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Abstract
PURPOSE Although the autonomic and cardiovascular responses to arm and leg exercise have been studied, the sympathetic adjustments to exercise of the neck have not. The purpose of the present study was twofold: 1) to determine sympathetic and cardiovascular responses to isometric contractions of the neck extensors and 2) to compare sympathetic and cardiovascular responses to isometric exercise of the neck and forearm. METHODS Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP), and heart rate were measured in nine healthy subjects while performing isometric neck extension (INE) and isometric handgrip (IHG) in the prone position. After a 3-min baseline period, subjects performed three intensities of INE for 2.5 min each: 1) unloaded (supporting head alone), 2) 10% maximal voluntary contraction (MVC), and 3) 30% MVC, then subjects performed two intensities (10% and 30% MVC) of IHG for 2.5 min. RESULTS Supporting the head by itself did not significantly change any of the variables. During [NE, MAP significantly increased by 10 +/- 2 and 31 +/- 4 mm Hg and MSNA increased by 67 +/- 46 and 168 +/- 36 units/30 s for 10% and 30% MVC, respectively. IHG and INE evoked similar responses at 10% MVC, but IHG elicited higher peak MAP and MSNA at 30% MVC (37 +/- 7 mm Hg (P < 0.05) and 300 +/- 48 units/30 s (P < 0.01) for IHG, respectively). CONCLUSIONS The data indicate that INE can elicit marked increases in MSNA and cardiovascular responses but that it evokes lower peak responses as compared to IHG. We speculate that possible differences in muscle fiber type composition, muscle mass, and/or muscle architecture of the neck and forearm are responsible for these differences in peak responses.
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Abstract
Muscle sympathetic nerve activity (MSNA) increases with head-down neck flexion (HDNF). The present study had three aims: 1) to examine sympathetic and vascular responses to two different magnitudes of HDNF; 2) to examine these same responses during prolonged HDNF; and 3) to determine the influence of nonspecific pressure receptors in the head on MSNA. The first experiment tested responses to two static head positions in the vertical axis [HDNF and intermediate HDNF (I-HDNF; approximately 50% of HDNF)]. MSNA increased above baseline during both I-HDNF and HDNF (from 219 +/- 36 to 301 +/- 47 and from 238 +/- 42 to 356 +/- 59 units/min, respectively; P < 0.01). Calf blood flow (CBF) decreased and calf vascular resistance increased during both I-HDNF and HDNF (P < 0.01). Both the increase in MSNA and the decrease in CBF were linearly related to the magnitude of the downward head rotations (P < 0.01). The second experiment tested responses during prolonged HDNF. MSNA increased (from 223 +/- 63 to 315 +/- 79 units/min; P < 0.01) and CBF decreased (from 3.2 +/- 0.4 to 2.6 +/- 0.04 ml. 100 ml-1. min-1; P < 0.01) at the onset of HDNF. These responses were maintained throughout the 30-min period. Mean arterial blood pressure gradually increased during the 30 min of HDNF (from 94 +/- 4 to 105 +/- 3 mmHg; P < 0.01). In a third experiment, head-down neck extension was performed with subjects in the supine position. Unlike HDNF, head-down neck extension did not affect MSNA. The results from these studies demonstrate that MSNA: 1) increases in magnitude as the degree of HDNF increases; 2) remains elevated above baseline during prolonged HDNF; and 3) responses during HDNF are not associated with nonspecific receptors in the head activated by increases in cerebral pressure.
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Ray CA, Gfell LE, Buller TL, Gregory RL. Interactions of Streptococcus mutans fimbria-associated surface proteins with salivary components. CLINICAL AND DIAGNOSTIC LABORATORY IMMUNOLOGY 1999; 6:400-4. [PMID: 10225843 PMCID: PMC103730 DOI: 10.1128/cdli.6.3.400-404.1999] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Streptococcus mutans has been implicated as the major causative agent of human dental caries. S. mutans binds to saliva-coated tooth surfaces, and previous studies suggested that fimbriae may play a role in the initial bacterial adherence to salivary components. The objectives of this study were to establish the ability of an S. mutans fimbria preparation to bind to saliva-coated surfaces and determine the specific salivary components that facilitate binding with fimbriae. Enzyme-linked immunosorbent assay (ELISA) established that the S. mutans fimbria preparation bound to components of whole saliva. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot techniques were used to separate components of whole saliva and determine fimbria binding. SDS-PAGE separated 15 major protein bands from saliva samples, and Western blot analysis indicated significant binding of the S. mutans fimbria preparation to a 52-kDa salivary protein. The major fimbria-binding salivary protein was isolated by preparative electrophoresis. The ability of the S. mutans fimbria preparation to bind to the purified salivary protein was confirmed by Western blot analysis and ELISA. Incubation of the purified salivary protein with the S. mutans fimbria preparation significantly neutralized binding of the salivary protein-fimbria complex to saliva-coated surfaces. The salivary protein, whole saliva, and commercial amylase reacted similarly with antiamylase antibody in immunoblots. A purified 65-kDa fimbrial protein was demonstrated to bind to both saliva and amylase. These data indicated that the S. mutans fimbria preparation and a purified fimbrial protein bound to whole-saliva-coated surfaces and that amylase is the major salivary component involved in the binding.
