Heidi A. Kluess

Neuroendocrine Activation in Heart Failure Is Modified by Endurance Exercise Training

Abstract OBJECTIVES The purpose of this study was to determine whether endurance exercise training could buffer neuroendocrine activity in chronic heart failure patients. BACKGROUND Neuroendocrine activation is associated with poor long-term prognosis in heart failure. There is growing consensus that exercise may be beneficial by altering the clinical course of heart failure, but the mechanisms responsible for exercise-induced benefits are unclear. METHODS Nineteen heart failure patients (ischemic disease; New York Heart Association [NYHA] class II or III) were randomly assigned to either a training group or to a control group. Exercise training consisted of supervised walking three times a week for 16 weeks at 40% to 70% of peak oxygen uptake. Medications were unchanged. Neurohormones were measured at study entry and after 16 weeks. RESULTS The training group (n = 10; age = 61 ± 6 years; EF = 30 ± 6%) and control group (n = 9; age = 62 ± 7 years; EF = 29 ± 7%) did not differ in clinical findings at study entry. Resting levels of angiotensin II, aldosterone, vasopressin and atrial natriuretic peptide in the training and control groups did not differ at study entry (5.6 ± 1.3 pg/ml; 158 ± 38 pg/ml; 6.1 ± 2.0 pg/ml; 37 ± 8 pg/ml training group vs. 4.8 ± 1.2; 146 ± 23; 4.9 ± 1.1; 35 ± 10 control group). Peak exercise levels of angiotensin II, aldosterone, vasopressin and atrial natriuretic peptide in the exercise and control groups did not differ at study entry. After 16 weeks, rest and peak exercise hormone levels were unchanged in control patients. Peak exercise neurohormone levels were unchanged in the training group, but resting levels were significantly (p CONCLUSIONS Our data indicate that 16 weeks of endurance exercise training modified resting neuroendocrine hyperactivity in heart failure patients. Reduction in circulating neurohormones may have a beneficial impact on long-term prognosis.

Mechanical compression elicits vasodilatation in rat skeletal muscle feed arteries

To date, no satisfactory explanation has been provided for the immediate increase in blood flow to skeletal muscles at the onset of exercise. We hypothesized that rapid vasodilatation is a consequence of release of a vasoactive substance from the endothelium owing to mechanical deformation of the vasculature during contraction. Rat soleus feed arteries were isolated, removed and mounted on micropipettes in a sealed chamber. Arteries were pressurized to 68 mmHg, and luminal diameter was measured using an inverted microscope. Pressure pulses of 600 mmHg were delivered for 1 s, 5 s, and as a series of five repeated 1 s pulses with 1 s between pulses. During application of external pressure the lumen of the artery was completely closed, but immediately following release of pressure the diameter was significantly increased. In intact arteries (series 1, n= 6) for the 1 s pulse, 5 s pulse and series of five 1 s pulses, the peak increases in diameter were, respectively, (mean ±s.e.m.) 16 ± 2, 14 ± 2 and 27 ± 3%, with respective times from release of pressure to peak diameter of 4.1 ± 0.3, 4.6 ± 0.7 and 2.8 ± 0.4 s. In series 2 (n= 9) the arteries increased diameter by 15 ± 2, 15 ± 2 and 30 ± 3% before and by 8 ± 1, 8 ± 1 and 21 ± 2% after removal of the endothelium with air. The important new finding in these experiments is that mechanical compression caused dilatation of skeletal muscle feed arteries with a time course similar to the change in blood flow after a brief muscle contraction. The magnitude of dilatation was not affected by increasing the duration of compression but was enhanced by increasing the number of compressions. Since removal of the endothelium reduced but did not abolish the dilatation in response to mechanical compression, it appears that the dilatation is mediated by both endothelium‐dependent and ‐independent signalling pathways.

