Citations

Objective Insulin has known sympathoexcitatory effects that have been historically attributed to primarily central mechanisms. Although controversy exists, recent evidence from rodents suggests the carotid chemoreceptors may play a role in the sympathoexcitatory response to hyperinsulinemia. Therefore, we sought to examine the contribution of the carotid chemoreceptors to insulin‐mediated increases in sympathetic nervous system activity in humans. We hypothesized reductions in carotid chemoreceptor activity would attenuate the sympathoexcitatory response to hyperinsulinemia in humans – thus supporting a role for the carotid chemoreceptors in insulin‐mediated sympathoexcitation. Methods Young, healthy adults (n=15, 8M/7F, 27±1 yrs, 24±1 kg/m 2 ) completed a 30‐min euglycemic baseline followed by a 90‐min hyperinsulinemic (1 mU/kg FFM/min), euglycemic (90–100 mg/dL) clamp. Heart rate (electrocardiography) and muscle sympathetic nerve activity (MSNA, microneurography of the peroneal nerve) were continuously measured. The role of the carotid chemoreceptors was assessed using the following protocols: 1) acute (1‐min) hyperoxia (n=13), 2) low‐dose dopamine (1–4 μg/kg/min; n=7), 3) acute hyperoxia + low‐dose dopamine (n=8). The nadir 15‐s value for MSNA within each hyperoxic condition was determined and the nadir at baseline was compared to the nadir during hyperinsulinemia. Results MSNA increased from baseline during the hyperinsulinemic, euglycemic clamp [12±2 to 18±2 bursts/min (p<0.01)]. In protocol 1, MSNA was reduced during acute hyperoxia at baseline (12±1 to 6±1 bursts/min, p<0.01) and during the hyperinsulinemic clamp (17±2 to 12±2 bursts/min, p=0.02); however, the fall in MSNA during hyperoxia did not differ between baseline and hyperinsulinemia (p=0.82). In protocol 2, when low‐dose dopamine was given prior to the hyperinsulinemic clamp, MSNA did not increase from baseline (19±2 to 22±5 bursts/min, p=0.51); this is in contrast to increases observed under saline conditions (14±3 to 22±4 bursts/min, p=0.03). In protocol 3, in the presence of low‐dose dopamine, MSNA was reduced during acute hyperoxia at baseline (16±3 to 9±2 bursts/min, p=0.048) and during the hyperinsulinemic clamp (16±4 to 9±3 bursts/min, p=0.02); however, the fall in MSNA with hyperoxia did not differ between baseline and hyperinsulinemia (p=0.97). Conclusions Low‐dose dopamine given prior to the onset of a hyperinsulinemic, euglycemic clamp attenuates the sympathoexcitatory response to hyperinsulinemia. In contrast, acute carotid chemoreceptor desensitization (1‐min hyperoxia) during steady‐state hyperinsulinemia does not augment the fall in MSNA observed at baseline. Our data suggest the carotid chemoreceptors do not contribute acutely to insulin‐mediated increases in sympathetic nervous system activity in healthy humans; however, they may play a role during longer‐term exposure. Support or Funding Information Support: DK090541 (MJJ); HL83947 (MJJ); HL130339 (JKL); AHA15SDG25080095 (JKL)

Peripheral chemoreceptors located within the carotid bodies activate cardiorespiratory reflexes in response to hypoxia. Carotid body chemoreceptor activity has been shown to be enhanced in conditions such as congestive heart failure, hypertension, and possibly aging. Nitric oxide (NO) has been proposed as an inhibitory modulator of carotid body chemosensitivity in response to hypoxia. Additionally, NO bioavailability is often reduced with cardiovascular risk factors such as aging. In the present study, we tested the hypothesis that increasing NO bioavailability via dietary nitrate (NO 3 ) supplementation would reduce cardiorespiratory responses to hypoxia in older adults. A double‐blind, randomized, placebo‐controlled, cross‐over study design was used to evaluate minute ventilation (V E ) and heart rate (HR) responses to acute hypoxia in 7 older adults (66±2 years; 5M/2F) before and after 4 weeks of NO 3 supplementation (beetroot powder) and placebo (beetroot powder devoid of NO 3 ). On each study