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Abstract
The purpose of the present study was to determine the effect of leg exercise training on sympathetic nerve responses at rest and during dynamic exercise. Six men were trained by using high-intensity interval and prolonged continuous one-legged cycling 4 day/wk, 40 min/day, for 6 wk. Heart rate, mean arterial pressure (MAP), and muscle sympathetic nerve activity (MSNA; peroneal nerve) were measured during 3 min of upright dynamic one-legged knee extensions at 40 W before and after training. After training, peak oxygen uptake in the trained leg increased 19 +/- 2% (P < 0.01). At rest, heart rate decreased from 77 +/- 3 to 71 +/- 6 beats/min (P < 0.01) with no significant changes in MAP (91 +/- 7 to 91 +/- 11 mmHg) and MSNA (29 +/- 3 to 28 +/- 1 bursts/min). During exercise, both heart rate and MAP were lower after training (108 +/- 5 to 96 +/- 5 beats/min and 132 +/- 8 to 119 +/- 4 mmHg, respectively, during the third minute of exercise; P < 0.01). MSNA decreased similarly from rest during the first 2 min of exercise both before and after training. However, MSNA was significantly less during the third minute of exercise after training (32 +/- 2 to 22 +/- 3 bursts/min; P < 0.01). This training effect on MSNA remained when MSNA was expressed as bursts per 100 heartbeats. Responses to exercise in five untrained control subjects were not different at 0 and 6 wk. These results demonstrate that exercise training prolongs the decrease in MSNA during upright leg exercise and indicates that attenuation of MSNA to exercise reported with forearm training also occurs with leg training.
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Walker EL, Ray CA, Piercey MF. The effects of (+)-UH232 and (-)-DS121 on local cerebral glucose utilization in rats. J Neural Transm (Vienna) 1999; 106:59-74. [PMID: 10195335 DOI: 10.1007/s007020050141] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Although (+)-UH232 (cis-(+)-5-methoxy-1-methyl-2-(n-dipropylamino)tetralin) and (-)-DS121 (S(-)-3-(3-(cyanophenyl)-N-n-propylpiperidine) are both preferential dopamine autoreceptor antagonists, (-)-DS121 is a more effective behavioral stimulant and dopamine releasing agent. To further compare these two agents, Sokoloff's 2-deoxyglucose autoradiography method was used to study the effects of (+)-UH232 and (-)-DS121 on regional brain energy metabolism. (+)-UH232, 30 mg/kg i.p., depressed metabolism in 37 of 65 brain regions and antagonized the stimulant effects of amphetamine. (-)-DS121, 30 mg/kg i.p., exhibited a strong, nonsignificant trend towards an increase in regional brain energy metabolism by itself and enhanced the stimulant effects of amphetamine. The data demonstrate dramatic differences in the effects of two autoreceptor antagonists on regional brain energy metabolism. It is concluded that, compared to (+)-UH232, (-)-DS121 is a more effective stimulant of brain energy metabolism and autoreceptor antagonist owing to its greater ability to increase DA release.
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Howard ST, Ray CA, Patel DD, Antczak JB, Pickup DJ. A 43-nucleotide RNA cis-acting element governs the site-specific formation of the 3' end of a poxvirus late mRNA. Virology 1999; 255:190-204. [PMID: 10049834 DOI: 10.1006/viro.1998.9547] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The 3' ends of late mRNAs of the ati gene, encoding the major component of the A-type inclusions, are generated by endoribonucleolytic cleavage at a specific site in the primary transcript [Antczak et al., (1992), Proc. Natl. Acad. Sci. USA 89, 12033-12037]. In this study, sequence analysis of cDNAs of the 3' ends of ati mRNAs showed these mRNAs are 3' polyadenylated at the RNA cleavage site. This suggests that ati mRNA 3' end formation involves cleavage of a late transcript, with subsequent 3' polyadenylation of the 5' cleavage product. The RNA cis-acting element, the AX element, directing orientation-dependent formation of these mRNA 3' ends, was mapped to a 345-bp AluI-XbaI fragment. Deletion analyses of this fragment showed that the boundaries of the AX element are within -5 and +38 of the RNA cleavage site. Scanning mutagenesis showed that the AX element contains at least two subelements: subelement I, 5'-UUUAU downward arrowCCGAUAAUUC-3', containing the cleavage site ( downward arrow), separated from the downstream subelement II, 5'-AAUUUCGGAUUUGAAUGC-3', by a 10-nucleotide region, whose composition may be altered without effect on RNA 3' end formation. These features, which differ from those of other elements controlling RNA processing, suggest that the AX element is a component of a novel mechanism of RNA 3' end formation.
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Barron KW, Croom JE, Ray CA, Chandler MJ, Foreman RD. Spinal integration of antidromic mediated cutaneous vasodilation during dorsal spinal cord stimulation in the rat. Neurosci Lett 1999; 260:173-6. [PMID: 10076895 DOI: 10.1016/s0304-3940(98)00972-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The purpose of this study was to determine the involvement of supraspinal centers and spinal synaptic integration in cutaneous vasodilation mediated by dorsal spinal cord stimulation (DCS). Laser Doppler flowmetry was used to assess cutaneous blood flow changes in the rat hindpaw during DCS with a unipolar ball electrode placed at the L2-L3 spinal level. Results demonstrated that transecting the spinal cord at the T10 spinal segment did not alter the DCS response while T13 spinal transection abolished the DCS-induced vasodilation. Inhibition of synaptic activity with topical application of muscimol (0.2 mM) on the dorsal surface of the spinal cord markedly attenuated the DCS response. In conclusion DCS-induced vasodilation involved synaptic integration but did not require input from rostral spinal sites or supraspinal areas.
