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Brooks VL, Fu Q, Shi Z, Heesch CM. Adaptations in autonomic nervous system regulation in normal and hypertensive pregnancy. HANDBOOK OF CLINICAL NEUROLOGY 2020; 171:57-84. [PMID: 32736759 DOI: 10.1016/b978-0-444-64239-4.00003-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
There is an increase in basal sympathetic nerve activity (SNA) during normal pregnancy; this counteracts profound primary vasodilation. However, pregnancy also impairs baroreflex control of heart rate and SNA, contributing to increased mortality secondary to peripartum hemorrhage. Pregnancy-induced hypertensive disorders evoke even greater elevations in SNA, which likely contribute to the hypertension. Information concerning mechanisms is limited. In normal pregnancy, increased angiotensin II acts centrally to support elevated SNA. Hypothalamic sites, including the subfornical organ, paraventricular nucleus, and arcuate nucleus, are likely (but unproven) targets. Moreover, no definitive mechanisms for exaggerated sympathoexcitation in hypertensive pregnancy have been identified. In addition, normal pregnancy increases gamma aminobutyric acid inhibition of the rostral ventrolateral medulla (RVLM), a key brainstem site that transmits excitatory inputs to spinal sympathetic preganglionic neurons. Accumulated evidence supports a major role for locally increased production and actions of the neurosteroid allopregnanolone as one mechanism. A consequence is suppression of baroreflex function, but increased basal SNA indicates that excitatory influences predominate in the RVLM. However, many questions remain regarding other sites and factors that support increased SNA during normal pregnancy and, more importantly, the mechanisms underlying excessive sympathoexcitation in life-threatening hypertensive pregnancy disorders such as preeclampsia.
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Affiliation(s)
- Virginia L Brooks
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR, United States.
| | - Qi Fu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, TX, United States; Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, United States
| | - Zhigang Shi
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR, United States
| | - Cheryl M Heesch
- Department of Biomedical Sciences and Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, United States
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Hines T, Veeh J, Grimes D. The Hypo-Osmolality of Pregnancy Does Not Alter Baroreceptor Responses to Acute Changes in Osmolality. Biol Res Nurs 2016; 7:214-21. [PMID: 16552949 DOI: 10.1177/1099800405283032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Reducing extracellular osmolality by 10-12 mOsm/L reduces baroreceptor firing in vitro in tissues from male rats. Pregnancy is associated with a similar reduction in plasma osmolality (pOsm) as well as with alterations in baroreceptor firing and reduced baroreceptor reflex activity. Mechanisms for reduced baroreflex activity are not yet understood, but they have important implications for maintenance of cardiovascular homeostasis in the pregnant female. Thus, this study was designed to test whether changes in plasma osmolality alter baroreceptor discharge during pregnancy. Late-gestation pregnant and virgin control rats were anesthetized, femoral vessels were cannulated for measurement of arterial pressure and drug infusion, and the aortic depressor nerve, containing baroreceptor afferents, was isolated and prepared for recording. Plasma osmolality was measured before and 30 min after graded intraperitoneal injections of NaCl (50-1500 mOsm/L). Arterial pressure, heart rate, and aortic depressor nerve activity (ADNA) were measured continuously before and after injections. A 50 mOsm/L NaCl injection significantly decreased pOsm but did not alter ADNA in either group. Likewise, 1200 mOsm/L NaCl injections significantly increased pOsm and had no effect on ADNA in either group. The 1500 mOsm salt load significantly increased pOsm and ADNA in pregnant rats, and in virgin animals, it increased pOsm but evoked a paradoxical decrease in ADNA. The authors’ studies indicate that pOsm has minimal effects on baroreceptor activity, which are not significantly different during gestation. Their findings suggest that in vitro data from male rats indicating a correlation between pOsm and baroreceptor discharge are not applicable in anesthetized intact female animals.
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Affiliation(s)
- Tina Hines
- University of Missouri, Kansas City School of Nursing, Kansas City, MO 64108, USA.