visit, subjects underwent two separate isocapnic hypoxic tests (self‐regulating, partial rebreathing system with 10% O 2 ). Subjects remained on 10% O 2 until SpO 2 reached ≤80%. The hypoxic exposures were separated by a 15‐minute washout period with the subjects breathing room air. V E , HR, and SpO 2 were continuously monitored throughout each hypoxic exposure. Data were grouped together using a 7‐breath average with the slope of the linear regression line for each dependent variable (V E and HR) versus SpO 2 serving as a measure of peripheral chemosensitivity. The slopes for the two hypoxia tests on each study visit were averaged and used for statistical comparisons. On study day one (true baseline) acute hypoxia increased both V E and HR ( P <0.05 for both). Four weeks of NO 3 supplementation reduced the hypoxic ventilatory response (−0.16 ± −0.05 vs. −0.06 ± −0.03 L/minute/%SpO 2 , P <0.05), whereas no change was observed following the placebo phase of the study (−0.14 ± −0.07 vs. −0.14 ± −0.08 L/minute/%SpO 2 , P=0.67). Additionally, the heart rate responses to acute hypoxia were also reduced following NO 3 supplementation (−0.49 ± −0.08 vs. −0.30 ± −0.05 beats/minute/%SpO 2 , P <0.05), but not with placebo (−0.54 ± −0.11 vs. −0.45 ± −0.08 beats/minute/%SpO 2 , P=0.21). Our preliminary findings suggest that supplementation of NO 3 to boost NO bioavailability in older adults blunts the cardiorespiratory responses to hypoxia. Future studies should examine the therapeutic potential of NO 3 in patient populations exhibiting exaggerated peripheral chemosensitivity. Support or Funding Information Research supported by Neogenis Inc.

The A‐splice variant of Na + ‐dependent, electrogenic bicarbonate transporter‐1 (SLC4A4, NBCe1‐A) is generally believed to be the only SLC4A4 isoform expressed in the mammalian proximal tubule, and to have critical roles in filtered bicarbonate reabsorption, proximal tubule ammonia metabolism and proximal tubule organic anion metabolism. The purpose of the current study was to examine expression of other splice variants in the mouse kidney. We used recently generated mice with TALEN‐generated deletion of A and D NBCe1 splice‐variants, but with intact expression of the B, C and E isoforms. RT‐PCR using primers specific to the B, C and E isoforms showed mRNA of non‐A,D splice variants was expressed in the kidney of mice with intact NBCe1‐A expression and with NBCe1‐A‐specific deletion. We then used an antibody that recognizes portions of NBCe1 present in all splice isoforms and examined immunolabel in the kidney of NBCe1‐A‐deletion mice. There was basolateral immunolabel in the proximal convoluted tubule in the cortex, and lesser intensity basolateral immunolabel in the proximal tubule straight tubule in both the cortex and outer medulla. Specificity of this antibody was demonstrated by identifying that mice with deletion of all splice variants had no detectable immunolabel. An antibody specific to the A‐splice variant showed basolateral immunolabel throughout the entire proximal tubule of mice with intact NBCe1‐A expression, but no detectable immunolabel in mice with NBCe1‐A‐specific deletion. Thus, an NBCe1 splice variant other than NBCe1‐A appears to be expressed in the mouse proximal tubule. In acid‐loaded NBCe1‐A‐deletion mice, immunolabel observed using the pan‐specific anti‐NBCe1 antibody showed increased immunolabel in the proximal straight tubule, particularly in the outer medulla. These studies show that splice variants of NBCe1 other than NBCe1‐A/D are present in the mouse kidney and that their expression appears to be increased with acid‐loading. We conclude that these splice variants may have important roles in proximal tubule filtered bicarbonate reabsorption, ammonia metabolism and organic anion metabolism. Support or Funding Information The studies were supported by funds from the NIH (R01–DK045788 to IDW, R01‐DK107798 to IDW and JWV, and R01‐EY017732 to MFR) and the Department of Veterans Affairs (1I01BX000818 to IDW).