The effect of aging on adrenergic and nonadrenergic receptor expression and responsiveness in canine skeletal muscle

We tested the hypothesis that adrenergic and nonadrenergic receptor responsiveness and protein expression would be altered with advancing age. Young (n = 6; 22 ± 1 mo; mean ± SE) and old (n = 6; 118 ± 9 mo) beagles were instrumented with flow probes and an indwelling catheter for continuous measurement of external iliac blood flow and arterial blood pressure. Vascular conductance (VC) was calculated as hindlimb blood flow/mean arterial pressure. Selective agonists for α-1, α-2, neuropeptide-Y (NPY), and purinergic (P2X) receptors were infused at rest and during treadmill running at moderate (2.5 mph) and heavy (4 mph with 2.5% grade) exercise intensities. Feed arteries were dissected from gracilis muscles, and α-1D, α-1B, α-2A, P2X-4, P2X-1, and NPY-Y1 receptor protein expression was determined. Phenylephrine produced similar decreases (P > 0.05) in VC in young and old beagles at rest (young: -62 ± 5%; old: -59 ± 5%) and during moderate (young: -67 ± 5%; old: -62 ± 4%) and heavy (young: -54 ± 4%; old: -49 ± 3%) exercise. Clonidine caused similar (P > 0.05) decreases in VC in old compared with young dogs at rest (young: -59 ± 8%; old: -70 ± 6%) and during moderate (young: -52 ± 6%; old: -47 ± 5%)- and heavy (young: -42 ± 5%; old: -43 ± 5%)-intensity exercise. NPY infusion resulted in a similar decline in VC in young and old beagles at rest (young: -40 ± 7%; old: -39 ± 9%) and during moderate (young: -47 ± 6%; old: -40 ± 6%)- and heavy (young: -40 ± 3%; old: -38 ± 4%)-intensity exercise. α-β-Methylene-ATP also produced similar decreases in VC in young and old beagles at rest (young: -36 ± 6%; old: -40 ± 8%) and during exercise at moderate (young: -42 ± 5%; old: -40 ± 9%) and heavy (young: -47 ± 5%; old: -42 ± 8%) intensities. α-1B receptor protein expression was elevated (P < 0.05) in old compared with young dogs, whereas there were no age-related differences in α-1D or α-2A receptor expression and nonadrenergic P2X-4, P2X-1, and NPY-Y1 receptor expression. The present findings indicate that postsynaptic adrenergic and nonadrenergic receptor responsiveness was not altered by advancing age. Moreover, the expression of adrenergic and nonadrenergic receptors in skeletal-muscle feed arteries was largely unaffected by aging.

ATP overflow in skeletal muscle 1A arterioles

The purpose of this study was to investigate the sources of ATP in the 1A arteriole, and to investigate age‐related changes in ATP overflow. Arterioles (1A) from the red portion of the gastrocnemius muscle were isolated, cannulated and pressurized in a microvessel chamber with field stimulation electrodes. ATP overflow was determined using probes specific for ATP and null probes that were constructed similar to the ATP probes, but did not contain the enzyme coating. ATP concentrations were determined using a normal curve (0.78 to 25 μmol l−1 ATP). ATP overflow occurred in two phases. Phase one began in the first 20 s following stimulation and phase two started 35 s after field stimulation. Tetrodotoxin, a potent neurotoxin that blocks action potential generation in nerves, abolished both phases of ATP overflow. α1‐Receptor blockade resulted in a small decrease in ATP overflow in phase two, but endothelial removal resulted in an increase in ATP overflow. ATP overflow was lowest in 6‐month‐old rats and highest in 12‐ and 2‐month‐old rats (P < 0.05). ATP overflow measured via biosensors was of neural origin with a small contribution from the vascular smooth muscle. The endothelium seems to play an important role in attenuating ATP overflow in 1A arterioles.