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Delp MD, Duan C, Ray CA, Armstrong RB. Rat hindlimb muscle blood flow during level and downhill locomotion. J Appl Physiol (1985) 1999; 86:564-8. [PMID: 9931192 DOI: 10.1152/jappl.1999.86.2.564] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During eccentrically biased exercise (e.g., downhill locomotion), whole body oxygen consumption and blood lactate concentrations are lower than during level locomotion. These general systemic measurements indicate that muscle metabolism is lower during downhill exercise. This study was designed to test the hypothesis that hindlimb muscle blood flow is correspondingly lower during downhill vs. level exercise. Muscle blood flow (determined by using radioactive microspheres) was measured in rats after 15 min of treadmill exercise at 15 m/min on the level (L, 0 degrees) or downhill (D, -17 degrees). Blood flow to ankle extensor muscles was either lower (e.g., white gastrocnemius muscle: D, 9 +/- 2; L, 15 +/- 1 ml. min-1. 100 g-1) or not different (e.g., soleus muscle: D, 250 +/- 35; L, 230 +/- 21 ml. min-1. 100 g-1) in downhill vs. level exercise. In contrast, blood flow to ankle flexor muscles was higher (e.g., extensor digitorum longus muscle: D, 53 +/- 5; L, 31 +/- 6 ml. min-1. 100 g-1) during downhill vs. level exercise. When individual extensor and flexor muscle flows were summed, total flow to the leg was lower during downhill exercise (D, 3.24 +/- 0.08; L, 3.47 +/- 0. 05 ml/min). These data indicate that muscle blood flow and metabolism are lower during eccentrically biased exercise but are not uniformly reduced in all active muscles; i.e., flows are equivalent in several ankle extensor muscles and higher in ankle flexor muscles.
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Carrasco DI, Delp MD, Ray CA. Effect of concentric and eccentric muscle actions on muscle sympathetic nerve activity. J Appl Physiol (1985) 1999; 86:558-63. [PMID: 9931191 DOI: 10.1152/jappl.1999.86.2.558] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of this study was to determine the effects of concentric (Con) and eccentric (Ecc) muscle actions on leg muscle sympathetic nerve activity (MSNA). Two protocols were utilized. In protocol 1, eight subjects performed Con and Ecc arm curls for 2 min, with a resistance representing 50% of one-repetition maximum for Con curls. Heart rate (HR) and mean arterial pressure (MAP) were greater (P < 0. 05) during Con than during Ecc curls. Similarly, the MSNA was greater (P < 0.05) during Con than during Ecc curls. In protocol 2, eight different subjects performed Con and Ecc arm curls to fatigue, followed by postexercise muscle ischemia, by using the same resistance as in protocol 1. Endurance time was significantly greater for Ecc than for Con curls. The increase in HR, MAP, and MSNA was greater (P < 0.05) during Con than during Ecc curls. However, when the data were normalized as a function of endurance time, the differences in HR, MAP, and MSNA between Con and Ecc curls were no longer present. HR, MAP, and MSNA responses during postexercise muscle ischemia were similar for Con and Ecc curls. Con curls elicited greater increase (P < 0.05) in blood lactate concentration than did Ecc curls. In summary, Con actions contribute significantly more to the increase in cardiovascular and MSNA responses during brief, submaximal exercise than do Ecc actions. However, when performed to a similar level of effort (i.e., fatigue), Con and Ecc muscle actions elicit similar cardiovascular and MSNA responses. These results indicate that the increase in MSNA during a typical bout of submaximal dynamic exercise is primarily mediated by the muscle metaboreflex, which is stimulated by metabolites produced predominantly during Con muscle action.
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Ray CA, Hume KM, Steele SL. Sympathetic nerve activity during natural stimulation of horizontal semicircular canals in humans. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:R1274-8. [PMID: 9756560 DOI: 10.1152/ajpregu.1998.275.4.r1274] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have shown that static head-down neck flexion elicits increases in muscle (MSNA) but not skin sympathetic nerve activity (SSNA) in humans. These findings suggest that stimulation of the otolith organs causes differential sympathetic outflow to vascular beds. The purpose of the present study was to determine whether yaw head rotation (YHR), which stimulates the horizontal semicircular canals, elicits sympathetic nerve responses. To test this question, we recorded MSNA (n = 33) and SSNA (n = 25) before and during 3 min of sinusoidal YHR performed at 0.1, 0.6, and 1.0 Hz. At all frequencies, YHR elicited no significant changes in heart rate and mean arterial pressure. Likewise, YHR did not significantly change either MSNA or SSNA at all frequencies. Our results indicate that stimulation of the horizontal semicircular canals by YHR does not alter SNA to either muscle or skin. Moreover, these results provide evidence to support the concept that the otolith organs but not the horizontal semicircular canals participate in the regulation of SNA in humans.
