differ significantly between Southern Asians and Caucasians. Significant differences were found in postural sway after triazolam when compared with placebo in both Caucasians (double stance: eyes open (DSEO): 172.9 +/- 82.9 vs 1138.9 +/- 1182.4; the 95% CI of the mean difference was -1897.2 to -34.4; P < 0.04; and Southern Asians (DSEO: 216.2 +/- 80.9 vs 1086.0 +/- 827.1; the 95% CI of the mean difference was -1564.2 to -175.6; P = 0.02; double stance: eyes closed (DSEC): 207.5 +/- 89.8 vs 1156.9 +/- 932.1; the 95% CI of the mean difference was -1718.5 to -178.5; P = 0.02; with no significant difference between the two ethnic groups. These results suggest that the large inter-ethnic difference in nifedipine clearance are not generalizable to all CYP3A4 substrates.

Attenuation of isoproterenol-mediated vasodilatation in blacks

BACKGROUND

The mechanism of enhanced vascular reactivity in young blacks, which may play a part in the development of hypertension, has not been defined. To determine the contribution of blunted vasodilatation mediated by beta 2-adrenergic receptors to this phenomenon, we compared forearm blood-flow responses to isoproterenol in young black and white normotensive men.

METHODS

We used venous-occlusion plethysmography to measure the responses of blood flow in the forearm to the intraarterial administration of isoproterenol (10 to 400 ng per minute) in 9 normotensive black men (mean [+/- SD] age, 31.3 +/- 8.0 years) and 13 normotensive white men (mean age, 32.9 +/- 5.6 years). Sympathetic activity in the forearm was measured simultaneously by isotope-dilution techniques.

RESULTS

Base-line blood flow in the forearm was similar in blacks and whites, but the degree of vasodilatation in response to isoproterenol was markedly lower in blacks. Isoproterenol at an infusion rate of 400 ng per minute produced a 9-fold increase in blood flow in whites but only a 3.5-fold increase in blacks (P < 0.001). The base-line rate of norepinephrine spillover in the forearm was higher in blacks (2.0 +/- 1.3 ng per minute [11.8 +/- 7.7 nmol per minute]) than in whites (0.6 +/- 0.5 ng per minute [3.5 +/- 3.0 nmol per minute], P = 0.002), but there was no difference between the groups after isoproterenol stimulation.

CONCLUSIONS

Forearm blood-flow responses to isoproterenol were markedly attenuated in normotensive blacks, indicating a blunting of vasodilatation mediated by beta 2-adrenergic receptors. Sympathetic activity in the forearm was greater in blacks than in whites, but isoproterenol-stimulated presynaptic beta 2-adrenergic responses (which facilitated norepinephrine release) did not differ significantly between blacks and whites. Our findings suggest that the mechanisms responsible for blunted vasodilatation in response to the administration of isoproterenol may contribute to enhanced vascular reactivity in blacks and may play a part in the pathogenesis of hypertension in blacks.

Regulation of norepinephrine release by beta 2-adrenergic receptors during halothane anesthesia

BACKGROUND

Presynaptic receptors control norepinephrine (NE) release. It has been hypothesized that epinephrine stimulates prejunctional beta 2-adrenergic receptors to facilitate NE release from sympathetic nerve endings, and therefore, presynaptic receptors controlling NE release are potential therapeutic targets to limit the adverse effects of excess sympathetic stimulation during anesthesia. We have previously demonstrated beta 2-adrenergic receptor-augmented release of NE in the human forearm and have shown that halothane inhibits sympathetic activity in vivo by decreasing the NE spillover rate into plasma. The goal of the current study was to determine the effect of halothane on beta 2-adrenergic receptor-augmented NE release in a canine hind-limb experimental model.

METHODS

Seven female dogs were studied awake and during halothane anesthesia (1.0 minimum alveolar concentration). A trace dosage of [3H]NE (15 microCi over a 1-min period and 0.6 microCi/min thereafter) was infused into the femoral vein. Before and during femoral arterial administration of isoproterenol at two dosages (30 and 80 mg/min), hind-limb blood flow was measured by an ultrasonic flow probe and hind-limb NE spillover by an isotope dilutional technique.