Nephrolithiasis is a painful and costly healthcare complication. The most common kidney stones are composed of calcium oxalate and thus renal handling of oxalate is an important facet of understanding the pathogenesis of nephrolithiasis. Recently, the Drosophila melanogaster Malpighian tubule (MT) has emerged as a robust model of trans‐epithelial ion transport and nephrolithiasis as MTs readily form luminal calcium‐oxalate crystals in the presence of oxalate. Drosophila Prestin (dPrestin, Slc26a6) transports oxalate across the apical surface of the MT into the lumen but a full model of the trans‐epithelial movement of oxalate in the Drosophila MT has been lacking as the basolateral oxalate transporter has remain uncharacterized. The objective of this work was to identify and characterize the Drosophila basolateral oxalate transporter through ex vivo real‐time quantification of intracellular pH (pH i ). pH i was monitored by using the GAL4/UAS system to selectively express pHerry, a pseudo‐ratiometric genetically‐encoded pH indictor (GEpHI) in the cytosol of the principal cells of the MT. Calibration of pHerry in extracted adult MTs yielded a p K a of 7.24. Basolateral perfusion of MTs in CO 2 /HCO 3 − ‐buffered solution produced a large acidification followed by rapid recovery in all three functionally distinct segments of the anterior MT (initial, transitional, and main). Recovery was likely due to HCO 3 − loading by HCO 3 − transporters and this process could be interrupted by basolateral application of 1mM oxalate (in the initial and transitional segments) or 1mM SO 4 2− (in all three segments). The response was most robust in the transitional segment and oxalate induced a more rapid acidification than SO 4 2− ( dpH i / dt = −0.60 ± 0.09 pH units min −1 compared to −0.06 ± 0.01). A putative ortholog of the mammalian renal basolateral oxalate transporter (SAT 1; Slc26a1) was identified through sequence homology. Tissue specific knock‐down of this protein with interference RNA (RNAi) reduced the rate of acid‐loading in the transitional segment of the MT with regard to oxalate but not SO 4 2− ( dpH i / dt = −0.34 ± 0.06 pH units min −1 ; p = 0.03 compared to controls, and −0.06 ± 0.01; p = 0.94 compared to controls for oxalate and SO 4 2− respectively). These data indicate this protein is likely the Drosophila basolateral MT oxalate transporter and the basolateral movement of oxalate is functionally coupled to movement of acid equivalents, potentially as oxalate/HCO 3 − exchange, oxalate/OH − exchange, or oxalate/H + co‐transport. Support or Funding Information Funding: T32‐DK007013 to AJR, GM075148 (JBA), DK092408 and DK100227 to MFR.

The human gastrointestinal (GI) tract is home to trillions of microorganisms. There is dynamic interaction between the gut microbiota and the human host, but how gut microbiota modulates GI physiology is largely unknown. A recent study from our laboratory showed that human gut microbiota increases host serotonin (5‐hydroxytryptamine, 5‐HT) biosynthesis. 5‐HT is an important neurotransmitter and a paracrine messenger in the GI tract that increases intestinal secretion primarily through 5‐HT 3 and 5‐HT 4 receptors. In this study we investigated whether gut microbiota modulate 5‐HT 3 R and 5‐HT 4 R expression and host secretory response to 5‐HT. Methods We used proximal colon mucosa‐submucosa preparations from germ free (GF) and humanized (ex‐GF colonized with human bacteria for 4–5 weeks; HM) male mice. The change in short circuit current (ΔIsc) was determined in response to increasing concentrations of 5‐HT (0.003–300μM) on the submucosal side either alone or in the presence of 5‐HT 3 R antagonist ondansetron (100nM) in an Ussing chamber. Receptor expression was quantified using rt‐PCR (normalized to L32) and western blot (normalized to GAPDH). Immunohistochemistry (IHC) was used to determine localization of 5‐HT 3 R in the paraformaldehyde‐fixed 10μm sections from proximal colonic epithelium. Differences between groups were tested using Mann‐Whitney U (Mdn; IQ range) with P ‐value lower than 0.05 considered significant. Results 5‐HT induced ΔIsc was significantly higher in GF than HM mice (218; 184–274 vs 163; 132–182 μA/cm 2 , n=6, P = 0.04). To determine if this change was due to an alteration in 5‐HTR, we quantified receptor expression. We found significantly higher 5‐HT 3 R mRNA expression (1.82; 1.08–2.80 vs 1.00; 0.33–1.38, n=8–9, P = 0.046) in GF compared to HM mice, but no change in 5‐HT 4 R expression. 5‐HT 3 R protein expression was also significantly higher in GF mice compared to HM (4.62; 1.06–6.14 vs 1.00; 1–1.3, n= 11–12, P = 0.01) mice. There was a significantly higher ΔIsc in GF compared to HM (87.1; 51.7–149 vs 37.0; 19.5–44 μA/cm 2 , n=5, P = 0.02) mice, following application of 2‐methyl 5‐hydroxytryptamine hydrochloride (selective 5‐HT 3 R agonist) suggesting increased receptor expression augments secretory response. Furthermore, ondansetron significantly blocked 5‐HT induced maximum ΔIsc in GF mice (201; 189–260 vs 117.6; 92–149 μA/cm 2 , n=6–8, P = 0.001) but not in HM mice (163; 132–182 vs 120; 107–150 μA/cm 2 , n=6, P = 0.24). To determine the expression of 5‐HT 3 R in mouse colon mucosa‐submucosa we used 5‐HT 3 –tagged GFP mice. IHC identified 5‐HT 3 R‐GFP positive cells in the mouse colonic epithelium. To ascertain if the significant difference in 5‐HT‐induced ΔIsc between GF and HM mice (188; 152–200 vs 125; 99–139 μA/cm 2 , n=5, P = 0.008) is driven by epithelial 5‐HT 3 R, we measured the response in the presence of TTX (block neuronal transmission). TTX (500 nM) had no effect of ondansetron inhibition of 5‐HT‐induced ΔIsc, suggesting a role for epithelial 5HT 3 R. Conclusion Gut microbial colonization decreases host secretory response to 5‐HT by downregulating 5‐HT 3 R expression. Epithelial 5‐HT 3 R may be important in gut microbiota modulation of intestinal secretion Support or Funding Information NIH K08 DK