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Brooks VL, Dampney RAL, Heesch CM. Pregnancy and the endocrine regulation of the baroreceptor reflex. Am J Physiol Regul Integr Comp Physiol 2010; 299:R439-51. [PMID: 20504907 PMCID: PMC2928618 DOI: 10.1152/ajpregu.00059.2010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2010] [Accepted: 05/19/2010] [Indexed: 02/07/2023]
Abstract
The purpose of this review is to delineate the general features of endocrine regulation of the baroreceptor reflex, as well as specific contributions during pregnancy. In contrast to the programmed changes in baroreflex function that occur in situations initiated by central command (e.g., exercise or stress), the complex endocrine milieu often associated with physiological and pathophysiological states can influence the central baroreflex neuronal circuitry via multiple sites and mechanisms, thereby producing varied changes in baroreflex function. During pregnancy, baroreflex gain is markedly attenuated, and at least two hormonal mechanisms contribute, each at different brain sites: increased levels of the neurosteroid 3alpha-hydroxy-dihydroprogesterone (3alpha-OH-DHP), acting in the rostral ventrolateral medulla (RVLM), and reduced actions of insulin in the forebrain. 3alpha-OH-DHP appears to potentiate baroreflex-independent GABAergic inhibition of premotor neurons in the RVLM, which decreases the range of sympathetic nerve activity that can be elicited by changes in arterial pressure. In contrast, reductions in the levels or actions of insulin in the brain blunt baroreflex efferent responses to increments or decrements in arterial pressure. Although plasma levels of angiotensin II are increased in pregnancy, this is not responsible for the reduction in baroreflex gain, although it may contribute to the increased level of sympathetic nerve activity in this condition. How these different hormonal effects are integrated within the brain, as well as possible interactions with additional potential neuromodulators that influence baroreflex function during pregnancy and other physiological and pathophysiological states, remains to be clearly delineated.
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Affiliation(s)
- Virginia L Brooks
- Dept. of Physiology and Pharmacology, L-334, Oregon Health & Science Univ., 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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Kvochina L, Hasser EM, Heesch CM. Pregnancy increases baroreflex-independent GABAergic inhibition of the RVLM in rats. Am J Physiol Regul Integr Comp Physiol 2007; 293:R2295-305. [PMID: 17898121 PMCID: PMC2841061 DOI: 10.1152/ajpregu.00365.2007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
During baroreceptor unloading, sympathoexcitation is attenuated in near-term pregnant compared with nonpregnant rats. Alterations in balance among different excitatory and inhibitory inputs within central autonomic pathways likely contribute to changes in regulation of sympathetic outflow in pregnancy. Both baroreflex-dependent and baroreflex-independent GABAergic inputs inhibit sympathoexcitatory neurons within rostral ventrolateral medulla (RVLM). The present experiments tested the hypothesis that influence of baroreflex-independent GABAergic inhibition of RVLM is greater in pregnant compared with nonpregnant rats. Afferent baroreceptor inputs were eliminated by bilateral sinoaortic denervation in inactin-anesthetized rats. In pregnant compared with nonpregnant rats, baseline mean arterial pressure (MAP) was lower (pregnant = 75 +/- 6 mmHg, nonpregnant = 115 +/- 7 mmHg) and heart rate was higher (pregnant = 381 +/- 10 beats/min, nonpregnant = 308 +/- 10 beats/min). Pressor and sympathoexcitatory [renal sympathetic nerve activity, (RSNA)] responses due to bilateral GABA(A) receptor blockade (bicuculline, 4 mM, 100 nl) of the RVLM were greater in pregnant rats (delta MAP: pregnant = 101 +/- 4 mmHg, nonpregnant = 80 +/- 6 mmHg; delta RSNA: pregnant = 182 +/- 23% control, nonpregnant = 133 +/- 10% control). Unexpected transient sympathoexcitatory effects of angiotensin AT(1) receptor blockade in the RVLM were greater in pregnant rats. Although excitatory responses to bicuculline were attenuated by prior RVLM AT1 receptor blockade in both groups, pressor responses to disinhibition of the RVLM remained augmented in pregnant rats. Increased influence of baroreflex-independent GABAergic inhibition in RVLM could contribute to suppressed sympathoexcitation during withdrawal of arterial baroreceptor input in pregnant animals.