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Ray CA, Dudley GA. Muscle use during dynamic knee extension: implication for perfusion and metabolism. J Appl Physiol (1985) 1998; 85:1194-7. [PMID: 9729599 DOI: 10.1152/jappl.1998.85.3.1194] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dynamic one-legged knee extension (DKE) is commonly used to examine physiological responses to "aerobic" exercise. Muscle blood flow during DKE is often expressed relative to quadriceps femoris muscle mass irrespective of work rate. This is contrary to the notion that increased force is achieved by recruitment in large muscles. The purpose of this study, therefore, was to determine muscle use during DKE. Six subjects had magnetic resonance images taken of their quadriceps femoris before and after 4 min of DKE at 20 and 40 W. Muscle use was determined by shifts in T2. The cross-sectional area of quadriceps femoris that had an elevated T2 was 16 +/- 1% (mean +/- SE) preexercise, and 54 +/- 5 and 94 +/- 4% after 20- and 40-W DKE, respectively. Volume of quadriceps femoris increased 11.4 +/- 0. 2% (P = 0.006), from 2,230 +/- 233 cm3 before exercise to 2,473 +/- 232 cm3 after 40-W DKE. Extrapolation of these data indicates that 1, 301 +/- 111 cm3 of quadriceps femoris were engaged during 20-W DKE compared with 2,292 +/- 154 cm3 during 40-W DKE. By using muscle blood flow data for submaximal DKE at 20 W [P. Andersen and B. Saltin. J. Physiol. (Lond.) 366: 233-249, 1985; and L. B. Rowell, B. Saltin, B. Kiens, and N. J. Christensen. Am. J. Physiol. 251 (Heart Circ. Physiol. 20): H1038-H1044, 1986] and estimating muscle use in those studies from our data (total muscle mass x 0.54), extrapolated blood flow to active muscle (263 and 278 ml . min-1 . 100 g-1, respectively) is comparable to that obtained during peak aerobic DKE when expressed relative to total muscle mass (243 and 250 ml . min-1 . 100 g-1, respectively). These findings indicate that increased power during aerobic DKE is achieved by recruitment. Additionally, they suggest that blood flow to the active quadriceps femoris muscle does not increase with increases in submaximal work rate but instead is maximal to support aerobic metabolism. Thus increases in muscle blood flow are directed to newly recruited muscle, not to increased perfusion of muscle already engaged.
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Ray CA, Mahoney ET, Hume KM. Exercise-induced muscle injury augments forearm vascular resistance during leg exercise. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:H443-7. [PMID: 9683431 DOI: 10.1152/ajpheart.1998.275.2.h443] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The purpose of the present investigation was to examine the effect of exercise-induced muscle injury on hemodynamic responses during exercise. Ten subjects performed unilateral isometric knee extensions (IKE) at 30% of preinjury maximum voluntary contraction to fatigue and for 3 min before and 48 h after muscle injury. Muscle injury was elicited by performing 8 sets of 10 repetitions of eccentric muscle actions of the knee extensor muscles (i.e., quadriceps muscles) by lowering a weight equivalent to 75% of eccentric maximum load. Exercise time to fatigue for IKE at 30% of maximum voluntary contraction in the injured leg was significantly decreased from preinjury to postinjury IKE (257 +/- 21 to 203 +/- 23 s; n = 10), but was unchanged in the control leg (244 +/- 16 to 254 +/- 20 s; n = 7). With the use of a 10-cm visual analog scale, ratings of muscle soreness in the injured leg increased from 0 to 5. 1 +/- 0.7 cm (P < 0.001) but were not changed in the control leg (0 both times). Both heart rate and mean arterial pressure responses to exercise were unchanged following muscle injury. Forearm blood flow and forearm vascular resistance were not different at rest and during the first minute of exercise before and after muscle injury. However, after muscle injury, forearm blood flow was significantly lower and forearm vascular resistance was significantly higher (P < 0.03) during the second and third minutes of exercise. There were no significant changes in any variables with the contralateral control leg. In four subjects, resting magnetic resonance images demonstrated a 23% greater relative cross-sectional area of the knee extensor muscles with an elevated transverse relaxation time in the injured versus control leg. The results indicate that forearm vascular resistance is augmented during isometric knee extension following muscle injury of the knee extensor muscles. The data suggest that muscle injury alters vascular control to non-exercising skeletal muscle during exercise.