A history of hypertensive disorders of pregnancy, including preeclampsia, place women at an elevated risk of developing hypertension and cognitive impairments as they age. The purpose of this study was to determine if aortic hemodynamics were related to cognition in postmenopausal women with a history of hypertensive disorders of pregnancy. We evaluated 33 postmenopausal women with a history of preeclampsia (PE: age = 59 ± 5 y; BMI = 29 ± 5 kg/m 2 ; years since last pregnancy = 35 ± 3 y) and 29 postmenopausal women with a history of normotensive pregnancy (NTP: age = 59 ± 5 y; BMI = 26 ± 5 kg/m 2 ; years since last pregnancy = 35 ± 3 y). Participants underwent a cognitive testing battery including letter‐number sequencing, trail making test B, letter fluency, and category fluency tests to evaluate executive functioning and working memory. Mean arterial pressure (MAP) was measured with a brachial blood pressure cuff. Applanation tonometry (SphygmoCor) was used to derive the aortic pressure waveform and calculate aortic systolic blood pressure (ASBP), aortic diastolic blood pressure (ADBP), augmentation index (AI), and augmented pressure (AP). There were no differences in cognitive scores between groups (p > 0.05). Brachial blood pressure (MAP: 103 ± 2 vs. 103 ± 3 mmHg) and aortic hemodynamic measures (ASBP: 123 ± 3 vs. 121 ± 3 mmHg; ADBP: 78 ± 2 vs. 77 ± 2 mmHg; AI: 31 ± 2 vs. 28 ± 1 %; AP: 17 ± 1 vs. 15 ± 1 mmHg) were also similar between PE women and NTP women, respectively (p > 0.05 for all). There were no associations between measures of aortic hemodynamics and cognitive scores in women independent of their pregnancy history (p > 0.05). When evaluating these relationships within each group, ADBP was significantly associated with worse scores for letter‐number sequencing and letter fluency in PE women (r = −0.433 and r = −0.441, respectively, p < 0.05). Taken together, our results indicate aortic hemodynamic measures are not associated with cognition in middle‐aged postmenopausal women with different pregnancy histories; however, future studies should address the influence of elevated aortic hemodynamic variables and the longitudinal change in cognitive function in postmenopausal women with different pregnancy histories. Support or Funding Information NIH AG44170, NIH 118154

Post‐mortem analyses have identified carotid body hypertrophy in conditions of chronic hypoxemia, including sleep apnea; however, post‐mortem assessment limits the clinical relevance of such findings. We tested the hypotheses that: 1) carotid body size can be detected in living individuals by computed tomographic angiography (CTA), and 2) patients with sleep disordered breathing [Apnea Hypopnea Index (AHI) ≥ 30 events/hour] exhibit larger carotid bodies than those without sleep disordered breathing (AHI < 5 events/hour). A chart review was conducted from patients seen at the Mayo Clinic between January 2000 and February 2015 who had undergone neck CTA and polysomnography. From an initial pool of 583, 109 patients met our strict inclusion criteria. Widest axial measurements of the right and left carotid bodies were performed independently by two radiologists blinded to condition and average carotid body size was calculated for each patient of interest. Carotid body identification was possible in 81% of patients. Intra‐class correlation coefficients ranged from 0.93 to 0.95 (right carotid body: 0.93; left: 0.94; average: 0.95). From subjects with identifiable carotid bodies, widest axial measurements were greater in patients with high AHI (n=32; right: 2.9±0.2mm, left: 3.1±0.2mm, average: 3.0±0.1mm) compared to patients with low AHI (n=46; right: 2.5±0.1mm, left: 2.7±0.1mm, average: 2.6±0.1mm; p=0.04, p=0.04, p=0.02, respectively). Because participants in the high AHI group were significantly older than those in the low AHI group (65±2 years vs. 50±2 years; p<0.01), an analysis of covariance was performed to control for the influence of age on carotid body size. After adjusting for age, no differences in carotid body size were observed between the patient groups (p=0.45, p=0.59, p=0.54 for right, left, and average carotid body, respectively). Main findings are two‐fold: 1) carotid body size can be identified by CTA in approximately 80% of patients with good inter‐observer agreement, and 2) adults that exhibit sleep disordered breathing do not have larger carotid bodies when compared to controls, after adjusting for age. Support or Funding Information This work was supported by the National Institutes of Health [grant numbers T32 GM008685 (ARE), R01 DK090541 (MJJ)].