Polyubiquitination of the neurotrophin receptor p75 directs neuronal cell survival

Specific binding of nerve growth factor (NGF) to p75 neurotrophin receptor (p75(NTR)) leads to p75(NTR) polyubiquitination and its subsequent interaction with TRAF6 resulting in neuronal cell survival. However, when the binding of NGF to p75(NTR) was blocked with p75 antiserum, p75(NTR) polyubiquitination and neuronal cell survival were impaired. Results showed that tyrosine phosphorylation of p75(NTR) increased the polyubiquitination of p75(NTR) and contributed to the observed apparent neuroprotective effects. Similar to p75(NTR) polyubiquitination, interaction of TRAF6 with p75(NTR) was NGF/tyrosine phosphorylation dependent suggesting that TRAF6 might function as an E3 ubiquitin ligase. In sum, the results show that specific binding of NGF to p75(NTR) mediates neuronal cell survival.

Neuropeptide Y overflow and metabolism in skeletal muscle arterioles

Non‐technical summary  Neuropeptide Y (NPY) is involved in a number of vascular physiological processes that affect sympathetic neurotransmission and angiogenesis. While NPY is of physiological significance, very little is known regarding local overflow characteristics at specific levels of the vasculature. Through the use of a new technique, we were able to quantify NPY overflow from isolated skeletal muscle arterioles of female rats. We observed age‐related differences in NPY overflow and its degradation via dipeptidyl peptidase IV. These results will provide insights into the release and breakdown of NPY at local levels of the vasculature.

Influence of estradiol supplementation on neuropeptide Y neurotransmission in skeletal muscle arterioles of F344 rats

The effects of estradiol on neuropeptide Y (NPY) neurotransmission in skeletal muscle resistance vessels have not been described. The purpose of this study was to determine the effects of long-term estradiol supplementation on NPY overflow, degradation, and vasoconstriction in gastrocnemius first-order arterioles of adult female rats. Female rats (4 mo; n = 34) were ovariectomized (OVX) with a subset (n = 17) receiving an estradiol pellet (OVE; 17β-estradiol, 4 μg/day). After conclusion of the treatment phase (8 wk), arterioles were excised, placed in a physiological saline solution (PSS) bath, and cannulated with micropipettes connected to albumin reservoirs. NPY-mediated vasoconstriction via a Y(1)-agonist [Leu31Pro34]NPY decreased vessel diameter 44.54 ± 3.95% compared with baseline; however, there were no group differences in EC(50) (OVE: -8.75 ± 0.18; OVX: -8.63 ± 0.10 log M [Leu31Pro34]NPY) or slope (OVE: -1.11 ± 0.25; OVX: -1.65 ± 0.34% baseline/log M [Leu31Pro34]NPY). NPY did not potentiate norepinephrine-mediated vasoconstriction. NPY overflow experienced a slight increase following field stimulation and significantly increased (P < 0.05) over control conditions in the presence of a DPPIV inhibitor (diprotin A). Estradiol status did not affect DPPIV activity. These data suggest that NPY can induce a moderate decrease in vessel diameter in skeletal muscle first-order arterioles, and DPPIV is active in mitigating NPY overflow in young adult female rats. Long-term estradiol supplementation did not influence NPY vasoconstriction, overflow, or its enzymatic breakdown in skeletal muscle first-order arterioles.

Heart rate variability and the exercise pressor reflex during dynamic handgrip exercise and postexercise arterial occlusion

BackgroundThe exercise pressor reflex is thought to be an important cardiovascular control mechanism that may be compromised in disease states such as congestive heart failure and other metabolic syndromes. The purpose was to describe the exercise pressor reflex by observing heart rate variability and blood pressure responses to handgrip-exercise and postexercise arterial occlusion. MethodsContinuous electrocardiography, arterial blood pressure, and pneumotachogram data were collected on 38 participants (age, 20 ± 1 year) during spontaneous breathing, venous-occluded exercise (60% maximal voluntary contraction, 0.5 Hz) and immediate postexercise arterial occlusion. Data were analyzed for mean R-R interval, standard deviation of R-R intervals (SDNN), normalized low (0–0.15 Hz) frequency power (LFnu), mean arterial pressure (MAP), and respiratory rate. ResultsDuring exercise, increases in respiratory rate (+4.55 ± 6.48 breaths/min), LFnu (+9.39 ± 16.83%), and MAP (+25.40 ± 17.55 mm Hg) were observed. Mean R-R interval (−230.73 ± 125.79 msec) and SDNN (−38.54 ± 36.02 msec) decreased (P < 0.05). Respiratory rate (+0.12 ± 4.61 breaths/min), SDNN (−17.89 ± 64.41 msec), and LFnu (9.89 ± 21.01%) recovered during forearm arterial occlusion (P < 0.05). However, Mean R-R interval and MAP remained elevated above spontaneous breathing (P < 0.05). ConclusionsThe sustained elevation in MAP during postexercise arterial occlusion suggests metaboreceptor-mediated heightened sympathetic activity. The increase in LFnu during exercise and its subsequent recovery during postexercise occlusion is consistent with dynamic exercise-induced parasympathetic withdrawal but a strong vagal activation upon cessation of dynamic activity despite persistent sympathetic activity originating from afferent input from the occluded forearm.