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Loparev VN, Parsons JM, Knight JC, Panus JF, Ray CA, Buller RM, Pickup DJ, Esposito JJ. A third distinct tumor necrosis factor receptor of orthopoxviruses. Proc Natl Acad Sci U S A 1998; 95:3786-91. [PMID: 9520445 PMCID: PMC19915 DOI: 10.1073/pnas.95.7.3786] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Cowpox virus Brighton red strain (CPV) contains a gene, crmD, which encodes a 320-aa tumor necrosis factor receptor (TNFR) of 44% and 22% identity, respectively, to the CPV TNFR-like proteins, cytokine response modifiers (crm) CrmB and CrmC. The crmD gene was interrupted in three other cowpox strains examined and absent in various other orthopoxviruses; however, four strains of ectromelia virus (ECT) examined contained an intact crmD (97% identity to CPV crmD) and lacked cognates of crmB and crmC. The protein, CrmD, contains a transport signal; a 151-aa cysteine-rich region with 21 cysteines that align with human TNFRII ligand-binding region cysteines; and C-terminal region sequences that are highly diverged from cellular TNFR C-terminal region sequences involved in signal transduction. Bacterial maltose-binding proteins containing the CPV or ECT CrmD cysteine-rich region bound TNF and lymphotoxin-alpha (LTalpha) and blocked their in vitro cytolytic activity. Secreted viral CrmD bound TNF and LTalpha and was detectable after the early stage of replication, using nonreducing conditions, as 60- to 70-kDa predominant and 90- to 250-kDa minor disulfide-linked complexes that were able to be reduced to a 46-kDa form and deglycosylated to a 38-kDa protein. Cells infected with CPV produced extremely low amounts of CrmD compared with ECT. Possessing up to three TNFRs, including CrmD, which is secreted as disulfide-linked complexes in varied amounts by CPV and ECT, likely enhances the dynamics of the immune modulating mechanisms of orthopoxviruses.
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Ray CA, Hume KM. Sympathetic neural adaptations to exercise training in humans: insights from microneurography. Med Sci Sports Exerc 1998; 30:387-91. [PMID: 9526884 DOI: 10.1097/00005768-199803000-00008] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Sympathetic nerve activity has long been regarded as an important regulator of blood flow and blood pressure. Its importance has been especially recognized during exercise. The present review examines sympathetic neural adaptations to exercise training in humans obtained by sympathetic nerve recordings to nonactive skeletal muscle. Little evidence exists from both cross-sectional and longitudinal studies indicating that training alters resting muscle sympathetic nerve activity (MSNA). However, MSNA responses during exercise appear to be attenuated after training. This attenuation of MSNA seems to be specific to the trained muscle and not generalizable to other muscle groups. The mechanisms for the decrease in exercise-induced MSNA have been attributed to changes in both the muscle metaboreflex and muscle mechanoreflex. In addition to exercise, training has generally not altered MSNA responses to other stressors such as cold pressor test, lower body negative pressure, and upright tilting. However, the effect of training on baroreflex control of MSNA is equivocal. These conclusions are based on few studies. More comprehensive training studies are needed to better understand the role of training on sympathetic neural outflow.
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Ray CA, Hume KM. Neck afferents and muscle sympathetic activity in humans: implications for the vestibulosympathetic reflex. J Appl Physiol (1985) 1998; 84:450-3. [PMID: 9475851 DOI: 10.1152/jappl.1998.84.2.450] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We have shown previously that head-down neck flexion (HDNF) in humans elicits increases in muscle sympathetic nerve activity (MSNA). The purpose of this study was to determine the effect of neck muscle afferents on MSNA. We studied this question by measuring MSNA before and after head rotation that would activate neck muscle afferents but not the vestibular system (i.e., no stimulation of the otolith organs or semicircular canals). After a 3-min baseline period with the head in the normal erect position, subjects rotated their head to the side (approximately 90%) and maintained this position for 3 min. Head rotation was performed by the subjects in both the prone (n = 5) and sitting (n = 6) positions. Head rotation did not elicit changes in MSNA. Average MSNA, expressed as burst frequency and total activity, was 13 +/- 1 and 13 +/- 1 bursts/min and 146 +/-34 and 132 +/- 27 units/min during baseline and head rotation, respectively. There were no significant changes in calf blood flow (2.6 +/- 0.3 to 2.5 +/- 0.3 ml.100 ml-1.min-1, n = 8) and calf vascular resistance (39 +/- 4 to 41 +/- 4 units; n = 8). Heart rate (64 +/- 3 to 66 +/- 3 beats/min; P = 0.058) and mean arterial pressure (90 +/- 3 to 93 +/- 3; P < 0.05) increased slightly during head rotation. Additional neck flexion studies were performed with subjects lying on their side (n = 5), MSNA, heart rate, and mean arterial pressure were unchanged during this maneuver, which also does not engage the vestibular system. HDNF was tested in 9 of the 13 subjects. MSNA was significantly increased by 79 +/- 12% (P < 0.001) during HDNF. These findings indicate that neck afferents activated by horizontal neck rotation or flexion in the absence of significant force development do not elicit changes in MSNA. These findings support the concept that HDNF increases MSNA by the activation of the vestibular system.
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Ray CA, Hume KM, Gracey KH, Mahoney ET. Muscle cooling delays activation of the muscle metaboreflex in humans. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:H2436-41. [PMID: 9374782 DOI: 10.1152/ajpheart.1997.273.5.h2436] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Elevation of muscle temperature has been shown to increase muscle sympathetic nerve activity (MSNA) during isometric exercise in humans. The purpose of the present study was to evaluate the effect of muscle cooling on MSNA responses during exercise. Eight subjects performed ischemic isometric handgrip at 30% of maximal voluntary contraction to fatigue followed by 2 min of postexercise muscle ischemia (PEMI), with and without local cooling of the forearm. Local cooling of the forearm decreased forearm muscle temperature from 31.8 +/- 0.4 to 23.1 +/- 0.8 degrees C (P = 0.001). Time to fatigue was not different during the control and cold trials (156 +/- 11 and 154 +/- 5 s, respectively). Arterial pressures and heart rate were not significantly affected by muscle cooling during exercise, although heart rate tended to be higher during the second minute of exercise (P = 0.053) during muscle cooling. Exercise-induced increases in MSNA were delayed during handgrip with local cooling compared with control. However, MSNA responses at fatigue and PEMI were not different between the two conditions. These findings suggest that muscle cooling delayed the activation of the muscle metaboreflex during ischemic isometric exercise but did not prevent its full expression during fatiguing contraction. These results support the concept that muscle temperature can play a role in the regulation of MSNA during exercise.