Introduction Adenosine triphosphate (ATP) is a vasodilating metabolite that plays a role in exercise hyperemia. In humans, exogenous infusion of ATP elevates skeletal muscle blood flow values to that observed during moderate‐intensity exercise. Recently ATP has been shown to evoke prolonged vasodilation over 150 minutes without tachyphylaxis. However, the steady‐state hyperemic responses to superimposed forearm exercise remain unaltered. The kinetics of blood flow during the initiation of exercise remains not well understood. Therefore we evaluated the effects of prolonged exogenous infusion of ATP on exercise hyperemia during the transition between rest and initiation of exercise. Methods While supine, eight healthy young participants (4M/4F; 25±1 years) performed 5 minutes of rhythmic dynamic handgrip exercise bouts (20% of maximum), first during saline (control), then at minute 5 and minute 150 during a continuous ATP infusion into the brachial artery. Each duty cycle consisted of 1 second contraction and 2 second relaxation. Mean blood velocity (MBV; cm/s), forearm vascular conductance (FVC; ml/minutes/100 mmHg), and shear rate (8*MBV/diameter; seconds −1 ) were calculated. The kinetics at the onset of exercise was assessed by calculating the slope of the FVC responses for the first 20 duty cycles after the start of contractions. Data are presented as means ± SEM. Results During saline control FVC was 3.9±0.3 at rest and with exercise rose to 22.7±0.84 and 27.8±1.2 ml/minute/100mmHg at 30 seconds and 1 minute, respectively (P<0.05 for both). Infusion of ATP increased FVC (3.9±0.3 vs 43.1±2.0 ml/minutes/100 mmHg, P<0.05) at five minutes and to 61.0±1.1 ml/minutes/100 mmHg at 150 minutes (P<0.05) with no systemic hemodynamic changes. Prolonged infusion of ATP did not alter the kinetics at the onset of contractions over 20 duty cycles of exercise hyperemic responses compared to control (0.71±0.1 control vs 1.01±0.1 ml/minutes/100mmHg/cycle at 5 minutes and vs 0.65±0.1 at 150 minutes, P>0.05 for all). Shear rate significantly increased compared to control (92±5 vs 751±57 seconds −1 , P<0.05) but was not different across exercise responses during ATP infusion (751±57 at 5 minutes vs 549±46 seconds −1 at 150 minutes, P>0.05). Conclusions Our findings demonstrate that despite the ability of ATP to elevate blood flow to that observed during exercise, the blood flow kinetics for the initiation of dynamic exercise hyperemic response are unaffected and remain unaltered after 150 minutes of prolonged ATP infusion. Further investigation in needed to understand the role of ATP in regulating the blood flow kinetics during dynamic exercise in humans. Support or Funding Information This research was supported by National Institutes of Health Research Grants HL‐119337 and by CTSA UL1 TR000135. The Caywood Professorship via the Mayo Foundation also supported this study.