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Affiliation(s)
- Lyudmyla Kvochina
- Department of Biomedical Sciences, Univ. of Missouri, 134 Research Park, Columbia, MO 65211, USA
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Hines T, Abhyankar SS, Veeh JM. Right atrial dimension-pressure relation during volume expansion is unaltered by pregnancy in the rat. Am J Physiol Heart Circ Physiol 2005; 288:H116-20. [PMID: 15374826 DOI: 10.1152/ajpheart.00551.2004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Blood volume expands significantly during pregnancy, but afferent signals from cardiac receptors are reduced. In addition, during exogenous volume expansion, right atrial pressure (RAP) increases more for equivalent volumes in pregnant animals, implying reduced atrial compliance. To examine possible gestational alterations in atrial dimension during volume expansion, we compared the effects of volume expansion on RAP and right atrial dimension (RAD) in pregnant vs. virgin rats. Anesthetized animals were ventilated and catheterized for measurement of arterial pressure and RAP and for drug infusion. Through a parasternal incision, ultrasonic crystals were glued to the medial and lateral surfaces of the right atrium for measurement of RAD. Plasma volume and hematocrit were determined before experimentation. RAP, RAD, and arterial pressure were recorded at baseline and during progressive volume expansion (6% dextran, 60% of initial blood volume). Baseline RAP was similar in the two groups: 2.82 ± 0.40 and 2.72 ± 0.47 mmHg in pregnant and virgin rats, respectively. Basal RAD was significantly larger in pregnant than in virgin rats: 4.36 ± 0.66 vs. 3.36 ± 0.48 mm. Despite increased basal RAD in pregnant rats, the slope of the RAD-RAP relation during volume expansion was similar in the two groups. Results indicate that resting RAD is increased in pregnant rats and that the change in dimension during volume loads is similar to that in virgin rats. Thus, during pregnancy, the right atrium appears to accommodate the increased blood volume, and reduced afferent signaling most likely is due to mechanisms other than mechanical alterations of the atrium by expanded volume.
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Affiliation(s)
- Tina Hines
- University of Missouri Kansas City School of Nursing, 2220 Holmes St., Kansas City, MO 64108, USA.
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Storey E, Kaufman S. Effect of pregnancy and 5α-pregnan-3α-ol-20-one on atrial receptor afferent discharge in rats. Am J Physiol Regul Integr Comp Physiol 2004; 287:R1427-33. [PMID: 15319223 DOI: 10.1152/ajpregu.00693.2003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The atrial volume reflex is attenuated in pregnancy. This may be mimicked by chronic administration of 5α-pregnan-3α-ol-20-one (pregnan). We investigated whether afferent output from sensory receptors may be suppressed at this time. Vagal afferent nerve activity was measured during discrete localized stimulation of the atrial volume receptors by inflation of a balloon at the superior vena caval-right atrial junction. The receptors were classified as high- (HF) or low- (LF) frequency subtypes on the basis of their response to graded atrial distension. Although both HF (regression coefficient = 0.50 ± 0.11 Hz/μl, r2 = 0.47, P < 0.001) and LF (regression coefficient = 0.03 ± 0.05 Hz/μl, r2 = 0.009, P = 0.613) subtypes could be identified in virgin rats, only LF (regression coefficient = 0.09 ± 0.05 Hz/μl, r2 = 0.044, P = 0.099) receptors were found in late-pregnant animals. Similarly, in virgin rats treated chronically with pregnan (500 μg/24 h for 2 days), only LF receptors were identified (regression coefficient = −0.004 ± 0.078 Hz/μl, r2 = 0.000, P = 0.962), whereas both subtypes were present in the vehicle-treated animals (HF regression coefficient = 0.626 ± 0.255 Hz/μl, r2 = 0.317, P = 0.029; LF regression coefficient = −0.012 ± 0.071 Hz/μl, r2 = 0.002, P = 0.866). By contrast, acute intracardiac pregnan (2.6 μg/kg) did not alter vagal afferent nerve activity. In conclusion, stretch-induced discharge of high-frequency atrial receptors is suppressed during pregnancy, whereas that of low-frequency receptors is preserved. This effect may be mimicked by chronic, but not acute, pregnan. We propose that, during pregnancy, pregnan alters the transducer properties of the atrial volume receptors, thus allowing blood volume to increase.