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Ray CA, Hume KM, Shortt TL. Skin sympathetic outflow during head-down neck flexion in humans. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:R1142-6. [PMID: 9321897 DOI: 10.1152/ajpregu.1997.273.3.r1142] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have previously demonstrated increases in muscle sympathetic nerve activity during head-down neck flexion (HDNF). The purpose of the present study was to determine if HDNF also activates skin sympathetic nerve activity (SSNA). SSNA, heart rate, arterial pressure, skin blood flow, calf blood flow, and calculated calf vascular resistance (mean arterial pressure/calf blood flow) were determined in 12 subjects during 3 min of baseline (lying prone with chin supported) and 3 min of HDNF. There were no significant changes in heart rate and arterial pressures during HDNF; however, diastolic and mean arterial pressure tended to increase slightly. Calf blood flow decreased 22% and calf vascular resistance increased 46% during HDNF. SSNA did not significantly change during HDNF. In three subjects we measured both muscle and skin sympathetic nerve activity during HDNF. In these trials, muscle sympathetic nerve activity consistently increased, but SSNA did not. The results indicate that HDNF in humans activates muscle sympathetic nerve activity, but does not activate SSNA. Thus vestibular stimulation may elicit differential activation of sympathetic outflow in humans.
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Ray CA, Gracey KH. Augmentation of exercise-induced muscle sympathetic nerve activity during muscle heating. J Appl Physiol (1985) 1997; 82:1719-25. [PMID: 9173932 DOI: 10.1152/jappl.1997.82.6.1719] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The muscle metabo- and mechanoreflexes have been shown to increase muscle sympathetic nerve activity (MSNA) during exercise. Group III and IV muscle afferents, which are believed to mediate this response, have been shown to be thermosensitive in animals. The purpose of the present study was to evaluate the effect of muscle temperature on MSNA responses during exercise. Eleven subjects performed ischemic isometric handgrip at 30% of maximal voluntary contraction to fatigue, followed by 2 min of postexercise muscle ischemia (PEMI), with and without local heating of the forearm. Local heating of the forearm increased forearm muscle temperature from 34.4 +/- 0.2 to 38.9 +/- 0.3 degree C (P = 0.001). Diastolic and mean arterial pressures were augmented during exercise in the heat. MSNA responses were greater during ischemic handgrip with local heating compared with control (no heating) after the first 30 s. MSNA responses at fatigue were greater during local heating. MSNA increased by 16 +/- 2 and 20 +/- 2 bursts per 30 s for control and heating, respectively (P = 0.03). When expressed as a percent change in total activity (total burst amplitude), MSNA increased 531 +/- 159 and 941 +/- 237% for control and heating, respectively (P = 0.001). However, MSNA was not different during PEMI between trials. This finding suggests that the augmentation of MSNA during exercise with heat was due to the stimulation of mechanically sensitive muscle afferents. These results suggest that heat sensitizes skeletal muscle afferents during muscle contraction in humans and may play a role in the regulation of MSNA during exercise.
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Pott F, Ray CA, Olesen HL, Ide K, Secher NH. Middle cerebral artery blood velocity, arterial diameter and muscle sympathetic nerve activity during post-exercise muscle ischaemia. ACTA PHYSIOLOGICA SCANDINAVICA 1997; 160:43-7. [PMID: 9179309 DOI: 10.1046/j.1365-201x.1997.00126.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
During exercise the transcranial Doppler determined mean blood velocity (Vmean) increases in the middle cerebral artery (MCA) and reflects cerebral flood flow when the diameter at the site of investigation remains constant. Sympathetic activation could induce MCA vasoconstriction and in turn elevate Vmean at an unchanged cerebral blood flow. In 12 volunteers we evaluated whether Vmean relates to muscle sympathetic nerve activity (MSNA) in the peroneal nerve during rhythmic handgrip and post-exercise muscle ischaemia (PEMI). The luminal diameter of the dorsalis pedis artery (AD) was taken to reflect the MSNA influence on a peripheral artery. Rhythmic handgrip increased heart rate (HR) from 74 +/- 20 to 92 +/- 21 beats min-1 and mean arterial pressure (MAP) from 87 +/- 7 to 105 +/- 9 mmHg (mean +/- SD; P < 0.05). During PEMI, HR returned to pre-exercise levels while MAP remained elevated (101 +/- 9 mmHg). During handgrip contralateral MCA Vmean increased from 65 +/- 10 to 75 +/- 13 cm s-1 and this was more than on the ipsilateral side (from 63 +/- 10 to 68 +/- 10 cm s-1; P < 0.05). On both sides of the brain Vmean returned to baseline during PEMI. MSNA did not increase significantly during handgrip (from 56 +/- 24 to 116 +/- 39 units) but the elevation became statistically significant during PEMI (135 +/- 86 units, P < 0.05), while AD did not change. Taken together, during exercise and PEMI, Vmean changed independent of an elevation of MSNA by more than 140% and the dorsalis pedis artery diameter was stable. The results provide no evidence for a vasoconstrictive influence of sympathetic nerve activity on medium size arteries of the limbs and the brain during rhythmic handgrip and post-exercise muscle ischaemia.