The purpose of this study was to explore dose dependent vasodilation responses of the individual compounds of Shakuyakukanzoto (SKT), a 1:1 combination of extracts from Paeony and Licorice roots: glycyrrhetic acid (GA), paeoniflorin (PF), and isoliquiritigenin (ISO). 20 young, healthy participants (13M/7W) had four intradermal microdialysis fibers placed in the forearm skin for local delivery of: 1) control (diluent), 2) GA, 3) PF, or 4) ISO at doses of 1, 10, 50, or 100 μm. Cutaneous red cell flux, an index of skin blood flow, was measured by laser‐Doppler flowmetry. Blood pressure (BP) was monitored continuously during fixed measurement periods via finger photo‐plethsmography (Finapres). Cutaneous vascular conductance (CVC) was derived as red cell flux divided by BP and was normalized as a percentage of baseline (%CVCbl, saline at 4 μl/min) and the maximum CVC (%CVCmax, 28mM sodium nitroprusside at 4 μl/min, local temperature 43°C). Mean CVC did not statistically differ between baseline and individual compound plateau (average of last 5 minutes of infusion) at any dose. The peak flux was significantly higher from baseline at doses 50 and 100 μm for control (56.17±13.32 vs. 96.73±20.32 and 44.64±5.68 vs. 80.21±9.54), PF (62.70±10.09 vs. 115.72±16.16 and 62.37±16.2 vs. 150.21±34.26), GA (48.37±4.41 vs. 71.76±7.16 and 58.36±13.68 vs. 91.51±3.41), and ISO (96.50±23.20 vs. 128.57±27.90 and 44.95±8.78 vs. 91.18±20.37) (p<0.05). However, peak CVC was significantly higher only for GA at dose 50 μm, as well as for control and PF at dose 100 μm compared to their respected baselines (GA: 0.60±0.06 vs. 1.01±0.11, control: 0.61±0.09 vs.1.55±0.61, PF: 0.81±0.20 vs. 1.30±0.30, p<0.05). There were no other significant differences between the control and the compounds for change in CVC from baseline to peak (ΔCVC), %CVCbl, or %CVCmax. There were no significant differences between doses 1, 10, or 50 as compared to 100 μm for other variables. These results suggest that the doses may be lower or below the threshold to cause a vasodilatory effect. Future studies that investigate higher doses of these compounds may be needed. Support or Funding Information The University of Oxford Systems Biology Project sponsored by Tsumura.

Skeletal muscle blood flow during exercise is typically reduced in older compared with young adults, which may be mediated in part by age‐related reductions in local vasodilator molecules such as nitric oxide (NO) and ATP. Despite this, muscle blood flow does increase substantially to contracting muscle of older adults. We questioned whether reductions in muscle blood flow with age, particularly at the onset of exercise, leads to greater accumulation of local metabolites that could play a more prominent role in contraction‐induced vasodilation compared with young adults. Thus, in the present study we tested the hypothesis that the contribution of adenosine (ADO) to contraction‐induced vasodilation is greater in older vs. young adults. In young (25 ± 2 years; n=8) and older (65 ± 2 years; n=8) adults, forearm vascular conductance (FVC) responses to a single 20% maximum voluntary contraction (MVC) handgrip contraction and to 5 minutes of 10% MVC rhythmic handgrip exercise were measured using Doppler ultrasound of the brachial artery before and after brachial artery infusion of the ADO receptor blocker aminophylline (APH). In order to determine the effect of APH infusion that was due specifically to the blockade of ADO receptors as opposed to the elevated baseline FVC that often occurs as an off‐target effect of APH, FVC responses to contraction were also measured after sodium nitroprusside (SNP) infusion to match the APH‐induced increase in baseline FVC. In response to a single contraction, both total FVC area under the curve (AUC) and the absolute change in FVC from baseline to peak were lower in older vs. young adults (−61.2% and −56.1%, respectively; p < 0.05) under control conditions. There was no significant effect of APH on total FVC AUC in young (−5.4 ± 7.8%) or older (16.6 ± 12.4%) adults vs. control, whereas the absolute change in FVC from baseline to peak was significantly lower in young adults (−22.5 ± 7.7%; p < 0.05), but unaffected in older adults (4.1 ± 7.8%) vs. control. During rhythmic handgrip exercise, FVC was significantly lower in older adults in the first 60 sec of exercise (~45–50%) as well as during steady‐state (~25%; 110.0 ± 14.9 vs. 149.5 ±12.6 mL/min/100mmHg; both p < 0.05) under control conditions. APH had no effect on the FVC response throughout the first 3 min of exercise onset in young (range: 0.8–6.2%) or older (range: −3.9 to 10.5%) adults vs. control (p > 0.05), and did not alter the absolute change in FVC from baseline to steady‐state exercise in either group (p > 0.05). SNP had no effect on these FVC responses during single contractions or rhythmic handgrip exercise in either age group (p > 0.05). We conclude that that ADO contributes to the peak vasodilatory response to a single contraction in young but not older adults, and that advancing age is not associated with a greater reliance on ADO for local vasodilation during skeletal muscle contractions. Support or Funding Information HL095573, HL119337