RESULTS

In awake dogs, isoproterenol significantly increased hind-limb blood flow and NE spillover into the hind limb. Halothane had no effect on baseline or isoproterenol-stimulated hind-limb blood flow (a postjunctional beta 2 effect) but significantly inhibited the isoproterenol-induced increase in hind-limb NE spillover (a prejunctional beta 2 effect).

CONCLUSIONS

The isoproterenol-mediated increase in NE release is inhibited by halothane anesthesia, indicating that halothane inhibits prejunctional beta 2-adrenergic receptor regulation of NE release.

Effect of enflurane and isoflurane on norepinephrine kinetics: a new approach to assessment of sympathetic function during anesthesia

We investigated the effects of enflurane [1.0 and 1.5 minimum alveolar concentration (MAC)] and isoflurane (1.0, 1.5, and 2.0 MAC) on norepinephrine (NE) spillover (a measure of NE release rate) and NE clearance in 16 dogs, by using an isotope (3H-NE) dilution technique. During anesthesia with either enflurane or isoflurane, endogenous NE concentrations decreased markedly. In contrast, 3H-NE concentrations increased or remained unchanged. There was a significant (P < 0.05) reduction in NE spillover with both anesthetics at all doses studied. NE spillover decreased by 54% +/- 6% and 68% +/- 4% at 1.0 MAC enflurane and 1.5 MAC enflurane, respectively. Isoflurane decreased NE spillover by 54% +/- 8%, 59% +/- 9%, and 71% +/- 8% at 1.0 MAC, 1.5 MAC, and 2.0 MAC isoflurane, respectively. NE clearance was reduced by both anesthetics; enflurane reduced NE clearance (P < 0.05) at all concentrations studied, whereas NE clearance was reduced by 24% +/- 8% from awake values only at the highest dose of isoflurane (P < 0.05, 2.0 MAC). For enflurane, NE clearance was decreased by 17% +/- 5% at 1.0 MAC and 37% +/- 7% at 1.5 MAC enflurane. Because decreased NE clearance would otherwise have increased NE plasma concentration, our measured decreases in endogenous plasma NE concentrations probably did not reflect the actual extent of sympathetic inhibition produced by enflurane and isoflurane.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimization of high-performance liquid chromatographic assay for catecholamines. Determination of optimal mobile phase composition and elimination of species-dependent differences in extraction recovery of 3,4-dihydroxybenzylamine

This paper describes the application of a window diagram technique to optimize the four components of eluent (sodium acetate, sodium heptanesulfonate, acetonitrile and pH adjusted by monochloroacetic acid), for complete separation of five catecholamine compounds and the internal standard (3,4-dihydroxybenzylamine, DHBA). In addition, studies were performed to address the problem of the variable recovery of DHBA from dog plasma due to a time-dependent loss of DHBA. We found that this phenomenon can be prevented by pH adjustment prior to addition of DHBA, allowing development of an accurate high-performance liquid chromatographic assay for plasma catecholamines in dogs.

Effects of anesthesia on norepinephrine kinetics. Comparison of propofol and halothane anesthesia in dogs

Alteration of sympathetic function is a major determinant of the cardiovascular effects of anesthetic agents. Plasma norepinephrine (NE) concentrations are determined not only by the rate of NE release from sympathetic nerves but also by NE clearance rate. Therefore, NE concentration in plasma may be an inadequate index of sympathetic activity. We used an isotope dilution technique to investigate the effects of halothane and propofol anesthesia on NE kinetics. A relationship of NE kinetics to halothane dose was determined in six dogs. Halothane 1.0 MAC reduced plasma NE concentration by 35 +/- 9% versus awake (P less than 0.05). This was due to a reduction of 52 +/- 9% in NE spillover (P less than 0.05) accompanied by a reduction of 27 +/- 5% in NE clearance (P less than 0.005). The clearance changes were dose-dependent: reductions were 34 +/- 4% at 1.5 MAC (P less than 0.05 vs. 1.0 MAC) and 45 +/- 5% at 2.0 MAC (P less than 0.05 vs. 1.5 MAC). Six dogs were studied with a single halothane dose (1.0 MAC) and NE concentration, spillover, and clearance were found to be stable over a period of 5.5 h of anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)