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Shortt TL, Ray CA. Sympathetic and vascular responses to head-down neck flexion in humans. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 272:H1780-4. [PMID: 9139962 DOI: 10.1152/ajpheart.1997.272.4.h1780] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Animal studies have demonstrated increases in sympathetic nerve outflow with vestibular stimulation. The purpose of the present study was to determine whether vestibulosympathetic reflexes are engaged in humans. Muscle sympathetic nerve activity (MSNA), heart rate, arterial pressure, calf blood flow (CBF), and calculated calf vascular resistance (CVR; mean arterial pressure/CBF) were determined during 10 min of baseline (laying prone with chin supported) and 10 min of head-down neck flexion (HDNF). MSNA responses were measured in nine subjects, and calf vascular responses were determined in seven of these subjects. Heart rate increased during the first minute of HDNF (71 +/- 2 to 76 +/- 3 beats/min; P < 0.05) and remained slightly elevated (71 +/- 2 to 74 +/- 3 beats/min; P < 0.05) for the duration of HDNF. Diastolic and mean arterial pressures also increased slightly with HDNF (80 +/- 3 to 82 +/- 3 and 96 +/- 3 to 98 +/- 3 mmHg, respectively; P < 0.05). Systolic arterial pressure did not change significantly during HDNF. CBF decreased 14% (4.63 +/- 0.78 to 3.97 +/- 0.60 ml x min(-1) x 100 ml(-1); P < 0.05), and CVR increased 12% (24.0 +/- 4.3 to 27.4 +/- 4.7 units; P < 0.05) during HDNF. These changes corresponded with significant increases in MSNA during HDNF. MSNA, expressed as burst frequency, increased from 14 +/- 2 to 20 +/- 2 bursts/min (P < 0.05) and increased 63 +/- 23% (P < 0.05) when expressed as the percent change in total activity. All variables returned to baseline during recovery. Thoracic impedance measured in five subjects did not change during HDNF (19.6 +/- 1.2 to 19.7 +/- 1.5 omega), suggesting no major change in central blood volume. The results indicate that HDNF elicits increases in CVR that are mediated by the augmentation of MSNA. Arterial pressure responses and thoracic impedance data suggest that high and low pressure baroreflexes were not the mechanism for sympathetic activation. The immediate increase in MSNA with HDNF suggests a role for vestibulosympathetic reflexes.
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Ray CA, Pickup DJ. The mode of death of pig kidney cells infected with cowpox virus is governed by the expression of the crmA gene. Virology 1996; 217:384-91. [PMID: 8599227 DOI: 10.1006/viro.1996.0128] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Pig kidney cells (LLC-PK1) were infected with one of three viruses: wild-type cowpox virus (Brighton red strain) expressing the crmA gene; recombinant cowpox virus A602, lacking the crmA gene; or cowpox virus A604, a revertant of virus A602, expressing the crmA gene. The wild-type virus and virus A604 produced identical cytopathic effects consistent with death by necrosis. In these cells, the structural features of the plasma membrane, the nuclear membrane, and the chromatin were maintained until lysis of the cells. In contrast, cowpox virus A602 produced cytopathic effects consistent with death by apoptosis. These effects included loss of microvilli on the cell surface, margination and condensation of the chromatin, progressive convolution of the nuclear membrane, release of dense chromatin masses on disintegration of the nucleus, fragmentation of the DNA, and the generation of apoptotic bodies. These results suggest that the crmA gene is necessary to inhibit processes of apoptosis induced in LLC-PK1 cells by infection with cowpox virus. Thus in cells of certain types, the crmA gene can act with other viral genes to control the mode of death of the virus-infected cell. This capability may be advantageous to virus replication in vivo, potentially facilitating both virus trafficking and interference with antiviral immune defenses.
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Casey BL, Ray CA, Piercey MF. Antagonism of cocaine's stimulant effects on local cerebral glucose utilization by the preferential autoreceptor antagonist (+)-AJ 76. J Neural Transm (Vienna) 1996; 103:277-85. [PMID: 8739839 DOI: 10.1007/bf01271239] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
(+)-AJ 76 is a stimulant dopamine (DA) antagonist, which has a putative preferential action at DA nerve terminal autoreceptors. Because it is both a mild stimulant and a DA antagonist, it has previously been suggested that (+)-AJ 76 might antagonize both the euphoria and craving associated with cocaine abuse and withdrawal, respectively. To evaluate this hypothesis further, (+)-AJ 76 was evaluated for its ability to affect cocaine-induced changes in regional brain energy metabolism. Using Sokoloff's 2-deoxyglucose autoradiographic technique, (+)-AJ 76 antagonized the stimulant effect of cocaine. Although classical DA antagonists are known to depress regional brain energy metabolism, (+)-AJ 76 by itself had no effect. It is concluded that the results are consistent with the previously stated hypothesis that (+)-AJ 76 might be useful as a pharmacotherapy for treatment of cocaine abuse.