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Affiliation(s)
- Elaine Storey
- Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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Tam SL, Kaufman S. NOS inhibition restores renal responses to atrial distension during pregnancy. Am J Physiol Regul Integr Comp Physiol 2002; 282:R1364-7. [PMID: 11959677 DOI: 10.1152/ajpregu.00705.2001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Nitric oxide (NO) biosynthesis increases during pregnancy and has been shown to suppress baroreceptor activity. The renal response to a simulated increase in circulating blood volume (atrial distension) is also attenuated at this time. We hypothesized that blocking NO biosynthesis during pregnancy would restore the renal response. Female rats were implanted with indwelling intracardiac balloons and central venous cannulas. After recovery, they were mated, and on day 14 of pregnancy, osmotic minipumps containing the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) or its inactive enantiomer N(G)-nitro-D-arginine methyl ester (D-NAME) (120 mg/2 ml at 10 microg/min) were implanted. In response to atrial distension (1 h), urine output increased in the D- and L-NAME-treated virgin rats. During pregnancy (day 20), this response was attenuated in the D-NAME-treated, but not the L-NAME-treated, animals, i.e., after a simulated increase in circulating blood volume, inhibition of NO biosynthesis restored the renal response of pregnant rats to that seen in virgin animals. We conclude that, during normal pregnancy, increased NO biosynthesis blunts the reflex renal response to atrial distension.
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Affiliation(s)
- Siu Lin Tam
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
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Lo F, Kaufman S. Effect of 5α-pregnan-3α-ol-20-one on nitric oxide biosynthesis and plasma volume in rats. Am J Physiol Regul Integr Comp Physiol 2001; 280:R1902-5. [PMID: 11353698 DOI: 10.1152/ajpregu.2001.280.6.r1902] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Plasma 5α-pregnan-3α-ol-20-one (pregnan) levels and nitric oxide (NO) biosynthesis increase during pregnancy. These factors have independently been implicated in the control of blood pressure and volume. We wished to determine whether pregnan might be responsible both for the increase in NO biosynthesis and for the increase in plasma volume observed during pregnancy. Virgin female Long-Evans rats were implanted with indwelling cannulas and maintained on a low nitrate/nitrite diet. After the rats recovered from surgery, 500 μg of pregnan or vehicle were given daily for 2 days. NO biosynthesis and plasma volume were measured in conscious animals before and after treatment. Pregnan caused a significant increase in NO biosynthesis (1.9 ± 0.8 μmol/24 h, n = 10) compared with the vehicle-treated control group (0.3 ± 0.4 μmol/24 h, n = 10, P < 0.05). Similarly, there was a significant increase in plasma volume in the pregnan-treated group (0.7 ± 0.2 ml/100 g, n = 11) compared with the vehicle-treated control group (0.2 ± 0.1 ml/100 g, n = 11, P < 0.05). These results confirm that pregnan can mimic pregnancy by its ability to increase both NO biosynthesis and plasma volume.
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Affiliation(s)
- F Lo
- Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2S2, Canada.