Frequency and pattern dependence of adrenergic and purinergic vasoconstriction in rat skeletal muscle arteries

Sympathetic nerves fire in bursts followed by brief periods of quiescence. Periods of quiescence may be a valuable part of coding for different neurotransmitters. We compared adrenergic‐ and non‐adrenergic‐mediated vasoconstriction with repeating burst patterns versus constant frequency stimulation. Seventeen rats were killed, and the femoral arteries dissected out and mounted in organ tissue baths at 37°C and pH 7.4. Field stimulation was applied to artery rings from five rats at constant frequencies of 2–6 Hz for 144 impulses. In 12 rats, artery rings were stimulated with two burst pattern protocols consisting of repeating pairs, triplets, quadruplets or sextuplets performed using either 8 or 30 Hz as the instantaneous frequency for a total of 144 impulses. All protocols were repeated with the P2 purinergic antagonist pyridoxal‐phosphate‐6‐azophenyl‐2′4′‐disulphonic acid (PPADs; 0.42 m) or the α1‐antagonist prazosin (1.59 μm). Tension was decreased by the addition of the P2 antagonist PPADs (P < 0.05). Prazosin abolished tension at all constant frequencies (P < 0.05). P2 and α1‐antagonism decreased tension with 8 and 30 Hz burst pattern field stimulation. However, the magnitude of decrease in tension with prazosin was less with burst patterns compared to the same average constant frequencies (P < 0.05). It appears that P2X receptors and α1‐receptors in the femoral artery are sensitive to frequency and patterns of electrical stimulation.

The serine protease, dipeptidyl peptidase IV as a myokine: dietary protein and exercise mimetics as a stimulus for transcription and release.

Dipeptidyl‐peptidase IV (DPP‐IV) is an enzyme with numerous roles within the body, mostly related to regulating energy metabolism. DPP‐IV is also a myokine, but the stimulus for its release is poorly understood. We investigated the transcription and release of DPP‐IV from skeletal muscle in a three‐part study using C2C12 myotube cultures, an acute rat exercise and postexercise feeding model, and human feeding or human exercise models. When myotubes were presented with leucine only, hydrolyzed whey protein, or chemicals that cause exercise‐related signaling to occur in cell culture, all caused an increase in the mRNA expression of DPP‐IV (1.63 to 18.56 fold change, P < 0.05), but only whey protein caused a significant increase in DPP‐IV activity in the cell culture media. When rats were fed whey protein concentrate immediately following stimulated muscle contractions, DPP‐IV mRNA in both the exercised and nonexercised gastrocnemius muscles significantly increased 2.5‐ to 3.7‐fold (P < 0.05) 3–6 h following the exercise/feeding bout; of note exercise alone or postexercise leucine‐only feeding had no significant effect. In humans, plasma and serum DPP‐IV activities were not altered by the ingestion of whey protein up to 1 h post consumption, after a 10 min bout of vigorous running, or during the completion of three repeated lower body resistance exercise bouts. Our cell culture and rodent data suggest that whey protein increases DPP‐IV mRNA expression and secretion from muscle cells. However, our human data suggest that DPP‐IV is not elevated in the bloodstream following acute whey protein ingestion or exercise.