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Ray CA, Mark AL. Sympathetic nerve activity to nonactive muscle of the exercising and nonexercising limb. Med Sci Sports Exerc 1995; 27:183-7. [PMID: 7723640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The purpose of this study was to determine whether efferent sympathetic nerve activity is different to resting skeletal muscles from the exercising and nonexercising limb. MSNA was measured by microneurography in both legs (peroneal nerve) in six subjects during 2 min of unilateral isometric knee extension (IKE; 10-30% of maximum voluntary contraction (MVC)) followed by postexercise circulatory occlusion (PECO). Additional studies using isometric handgrip (30% MVC) followed by PECO were performed. IKE produced significant increases in mean arterial pressure (15 +/- 2 mm Hg) and heart rate (10 +/- 2 bpm). During PECO, mean arterial pressure remained significantly elevated (6 +/- 1 mm Hg) whereas heart rate returned to control. MSNA (bursts.min-1) was not different between the two limbs during control, IKE, PECO, and recovery. Seventy-five to eighty percent of all sympathetic nerve discharges occurred simultaneously in both legs, with the remaining percentage of sympathetic nerve discharges being divided almost equally between the nonexercising and exercising leg. Isometric handgrip produced significant increases in MSNA to the two resting legs with the percent of sympathetic discharges to the two legs being similar to that during IKE. These results indicate that MSNA is similar to the resting muscle in the exercising and nonexercising leg during brief, submaximal isometric exercise (< or = 30% MVC) and postexercise muscle ischemia.
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Komiyama T, Ray CA, Pickup DJ, Howard AD, Thornberry NA, Peterson EP, Salvesen G. Inhibition of interleukin-1 beta converting enzyme by the cowpox virus serpin CrmA. An example of cross-class inhibition. J Biol Chem 1994; 269:19331-7. [PMID: 8034697] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We reported previously that human interleukin-1 beta converting enzyme (ICE) is regulated by the CrmA serpin encoded by cowpox virus. We now report the mechanism and kinetics of this unusual inhibition of a cysteine proteinase by a member of the serpin superfamily previously thought to inhibit serine proteinase only. CrmA possesses several characteristics typical of a number of inhibitory serpins. It is conformationally unstable, unfolding around 3 M urea, and stable to denaturation in 8 M urea upon complex formation with ICE. CrmA rapidly inhibits ICE with an association rate constant (kon) of 1.7 x 10(7) M-1 s-1, forming a tight complex with an equilibrium constant for inhibition (Ki) of less than 4 x 10(-12) M. These data indicate that CrmA is a potent inhibitor of ICE, consistent with the dramatic effects of CrmA on modifying host responses to virus infection. The inhibition of ICE by CrmA is an example of a "cross-class" interaction, in which a serpin inhibits a non-serine proteinase. Since CrmA possesses characteristics shared by inhibitors of serine proteinases, we presume that ICE, though it is a cysteine proteinase, has a substrate binding geometry strikingly close to that of serine proteinases. We reason that it is the substrate binding geometry, not the catalytic mechanism of a proteinase, that dictates its reactivity with protein inhibitors.
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Ray CA, Pawelczyk JA. Naloxone does not affect the cardiovascular and sympathetic adjustments to static exercise in humans. J Appl Physiol (1985) 1994; 77:231-5. [PMID: 7961239 DOI: 10.1152/jappl.1994.77.1.231] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Previous studies suggested that endogenous opiates may attenuate the cardiovascular and sympathetic adjustments to static exercise. We tested whether this effect originates from exercising skeletal muscle. Eight men performed 2 min of static handgrip (30% maximum) followed by 2 min of posthandgrip muscle ischemia after three interventions: 1) control, 2) intra-arterial injection of naloxone HCl (60 micrograms) or vehicle (saline) in the exercising arm, and 3) systemic infusion of naloxone (4 mg) or vehicle. Naloxone and vehicle trials were performed double blind on separate days. Preexercise baseline muscle sympathetic nerve activity (burst frequency), heart rate, and blood pressure were similar across interventions on either day. During static handgrip, control, intra-arterial, and systemic administration of vehicle and naloxone elicited similar increases in total muscle sympathetic nerve activity (58 +/- 24 vs. 68 +/- 26, 146 +/- 49 vs. 132 +/- 42, 137 +/- 54 vs. 164 +/- 44%, respectively), heart rate (9 +/- 2 vs. 8 +/- 3, 16 +/- 3 vs. 16 +/- 2, 20 +/- 4 vs. 19 +/- 3 beats/min, respectively), and mean arterial pressure (22 +/- 4 vs. 21 +/- 4, 29 +/- 5 vs. 26 +/- 3, 28 +/- 4 vs. 27 +/- 4 mmHg, respectively). Additionally, there were no differences between vehicle and naloxone trials during posthandgrip muscle ischemia. Thus, contrary to previous reports, we conclude that the endogenous opiate peptide system does not modulate cardiovascular and sympathetic responses to brief periods of static exercise or muscle ischemia in humans.
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