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Hines T, Herzer WA. Effect of cardiac receptor stimulation on renal vascular resistance in the pregnant rat. Am J Physiol Regul Integr Comp Physiol 2000; 278:R171-8. [PMID: 10644636 DOI: 10.1152/ajpregu.2000.278.1.r171] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stimulation of cardiac receptors (CR) evokes blunted reflex reductions in mean arterial pressure (MAP) in pregnant compared with virgin rats. Because CR-mediated sympathoinhibition has preferential effects on the kidney, we tested whether, during pregnancy, renal vascular resistance (RVR) changes less in response to CR stimulation and investigated possible mechanisms. MAP, right atrial pressure, renal sympathetic nerve activity (RSNA), renal blood flow (RBF), and RVR were measured in anesthetized animals in response to CR stimulation by graded atrial injections of saline. Baseline MAP and RVR and reflex changes in these variables during CR stimulation were reduced in late-pregnant vs. virgin rats (P<0.05). Reflex changes in RSNA were attenuated in pregnant rats, but changes in RBF as a function of RSNA were similar in both groups. ANG II AT(1)-receptor blockade increased basal RBF more in virgin rats (P<0.05), but between-group differences in reflex changes in MAP, RSNA, and RVR were maintained after AT(1) blockade. Thus during CR simulation, reflex changes in RVR were reduced in pregnant versus virgin rats. This difference does not appear to involve differential effects of ANG II.
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Affiliation(s)
- T Hines
- University of Pittsburgh School of Nursing and School of Medicine, Center for Clinical Pharmacology, Pittsburgh, Pennsylvania 15261, USA. thine+@pitt.edu
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Hines T, Hodgson TM. Pregnancy alters cardiac receptor afferent discharge in rats. Am J Physiol Regul Integr Comp Physiol 2000; 278:R149-56. [PMID: 10644633 DOI: 10.1152/ajpregu.2000.278.1.r149] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Reflex effects of cardiac receptor (CR) stimulation are attenuated in pregnant rats. We tested whether CR afferent discharge is reduced during pregnancy by measuring single fiber activity in response to increases in right atrial pressure (RAP) in anesthetized pregnant and virgin rats with sinoaortic denervation. Single fiber activity was isolated from fine filaments of the right cervical vagus nerve. Changes in CR discharge, RAP, and arterial pressure were recorded in response to atrial saline injections (25-300 microl). Resting RAP was similar between groups, and spontaneous CR discharge was similar in pregnant rats (1.95+/-0.21 Hz) and in low-frequency (LF) receptors in virgin rats (1.30+/-0.2 Hz). In virgin, but not pregnant rats, a subset (24%) of CR had higher-frequency (HF) spontaneous discharge (9.91+/-1.19 Hz). During stimulation, the level of RAP above which CR firing increased was significantly higher in pregnant rats, but CR activity was clustered into an LF discharge range. Thus gestation appears to reduce the activity of CR afferents, possibly by increasing stimulus threshold or by selective inactivation of a subset of HF discharging receptors.
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Affiliation(s)
- T Hines
- University of Pittsburgh School of Nursing, Pittsburgh, Pennsylvania 15261, USA. thine+@pitt.edu
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Abstract
1. We investigated the control of atrial natriuretic factor (ANF) secretion during pregnancy. 2. Plasma ANF levels were measured in conscious virgin female rats under basal conditions, and after atrial distension with an indwelling balloon catheter. The rats were then mated, and the measurements repeated at 7, 14 and 21 days of pregnancy, and at 1 week postpartum. Plasma ANF levels were also measured in ovariectomized rats injected with progesterone, oestradiol, or oestradiol plus progesterone. 3. Basal plasma ANF levels were elevated at 7 and 14 days of pregnancy, but returned to prepregnant levels by 21 days. At 1 week postpartum, they were again elevated. 4. In response to atrial stretch, plasma ANF increased significantly in virgin rats (from 100 +/- 10 to 148 +/- 13 pg ml-1, P < 0.001, n = 20). In contrast, there was no such secretory response observed in the pregnant and postpartum animals i.e. stretch-induced secretion of ANF was markedly attenuated. 5. Treatment with exogenous oestradiol caused a significant increase in plasma ANF levels in acyclic rats. However, neither progesterone nor a combination of oestradiol plus progesterone had any effect. 6. It is concluded that basal and stretch-induced ANF secretion are differentially influenced by pregnancy; oestradiol is identified as a potential stimulatory factor.
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Affiliation(s)
- Y Zhang
- Department of Medicine, University of Alberta, Edmonton, Canada
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